Current trends in radiation protection 9782759801176, 9782868837257

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Current Trends in Radiation Protection On the occasion of the 11th international congress of the international radiation protection association 23-28 May 2004, Madrid, Spain

Edited by H. Metivier, L. Arranz, E. Gallego and A. Sugier

SCIENCES 17, avenue du Hoggar Pare d'Activite de Courtaboeuf, BP 112 91944 Les Ulis Cedex A, France

The editing of this book has been supported by : - Sociedad Espanola de Proteccion Radiologica

and

de

- Comunidad de Madrid, Consejeria de Sanidad y Consumo

CONSEJERIA DE SANIDAD Y CONSURSG

CSN

CONSEJO DE SEGURIDAD NUCLEAR

enresa

- Consejo de Seguridad Nuclear

- Empresa Nacional de Residues Radiactivos, S.A.

- World Health Organisation

Cover Design : Eric Sault

ISBN 2-86883-725-5 This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, re-use of illustrations, recitation, broad-casting, reproduction on microfilms or in other ways, and storage in data banks. Duplication of this publication or parts thereof is only permitted under the provisions of the French and German Copyright laws of March 11, 1957 and September 9, 1965, respectively. Violations fall under the prosecution act of the French and German Copyright Laws.

© EDP Sciences 2004 Printed in France

FOREWORD

With the objective of spreading the Radiation Protection cultural context, and to facilitate its understanding by the public, this book contains a compilation of the main lectures pronounced between May 23 and 28, 2004, with the occasion of the 11th International Congress of the International Radiation Protection Association (IRPA11). This volume contains a summary of the advances in the Radiological Protection field and its main application areas, which undoubtedly will have a direct impact to the most immediate future. When introducing it, I wish to devote an emotive remembrance to the memory of the eminent scientist Dan Beninson, who unfortunately did not live enough to participate in this Congress that he enthusiastically supported since its initial project. I also wish to express mi deepest and sincere gratitude to all the authors, to Henri Metivier, the genuine promoter of this publication, and to all those who helped me towards the success of this great scientific meeting.

Leopoldo Arranz IRPA Vice-President for Congress Affaires Chairman of IRPA 11 International Congress Organising Committee

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INTRODUCTION

The IRPA congresses constitute unique opportunities to gather all actors of radiological protection, irrespective of their origin or their field of action in the vast world of radioprotection. The IRPA11 Congress in Madrid will perpetuate this tradition at the very moment where all stakeholders, whether researchers, radioprotectionists, regulators, private industrial operators or national institutions, feel a need for widening the scope of this profession. Radiological protection falls now under the public's active scrutiny. Its perception of risks and the measures taken to reduce them as much as possible, whilst maintaining the activities necessary to the well being of humankind need now to be explained. This congress directly fulfils this new line of action, a perfect illustration lying in the title that has been chosen: "Widening the radiation protection world". However, this widening should also become apparent on the libraries shelves and the fruitful debates of IRPA congresses should evolve beyond the restricted circles of specialists. This is why we have launched this new series of books "Trends in radiation protection" which will spread the state of the art in radiological protection to the entire world, researchers, regulators, experts. In order to guarantee an information of high quality and devoid of passion, we have called on board renowned experts in their various fields of activities. Their immediate agreement upon our invitation constitutes the first success of this book. We are very grateful to all of them without whom this book would not exist. While keeping a single objective, radioprotection, the book offers a variety of topics. For us, it was clear that a synthesis of biological knowledge deserved to start the book with, but as this was traditionally oriented towards humans, we have deliberately wanted also to review the status of the necessary evolution towards environmental protection. ICRP recommendations being endorsed throughout the world, a critical analysis of their impact on current life was necessary: how are the recommendations applied, what are the physical tools necessary for their application, how professionals must be educated and especially the medical world that is the big responsible for the collective irradiation of populations.

Introduction

But beyond such recommendations and the application of rigorous safety rules, incidents with radioactive sources and nuclear accidents remain possible. It is thus necessary to reconstruct such difficult situations in terms of exposure, to properly evaluate the contamination of the affected territories, and to promote coherent and practical proposals for remediation. The experimental feedback from such situations is a tremendous source of progress for their prevention. In addition, radiological protection also addresses non-ionizing radiation: citizens are increasingly concerned about mobile telephones, and less by the nevertheless omnipresent lasers. This aspect also captured our attention when constructing this book. We believe that this book will answer a number of questions that are asked by the various actors of our society who are not necessarily experts in our field. The pedagogical efforts of the authors would allow to meet our objective: "Widening the radiation protection world".

H. Metivier, L. Arranz, E. Gallego, A.Sugier Editors

International Congress Programme Committee Core Group members Dr. Annie SUGIER (ICPC Chairperson) Institut de Radioprotection et de Surete Nucleaire, France Dr. Leopoldo ARRANZ (IRPA Vice-President for Congress Affairs) Hospital Ramon y Cajal, Spain Prof. Eduardo GALLEGO (ICPC Scientific Secretary) Universidad Politecnica Madrid, Spain Dr. Jacques LOMBARD (ICPC Chairperson Assistant) Societe Francaise de Radioprotection, France

Dr. Andre BOUVILLE National Cancer Institute, USA Dr. John COOPER National Radiological Protection Board, United Kingdom Dr. Bobby CORBETT Hairmyres Hospital, United Kingdom Dr. Renate CZARWINSKI Federal Office for Radiation Protection, Germany Dr. Antonio DELGADO Centre de Investigaciones Energeticas, Medioambientales y Tecnologicas, Spain Dr. Rick JONES U.S. Department of Energy, USA Dr. Juan Carlos LENTIJO Consejo de Seguridad Nuclear, Spain Dr. Sigurdur MAGNUSSON Icelandic Radiation Protection Institute, Iceland Dr. Ches MASON International Atomic Energy Agency , Austria Prof. Henri METIVIER Institut de Radioprotection et de Surete Nucleaire, France Dr. Alastair MCKINLAY National Radiological Protection Board, United Kingdom Prof. Xavier ORTEGA Universitat Politecnica de Catalunya, Spain Dr. Eliseo VANO Universidad Complutense de Madrid, Spain

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Current trends in radioprotection Contents Foreword Leopoldo Arranz

Ill

Introduction Henri Metivier, Leopoldo Arranz, Eduardo Gallego, Annie Sugier

V

International Congress Programme Committee - Core Group Members Non-Targeted Effects of Ionizing Radiation: Implications for Radiation Protection John B. Little, MD

VII 1

Effects of Ionising Radiation in the Low Dose Range - Radiobiological Basis Christian Streffer

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ICRP and Radiation Protection of Non-Human Species Lars-Erik Holm

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From Recommendations to Reality - A Critical Overview with a Historical Perspective G. Ches Mason

45

Active Methods & Instruments for Personal Dosimetry of External Radiation: Present Situation in Europe and Future Needs Teresa Bolognese-Milsztajn, Merce Ginjaume, Filip Vanhavere Training Users of Medical Radiation Fred A. Mettler Jr. M.D, M.P.H. Occupational Radiation Protection in the European Union: Achievements, Opportunities and Challenges Klaus Schnuer , Augustin Janssens , Jochen Naegele, Pascal Deboodt

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Education and Training Needs in Radiation Protection Agustin Alonso

107

Realistic Retrospective Dose Assessment Jane Simmonds

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Quality assurance and the Evaluation of Uncertainties in Environmental Measurements Lourdes Romero Gonzalez

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Site Restoration and Cleanup of Contaminated Areas Gordon Linsley

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The Lessons to be Learned from Incidents and Accidents John Croft

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Current Trends in Radiation Protection

Safety and Security of Radioactive Sources: Conflicts, Commonalities and Control Brian Dodd

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Mobile Telephony: Evidence of Harm? Bernard Veyret

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Laser Radiation Protection David H. Sliney

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What Policy Makers Need for Radiation Protection? Junko Matsubara

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Living in Contaminated Territories: A Lesson in Stakeholder Involvement Jacques Lochard

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Current Trends in Radiation Protection H. Metivier, L. Arranz E. Gallego and A. Sugier (eds.)

Non-Targeted Effects of Ionizing Radiation: Implications for Radiation Protection John B. Little, MD1 Laboratory ofRadiobiology, Harvard School of Public Health, 665 Huntington Avenue,Boston, MA 02115 USA

Abstract. It is widely accepted that damage to DNA is the critical event in irradiated cells, and that double strand breaks are the primary DNA lesions responsible for the biological effects of ionizing radiation. This has led to the long standing paradigm that these effects, be they cytotoxicity, mutagenesis or malignant transformation, occur in irradiated cells as a consequence of the DNA damage they incur. Evidence has been accumulating over the past decade, however, to indicate that radiation may induce effects that are not targeted to the irradiated cell itself. Two "non-targeted effects will be described in this review. The first, radiation-induced genomic instability is a phenomenon whereby signals are transmitted to the progeny of the irradiated cell over many generations, leading to the occurrence of genetic effects such as mutations and chromosomal aberrations arising in the distant descendants of the irradiated cell. Second, the bystander effect, is a phenomeon whereby irradiated cells transmit damage signals to non-irradiated cells in a mixed population, leading to genetic effects arising in these "bystander" cells that received no radiation exposure. The model system described in this review involves dense monolayer cultures exposed to very low fluences of alpha particles. The potential implications of these two phenomena for the analysis of the risk to the human population of exposure to low levels of ionizing radiation is discussed.

1. INTRODUCTION Ionizing radiation has many unique characteristics as a mutagen and carcinogen. These derive from its ability to penetrate cells and tissues and to deposit energy within them in the form of ionizations; that is, the ejection of orbital electrons from atoms or molecules. This event may lead to irreversible damage in the molecule involved, or the resultant free radical (an atom or molecule containing an unpaired electron) may initiate a chain of chemical reactions mediated through cellular water with the ultimate biologic damage occurring in another molecule in the cell. Ionizing radiation is thus non-selective in the damage it produces, depositing

1

E-mail: [email protected]

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Current Trends in Radiation Protection

energy at random by means of ionizations within all cells and tissues. Unlike most chemical agents, it is not organ specific in its effects. Its toxicity does not depend upon absorption, excretion, or localization within the body. It does not depend upon the presence of specific binding sites or receptors in cells, nor on mechanisms of activation or detoxification common to genotoxic chemical agents. Ionizing radiation also has unique characteristics as a genotoxic agent in terms of the DNA damage it produces. Most chemical carcinogens and mutagens produce specific damage to DNA bases, often as a consequence of the formation of DNA adducts or alkylation products. This is also the case for ultraviolet light radiation. Such base damage is readily restored by metabolic nucleotide or base excision repair processes whereby the damaged base is excised and resynthesized using the complementary DNA strand as a template. While such damage can lead to mutations owing to inaccurate repair, base damage is not very cytotoxic to cells and appears to play a minor role in mutagenesis induced by ionizing radiation [1]. For example, an exposure to 254 nm ultraviolet light that kills 63% of the cells (Dsr) will produce approximately 400,000 pyrimidine dimers in each cell whereas, for a similar level of cell killing, ionizing radiation will induce only 40 DNA double strand breaks. The double strand break (DSB) is now considered to be the characteristic DNA lesion responsible for the biologic effects of ionizing radiation [1,2]. In some experimental systems, it has been estimated that a single unrepaired DSB may lead to cell cycle arrest [3,4], whereas a single complex DSB in a specific gene has a high probability of producing a mutation in that gene [5]. Double strand breaks can arise from opposed single strand breaks (SSB) arising from either random ionizations or free radical attack leading to breaks in the individual strands. It has been estimated that DSB can arise from SSB occurring in opposite strands within a distance of about 13 base pairs of each other. There is now considerable evidence, however, to indicate that most DSB are a consequence of the specific nature of the energy deposition and distribution of ionizations within DNA caused by radiation. This results in what has been termed "clustered damage", multiple closely associated DNA lesions including single strand breaks and base damage [1,6]. Such clustered damage occurs after low as well as high radiation doses, and has a high probability of producing complex DNA double strand breaks which may be difficult for the cell to restore accurately by metabolic DNA repair processes [6].

1.1. DNA Repair Processes There has been intense interest over the past decade in the metabolic processes by which cells repair DNA damage, specifically DSB. It has become evident that mammalian cells possess complex enzymatic pathways for the recognition, signaling and repair of DNA DSB. A detailed description of these pathways is beyond the scope of the present paper. The ATM (ataxia telangiectasia mutated) protein plays a central role in the damage recognition process [7] by detecting DSB and undergoing rapid autophosphorylation converting it to an active monomer [8], leading to phosphorylation of histone H2AX and subsequent signaling to a variety of downstream transducer and effector proteins. These include the Mrell-Rad50-NBSl complex, which may also act as a damage sensor [9], as well as being involved in both non-homologous end joining (NHEJ) and homologous recombination, the two mechanisms specifically associated with the repair of DSB [10]. NHEJ repair occurs throughout the cell cycle, whereas homologous recombination takes place primarily in cells in the late S and G2 [11]. Other proteins involved include the breast cancer susceptibility' proteins BRCA1 and BRCA2, the latter being particularly associated with homologous recombination, as well as modifiers of DNA topology including the BLM (Bloom's Syndrome) and WRN (Werner's Syndrome) helicases. The NHEJ pathway involves a specific group of proteins, the DNA-PK complex, which recognize broken ends and catalize their joining [12,13]. This joining occurs with little or no requirement for sequence homology. The DNA-PK complex consists of the catalytic subunit DNA-TKcs; and two proteins called Ku70 and Ku80. While the molecular mechanisms by which these proteins effect endjoining are not fully

Non-Targeted Effects of Ionizing Radiation

3

understood, recent evidence suggests that DNA-TKcs undergoes autophosphorylation in response to DNA damage and colocalizes with H2AX [14]. The phosphorylated form of DNA-TKcS may be involved in recruiting the Ku70/Ku80 proteins to the broken ends, initiating their rejoining. Although the joining of broken ends is carried out efficiently by NHEJ repair, this process is error prone. Mammalian cells unable to carry out NHEJ are highly sensitive to the induction of large-scale mutations and chromosomal aberrations by ionizing radiation.

Non-Targeted Effects of Radiation All of the above findings point to the DNA molecule as the critical target in the cell, and DSB as the critical radiation induced lesion. In reality, this has been an accepted paradigm for several decades. Early studies with microbeam irradiation identified the cell nucleus as the important target for the cytotoxic effects of radiation [15], and later studies showed that radiosensitivity was markedly influenced by DNA repair processes [16]. Radiation exposure confined to the DNA molecule by incorporation of the Auger electron emitting radionuclide Iodine-125 incorporated into lododeoxyuridine was extremely cytotoxic and mutagenic [5]. The intense release of energy occurring within a few base pairs of the site of decay of the Iodine-125 in DNA leads to the production of complex DNA double strand breaks which are difficult to accurately repair. A corollary assumption following on this paradigm was that the biological effects of radiation in cells, be they cytotoxicity, mutations or malignant transformation, would occur in the irradiated cells themselves presumably as a consequence of the DNA damage they incurred. Evidence has been accumulating over the past decade, however, indicating that this may not always be the case. It has become evident that radiation can induce a type of genomic instability in irradiated cells that is transmitted to their progeny over many generations of cell replication, leading to enhanced rate at which genetic effects such as mutations and chromosomal aberrations arise in the distant descendants of the irradiated cell. It has also been discovered that irradiated cells may transmit damage signals to non-irradiated cells in a mixed population leading to the occurrence of such genetic effects in these "bystander" cells that receive no radiation exposure. These two phenomena have been termed "non-targeted" effects of radiation. Discussion will be limited in this review to bystander effects observed in dense monolayer cell cultures. There is also an extensive literature on effects arising in normal cells incubated in conditioned medium from irradiated cells, owing to factors released into the medium.

Radiation-Induced Genomic Instability Early evidence for this phenomenon arose from an examination of the kinetics of radiation-induced malignant transformation of cells in vitro [17,18]. Transformed foci did not appear to arise from a single radiation damaged cell; rather, radiation appeared to induce a type of instability in 20-30% of the irradiated cell population which had the effect of enhancing the probability of the occurrence of a second neoplastic transforming event. This second event was a rare one and involved the actual transformation of one or more of the progeny of the original irradiated cells after many rounds of cell division. This transforming event occurred with a constant frequency per cell per generation, and had the characteristics of a mutagenic event [18]. These findings were consistent with the hypothesis that radiation induces transmissible genetic instability in cells that enhances the rate at which malignant transformation or other genetic effects arise in the descendants of the irradiated cells after many generations of cell replication. This hypothesis was subsequently confirmed for the induction of specific gene mutations [19,20] and chromosomal aberrations [21]. This phenomena is usually studied by examining the occurrence of such genetic effects in clonal populations derived from single cells surviving radiation exposure. In terms of mutagenesis, approximately 10% of clonal populations derived from irradiated single cells showed a significant elevation in the frequency of spontaneously arising mutations as compared with clonal populations derived

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Current Trends in Radiation Protection

from non-irradiated cells [20,22]. This increased mutation rate persisted for approximately 30 generations post-irradiation. The molecular structural spectrum of these late-arising mutants resemble those of spontaneous mutations in that the majority of them are point mutations [22,23], indicating that they arose by a different mechanism from that of direct x-ray-induced mutations which involve primarily deletions. An enhancement of both minisatellite [24] and microsatellite [25] instability has also been observed in the progeny of irradiated cells selected for mutations at the thymidine kinase locus, further evidence that a subpopulation of genetically unstable cells arises in irradiated populations. It is of interest that instability as measured in minisatellite sequences of x-ray-transformed mouse lOT^ cells was markedly enhanced when the cells were grown in vivo as compared to prolonged cultivation in vitro [26]. An enhanced frequency of non-clonal chromosomal aberrations was first reported in clonal descendants of mouse hematopoietic stem cells examined 12-14 generations after exposure to alpha radiation [21]. Persistent radiation-induced chromosomal instability was subsequently demonstrated in a number of other cellular systems [22,27-32]. Susceptibility to radiation-induced chromosomal instability differs significantly among cells from different strains of mice [31,33], and similar differences in genetic susceptibility to radiationinduced chromosomal instability have been observed in different strains of human diploid fibroblasts [34]. The fact that Dugan and Bedford [35] found no evidence for induced chromosomal instability in a normal human diploid fibroblast strain may be related to such genetic factors [34]. Furthermore, delayed reactivation of p53 and a persistent induction of reactive oxygen species have been reported in normal human fibroblasts [36] as well as in human fibrosarcoma cells [37]. A persistently increased rate of cell death also occurs in cell populations many generations after irradiation [38-40]. This phenomenon has been variously referred to as "lethal mutations" or "delayed reproductive failure", but has been measured as a reduction in the ability of cells to attach and form macroscopic colonies in a classic clonogenic survival assay. In some cellular systems, an increased rate of apoptotic cell death has been shown to accompany this phenomenon [40-42]. Persistent reproductive failure has been linked to chromosomal instability [42] and malignant transformation [43,44], and evidence presented to suggest that DNA is at least one of the critical targets in the initiation of this phenomenon [45]. Instability was attenuated by treating the irradiated cells with free radical scavengers or allowing potentially lethal damage to be repaired by confluent holding prior to analysing the subsequent development of chromosomal instability [46]. It has been proposed that oxidative stress perhaps consequent to enhanced, p53-independent apoptosis may contribute to the perpetuation of the instability phenotype in these populations [42,44]. The transmission of chromosomal instability in vivo has been reported in several distinct experimental models [47-50], though not in others [51]. Evidence for transmissible instability in irradiated human populations is at present weak [52,53]. While it has been suggested that instability induced in X-irradiated mouse hematopoietic stem cells may be related to the occurrence of the non-specific genetic damage found in radiation-induced leukemias in these mice [54], other work from this laboratory indicates that susceptibility to radiation-induced leukemia/lymphoma is generally separable from sensitivity to induced genomic instability [55]. One interesting model involves the induction of mouse mammary tumors by radiation. Sensitivity to tumor induction was found to be strain specific and to correlate with the induction of chromosomal instability in mammary epithelial cells irradiated in vivo [50]. The induction of such instability was dose dependent. It was subsequently shown that reduced expression of the DNA repair protein DNA-PKcs occurred in the sensitive, cancer-prone mouse strain (BALB/c), leading to inefficient end-joining of DNA double strand breaks induced by radiation [56]. This finding is of interest in relation to the evidence for the involvement of chromosome telomeres in radiation sensitivity and genomic instability [57]. DNA-PKcs has been shown to play an essential role in telomere function and capping [58, 59]. A high frequency of telomere fusions occur in DNA-PKcs deficient cells [59]; the loss of telomeres has been associated with

Non-Targeted Effects of Ionizing Radiation

5

the development of chromosomal instability in cancer cells [60]. Transmissible instability might thus be a consequence of successive bridge-breakage-fusion cycles resulting from telomere loss.

The Bystander Effect in Irradiated Cell Populations The experimental model employed in the studies of the bystander effect to be discussed here involves the exposure of dense monolayer cultures of mammalian cells to very low fluences of alpha particles, fluences whereby only a very small fraction of the nuclei in a cell population will actually be traversed by an alpha particle. This may be accomplished by irradiation from an external source of alpha particles [61] or by use of precision microbeam irradiators whereby specific cells can be targeted [62-64]. The first evidence for this phenomenon was derived from studies of the induction of sister chromatid exchanges (SCE) in monolayer cultures by very low fluences of alpha particles from an external source [65]. An enhanced frequency of SCE was observed in 20-40% of the cells exposed to fluences whereby only about 1/1000 to 1/100 cell nuclei were actually traversed by an alpha particle. This finding was later confirmed and evidence presented to suggest that the phenomenon involved secretion of cytokines or other factors by irradiated cells leading to the upregulation of oxidative metabolism in bystander cells [66,67]. An enhanced frequency of specific gene mutations also occurs in bystander cells in populations exposed to very low fluences of alpha particles [68]. As a result, the induced mutation frequency per alpha particle track increases at low fluences where bystander as well as directly irradiated cells are at risk for the induction of mutations. This leads to hyperlineality of the dose-response curve in the low dose region, and thus a greater effect than that predicted by a linear extrapolation from higher doses. Studies with various sources of microbeam irradiation have provided evidence for an enhanced frequency of micronucleus formation, cell killing and apoptosis in bystander cells [64,69-71], as well as an enhanced frequency of mutations [72,73] and malignant transformation [74]. Changes in gene expression also occur in bystander cells in monolayer cultures; the expression levels of p53, p21Wafl, CDC2, cyclin-Bl and radSl were significantly modulated in non-irradiated cells in confluent human diploid cell populations exposed to very low fluences of alpha particles [75]. These experiments were carried out by western blotting and in situ immunofluorescence staining techniques utilizing confocal microscopy; although only about 1-2% of the cell nuclei were actually traversed by an alpha particle, clusters of cells showed enhanced expression of p21Wafl. This phenomenon involved cell-to-cell communication via gap junctions [75,76], as has also been shown for micronucleus formation [77] and mutations [73]. It appears that radiation exposure itself can enhance intercellular communication as evidenced by an upregulation of Connexin 43 [78]. Evidence for DNA damage in bystander cells was provided by examining micronucleus formation, a surrogate measure of DNA damage; that the upregulation of the p53 damage response pathway in bystander cells was a consequence of this DNA damage is supported by the observation that p53 was phosphorylated on serine 15 [76]. DNA damage occurring in bystander cells, however, appears to differ from that induced in directly irradiated cells. Mutations induced in directly irradiated cells are primarily partial and total gene deletions, whereas over 90% of those arising in bystander cells were point mutations [79]. This finding would be consistent with the evidence that oxidative metabolism is upregulated in bystander cells [67,80], and has led to the hypothesis that the point mutations are a result of oxidative base damage occurring in bystander cells [79]. A similar mechanism has been proposed for the observation that localized cytoplasmic exposure from a microbeam irradiator led to a significant increase in the frequency of point mutations which appeared to involve the generation of reactive oxygen species [81]. Bystander cells defective in the NHEJ DNA repair pathway including mouse knockout cell lines for Ku80, Ku70 and DNA-PKcs are extremely sensitive to the induction of mutations and chromosomal aberrations [82,83]. The mutations in these repair deficient bystander cells were primarily the result of partial and

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Current Trends in Radiation Protection

total gene deletions [83], whereas those in wild type bystander cells were predominantly point mutations. The marked sensitization of repair-deficient bystander cells to the induction of large-scale mutations and chromosomal aberrations may be a consequence of unrejoined DNA double strand breaks occurring as a result of clustered damage arising from opposed oxidative lesions and single strand breaks. In earlier studies, it was reported that alpha particle irradiation could induce the intracellular generation of reactive oxygen species (ROS) including the superoxide anion and hydrogen peroxide [67]. The role of oxidative stress in modulating signal transduction and micronucleus formation in bystander cells was examined in confluent monolayer populations of human diploid cells exposed to low fluences of alpha particles [80,84]. The results support the hypothesis that superoxide and hydrogen peroxide produced by flavin containing oxidase enzymes mediate the activation of several stress inducible signaling pathways as well as micronucleus formation in bystander cells. These include the p53 damage response pathway as well as the MAP kinase family of signaling pathways. It has also been reported that nitric oxide may initiate intercellular signal transduction pathways influencing the bystander response to radiation [85, 86]. It thus appears that ROS may be the primary mediators of the bystander response, reminiscent of the effect associated with radiation-induced genomic instability [44,46]. The activation of MAP K proteins and their downstream effectors in bystander cells [80] is of particular interest in terms of the observation that membrane signaling is involved in the bystander effect in monolayer cultures [87]. Overall, these results support the hypothesis that an upregulation of oxidative metabolism occurs in bystander cells in monolayer cultures. This conclusion is consistent with findings in other model systems [64, 88, 89], and suggests that oxidative metabolism is intimately involved in the bystander response for mutations and chromosomal aberrations. Over 90% of the mutations occurring in bystander cells were point mutations [79] as are classically associated with oxidative base damage. ROS can induce DNA double strand breaks, particularly as a result of opposed oxidative lesions and single strand breaks. However, most of these DSB should be restored in normal cells by recombinational repair, leaving oxidative base damage as the primary mutagenic lesions. When the NHEJ pathway is inactivated, however, DSB repair is compromised and a markedly increased bystander effect was observed; that is, many more bystander cells in the population were susceptible to the induction of these genetic effects. This hypothesis is consistent with the finding that mutations occurring in repair deficient bystander cells were primarily partial and total gene deletions [83], as would result from mis-repaired or non-repaired DSB. The marked increase in the fraction of cells with gross chromosomal aberrations [82] is also consistent with this finding. The relatively small bystander effect for mutagenesis and chromosomal aberrations in wild type cells is thus a consequence of oxidative base damage to DNA. When the bystander cells in the population cannot repair DNA double strand breaks, however, they become much more sensitive to the induction of these genetic effects as manifested by deletion mutants and gross chromosomal aberrations. The results of all of these studies indicate clearly that damage signals can be transmitted from irradiated to non-irradiated cells. In confluent monolayer cultures, this phenomenon involves gap junction mediated cell to cell communication, and appears to involve both the induction of reactive oxygen species and the activation of extra-nuclear signal transduction pathways. Multiple biological effects may occur in bystander cells including cell killing, the induction of mutations and chromosomal aberrations, and the modulation of gene expression. Some evidence suggests that regulation of the p53 damage response pathway may be central to this phenomenon. Finally, preliminary studies with co-culture models both in vitro [90-92] and in vivo [93], as well as with tissue explant models [94] and a mouse bone marrow stem cell transplant system [49], suggest that a bystander effect may occur in vivo.

Implications for Radiation Protection Loeb et al [95] and others have postulated that early in the process of carcinogenesis a mutation may arise in a gene that is important in maintaining genomic stability, yielding a cell lineage with a mutator phenotype.

Non-Targeted Effects of Ionizing Radiation

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This phenotype would enhance the frequency with which spontaneous mutations arise in these cells, and thus facilitate the accumulation of the requisite number of genetic events necessary to produce an invasive cancer. Such an example involves hereditary non-polyposis colon cancer which is associated with a germline defect in DNA mismatch repair. While genomic instability is a hallmark of tumor cells, most types of cancer have not been associated with specific DNA repair defects. The finding that radiation itself may induce an instability phenotype has thus attracted considerable interest. It would suggest that the initial radiation-induced event may be a frequent one involving as many as 10 — 20% of the population, rather than a rare mutagenic event. This increased level of instability which is transmissible over many generations of cell replication would thus enhanced the rate at which multiple genetic events important to the development of cancer would arise in the cell population. However, the degree to which this radiation-induced phenomenon may be of importance in carcinogenesis remains unknown. The fact that it appears to saturate at fairly low doses (of the order of 10-50 cGy) implies that it could influence the extrapolation to low dose effects. Additional research is clearly needed to determine the mechanisms involved in radiation-induced genomic instability, in terms of both the initiating event and how the effect is transmissible for many generations of cell replication, before its implications for the assessment of the carcinogenic risk of low dose, low dose-rate exposure to ionizing radiation can be clarified. Another area where this phenomenon could well be of significance involves potential transgenerational effects of irradiation. The sum of the available evidence suggests that such instability is induced in the germ cells of irradiated parents and is transmitted to the offspring born to them [96]. If exposure to low levels of ionizing radiation thus induces the instability phenotype in germ cells of the offspring of irradiated parents, it is entirely feasible that this instability could increase their susceptibility to cancer or other genetic effects. For example, Pils et al [97] reported that genomic instability manifested by lethal and teratogenic effects may be passed on to two successive generations of offspring in mice after irradiation of the zygote, while Niwa and Kominami [98] and Dubrova and his colleagues [99,100] presented evidence for transmissible germline instability at mouse minisatellite loci. There is preliminary experimental evidence to suggest that an increased susceptibility7 to the induction of tumors may occur in the offspring of irradiated mice [101,102]; the induction of transmissible genomic instability by radiation in germ cells would provide a mechanism for such transgenerational effects. The bystander effect has clear implications in terms of human exposures to very low fluences of high LET particulate radiation, such as alpha particles from environmental radon or densely-ionizing galactic cosmic rays in space [103]. In the case of radon, for example, only a small fraction of a person's bronchial epithelial cells, the presumed target for lung cancer, will be hit each year by an alpha particle arising from residential radon exposure. In the past, the genetic or carcinogenic risk has been assumed to be related directly to the number of cell nuclei actually traversed by an alpha particle, thus yielding a linear dose response relationship. The evidence that irradiated cells may transmit damage signals to neighboring non-irradiated cells that result in genetic alterations in these "bystander" cells would invalidate this assumption. Rather, it would suggest that the dose-response curve may be non-linear at low mean doses yielding a greater effect than that predicted on the basis of the dose received by individual cells at low alpha particle fluences. Evidence for the convergence of these phenomenon is also of interest [104,105]. Studies involving both in vitro and in vivo assays have shown, for example, that transmissible genomic instability may arise in bystander cells [106,107]. Defects in the NHEJ DNA repair pathway have been associated with both radiation-induced genomic instability [56] and the bystander effect [82]. It has been reported that conditioned medium from certain (but not all) unstable clones harvested many cell generations post-irradiation is highly cytotoxic to unirradiated cells [108]. Finally, oxidative stress manifested by enhanced levels of reactive oxygen species has been implicated in both phenomena.

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When considered as a whole, the emerging results suggest that the risk of low level exposure to ionizing radiation remains uncertain; a simple extrapolation from high dose effects may not always be justified. In some cases, such as the induction of mutations by exposure to very low fluences of high LET particles, or as reported for the cytotoxic effects of very low doses of x-rays [109], the effect may be greater than predicted by a linear extrapolation from higher doses. On the other hand, certain studies of malignant transformation have revealed a reduced effect for very low doses [110,111]. Overall, however, these findings imply that the biological effects of radiation in cell populations may not be restricted to the response of individual cells to the DNA damage they receive, but rather that tissues respond as a whole. A better understanding of the mechanisms for these phenomenon, the extent to which they are active in vivo, and how they are interrelated is needed before they can be evaluated as factors to be included in the estimation of potential risk to the human population of exposure to low levels of ionizing radiation.

ACKNOWLEDGMENTS Supported by Research Grant DE-FG02-98ER62685 from the U.S. Department of Energy.

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Current Trends in Radiation Protection H. Metivier, L. Arranz E. Gallego and A. Sugier (eds.)

Effects of Ionising Radiation in the Low Dose Range Radiobiological Basis Christian Streffer1 Institute for Science and Ethics, FB Philosophic, University of Dmsburg-Essen, D-45117 Essen, Germany

Abstract. Risk assessment after exposures to low radiation doses is performed by extrapolation from measured data in higher dose ranges to low doses where no significant increase of health effects predominantly cancers can be observed. For this process the LNT dose response is used which has not been proven on a strong scientific basis and bears uncertainties. In the low dose ranges not all cells are hit but the radiation dose per hit cell especially with high LET radiation can be appreciable. The damaged sites in the critical target molecule DNA which frequently occur in clusters can be repaired, however, also misrepair exists. The consequences are chromosomal aberrations, cell transformations and mutations. These events measured even after 10 mSv can be best described generally by dose responses without a threshold. Also animal experiments are very valuable for the evaluation of cancer risk after radiation in order to study dependences on radiation dose, dose rate and radiation quality although significant effects need doses higher than 100 mGy. Several dose modifying biological phenomena like adaptive response, apoptosis, hyperradiosensitivity genetic predisposition, genomic instability, bystander effects and immune response have to be considered when a judgement is done with respect to the dose response.

1. INTRODUCTION The risk assessment for exposures to ionising radiation in the low low dose range is a very important question for radiological protection. For risk evaluations, the shape of the dose effect curves for the various radiation effects is of eminent significance. Two principal categories of dose effect relationships have been described. The most significant feature is whether a threshold dose does exist (deterministic or non-stochastic effects), or whether no threshold is assumed (stochastic effects) [1]. Manifold experimental studies of radiation effects with molecular structures, cells and animals after radiation exposures and clinical experiences as well as epidemiological studies which have been observed after the exposure to ionising radiation in man are the

1

E-mail: [email protected]

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basis for these discussions [2-7]. In the first case radiation effects are only observed when the radiation doses are higher than the corresponding thresholds. Especially the acute but also some late radiation effects, which are mainly caused by cell killing in the corresponding organs and tissues, fall into this category. As the thresholds for these effects are higher than several hundred mSv (or mGy in the case of low LET radiation), these effects have no or only little relevance for the risk assessment in the low dose range. For the second type of dose effect relationships, it is assumed that a threshold dose does not exist. Into the category of these stochastic effects fall genetic effects, the induction of cancer [8] as well as some developmental changes after prenatal radiation [9]. For the development of these radiation effects, non-lethal changes of the genome in the corresponding cell nuclei are of significance (mutation, cell transformation). For the mechanisms on which such dose effect relations are based it is assumed that genetic changes in a single cell are sufficient in order to induce this type of damage [6,10-12]. For risk evaluation, it is assumed further that stochastic effects increase proportionally in the low and medium dose range with radiation dose. In the higher dose range the frequency of radiation effects may decrease when cell killing occurs and dominates the dose effect curve [8]. The shape of these dose effect relationships especially the concept of no-threshold is under strong debate. This major arguments will be discussed in the follwing especially with respect to carcinogenesis. The importance of the number of cells in the initiating process for the development of radiation late effects have been shown in experiments with the very early stages of the mammalian development. Studies on the induction of a specific malformation (gastroschisis) have shown that a dose response without a threshold dose is only observed when the radiation effect develops from one damaged cell. In this case the mouse zygote (1-cell embryo) was irradiated 1 to 3 hours post conception and this resulted in a dose response curve without a threshold while the irradiation of a multi-cellular preimplantation mouse embryo (32- to 64-cell embryos) resulted in a dose response with a threshold [11]. Such a mechanism originating from one damaged cell is obvious for genetic, but less obvious for carcinogenic and under certain conditions for developmental effects. If the genome is changed in one single germ cell and if this germ cell becomes fertilised or fertilises a female mature germ cell, organisms will develop which carry the genetic mutation. Similarly, it is assumed that cancers can develop from one damaged cell after a radiation exposure which would also result then in a dose effect curve without a threshold. Measurable effects have been observed, however, only after radiation doses of around 100 mSv. Only in some special cases it has been found that doses below 100 mSv induce such carcinogenic or developmental effects. After chronic exposures (exposures over a longer period usually weeks, months or even years) the dose ranges may be even higher before measurable effects occur. In order to assess the radiation risk in the lower dose range it is necessary to extrapolate from the higher dose ranges where measured data are available. (Figure 1). The so-called Linear-No-Threshold (LNT) concept has been proposed and used for risk evaluation through extrapolation into the low dose range [8]. During recent years it has been intensively and passionately discussed whether the shape of the dose effect relationship can be described with a linear dose response and no threshold (LNT), whether a threshold or even a superlinearity exists in a dose range in which no health effects can be measured directly. The LNT is proposed by most international bodies, which are responsible for radiological protection, like ICRP (Figure 1). There are numbers of biological processes, as DNA repair, adaptive response, apoptosis, stimulation of immune responses which may modify the primary molecular and cellular radiation damage in that way that the health effects of ionising radiation are lowered and an apparent threshold occurs or even beneficial effects of ionising radiation are assumed (hormesis) [13,14] (Figure 1). It is also discussed that the induction of genomic instability and of effects in non-hit cells (bystander effect) may increase the radiation effect in the low dose range and then may lead to a supralinear dose response (Figure 1) [12]. This means that the

Effects of Ionising Radiation in the Low Dose Range

15

Possibilities of Extrapolation into the lower Dose Range

Figure 1. Different extrapolation possibilities of effects from medium and high radiation doses to lower dose ranges (modified from Streffer et al. in press [68])

question of a linear dose effect relation without a threshold remains open and is a matter of debate (Workshop Report: Cellular Responses to Low Doses of Ionising Radiation, United States Department of Energy and the National Institutes of Health) [15]. The uncertainties for the radiation effects in the low dose range are high especially for carcinogenesis. In order to improve these extrapolations, knowledge about the development of stochastic radiation effects and their mechanisms is very important and must be improved. The manifestation of a clinically diagnosed cancer is the endpoint of a sequence of mutations connected with changes of gene expression and of the regulation of cell proliferation. Under the consideration that cancer is induced through several mutation steps [16] it is not clear to which extent intermediate cells in the process of malignant cell transformation appear, at which time the first malignant cells are really formed and clonal growth of malignant cells starts for the development of a cancer. The question is unsolved whether these processes start already during the first steps of malignant cellular transformation or whether these processes develop only in a preneoplastic lesion several years after radiation exposures. While cell transformation can be investigated in vitro, the later processes of carcinogenesis can only be studied indirectly in animals and humans. Investigations of cancer incidence and mechanisms suggest that four to six independent steps are necessary for most cancers. For the development of leukaemias the number of mutation steps may be smaller. In many studies during recent years it has been shown that genomic instability develops many cell generations after radiation exposures [17,18] and these phenomena may accelerate the development of cancer, as the mutation rate in tissues with these genetically instable cells is increased. An apparent threshold dose can be caused by the long latency period between a radiation exposure and the manifestation of cancer [19]. This latency period may be longer than the lifetime of an exposed

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individual. These considerations show clearly that it is absolutely necessary to obtain a better knowledge about the mechanisms for the development of cancer after radiation in order to evaluate the measurements and extrapolation procedures for the low dose ranges. For a better understanding of the mechanisms, it is necessary to describe the molecular and cellular effects of ionising radiation, which are connected to the development of cancer. Further experimental data with animals will be reported which are important for the evaluation of these mechanisms. The development of genetic mutations will be considered in the same way. In this connection, it is necessary not only to discuss the effects of low LET radiation but also to analyse the effects of high LET radiation and to include these investigations into the risk evaluation. In this connection, it should be mentioned that large parts of the exposures from natural sources are caused by high LET radiation (e.g. radon and its decay products). During recent years, it has become increasingly apparent that individual radiosensitivity can be very different. A number of genetic syndromes have been recognised with increased individual radiosensitivity [20]. These have been especially observed with patients who received radiotherapy and showed a remarkable increase of radiosensitivity. Cellular and molecular investigations with biological material from such patients make it possible to study radiation effects in smaller dose ranges than with persons of normal radiosensitivity. Therefore, it is important to include such studies with hypersensitive patients into the discussion.

2. DEFINITION OF A LOW RADIATION DOSE It has already been pointed out that health effects of ionising radiation cannot be observed in the dose ranges to which our populations are exposed in the environment or usually at working places. Dose distribution is dependent on the physical processes, which occur when the energy of ionising radiation is absorbed by interaction with atoms or molecules of the living organism. The spatial and temporal distributions of these events and the following biological processes are important for the development of radiation effects. Therefore, physical and biological considerations must be discussed for the definition of a low radiation dose. With the transfer of energy of ionising radiation within materials, energy absorption takes place, covalent bonds are broken and ions or radicals are formed. These reactions can directly occur in biologically essential molecules like DNA (direct radiation action) or with water molecules of which the number in living cells is largest. In the latter case radicals of the water (cf. H, OH) are formed which then can react with other molecules like DNA and lead to corresponding damaging events with chemical reactions (indirect radiation action). The transfer of energy occurs in cells and tissues in discrete energy packages. For the development of stochastic radiation effects the changes in the DNA by both direct and indirect radiation actions are considered important. The averaged energy dose (dE/dm), used in radiological protection, does not describe the large variability of energy absorption in micro-regions which results from the stochastic nature of energy deposition events in individual cells and molecules especially when the energy dose is considered in the low dose range.In medium to high dose ranges of low LET radiation (100 mSv and higher) a relatively homogeneous exposure of cells and tissues occurs. This changes in the low dose range when the effects of single ionising particles have to be considered. On the cellular and sub-cellular level microdosimetric considerations have to be introduced under these conditions. Thus the absorbed dose in a single cell nucleus amounts in average to 1 mGy for cobalt-60 (Co-60) 7-radiation when in average one ionising particle of this radiation passes through the spherical cell nucleus with a diameter of 8 um [6,21]. When a tissue with many cells (several hundred millions cells per g tissue) receives an averaged dose of 1 mGy only 63.2% of the cells in the tissue will be hit. Some cells experience a track of one particle others will be hit by several particles. This percentage of unhit cells increases with decreasing dose. With an average tissue dose of 0.1 mGy about 9% of the cells will be hit and around 0.5% of the cells will have more than one track of ionising particleslf the energy deposition in a single cell nucleus is sufficient for the induction of radiation damage and an interaction between damaged cell nuclei is not necessary for the cancer development, it is very probable that a dose effect

Effects of Ionising Radiation in the Low Dose Range

17

relationship without a threshold dose exists. However, the possibility must be considered that especially for low LET radiation at least two independent particles have to pass the cell nucleus in order to develop a radiation damage. From more recent experiments, however, it has to be considered that unhit cells can show an altered gene expression when a cell was hit in the neighbourhood. Thus, an increased expression of the protein p21 was observed even in unhit cells [18]. The mechanism of these phenomena is unexplained up to now. In addition, the development of other radiation effects have been observed in non-irradiated cells in the neighbourhood of irradiated cells (bystander effect) [15]. The situation with respect to dose distribution is completely different for the exposure to densely ionising radiation with high LET. a-Particles have a very short range in tissue that is dependent on the energy of the a-particles which are formed through radioactive decay of the corresponding radioactive isotopes. Thus for a-particles which are released after the radioactive decay of radium-226 (Ra-226) with its radioactive daughter products with energies of up to about 7.8 MeV a maximal range of around 80 um is observed in mammalian tissues. For 5 MeV a-particles of plutonium-239 (Pu-239) the maximal range is around 40 um in biological tissues. If one considers that the diameter of cell nuclei of human cells is in the range of 5 to 10 urn and the diameter of the cells in the range of 10 to 30 um this demonstrates that a-radiation can reach in average around 1 to 2 and maximally up to 5 cell layers from their place of origin. The energy, which is deposited by one single a-particle passing through the cell nucleus, which is thought to be the radiosensitive target of the cell, is extremely variable. The energy dose can vary from very small doses (in the range of mGy) up to more than one Gy even between microregions of the same cell nucleus. These considerations demonstrate clearly that the definition of average tissue doses is an oversimplification for energy deposition of high LET radiation. Under these circumstances only less than 0.2% of the cell nuclei are hit by an a-particle if the cells of a tissue receive an averaged dose of 1 mGy of a-radiation, while more than 60% of the cells are hit by Co-60 7-radiation at the same averaged tissue dose. With such an averaged radiation dose of 7radiation, around 99.8% of the cells experience no radiation event at all. On the other hand, when an a-particle (with energy of around 5 MeV) hits a cell nucleus a high-energy deposition will occur in the corresponding cell nucleus on average in the range of 370 mGy [6]. Thus in the low dose ranges (averaged tissue doses of 1 mGy or smaller) ionisation events will occur only in a part of the cells and the number of hit cells depends significantly on the radiation quality (radiation energy and type of radiation). This means that small doses can be defined based on these microdosimetric considerations and they are very heterogeneously distributed on the cellular and sub-cellular level. By means of computer programs which are based on Monte-Carlo calculations it is possible today to calculate the exact position of ionisations and excitations in the track of ionising particles. If one traces the tracks of these particles in the tissue, one can observe that low LET ionising particles, like electrons, meandrise in tissues through the processes of diffraction and they can migrate into very different directions. In contrast to electrons, heavy charged particles (cf. helium, carbon, and argon nuclei) migrate on more straight tracks in well-defined modes through the tissue. The structures of the tracks and the following energy deposition with the ionisation events are of great significance for the development of biological effects. Clusters of energy deposition and of primary chemical changes occur which then develop into biological effects [6,22,23]. The ionising events are caused by secondary electrons, which are released by the interaction of the photons from X- or 7-rays with cellular molecules. Thus, in average around 70 ionisations occur through these electrons at a nuclear passage of a quantum of Co-60 7-radiation. This corresponds to an averaged observed energy dose of 1 mGy in the cell nucleus as it has been described before. In case of an 4 MeV a-particle around 25,900 ionisations occur when the particle passes through a cell nucleus. This corresponds to an observed dose of around 370 mGy [6]. In a cell, the indirect effects, which are mainly caused by formation of water radicals and their reactions with biological macromolecules (e.g. DNA) also occur in a range of small distances of several nm. The presence of radicals at a certain time is very limited in tissues due to the high chemical reactivity of the radicals.

18

Current Trends in Radiation Protection

Although it is difficult to estimate the contribution of direct or indirect effects for the damage of DNA through low LET radiation, studies with radical scavengers demonstrate that around 35% of the primary DNA damage comes exclusively from direct effects and 65% of the damage is caused by contributions through indirect effects. It is not completely clear whether the molecular nature of the damage in biological molecules, cf. in the DNA, differs from direct or indirect radiation damage. Another possibility exists in order to describe the low dose range based on biological effects. After the exposure to low LET radiation (Brays, 7- and X-rays) the extent of radiation effects can be described by dose effect relations with a linear and a quadratic term of the dose cf. for chromosomal aberrations, somatic mutations and cell transformation. Further, it has to be regarded that biological effects, which are observed after radiation exposures, like chromosomal aberrations, mutations or cancer, already occur without any radiation (spontaneous effects). For this reason, a constant term "C" has to be considered additionally in possible equations. A dose effect curve can then be written in the form: E(D) = aD + BD2 + C.

(eq.l)

In this formula a, and B are constant coefficients for the linear and quadratic term of the dose respectively. These coefficients vary for different endpoints and possibly also for various defined radiation conditions. Such dose effect relationships have been studied after radiation exposures especially for chromosomal aberrations, mutations and cell killing. Frequently a/B-ratios of around 200 mGy have been observed for Co-60 7-radiation. This corresponds to a medium radiation dose after which the linear and the quadratic terms contribute to the radiation effects to about the same extent. From such a value it results by calculation that the action of radiation increases in a linear way in the low dose range with radiation doses up to around 20 mGy, as the contribution of the quadratic term is low in this dose range. Then the contribution of the quadratic term amounts to around 9% of the whole radiation effect. Even after 40 mGy the contribution of the quadratic term is only around 17% of the total radiation effect. On this basis and convention a radiation dose in the range of 20 to 40 mGy has been called a low dose [6]. In an earlier UNSCEAR report [4] experimental data were analysed for the carcinogenesis after irradiation (especially of mice) with various dose rates of a low LET radiation. It was concluded and proposed based on these data that a dose rate of around 0.06 mGy per minute can be considered as a low dose rate when the exposure lasted for some days or even weeks. With such a dose rate, the induction of the tumour frequency was reduced in comparison to higher dose rates when equally total doses were compared. With smaller dose rates than 0.06 mGy per minute, no further reduction of the tumour rate per dose unit was obtained. The UNSCEAR committee therefore concluded that a dose rate of 0.05 mGy per minute could be considered as a low dose rate. The evaluation of epidemiological data for carcinogenesis in humans resulted that a radiation dose of less than 100 mGy (mSv) of low LET radiation was considered as a low dose, as no radiation effect can be observed in this dose range for general populations (both sexes, all age groups). After exposures to high LET radiation, dose effect relations are generally observed where only the linear dose term of equation (eq.l) is relevant, the quadratic term becomes very small. Then equation 1 is modified to equation 2. The impact of dose rate is apparently not very important for high LET radiation.

3. DNA DAMAGE AND ITS REPAIR DNA strand breaks (breaks of the polynucleotide chain), as well as changes or loss of DNA bases can occur by energy absorption of ionising radiation. DNA strand breaks can be formed in one DNA strand (single strand break, SSB) or in both DNA strands near to each other (double strand breaks, DSB). With low LET radiation these events can be singular, isolated processes. Such isolated damaging events can generally be

Effects of Ionising Radiation in the Low Dose Range

19

repaired very rapidly by various cellular enzymes (within minutes and few hours). This is especially the case for base damage and SSB. The repair of DSBs is more complex and takes a longer time and misrepair is more frequent for DSB than for SSB or base damage [6,24]. However, clusters of damaging events in the DNA can also occur which lead to more complex DNA damages. Thus, a second DSB, SSB or base damage can occur in the direct neighbourhood of a SSB or DSB in the DNA [22,23]. Such clusters are only slowly repaired or misrepaired. The complex radiation damaging events in the DNA occur to a much larger extent through an ionising particle with high LET than through low LET radiation [25]. Clusters are more frequent and the number of damaging events in these clusters is higher. This is probably the reason that DNA damages which occur after exposures to high LET radiation are repaired to a smaller extent than DNA damages caused by low LET radiation and the repair takes longer. The DNA repair measured through the comet assay [26] in human cancer cells after exposure to X-rays or cyclotron neutrons (6 MeV). In principle, the same occurs in all living cells including normal cells. In many cases the products of radiation damage to DNA have been identified with respect to their chemical nature and classified. In Table 1, the most important classes of damage to DNA and chromosomes, which have been measured after exposures to low LET radiation, are described and numbers are given. These quantitative data are rough estimates after an absorbed dose of 1 Gy. The data in Table 1 show that after a radiation dose of 1 Gy of low LET radiation around 70.000 ionisations occur in the cell nucleus of which around 2.000 are directly occurring in the DNA. These primary physical events lead to the listed chemical/biochemical changes in the DNA. Mainly DNA SSB and base damages are formed. For the development of biological effects the DSB, however, are of greatest significance and are most relevant for the development of radiation effects. Studies show this with correlation of complex DSB which remain unrepaired or which are misrepaired and biological effects like chromosomal aberrations and cell death after irradiation. The numbers make clear that due to the efficient DNA repair apparently only a small part of the DNA damaging events lead to severe genetic changes like chromosomal aberrations and cell transformations which can lead to health effects like cancer and mutations. It can be assumed that the number of these damaging effects decreases in a proportional manner with a decreasing radiation dose. Thus, the severity and rate of radiation health effects result not from the total number of primary damaged sites in the DNA but from the remaining unrepaired or misrepaired damages. The probability with which the DNA damages are repaired or not correctly repaired has a great influence. After exposures to high LET radiation the latter are doubtlessly higher. Some of the DNA damages, which are caused by ionising radiation, are similar or equal to those damages, which develop from endogenous processes, especially from metabolically formed oxidative radicals in the cell. This is especially valid for ionising radiation with low LET. These "spontaneous damaging events" are caused through the thermic instability of DNA as well as through endogenous oxidative and enzymatic processes [6]. Oxidative radicals are produced within cells by a large number of metabolic processes, like amino acid oxidase and others. These radicals attack the DNA and lead to base damages as well as to nucleotide breaks. However, these events are randomly distributed over the whole genome mostly as single events. A similar situation is valid for chemical substances especially in the low ranges of concentrations because the reactions of single molecules (cf. alkylation of DNA bases) are again more randomly distributed in the DNA and occur as singular events. Therefore, changes of the DNA through ionising radiation are different from other damaging processes of DNA as by oxidative radicals especially in low dose ranges. While SSBs and DNA base damages can be repaired very rapidly in most cases a repair of DSBs is much more difficult and different enzymatic processes are necessary. In order to repair such damages successfully, several enzymes from different repair pathways may be needed. A large number of DNA repair enzymes have been described as cellular proteins. Special enzymatic proteins recognise the damaged positions, cf. damaged DNA bases, and these positions can be removed from the DNA polynucleotide chain by nucleases. A new DNA repair synthesis then follows the broken polynucleotide chain is closed again. The principle

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Current Trends in Radiation Protection

Table 1. Some types and numbers of the damage in a mammalian cell nucleus from 1 Gy of low-LETradiation (modified from Goodhead 1994, [23])

Initial physical damage

Numbers of damage

lonisations in cell nucleus

~ 70, 000

lonisations directly in DNA

~ 2, 000

Excitations directly in DNA

~ 2, 000

Selected biochemical damage (Ward 1988) DNA single-strand breaks

1,000

8-Hydroxyadenine

700

T* (thymine damage)

250

DNA double-strand breaks

40

DNA-protein cross links

150

Selected cellular effects Lethal events

~ 0.2 -0.8

Chromosome aberrations

~1

HPRT-mutations

~ 10 -5

enzymatic processes are the same or similar to those which perform the normal DNA metabolism (cf. DNA polymerases, DNA ligases etc.). However, very different types of DNA polymerases and ligases have been identified which have different functions concerning the repair of different damage classes. Theses repair processes are not verified in all steps; especially the connected processes of regulation of the connected enzymatic processes are only partly understood. In mammalian cells, including human cells, processes of recombination of DNA helices have apparently significant importance [6]. The numbers of enzymes, which are necessary for such events, are much larger. It is also possible that illegitimate recombination and misrepair processes occur under these conditions. Under these circumstances it is possible that changes of the DNA sequence and loss of DNA sequences occur. Especially illegitimate recombination processes, which occur very rapidly after high radiation doses, can lead to mistakes [6]. The complex severe damages which apparently occur also in the low dose range, although with less probability, lead to the situation, however, that a part of these damaging effects after exposure to ionising radiation cannot be repaired or misrepair occurs even after low radiation doses. In this connection it is of special interest that the numbers of measured DSBs do not show large differences when they are measured directly after the exposures to ionising radiation with comparable energy doses of low or with high LET. Such differences, however, are seen when the cells have had time for DNA repair. The RBE-values for DSBs are almost one directly after radiation exposures but they increase generally into the range of 2 —10 or in special cases even higher when chromosomal aberrations, mutations and other health effects are measured. This finding underlines that the DNA damage observed directly after radiation exposures is not so relevant for the risk evaluation as the remained DNA damage after completion of DNA repair.

The damaged DNA sites are apparently recognised very quickly in living cells by specialised enzymes and can be repaired to a large extent if the complications discussed above do not occur. The irradiation of human lymphocytes in vitro with 2 Gy X-rays (low LET radiation) and the observation of DNA repair

Effects of Ionising Radiation in the Low Dose Range

21

have demonstrated that the repair occurs in normal persons with an efficient DNA repair capacity within about 3 hours to a large percentage of the damage. However, in these experiments only the disappearance of DNA strand breaks has been investigated [26]. This also includes misrepair. The repair capacity can vary strongly between individual persons. A number of syndromes have been described where through a genetic predisposition certain DNA repair pathways are reduced or are deficient. Frequently it has been observed that in such individuals the DNA repair of radiation damage is less and the radiosensitivity is increased. It has been observed by molecular genetic studies that the genes which are necessary for the expression of DNA repair enzymes can be mutated or deleted in human individuals which leads to genetically based diseases (c.f. xeroderma pigmentosum, ataxia telangiectasia AT, cokayne-syndrome, Fanconi-anaemia and others). Further, it has been shown that a number of enzymes, which participate in DNA repair, have an influence on the regulation of the cell proliferation cycle. After a mitotic cell division, proliferating daughter cells have to go through several phases before a next cell division can take place. During the GI-phase, the cells prepare with RNA- and protein synthesis for DNA synthesis in the S-phase. After the doubling of the DNA there follows the G2-phase again with RNAand protein synthesis and the preparation for the next mitosis. These processes are regulated by a number of proteins frequently phosphorylated. One of these key proteins is p53, which is the gene product of a tumour suppressor gene. This gene is mutated and produces therefore an inactive protein in around 50% of human cancers [27]. The active p53 also stimulates apoptosis. After radiation exposures, a block in the cell cycle is observed before the cell enters into the S-phase (Gi-block) or into mitosis (G2-block). These blocks apparently give the cells additional time for DNA repair and they are therefore called checkpoints [6, 28,29] This means that regulating processes of the DNA repair are frequently connected with those of cell proliferation. These processes have a high significance for the development or inhibition of radiation effects especially in the low dose range. In conclusion, living cells are equipped with very rapid and efficient DNA repair systems. They recognise radiation-induced DNA damage very quickly. They try to eliminate the damage and to achieve a restitution of the original structure and genetic information. There exist many different repair mechanisms for the various types of DNA damage, which differ with respect to the velocity and the fidelity of the repair. Misrepair can occur which happens apparently especially with complex DSBs. Damage after exposure to high LET is less efficiently repaired than damage after low LET radiation. This is one decisive reason why high LET radiation is biologically more effective than low LET radiation when the same energy doses are compared. The regulation of DNA repair systems is very important. As many genes are involved, DNA repair deficiencies occur by mutations of these genes with a comparatively high frequency in human populations. Such genetic disorders lead to individual differences in radiosensitivity.

4. CELLULAR DAMAGES Many investigations have been performed with mammalian including human cells after exposure to ionising radiation in vitro. Cell killing, chromosomal aberrations, cell transformation and gene mutations have been studied. Cell killing usually has been observed after doses above 0.5 Gy low LET radiation whereas an appreciable number of investigations of the other endpoints have also been published with lower radiation doses. For all these radiation effects, irreversible DNA damage is decisive which has not been repaired or is misrepaired. In the case of cell death, two main mechanisms can be distinguished. On the one hand chromosomal damage develops from direct ionising events in the cell nucleus, the cells go despite this chromosomal damage through several cell cycles and die in later cell generations, they loose the ability of clonogenicity. This process is called reproductive cell death. On the other hand through signals at the cell membrane and signal transduction, a cascade of hydrolytic enzymatic processes is started which leads to hydrolytic degradation of cellular macromolecules. This process is called apoptosis (cell suicide). During mitotic cell divisions

22

Current Trends in Radiation Protection

after radiation exposures chromosomal breaks are observed, also translocations occur which can be the basis for cell transformations. This is apparently the first step for the development of a cancer. If the radiation damage of the DNA is not so severe, the cell can further proliferate, it does not loose its clonogenicity and a clonogenic cell with a mutation develops. Experimental data with respect to the mechanisms demonstrate that especially DSBs in the DNA are the decisive primary radiation events from which cell transformation and chromosomal aberrations, as well as gene mutations, develop. For these effects interactions between several damaged cells are apparently not necessary and recent investigations in which single cell irradiations have been performed have yielded that the passage of one ionising particle through the cell is sufficient in order to cause such damages. This is the case even after exposures to radiation with low LET. A threshold dose for such effects can only be expected if a complete DNA repair could be performed. As it has been discussed already before, there are no indications that such a perfect DNA repair exists. However, under certain circumstances it is possible that DNA repair can apparently be stimulated and then a so-called "adaptive response" can be observed. These phenomena will be discussed later.

4.1. Chromosomal aberrations For the investigation of chromosomal aberrations, peripheral human blood lymphocytes have been used in many cases. The studies of dicentric chromosomal aberrations after the exposure to ionising radiation are dominating. These types of aberrations are relatively specific for ionising radiation as they are induced significantly by ionising radiation but only by a few chemical substances. Very extended investigations of the dose relationships after exposures to X-rays or 7-radiation have yielded that radiation doses in the range of 100 mGy lead to a significant increase of dicentric chromosomal aberrations. Linear dose relationships have been found in the low dose range for X-rays under very careful studies and the evaluation of large numbers of cells. With high efforts, it is possible to detect also radiation doses below 100 mGy down to around 20 mGy [30]. Based on these careful and extended studies it can be expected that an observation of significant effects for chromosomal aberrations is not possible below 20 mGy. Therefore, the possibility of a threshold dose in the range around below 10 mGy cannot be excluded for this effect in principle. However, extrapolations give the best fit with dose effect relations without a threshold. Irradiation with high LET radiation lead to linear dose effect curves over the whole dose range of low doses up to around 1—3 Gy. A reduction of this effect with decreasing dose rates does not occur in the case of high LET radiation. Therefore, the occurrence of threshold doses can apparently be excluded for such radiation qualities. In contrast, irradiation with low dose rates lead to reduced effects in comparison to high dose rates after exposures to low LET radiation.

4.2. Cell transformation Cell transformations after the exposure to ionising radiation and the damage of the genetic material e.g. by forming DSBs have been understood as the initiating step for the development of cancer. With the present knowledge, DSBs and possibly their misrepair are apparently participating in these processes [6]. These events have been studied in manifold experiments with cell systems in vitro. Normal cells, like fibroblasts, grow in in vitro cultures in monolayers. However, when cultured cells are transformed to malignant cells these cells grow in a multilayer manner, they form large clones. It has also been shown that these transformed cells can form tumours when they are injected into mammals e.g. murine cells into mice. Most studies of cell transformation have been performed with the cell lines C3H10T1/2 and BALB/C3T3. Both cell lines originate from fibroblasts, which have been obtained during the prenatal development of mice. In the course of recent years it has been shown that these cell systems are not ideal for the investigation of tumour development in humans as they develop into fibrosarcoma after the transformation in vitro and

Effects of Ionising Radiation in the Low Dose Range

23

transplantation of the transformed cells into mice. However, in humans epithelial cancers and not fibrosarcoma are increased after irradiation. Until recently, the search for an appropriate human cell system was not very successful. Therefore, the data, which have been obtained with murine cell lines, will be reported here. Generally, it has been shown that radiation doses of 100 mGy and higher are necessary in order to observe significantly increased effects. As with chromosomal aberrations linear and linear-quadratic dose effect curves have been described for these radiobiological effects. After exposure to low LET radiation, a dose rate effect has been found again as has been described for chromosomal aberrations. In a larger study with six laboratories, the dose dependence of cell transformation with low LET radiation inCSHIOT1/2cells has been studied [31]. The irradiation and the cell cultures have been performed under identical conditions in these experiments. The irradiation with 250 kVp X-rays in a dose range of 250 mGy to 5 Gy and the culture was performed in one of the six laboratories. The evaluation of the cultures was performed in all six laboratories in a parallel fashion. With these extended studies a linear dose effect relationship was found in the investigated dose range when the frequency of transformed cells was calculated based on surviving cells. These data and the analysis of the resulting dose effect curves do not give an indication that a threshold or a super-linear shape of the dose effect curve occurs in the low dose range. The dose effect curve for the rate of transformations per surviving cell shows a linear term of the dose (value for the constant a) in the range of 0.83 ± 0.08 X 10-4 . As the same methods have been used in all six laboratories, the deviations were smaller than a factor 2 in the individual laboratories. Therefore, a very good agreement has been found for these transformation rates between the different laboratories. For the effect of cell transformation, an adaptive response has also been described. In a dose range of 1 to 100 mGy, given as adapting dose, it was possible to reduce the cell transformation rate with C3H1OT1/2-cells after higher doses than it was seen with cells without an adapting dose. Higher frequencies of transformed cells were observed after high LET radiation than after low LET radiation comparing the same absorbed radiation dose. The phenomenon of dependence of radiation effects on radiation quality is also seen for cell transformation as it has been described with other radiation effects. Studies of single cell irradiation again with CSHlOT1/2-cells have also been performed with a-particles. The effects of single a-particles were compared with the effects of up to 8 a-particles per cell. If only laparticle passes through a single cell nucleus an increase of the transformation rate per cell of about 30% was observed. However, this effect was not statistically significant. In contrast, the transformation rate increased significantly in a cell population when the cells were hit by la-particle on the average. However, under these circumstances the possibility existed that in some single cells several a-particles per cell could pass the cell nucleus. The possibility exists that under these conditions an appreciable number of transformed cells was caused in cells which were passed by several a-particles and that these multiple passages were the decisive mechanisms of cell transformation [32].

4.3. Gene mutations in somatic cells The investigation of gene mutations after radiation yielded principally very similar data as has been observed for cell transformation. This is valid for low LET as well as for high LET radiation. Again, linear dose effect relationships with the smallest dose of 250 mGy as a statistically effective dose were observed. For a -particles, a RBE of 4 was found [33]. A gene mutation is a relatively rare event. Experimental systems have been developed in which a gene mutation leads to the loss of an enzyme (gene product) which usually metabolises a substrate so that it becomes toxic for the cells. If the enzyme is lost, the metabolic reaction cannot take place and the corresponding cells survive [6]. With respect to gene mutations, frequently the mutation rate in the gene for the enzyme hypoxanthine-guanine-phosphoribosyltranferase (HPRT) was studied. After mutation of this gene an inactive enzyme protein is synthesised, the cells lose the ability to metabolise 6-thioguanine and thus gain resistance against this drug and the cells with the mutation survive. In a similar

24

Current Trends in Radiation Protection

mode, mutations can be studied in the gene for the enzyme thymidin-kinase. These enzyme systems are found as very appropriate biological systems for such studies as the survival test is comparatively simple. It has already been pointed out that DSBs in the DNA are the essential damaging events for the development of cellular radiation effects (chromosomal aberration, cell transformation and gene mutation). It has been indicated by many experimental studies, however, that there is no stringent proof for such a developing chain. Comparative studies on the induction of DSBs in DNA, and for various cellular effects after irradiation with different radiation qualities, have demonstrated that the RBE values for these various endpoints do not agree with each other if DNA repair has not taken place. While RBE values in the range of around 5 — 20 have been observed for the induction of chromosomal aberrations, cell transformation and genetic mutations, the RBE values for primary DSBs measured directly after irradiation (before DNA repair could take place) which have been reported for a-particles and heavy ions in mammalian cells are in the range of around 0.5 to 2. Only in few cases, RBE values have been observed which exceed values of 2 for DSBs. Most of the RBE values for this effect are in the range of 1. It is of interest in this connection that the RBE values after exposures to 250 kV-X-rays as well as 6 MeV cyclotron neutrons change in dependence on the cell proliferation if chromosomal aberrations are analysed. For chromosomal aberrations, which have been determined during the first mitosis after radiation, a RBE value around 3 is found. In the second and third mitosis after irradiation the RBE values increase and reach values of five to eight [34]. It may be possible that such latent DNA damages are of special significance for the development of health effects. This question needs further clarification. A very radiosensitive mutation assay is the pink-eyed unstable mutation in the mouse [35]. In this assay the reduction of the pigment in the eye is studied as a result of gene duplication and its reversion to the wild type by deletion of one copy. The reversion frequency is much higher than the rate of other recessive mutations. Female mice, homozygous for the reversion, were irradiated with X-ray doses of 10 to 1,000 mGy and the number of reversions measured. Even after a radiation exposure with 10 mGy the reversion rate was increased threefold. Another sensitive mutation system has been studied with the plant Tradescantia. The normal dominant blue colour can be mutated to the recessive pink. Dose response curves for pink mutations have a linear dose response between 2.5 to 50 mGy for 250 kV X-rays and between 0.1 to 80 mGy for 0.43 MeV neutrons [36]. These experimental data demonstrate that significant biological effects can be measured with radiosensitive biological systems in radiation dose ranges as low as 10 mSv.

5. DOSE MODIFYING PHENOMENA The described biological radiation effects can be modified by a number of biological processes and chemical substances. As has already been mentioned cancer develops through multistep processes, which are mainly determined by mutations and changes in the regulation of cell proliferation. On the basis of these mechanisms it is understandable that the radiation-induced carcinogenesis can be enhanced especially by promoting substances like phorbol ester (TPA) and estrogens as well as other hormone like agents [6,37]. Some of the relevant modifying biological processes have already been mentioned but shall be evaluated now somewhat deeper. These phenomena are besides DNA repair, adaptive response, apoptosis, genetic instability (bystander) and genetic predisposition. In a number of experiments, it has been found that an irradiation of cells with low radiation doses can lead to an enhanced resistance of these cells [38]. This increase of radioresistance is manifested by the observation that after a small radiation dose of 10-100 mGy (adapting dose) a following radiation dose in the range of 1 to 2 Gy (challenging dose) results in smaller radiation effects than with cells which have not received the adapting dose in the small dose range. This phenomenon has been termed adaptive response [5, 39]. The data reported in the literature can be summarised in the following way: Adaptive response to low

Effects of Ionising Radiation in the Low Dose Range

25

LET radiation exposures has been found widely distributed with living organisms: in bacteria, yeast, plants and animals. It has been also observed in a number of different human as well as of rodent cells. Mainly chromosomal aberrations but also gene mutations, cell survival/cell death by the clonogenic assay as well as apoptosis have been investigated [5,40]. The following parameters and conditions are very important and have to be kept in certain ranges with respect to treatment/observation periods or radiation dose in order to obtain an adaptive response: Adapting Dose (AD), Challenge Dose (CD), Interval AD-CD, Persistence of Adaptive Response, Cell Proliferation/Cell Cycle, In vitro/in vivo-Situation, Induction of DNA Repair, Induction of Protein Expression, Cell Type, Stimulation of Immune System, Genetic Disposition In order to achieve an adaptive response the adapting radiation dose has to be in the range of 5 to 200 mGy and has to be given some hours (usually 6 to 18 hours) before a challenge dose in the range of one to several Gy was applied. In addition, the dose rate of the adapting dose must be kept in certain ranges in order to achieve an adaptive response. The adaptive response was especially successful in mammalian cells when the conditioning radiation exposure took place during the S/G2 phases of the cell cycle. The cellular response was transient and lasts for about three cell cycles or two to three days. The adaptive response was mainly studied in lymphocytes of humans or rodents. It was also observed in fibroblasts, bone marrow cells and some other cell lines. There is no definite proof for the underlying mechanism of the induction of adaptive response until now. Nevertheless, a number of experimental data support the assumption that the induction of DNA repair is very probably involved. For this mechanism an enhanced protein expression is necessary as has been shown with inhibitors of protein synthesis which also prevent adaptive response [38-40]. No adaptive response has been observed during the prenatal development of rodents and this can probably be extrapolated to humans. Further, there is an enormous variation in the quantitative response between individual donors. In cells from some individuals, no adaptive response could be observed at all. This is especially valid for individuals with a genetically disposed deficiency of DNA repair as observed in AT patients. Adaptive response and its development by low radiation exposures is apparently very much dependent on the individual genetic disposition. Further, there is no good evidence for an adaptive response after exposures to high LET radiation. However, it appears if there is any adaptive response for high LET radiation, it will be considerably smaller than with low LET radiation. The lack of adaptive response in connection with these radiation qualities would be in agreement with the findings that little DNA repair occurs after such exposures [40]. In conclusion, in many biological systems the development of an adaptive response in direction of an increased radioresistance has been observed after small doses of low LET radiation. A dose-modifying factor in the range of 1.5 to 2.0 has usually been found. However, these processes do not occur as an universal principle in all individuals and in all developmental stages of a living organism. This is especially the case in individuals with an increased radio sensitivity. This lack has to be taken into account if adaptive response is discussed for practical radiological protection. Under these consideration it appears doubtful whether credit can be given to adaptive response with respect to general regulations and risk factors in radiological protection. Investigations on survival of mammalian cells have demonstrated a higher radiosensitivity with respect to cell killing in the dose region below 0.5 Gy low LET radiation. This phenomenon has been termed hyperradiosensitivity (HRS). This HRS has been observed down to radiation doses below 100 mGy. It precedes a dose region (around 0.5 to 1 Gy) in which the radioresistance of the cells increases and cell killing is almost constant although the radiation dose increases (increased radioresistance, IRR). The phase of IRR shows some analogy to adaptive response, although the dose range is somewhat higher. The adaptation

26

Current Trends in Radiation Protection

process can be suppressed by inhibitors of protein synthesis [40,41]. These phenomena have been studied with a number of normal and of malignant cells and it has been found that the HRS as well as the IRR differs from cell line to cell line. Generally, the phase of HRS is most expressed by the cells, which become more radioresistant at the higher dose ranges. The phenomena of HRS and IRR have also been observed with respect to radiation response with tissues in vivo. The induction of DNA repair, which leads to IRR, reduces to normal values within hours after radiation exposures. As has been mentioned before cell death can be induced by signal transduction mechanisms (programmed cell death, apoptosis). An activation of intracellular hydrolytic enzymes especially of caspases with protease activities [42] leads to a breakdown of biological macromolecules including DNA. Apoptosis is very important for normal developmental processes but also for the elimination of damaged and possibly malignant cells. It has therefore been proposed that apoptosis can reduce the radiation risk and this is supported by the induction of the apoptotic activity after radiation exposures [15]. This has especially been demonstrated with respect to malformations after prenatal irradiation during the organogenesis with 2 Gy X-rays [43,44]. The tumour suppressor gene p53 is involved in triggering the process of apoptosis. In p53 knockout mice, the rate of radiation-induced malformations was higher than in wild type mice. In this connection, it is of interest that unrepaired DSBs apparently stimulate apoptosis. Recent data demonstrate that different trigger mechanisms exist for the induction of apoptosis and these behave differently with respect to the induction by irradiation. Further it has been observed that very little apoptosis occurs in tumour cells with p53 mutations [45]. Such p53 mutations have been found in around 50% of all human tumours [27]. Adaptive response has also been seen for the induction of apoptosis in human lymphocytes, but again the individual variability for this effect was very large [46]. The RBE of fast neutrons was 1 for apoptosis in mouse thymocytes [47], however, for intestinal crypts the RBE values for 14.7 MeV and 600 MeV neutrons were 4 and 2.7 respectively [48]. The influence of apoptosis on radiation risk is certainly an interesting approach, however, apparently it is not an universal mechanism and there are many open questions. During recent years, investigations on the induction of genomic instability by ionising radiation have obtained high interest. This phenomenon has been observed in skin fibroblasts from mouse fetuses, which were irradiated 1 to 3 hours after conception during the zygote stage (1-cell stage). Around 30 to 40 cell generations after this radiation exposure, the fibroblasts developed new chromosomal aberrations [17]. This effect could only be explained by an increase of genomic instability, which is induced by ionising radiation. In further experiments genomic instability after irradiation has been observed with quite a number of cell systems in vitro and in vivo for chromosomal aberrations, cell survival and gene mutations [18,49]. Such effects have been observed with low as well as with high LET radiation. Thus, this phenomenon is generally accepted today although the mechanism of this effect is unknown [50, 51]. It further has been demonstrated that these effects not only occur in cells which have been hit by ionising particles but also in neighbour cells of the hit cells when irradiation of single cells was performed with a-particles. This effect is called bystander effect. At present, the mechanisms of induction of genomic instability and bystander effects by ionising radiation are not understood. It is also not clear whether only one mechanism exists for the various endpoints. Genomic instability is apparently not directly connected with a well-defined gene or chromosomes; it appears as a general phenomenon in which the whole genome is affected. Many possibilities are discussed. As the frequency of this effect is higher than the rate of mutations on the cellular level, an epigenetic mechanism has been discussed [53, 54]. In addition, the involvement of free radicals especially reactive oxygen species has been proposed. Further attractive proposals are that the development of genomic instability is connected to the structure of telomeres which stabilise the structure of chromosomes or to imprinting processes in the DNA which are involved in regulating the activation and deactivation of genes [55]. DNA repair may be impaired under these conditions. In this connection it is of interest that quite a number of syndromes with increased radiosensitivity and enhanced frequencies of cancers through genetic predisposition show also an increased genomic instability [20]. The increased genomic instability induced by ionising radiation can be transmitted to the next generation in mice [56].

Effects of Ionising Radiation in the Low Dose Range

27

All stochastic late effects of ionising radiation are multistep processes. Best defined are these events for carcinogenesis. Many experimental and clinical studies have demonstrated that cancer develops through several sequential mutation steps. Such a model has been proposed for colorectal cancer [16]. For such a model, the development of genomic instability would be of a very high significance, as these phenomena increase the mutation frequency and therefore increase the probability of a second or third mutation in an individual cell [18]. As mutation frequencies are usually very low even after irradiation, genomic instability would facilitate the multistep processes considerably when the mutation frequency can be increased by a factor of 10 to 10,000 as it has been shown [53]. The increased genomic instability in individuals with a genetically predisposed higher radio sensitivity may also explain partly the higher cancer risk in these individuals [20]. Therefore the evaluation of the mechanisms how genomic instability develops after irradiation would be extremely important in order to improve our understanding of the mechanisms of carcinogenesis especially and stochastic radiation late effects in general. This is essential for a better evaluation of radiation risks in the low dose range. It has been mentioned that individual radiosensitivity can vary strongly. This has especially been observed with cancer patients in radiotherapy when a patient suffers from acute radiation effects after radiation doses which are tolerated by the vast majority of patients without any serious adverse symptoms [20]. Cellular and molecular studies in vitro have contributed in recent years to the understanding of the mechanisms, which are responsible for the increased radiosensitivity. Generally, deficiencies of specific DNA repair pathways and disturbances of the regulation of the cell cycle in proliferating cells have been observed mainly in fibroblasts and stimulated lymphocytes from radiosensitive patients. After irradiation specific blocks occur within the proliferation cell cycle in the GI-phase and in the G2 -phase. These blocks give the damaged cells some more time in order to repair the damage. Therefore, both processes (DNA repair and regulation of the cell cycle) are connected with each other. From these investigations it has been possible to define and describe the following syndromes, which are genetically inherited: Ataxia telangiectasia, Fanconi anemia, Li Fraumeni syndrome, Neurofibromatosis, Nevoid basal cell carcinoma syndrome, Nijmegen breakage syndrome, Retinoblastoma. Several of these syndromes are inherited in a recessive trait. These are only manifested in the homozygotic carriers which have frequencies in the range of 1:40,000 to 1:100,000. There may occur an increase of radiosensitivity by a factor of 5 to 10 in patients with these genetic syndromes [20]. No data are available for an increased cancer rate in the low dose range but enhanced frequencies of secondary cancers have been observed in patients who have received radiotherapy for a treatment cf. of retinoblastoma. In these studies, it clearly was found that the radiation-induced cancer risk was increased in patients with a genetic defect in the Rb-gene. In mice a dramatic increase of the tumour rate and a reduction of the latency period for tumours have been observed when the p53 gene was knocked out. The cellular and molecular studies further showed that the heterozygotes are also more radiosensitive than normal individuals, however, this is much less than with the homozygotes. Nevertheless, the heterozygotic carriers appear in the range of some percent of the total population. Such data have been obtained with cytogenetic studies of lymphocytes from patients with breast and colorectal cancers [57]. It is also of interest that individuals with the described genetic syndromes have an increased genomic instability and an enhanced rate of certain "spontaneous" malignancies. In conclusion, a modification of radiation response by various mechanisms is possible. A number of these modifying factors lead to an increase of radioresistance like adaptive response, apoptosis and induction of immune response, but also increased radiosensitivity takes place as by induction of genomic instability. Most effects have been observed with cellular systems in vitro. The effects like adaptive response are bound to comparatively narrow conditions with respect to time windows and dose ranges. Under conditions where dose modifications are observed after exposures to low LET radiation, these effects are not seen after exposures to high LET radiation. The extent of modifying processes varies very much from individual to

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individual; it is connected to the genetic disposition. If dose response curves are modified by adaptive response, apoptosis etc. the slope of the dose response curve changes but this does not touch the principle problem whether a threshold dose does exist or not. Genetic disposition and mechanisms of induction of genomic instability as well as bystander effects may enhance the radiosensitivity.

6. ANIMAL EXPERIMENTS Experimental studies with animals have a great importance for the knowledge about the expected late effects of radiation in humans. Considerable information can be obtained for radiation-induced cancer and hereditary diseases from such investigations. There are certain limitations, which have to be taken into account. It is not possible to use such experimental data for quantitative risk estimates especially in cancer induction. However, mechanisms can be evaluated from such studies and especially the influence of various factors such as radiation quality, dose protraction or fractionation as well as dose rate, the sensitivity of individual organs and tissues as well as the age at exposure on the tumour response. The principal form of dose response relationships can be evaluated over a wide range of radiation doses. Further, it is possible to get a better understanding of the molecular and cellular mechanisms, which are important for the development of cancers after radiation exposures [6]. Most of these investigations on carcinogenesis have been performed with rodents (especially mice) and dogs. The vast majority of experimental animal studies have been performed with inbred strains of rats and mice with the presence of spontaneous diseases that can be different in some cases from those which are observed in humans. The frequency of spontaneous tumours and the radiosensitivity of different mouse strains can be very variable. In different strains of mice and rats different tumour entities can dominate. In addition, the differences between gender and age with respect to the incidence of specific tumour types can vary considerably. Nevertheless a number of cancers which also occur in humans like myeloid leukaemia and cancers of the breast, lung, ovary, pituitary and thyroid have been successfully studied mainly in mice and extrapolations to humans are possible under the above mentioned precautions. There are also some investigations available in larger animals as dogs and other species including primates. By analysing these studies it has to be taken into account that the life-span of most experimental animals compared with humans is rather short and that often the rates of cell turnover are quite different. Also a number of modifying factors are different and can influence the cancer rates without radiation and after radiation exposure. Laboratory animals are kept under very well defined conditions, which is not the case for a study population of humans. This certainly also has a considerable influence on the experimental outcome. However, the principal mechanisms for the development of cancers spontaneously and after radiation exposures are the same or analogous in humans as well as in laboratory animals. The possibility to detect radiation effects on cancer induction after low radiation doses depends very much on the number of animals, on the spontaneous incidence of cancers in the various tissues and organs as well as on the radiation sensitivity of these tissues and organs with respect to cancer induction. Very large numbers of animals are needed if a chance should exist to detect radiation effects in dose ranges of 1 to 10 mGy. Also a strong dependence on the spontaneous cancer incidence exists. As the incidence of myeloid leukaemia is very low in CBA-mice, only 300 animals would be needed in order to detect the effect of 100 mGy. However, in RFM-mice 120,000 animals would be necessary for the same radiation dose. Nevertheless, studies with laboratory animals in comparison to epidemiological studies with humans can be planned in a much better manner. The numbers of animals for various dose groups and other experimental conditions can be exactly determined through the design of the experiment in order to get the best possible information. The animals can be exposed under very controlled conditions with well defined dose rates or fractionations schedules and the dose estimates have a high certainty. Further the exposed animals are genetically more homogeneous and also the conditions of feeding and other parameters of lifestyle are more constant and well-defined than with human populations.

Effects of Ionising Radiation in the Low Dose Range

29

In a number of studies it has been shown that after exposures to low or medium radiation doses (below 1 Gy) up to a range of doses of a few Gy (low LET radiation) life shortening of experimental animals is mainly the result of an increased cancer development and mortality from these diseases [4, 6,7]. Only after higher radiation doses radiation effects to the renewal of blood cells and to the blood vasculature as well as radiation effects to other tissues, become so significant that animals die from such causes. As the death of an animal is a very precise biological endpoint and easy to measure the investigation of life shortening after radiation exposures can be very informative with respect to cancer induction. In BALB/c mice, a linear function of dose was found between 0.25 and 6 Gy for life shortening after exposures to 7-radiation (Cs137). The life shortening in these studies was 46.2 ± 4.3 days per Gy [6, 58]. Studies with other mammalian species have been summarised in an UNSCEAR report [59] and come to similar conclusions. Some studies have been performed after dose fractionation. In general it seems that dose fractionation has only a small effect on life shortening. On the other hand protracted exposures over several months to years result in a reduced effect on life shortening. Factors for the necessary dose enhancement between about 2 to 5 can be calculated in order to get the same effects for chronic exposures as for exposures with high dose rates. Studies have also been performed after exposures to high LET radiation and come in principle to the same conclusion. Again a linear dose response has been observed with no effect by dose fractionation and also by dose protraction after exposures with high LET radiation as this has already been described for cellular effects [6]. Very extensive studies on tumour induction in mice have been published by Ullrich and Storer [60-62] after exposures to low LET radiation. Numbers of cancers have been investigated like myeloid leukaemia and cancers of the breast, lung, ovary, pituitary and thyroid. Female RFM mice were exposed to 7-rays (Cs-137, 0.45 Gy per minute) with radiation doses from 0.1 to 3 Gy and followed for their life-span. After death the animals were autopsied and diagnosed for the various types of cancers. Significant increases of acute myeloid leukaemia were obtained after radiation doses of 1 Gy and above and a linear dose response curve was observed. However, the dose response curve could also be described by a linear - quadratic model for the data of these experiments [60-62]. The combined analysis with a further study resulted in a significant increase of myeloid leukaemia after a radiation dose of about 0.5 Gy. In this study the data could also be fitted to a threshold-linear model. The threshold dose would be 0.22 Gy under such an evaluation. Although 18.000 mice were used in these studies the increase of myeloid leukaemias in the lower dose range was uncertain, as the number of leukaemia cases was very small. Several studies of the induction of mammary cancers after radiation exposures demonstrated that the sensitivity of various mouse strains was very different. The same was observed with rats [6]. Generally a linear dose response curve was found after exposures to X-rays as well as to 0.5 MeV neutrons. Ullrich et al. [63] observed that the variability in sensitivity of the various mouse strains correlated with the sensitivity of the breast epithelial cells to radiation-induced malignant transformation. For the induction of lung tumours it was found that the frequency of cancers was less after low dose rates in comparison to high dose rates of 7-radiation (Co-60). After exposures with a high dose rate (0.4 Gy per minute) a linear dose response curve was observed. After a low dose rate (0.06 mGy per minute) the slope of the dose effect curve was smaller. The dose response could also be described by a linear response curve. In addition, a linear-quadratic dose response was possible for both dose rates (0.4 Gy per minute and 0.06 mGy per minute [62]. Maisin et al. [58] found a dose response curve with a threshold after a single or fractionated dose of 7-radiation (Cs-137) in the dose range from 0.25 to 6 Gy when the induction of thymic lymphomas was studied in mice. On the other hand Ullrich and Storer [62] found with a dose rate of 0.45 Gy per minute a quadratic dose effect curve with a significant increase of lymphomas after radiation doses of 0.25 Gy and higher and a threshold of 0.1 Gy could not be excluded. For the induction of ovary cancers data were also obtained in mice which could be described by a dose effect curve with a threshold. The form of the dose response was discussed under the aspect that a substantial killing of ovary cells occurs at higher doses and conditions, which lead to an appreciable change

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Current Trends in Radiation Protection

in the hormonal status of the animals. With bone tumours dose effect curves with a threshold have been found in a number of experimental studies too [62]. However, a number of further experimental studies on cancer induction after exposures to ionising radiation have shown dose effect curves without a threshold as mentioned before. The lowest dose with a significant effect on cancer induction varies considerably in the various studies. The results certainly depend on factors, which influence the statistical power, such as the number of mice and the spontaneous cancer rate of the animals in these investigations. After high LET exposures linear dose response curves without a threshold are dominating. This is the case in the lower and medium dose range (0.1 to 0.5 Gy neutrons). The smallest doses of low LET-radiation after which cancer induction is significantly increased was found for mammary carcinomas with 0.20 Gy 7-rays and ovarian cancers with 0.16 Gy X-rays [6]. This is interesting as these two cancers entities are very much dependent on the hormonal status of the animals which has apparently a significant impact on carcinogenesis in these cases and has been described in connection with promoting effects in a review on combined effects of chemicals (cf. hormones) and radiation [37]. The lowest radiation dose after which a significant increase of myeloid leukaemia was observed in mice was 0.25 Gy (X-rays). This was only found in one study. In further studies the doses with a significant enhancement of leukaemias were higher [6]. It is of interest to see whether radon and its decay-products will also be able to induce lung cancers in animals and whether it will be possible to study radon exposures in a low dose range which is found in human residences. Such studies have demonstrated that animal tumours in the respiratory tract can be observed after exposure to radon [64]. An increase of tumours in rats was observed after exposure levels below 100 WLM (0.35 J x h x m - 3 ) even at exposures down to 25 WLM (0.08 J x h x m - 3 ). It is of great interest that in these animal studies an inverse dose rate effect was observed. This means that a long duration of exposure at a lower dose rate yielded more lung cancers than exposures for a shorter duration at a higher dose rate. Rats where exposed to 50 or 500 WLM per week and in most exposure groups there was a significantly higher frequency of cancers in the groups exposed to 50 WLM than to 5000 WLM per week when the same total doses were compared. In addition, the cancer spectrum shifted somewhat to the epidermoid carcinomas when a lower dose rate was used. In a later series of experiments it was found, however, that protracted exposures over 18 months at an a energy of 2 WL (0.0042 mj.m -3 ) resulted in a smaller frequency of lung tumours in rats (0.6% 95% CI: 0,32-2,33) than an exposure with an a energy of 100 WL protracted over four months (2.2%) or over six months (2.4%) [65, 66]. These data show that the outcome of.a protracted exposure can be quite variable in comparison to an acute exposure especially for high LET radiation. In a recent review animal data were carefully analysed with respect to a possible appearance of a threshold dose for carcinogenesis of skin tumours [67]. It was demonstrated that under certain conditions the resulting dose response curves for cancer induction can be best described with a threshold or a "practical threshold" occurs. Skin tumours in mice can be induced only with comparatively high doses of B-radiation from 90Sr-90Y. There is apparently a wide dose range where no tumours are induced. This effect is mouse strain dependent and cancer induction can be enhanced when the radiation is applied in a fractionated manner in one mouse strain. In addition, with high LET radiation the time factor can be important. Besides the mentioned inverse dose rate effect a reduction of the cancer rate with a decreasing dose rate is also possible. Apparently a host tolerance to tumour induction can develop which may be caused by immunological responses. It is not surprising that such diverse situations have been observed for cancer induction, as the development of cancers is very complex and long-lasting. Mechanisms are manifold in different tissues. A promoting effect of ionising radiation is also possible. The question arises whether such a mechanism can also occur at very low doses. The genetic disposition is very important although not the only determining factor. Cancer development is a multifactorial process [6].

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31

7. CONCLUSIONS For risk estimates the knowledge of the shape of dose response curves after exposures to toxic agents is essential. This is also the case for the evaluation of radiation risk. For a number of radiation effects it has been shown that the dose effect curve has a threshold and these radiation responses are only seen after radiation doses above the threshold doses which are in the range 100 mSv and higher. The underlying mechanisms are multicellular processes in which many cells have to be damaged for the development of these health effects. Usually death of stem cells is responsible for these effects. However, for the induction of hereditary defects and of cancers it is assumed that dose response curves exist without a threshold dose and this appears also to be the case for certain developmental effects in cases where a genetic predisposition for such developmental effects exists. The observed radiation effects e. g. the radiation-induced cancers do not have specific features with respect to biological or clinical behaviour. They cannot be distinguished by their clinical appearance or molecular changes from the "spontaneous" health effects, which develop without any radiation exposure. This means: Exposures to ionising radiation increase health effects, which are also found without these exposures. Radiation only increases the frequencies of these "spontaneous" events. This is apparently also the case for chromosomal aberrations, cell transformations and gene mutation in somatic cells. Therefore the radiation effects must be higher than the scatter of the spontaneous damage in order to be determined significantly. This is frequently the case only after radiation doses of around 100 mSv of low LET radiation. It is also not very surprising that under these circumstances no increased cancer rates are observed in regions with high background radiation. Besides other conditions the radiation dose rates are low and the doses are not high enough in order to cause a significant increase of cancer rates in the populations living in areas with high background radiation. The most important question for risk evaluation is: Are any effects induced below these radiation doses with measurable effects which only cannot be seen as they are within the variation of the baseline of cancer or do no radiation effects like mutations or cancers exist in the low dose range? In order to answer the questions, the mechanisms for the development of the radiation effects must be evaluated. These so-called stochastic effects develop through several steps before a manifestation of health effects like cancers occurs. The initial steps are apparently connected to radiation damage induced in the DNA although some more recent data demonstrate that changes of signal transduction from the cell membrane to the nucleus and regulation processes for gene expression may also be important. In principle, similar DNA damages (polynucleotide breaks, base damage) can be caused by endogenous processes cf. induced through metabolically formed oxygen radicals. However, ionising radiation leads to clusters of such damaging events, whereas with oxygen radicals isolated damaged sites are most frequent. In the low dose range it occurs that the dose distribution between individual cells shows a wide variability and cells will be found which have not been hit while neighbour cells experience comparatively high doses. In that way exposure to ionising radiation differs fundamentally with respect to the distribution of damaged sites in the DNA from exposures to chemicals. These microdosimetric considerations are important for the risk evaluation in the low dose range. Dose response curves for chromosomal aberrations, malignant cell transformations and gene mutations have been studied after exposures to a wide variety of radiation qualities in many cellular and molecular systems in vitro. The irradiation has taken place in single cell cultures. The results from these experiments show that in most cases the data can be best described by dose effect curves without a threshold, but curves with a threshold dose cannot be excluded. In the low dose range and with low dose rates a linear dose response is usually dominating. In the medium and higher dose range a linear quadratic dose effect curve has usually been observed with low LET radiation. In contrast with high LET radiation the dose response remains linear over a wider dose range. With low LET radiation the dose response becomes shallower when

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Current Trends in Radiation Protection

the dose rate decreases. The uncertainties in the low dose range are larger for low LET radiation than for high LET radiation. In the latter case the dose response curve can be fairly well and safely described by linearity without a threshold. The experimental studies on cancer in animals give more conflicting results with respect to the shape of dose response curves. In several cases the fit for the dose response was better with a threshold, however, in many cases the data could be fitted in a more adequate way with dose response curves without a threshold. This was especially the case for cancers with an endocrine regulation like mammary and ovary cancers, while bone cancers and frequently also skin cancers showed dose effect curves with a threshold. The dose response can be modified by a number of factors as time and duration of exposure, DNA repair, adaptive response, apoptosis, genetic instability, bystander effects and genetic disposition. With low LET radiation the biological effects are smaller when the radiation exposure takes place with a low dose rate than with high dose rates in the range of 0.5 to 1.0 Gy per minute. It seems that dose rates in the range of 1 - 10 mGy per minute lead to the highest reduction of the radiation effects. In addition, fractionation of the radiation dose frequently diminishes the effects. DNA repair is mainly responsible for these reductions. It is apparently possible to induce DNA repair by small radiation doses. However, this adaptive response only occurs under very limited conditions, it is dependent on radiation dose and dose rate. It is only seen to a small degree or not at all with high LET radiation. Adaptive response cannot be observed in all tissue systems, in the prenatally developing organism and not with all individuals. Very similar is the situation with respect to apoptosis, a biological mechanism for cell killing (suicide of the cell) which is triggered by signal transduction. In principle, it is possible through this mechanism, that damaged cells including malignant cells can be eliminated and can therefore reduce the manifestation of health effects. All these modifying factors vary strongly between different cell systems, tissues and individuals. With high LET radiation these modifications of the dose response are very small or they do not exist at all. With long lasting exposures other mechanisms like cell repopulation or a stimulation of the immune system may be important, however, the data about such effects are comparatively limited. The development of cancer is a very complex process and not only cellular phenomena have to be evaluated. The influence of tissue response as well as of the immune system is important, however, the knowledge about these processes is little understood until now. Clinical experiences as well as studies with cells from patients have shown that certain genetic syndromes exist with a strong hypersensitivity. These individuals fall clearly outside the normal distribution of radiosensitivity within our populations. Investigations of the mechanisms have demonstrated that very frequently deficiencies in certain DNA repair pathways and disturbances in the regulation of the cell proliferation cycle occur in these persons. An increase of acute and late radiation damages have been observed in persons with a genetic predisposition for an increased radiosensitivity. In addition, carcinogenesis is enhanced, however, there are no observations after small radiation doses available until now. This is probably because the numbers of individuals with such defects are small and therefore relevant epidemiological studies are very difficult if not impossible. For practical radiological protection where prospective estimates of risk have to be made and for risk evaluation as the basis for regulatory purposes which are based on such estimates it seems to be appropriate further to use a linear dose response without threshold doses for stochastic radiation effects although the uncertainties are high and there is no solid scientific proof for such a shape of the dose effect curve. This may be an overestimate of risk under certain conditions which is justified by taking into account precautionary principles.

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Effects of Ionising Radiation in the Low Dose Range

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Cross, F. T. A review of experimental animal radon health effects data. Radiation Research: A Twentieth-Century Perspective, J. D. Chapman Eds. (Academic Press, San Diego, 1992) pp. 476-481.

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Morlier J. P., M. Morin, J. Acad. Sci., Ser. 3 (315) (1992) 436-466.

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Streffer, C., H. Bolt, D. Follesdal, P. Halll, J. G. Hengstler, P. Jacob, D. Oughton, K. priess, E. Rehbinder and E. Swaton. Environmental Standards: Dose-Effect Relations in the Low Dose Range and Risk Evaluation, Springer, Berlin, Heidelberg (in press).

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Current Trends in Radiation Protection H. Metivier, L. Arranz E. Gallego and A. Sugier (eds.)

ICRP and Radiation Protection of Non-Human Species Lars-Erik Holm1 ]/Tice-Chairman of International Commission on Radiological Protection Swedish Radiation Protection Authority, SE-171 16 Stockholm, Sweden

Abstract. Up till now, the International Commission on Radiological Protection (ICRP) Commission has not published any recommendations on how to assess or management radiation effects in non-human species. The Commission has decided to develop a framework for the assessment of radiation effects in non-human species in order to fill a conceptual gap in radiological protection. The proposed system does not intend to set regulatory standards, but rather to provide guidance and help regulators and operators demonstrate compliance with existing legislation. ICRP will develop a small set of reference animals and plants, plus their relevant data bases to serve as a basis for the more fundamental understanding and interpretation of the relationships between exposure and dose, and between dose and certain categories of effect. This concept is similar to that of the reference individual (Reference Man) used for human radiological protection, in that it is intended to act as a basis for calculations and decisions. The Commission has now established a new Task Group to continue the work with defining effects end-points of interest, the types of reference organisms to be used by ICRP, and defining a set of reference dose models for assessing and managing radiation exposure in non-human species.

1. INTRODUCTION The 1972 United Nations (UN) Conference on the Human Environment in Stockholm was the first international conference to establish principles for the protection of the human environment [1]. Twenty years later, the UN Conference on Environment and Development in Rio de Janeiro laid down general principles for environmental protection, e.g. the Rio Declaration and the Convention on Biological Diversity [2]. This Convention stresses the importance of recognizing that all organisms contribute to the structure of the ecosystem and includes diversity within species, between species, and of ecosystems. Preservation of biological diversity thus does not mean conservation of a certain state. It rather means protection against harmful effects that would cause diversity to develop in a fashion that would not have been the case in the absence of the environmental contaminant.

1 E-mail: [email protected]

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Current Trends in Radiation Protection

There are different approaches to protecting the environment, and they can all be regarded as different facets of environmental management. These approaches include environmental exploitation (e.g., fisheries, forestry), conservation and protection of the natural environment, and pollution control [3]. Different ethical views affect the way in which people view the environment, and they have resulted in cultural, religious, and legal differences across the world. A recent IAEA study [4] identified the anthropocentric, biocentric, and ecocentric views about what has moral standing in the world. The advice of the ICRP targets the regulators and implementers that have the responsibility for establishing radiological protection standards. Environmental protection has made considerable progress since ICRP's current recommendations on radiological protection were published in 1991 [5]. ICRP has, up till now, not explicitly dealt with protection of the environment, except in those situations where radionuclide levels in non-human organisms were of relevance for the protection of humans. There has been no ICRP recommendations on protection of the environment, and there has, therefore, been little guidance as to how radiological protection of the environment should be carried out, or why. The human habitat has indirectly been afforded protection as a result of the ICRP's system of protection of humans. However, it is difficult to convincingly demonstrate that the environment has been or will be adequately protected in different circumstances, since there are no explicit sets of assessment criteria, standards or guidelines with international authority. The development of approaches to protect the environment is to a large extent driven by the needs of national regulators and by international organizations to safeguard a sustainable development. Different approaches have been used to address the many questions raised with respect to the application of ICRP's position on environmental protection, ranging from arguments that when man is protected, all other organisms are protected, to systematic frameworks to assess environmental impact of radiation in specific ecosystems [6]. The ICRP set up a Task Group in 2000 to advise it on the development of a policy for the protection of the environment, and to suggest a framework by which it could be achieved. The Task Group concluded that a systematic approach for radiological assessment of non-human species is needed in order to provide the scientific basis for managing radiation effects in the environment [6]. It has chosen an approach proposed by Pentreath [7] and that uses a reference set of dosimetric models and a reference set of environmental geometries, applied to reference animals and plants. This approach will allow judgements about the probability and severity of radiation effects, as well as an assessment of the likely consequences for either individuals, the population, or for the local environment. The Task Group further recommended that the radiationinduced biological effects in non-human organisms be summarized into broad categories: early mortality, reduced reproductive success, and scorable DNA damage. These categories comprise many different and overlapping effects and recognize the limitations of the current knowledge of such effects. The Task Group has proposed objectives for a common approach to the radiological protection of humans and the environment [6]. This includes to safeguard the environment by preventing or reducing the frequency of effects likely to cause early mortality, reduced reproductive success, or scorable DNA damage effects in individual fauna and flora to a level where they would have a negligible impact on conservation of species, maintenance of biodiversity, or the health and status of natural habitats or communities. The ICRP recently adopted the Task Group's Report, and has decided to develop a framework for the assessment of radiation effects in non-human species [8]. This decision has not been driven by any particular concern over environmental radiation hazards, but rather to fill a conceptual gap in radiological protection. The proposed system does not intend to set regulatory standards. It is a framework that can be a practical tool to provide high-level advice and guidance and help regulators and operators demonstrate compliance with existing legislation. The Commission has also established a new Task Group to continue the work with defining effects end-points of interest, the types of reference organisms to be used by ICRP, and defining a set of reference dose models for assessing and managing radiation exposure in non-human species.

ICRP and Radiation Protection of Non-Human Species

39

2. RADIATION AND THE ENVIRONMENT The Chernobyl accident in 1986 is the most serious accident involving radiation exposure. Large territories were contaminated and deposition of released radionuclides was measurable in all countries of the Northern Hemisphere. The accident thus focused attention also to the environmental effects. Over the last decade, protection against radiation effects in the environment has attracted increasing interest, concomitant with the general development of environmental protection. The first international symposium on ionizing radiation and protection of the natural environment took place in Stockholm in 1996 [9]. The Stockholm Conference explored the scientific basis for setting criteria and whether there was any movement in the scientific community to go further in the direction towards environmental protection approaches. A second symposium took place in Ottawa in 1999 [10]. The scope at that meeting had both widened and deepened with themes such as environmental management, public participation, and multiple stressors. The third international symposium took place in Darwin in 2002 [11]. The main focus of the meeting was the development and application of a system of radiological protection for the environment, reflecting the international work to define a framework for the assessment and management of radiation effects in the environment. The International Conference on the Protection of the Environment From the Effects of Ionizing Radiation took place in Stockholm in October, 2003 [12]. It was organized by the International Atomic Energy Agency (IAEA), in co-operation with the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), the European Commission (EC) and the International Union of Radioecology (IUR). The objective of the Conference was to promote the development of a coherent international policy on the protection of the environment from effects attributable to ionizing radiation exposure. The main finding of the Conference was that the time is ripe for launching a number of international initiatives to consolidate the present approach to controlling radioactive discharges to the environment by taking explicit account of the protection of species other than humans. The Conference recommended that an international action plan on the protection of the environment against the detrimental effects attributable to radiation exposure be prepared under the aegis of the IAEA. All relevant international organizations and senior experts from States should be invited to contribute to the preparation of such an action plan. The Conference was made aware of the proposals for a framework for assessing the impact of ionizing radiation on non-human species being developed by the ICRP. It was agreed that natural background radiation levels provide a valuable basis for comparison. The Conference supported the approach based on the development of Reference Animals and Plants, and it noted that these may also serve as a basis for site-specific assessments [12].

3. ICRP'S REFERENCE ANIMALS AND PLANTS The purpose of developing a systematic reference-animal-and-plant approach is to derive a reasonably complete set of related information for a few types of organisms that are typical of the major environments [6-8]. This approach cannot provide a general assessment of the effects of radiation on the environment as a whole, but it could provide the basis for judgements about the probability and severity of the likely radiation effects on such organisms. Using these and other environmental data, one should be able to assess the likely consequences for either individuals or the relevant population, in order to make managerial decisions relevant to the circumstances. In order to calculate radiation dose, a set of reference values is required to describe the anatomical and physiological characteristics of an exposed individual. Such reference values have since long been used for dose assessments in humans [13,14]. For the environment as a whole it will not be possible to provide a general assessment of the radiation effects. The concept of deriving such data sets for reference animals

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Current Trends in Radiation Protection

and plants is similar to that used for human radiological protection, in that it is intended to act as a basis for many calculations and decisions [6]. Each reference organism would serve as a primary point of reference for assessing risks to organisms with similar life cycles and exposure characteristics. More locally relevant information could be compiled for any other fauna and flora; but each such data set would then have to be shown to be related in some way to the reference organisms. For each reference animal and plant, one should obtain a fairly internally consistent set of data on basic life-cycle biology, pathways of exposure to radiation that can be expressed in terms of dose-per-unitexposure, dose model(s) to estimate doses received by the relevant organs, and radiation effects on individual organisms. Such data sets would also serve as 'default' values for use in various assessment scenarios. The reference animals and plants should also have some form of public or political resonance, so that both decision makers and the public are likely to know what these organisms actually are, in common language — such as a duck, or a crab. The variety of dose models needed for reference organisms, in addition to the considerations of target size and shape, will depend upon how the consequences of radiation result in the above categories of biological effect (early mortality, reduced reproductive success, or scorable DNA damage). Another question regarding the reference-animal-and-plant approach is how to interpret and apply data on the relationships between doses and biological effects. Derived consideration levels for reference animals and plants could be compiled by combining information on logarithmic bands of dose rates relative to normal natural background dose rates of such organisms, plus information on dose rates that may have an adverse effect on them (Figure 1). Additions of dose rate that are only fractions of their background might be considered to be of low concern, and those that are orders of magnitude greater than background would be of increasing concern because of their adverse effects on individual organisms [5].

Focussing the advice on individual animals or plants does not imply that the individual is necessarily the object of protection. A large number of animals and plants are already afforded protection at the level of the individual in international or national law, and it would be inappropriate to provide advice that could not be used in such legal contexts. Effects upon ecosystems are usually observed at the population or higher levels of organization, whereas information on dose responses is usually obtained at the individual level. Radiation effects at the population level - or higher - are mediated via effects on individuals of that population, and it therefore seems appropriate to focus on the individual for the purpose of developing an assessment framework [5]. Presenting data in terms of dose rates that are known to have particular radiation effects on different types of animals and plants would appear to be an appropriate and transparent format in which to provide general advice. This could be used to support legal frameworks at a national level, or in terms of using dose rates as the basis of any form of guidance or stricter form of legislative control. The aims of the work of ICRP's new Task Group on Reference Animals and Plants are to select and define reference animals and plants to be recommended by ICRP, and to define end-points for assessing radiation effects in non-human species. The Task Group shall develop a reference set of dose models and derived consideration levels for reference animals and plants; and agree upon a set of quantities and units that could be suggested for use for reference animals and plants. The criteria used in the selection of relevant reference animals and plants include: • the extent to which they are typical of a particular ecosystem; • the extent to which they are likely to be exposed to radiation;

ICRP and Radiation Protection of Non-Human Species

41

DERIVED CONSIDERATION LEVELS

Figure 1. Derived consideration levels for a reference animal or plant.

• the stage(s) in their life-cycle likely to be of most relevance for evaluating total dose or dose-rate, and of producing different types of dose-effect responses; • the extent to which their exposure to radiation can be modeled using simple geometries; • the possibility to identify radiation effects in an individual organism; • the amount of radiobiological information already available; • their amenability to future research; and, • the extent to which both decision makers and the public are likely to know what these organisms actually are [5]. The Task Group is currently considering eleven types of reference animals and plants, essentially as generalized to the taxonomic level of Family, although such details have not yet been finalized. They are as follows: rodent, duck, frog, freshwater fish, marine flat fish, marine snail, bee, earthworm, pine tree, grass, and brown seaweed. These represent organisms of the terrestrial, freshwater and marine habitats (Table 1). The objective of the reference-animals-and-plants approach is to provide a common basis for the assessment of exposure, radiation dose and possible responses for individual organisms. This, in turn, would be the starting point from which assessments for other individual organisms (e.g., different exposure pathways, bioaccumulation, geometries, etc.), and populations, could be made. The reasons for selecting each organism are, in summary, the following. The rodent (rats and mice) is a small mammal with a generic mammalian life cycle. There is a good database for effects and bioaccumulation kinetics, and for effects of other carcinogens. The rodent is amenable for experimental study, and data can be

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Current Trends in Radiation Protection

Table 1. Reference animals and plants in relation to their ecological spread.

Organism

Terrestrial

Rodent Duck Frog Freshwater fish Marine flat fish Marine snail Bee Earthworm Pine Tree Grass Brown Seaweed

X X X

X X X X X

Freshwater X X X

Marine

X

X X X

X

X

X X

extrapolated to and from small mammals in general. The duck is a bird with a generic bird-type life cycle. There is a limited database for effects and bioaccumulation kinetics, and for effects of other pollutants, including carcinogens. The duck is amenable for experimental study (both egg and adult) and it has public resonance and economic value. Data can be extrapolated to and from all birds in general. The frog is an amphibian with a life cycle that contrasts with other vertebrates. It is amenable to study at all stages of its life cycle. A limited database is already available. Frogs are farmed commercially in some countries, and they have ecological and public resonance. The freshwater fish (salmon and trout) lives in the free water column. There is a good database for effects and bioaccumulation kinetics and data are available for other carcinogens. Data can be extrapolated to and from most fish living in the water column. The marine flat fish (e.g. plaice and flounders) lives on the sediment surface. There is a limited database for effects and bioaccumulation kinetics. Data can be extrapolated to and from other fish living on the sediment. Both types of fish are amenable for experimental study (all stages of life cycle), and have public resonance and economic value. The gastropod mollusc (e.g. marine snail) has egg, larval and adult stages. There is a limited database for effects, with bioaccumulation kinetics available for marine species. The gastropod mollusc is amenable for experimental study (all stages of life cycle), and it has public resonance and economic value. Data can be extrapolated to and from gastropods, but not readily to and from other molluscs. The bee is a social insect of key ecological relevance with an insect-type life cycle. There is a limited database for effects and bioaccumulation kinetics. The bee is amenable for experimental study (all stages of life cycle), and it has public resonance and economic value. Data can be extrapolated to and from essentially all insects. For the earthworm there is a very limited database. The worm is amenable for experimental study (all stages of life cycle). It has public resonance, and ecological relevance. The pine tree is a radiosensitive gymnosperm, for which there is a reasonable database for effects, but limited for bioaccumulation kinetics. The pine is amenable for experimental study, and it has public resonance and economic value. Data can be extrapolated to and from other gymnosperms. For grass there is a limited database for effects and bioaccumulation kinetics. Grass is amenable for experimental study, it has public resonance and economic value, and is ecologically very important. Data can be extrapolated to and from other herbaceous angiosperms. Finally, for brown seaweed there is no database for effects, but a substantial one for bioaccumulation. Brown algae are amenable for experimental study (all stages of life cycle), have public resonance and economic value.

ICRP and Radiation Protection of Non-Human Species

43

The Task Group will consider these types of animals and plants in more detail. Once finally selected, it will describe each reference organism in a consistent manner and provide a short database for modeling (size, weight, height, lifespan, world distribution etc.). The Task Group will also provide a matrix of dose geometries and environmental geometries for each organism and for various relevant stages of their lifecycles. Results from FASSET (see www.fasset.org) will provide reference radionuclides in the environment to enable the calculation of background dose rates, plus data for other radionuclides, as appropriate. Data will also be collated with respect to what is known about the various effects of radiation on these types of animals and plants, or the nearest available information.

4. DISCUSSION ICRP will develop a small set of reference animal and plants, plus their relevant databases to serve as a basis for the more fundamental understanding and interpretation of the relationships between exposure and dose, and between dose and certain categories of effect. This concept is similar to that of the reference individual used for human radiological protection, and each reference organism will serve as a primary point of reference for assessing risks to organisms with similar life cycles and exposure characteristics. ICRP's framework will be designed so that it is harmonized with its proposed approach for the protection of humans. To achieve this, an agreed set of quantities and units, a set of reference dose models, reference doses-per-unit-intake, and effects-analysis will be developed. A limited number of reference animals and plants will be defined and developed to aid assessments, and others can then develop more area-andsituation-specific approaches to assess and manage risks to non-human species. The Commission's system of protection has evolved over time as new evidence has become available and as our understanding of underlying mechanisms has increased. Consequently the Commission's risk estimates have been revised regularly, and substantial revisions made at intervals of about 10-15 years. It is therefore likely that any system designed for the radiological protection of the environment would also take time to develop, and similarly be subject to revision as new information is obtained and experience gained in putting it into practice. ICRP can and is prepared to pay the key role, both in developing a limited set of reference animals and plants and in advising on a common international approach. At its meeting in Bariloche, Argentina, in October 2003, the Commission decided to establish a new Committee for the protection of non-human organisms, thereby showing its commitment for this rapidly developing area. A framework for radiological protection of the environment must be practical and, ideally, a set of ambient activity concentration levels would be the simplest tool. There is a need for international standards of discharges into the environment. At the Stockholm Conference in October 2003, the time was considered ripe for launching a number of international initiatives to consolidate the present approach to controlling radioactive discharges to the environment by taking explicit account of the protection of species other than humans. To achieve this, UNSCEAR should continue to provide findings on the sources and effects of ionising radiation that can be utilized as the authoritative scientific basis for the future international efforts in environmental radiation protection. The ICRP should continue to issue recommendations on radiation protection, including specific recommendations for the protection of non-human species. The IAEA should establish the appropriate international undertakings, including international standards and mechanisms for their worldwide application, to restrict releases of radioactive materials into the environment over time. The IAEA should also continue to foster information exchange by organizing international meetings on this subject [12]. The involvement of a broad stakeholder community, including intergovernmental organizations such as the Nuclear Energy Agency (NEA) of OECD and non-governmental organizations, is essential for identifying possible gaps in the evolving environmental radiation protection system and for increasing the understanding and acceptance of relevant recommendations.

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REFERENCES [1] United Nations. Declaration of the United Nations Conference on the Human Environment (1972). [2] United Nations. Rio Declaration on Environment and Development (1992). [3] R. J. Pentreath. What Models and Methodologies are currently available to understand Environmental Impact? In Workshop Proceedings from NEA Forum "Radiological Protection of the Environment - The Path Forward to a New Policy?" Taormina, Italy, 12- 14 February, 2002 (OECD, Paris, 2002) pp. 121 -130. [4]

International Atomic Energy Agency. Ethical Considerations in Protecting the Environment from the effects of Ionizing Radiation, IAEA-TECDOC-1270 (IAEA, Vienna, 2002).

[5]

The International Commission on Radiological Protection. 1990 Recommendations of the International Commission on Radiological Protection. ICRP Publication 60. Annals of the ICRP 21, 1-3 (1991).

[6]

The International Commission on Radiological Protection. A Framework for Assessing the Impact of Ionising Radiation on Non-Human Species. ICRP Publication 91, Annals of the ICRP 33, No. 3 (2003).

[7]

R. J. Pentreath. Radiation protection of people and the environment: developing a common approach. J. Radiol. Prot. 22: 1 -12 (2002).

[8]

R. Clarke R, L.-E. Holm. The Commission's Policy on the Environment. Guest Editorial. ICRP Publication 91, Annals of the ICRP 33, 201-203, (2003).

[9]

Protection of the Natural Environment - Proceedings from the International Symposium on Ionising Radiation, Stockholm, May 20-24 (Stockholm, 1996).

[10]

Environmental Protection Approaches for Nuclear Facilities - Proceedings from the Second International Symposium on Ionising Radiation, Ottawa, Canada, May 10- 14 (Ottawa, 1999).

[11]

Protection of the Environment from Ionising Radiation. Proceedings from the International Symposium on the Protection of the Environment from lonisingRadiation (SPEIR 3), 22 —26 July, Darwin, Australia. (International Atomic Energy Agency, Vienna, 2002).

[12]

The International Conference on the Protection of the Environment From the Effects of Ionizing Radiation, 6-10 October 2003, Stockholm, Sweden. The President's findings. IAEA-J9-CN-109 (IAEA, 2003).

[13]

The International Commission on Radiological Protection. Report of the Task Group on Reference Man. A report prepared by a task group of Committee 2. ICRP Publication 23 (1975).

[14]

The International Commission on Radiological Protection. Basic Anatomical and Physiological Data for Use in Radiological Protection: Reference Values. ICRP Publication 89. Annals of the ICRP 32, No 3-4 (2002).

Current Trends in Radiation Protection H. Metivier, L. Arranz E. Gallego and A. Sugier (eds.)

From Recommendations to Reality - A Critical Overview with a Historical Perspective G. Ches Mason1 Radiation Safety Section, International Atomic Energy Agency, Wagramer Strasse 5, P.O.Box 100, A-1400 Vienna, Austria

Abstract. a The International Commission on Radiological Protection is close to finalizing new recommendations on radiological protection to supersede ICRP Publication 60. In this context, the history of earlier ICRP recommendations is reviewed in summary and the evolving trends in protection principles and policy outlined. Developments are followed from the early policy of protection against deterministic effects in users of radiation sources, through a growing awareness and increasing scientific evidence of stochastic effects, to modern principles for safety based on justification of practices, optimization of protection and limitation of individual dose and risk. The key features of the current recommendations contained in ICRP60 are summarized and attention drawn to a number of perceived shortcomings and unresolved issues. The advice provided by the ICRP concerning its new recommendations is reviewed and the proposals assessed in the light of the problems they are intended to solve. The key issues have to do with the complexity of the recommendations, the bases for determining acceptability of risk, and the consequences of presuming a linear, no-threshold relationship between dose and effect. Finally, some comments are made concerning the proposal for a period of consultation and review by the ICRP before it publishes its new recommendations.

1. INTRODUCTION Perhaps the most striking feature of international practice in radiation protection over the past half-century has been the almost universal adoption by countries around the world of the recommendations of the International Commission on Radiological Protection (ICRP). Since taking on its present name in 1950, the ICRP has updated its recommendations several times and, on each occasion to date, the international community

a

Responsibility for the content of this paper rests with the author: it does not necessarily reflect the views of his employer or of Committee 4 of ICRP of which he is a member. E-mail: [email protected]

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has, for the most part, decided to adopt them. International acceptance has occurred presumably because each revision has been seen to be an improvement upon its predecessor and the best available guidance at the time. This phenomenon is reviewed below in Section 2 (the past) and Section 3 (the present). Now that the ICRP is once again contemplating new recommendations, questions arise as to whether changes in recommendations are needed at this time and, if they occur, whether international acceptance is likely to continue. Based on what is known, at the time of writing, of the intentions of the ICRP, Section 4 (the future) discusses some issues related to the new proposals. It reviews the alleged shortcomings of the present recommendations and examines the proposed solutions. Given what has been called a paradigm shift in expectations for standards setting, in particular in the development of stakeholder participation and critical review by people who are not radiation safety specialists, it is not clear that the same degree of acceptance of new recommendations will be as forthcoming as in the past, especially if little material benefit can be perceived from a change in regulatory practices. While the older, traditional style of developing recommendations by the ICRP has attracted some criticism, the Commission is wisely planning to release the recommendations as proposals for consultation. Section 5 comments on some of the possible benefits from a consultation process. The discussion presented here is restricted to the principal recommendations of the ICRP those publications carrying the title: 'Recommendations of the International Commission on Radiological Protection'. It also does not deal with recommendations concerning medical exposure. The other work of the ICRP, resulting in a large number of publications on specific topics related to radiological protection and providing elaborative guidance, is beyond the scope of this paper.

2. THE PAST The last fifty years has seen the ICRP establish an enviable record of leadership in standards setting for radiological protection. The process has not been without criticism, nor has acceptance always been swift or enthusiastic, but the eventual outcome has been that most countries of the world have adopted national standards for radiation protection based on the recommendations of the ICRP. The adoption by the ICRP of Publication 26 in 1977 marked the culmination of a process of evolution in protection philosophy and the start of period of stability and increasing international normalization lasting more than a decade. It made a fresh statement of the principles underlying the ICRP recommendations and made a number of improvements in logic, clarity and practicality, such as introducing the quantity 'dose equivalent' and adopting metric units. In what follows, the periods before and after 1977 are reviewed separately.

2.1. The 1950s to 1977 The earliest known harmful effects of ionizing radiation were those that became clinically manifest quite promptly, from erythema through to serious tissue burns. In addition there was concern about the possibility of genetic damage. Consequently, protection measures were designed to keep doses below the levels at which these effects were observed or thought to occur. This principle continued to form the basis of the ICRP's recommendations in 1950 [1] although the possibility of malignant disease, particularly leukemia, had already been recognized. Increasing awareness and understanding of cancer induction by ionizing radiation continued to influence the ICRP's recommendations through 1954 [2], 1958 [3] and 1962 [4], and by 1965 [5] the ICRP was recommending that 'doses be kept as low as is readily achievable, economic and social considerations being taken into account', although it felt unable to give quantitative guidance at that time on balancing risks and benefits. As this recommendation was unclear to many, the ICRP published an explanation in 1973 [6], in which it introduced the concept of population dose and cost-benefit analysis.

From Recommendations to Reality

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2.1.1. Principal features

The principal features of the ICRP recommendations through the 1950's and 1960's are indicated in Table 1. A progression can be clearly seen from protecting against what are now called deterministic effects and against genetic damage in the population to protection against stochastic effects in the individual. Also evident is a step-wise reduction in recommended occupational dose limits from 1 r/week prior to 1950 (about 500 mSv/year), through 0.3 r/week (150 mSv/year) in the 1950s, to 5 rem/year (50 mSv/year) by the 1960s, reflecting the growing evidence of harm in the form of late effects of radiation. As epidemiology progressed, and the causal connection between radiation exposure and induction of leukemia and other cancers became more compelling, the sense that a conservative or precautionary approach should be adopted for low doses increased. Consequently, the recommendations for protection of members of the public became more stringent although still, in 1965, based on an arbitrary factor of safety relative to recommended limits for radiation workers. 2.1.2. Achievements and implementation

The origins of the ICRP in the medical fraternity, particularly radiologists, and the continued presence of medical experts on the Main Commission and its Committees no doubt contributed to what seems to have been a generally welcoming acceptance of the ICRP's recommendations. The paradigm of medical expertise being authoritative and largely unquestioned by the population at large at that time helped in the adoption of the recommendations by governments into national regulatory instruments. It is also probably true that several of the members of ICRP were influential in health authorities and professional bodies in their own countries. Many developed countries enacted radiation control legislation based on ICRP recommendations over these years. As a consequence, there seems little doubt that working conditions and occupational health outcomes must have improved markedly for those involved in radiation work, although this is difficult to quantify in the literature. There is some evidence of reduction in occupational exposure of those workers who were monitored [7]. Among the achievements of the ICRP over this period, was the ready acceptance of the principle, in its various forms, of avoiding unnecessary exposure and keeping doses as low as practicable/achievable. This has become an unshakeable cornerstone of radiation protection philosophy, although in more recent years some critics have suggested that it may have unintentionally contributed to a distorted view by the general population of the level of risk associated with low levels of radiation. It has been a part of the ICRP's approach for over 50 years, first emerging when epidemiological evidence for a dose-response relationship was scarce indeed, and seems initially to have reflected an intuitive concern based on superimposing additional exposures on those received naturally and under which humankind has evolved. A less immediately obvious achievement perhaps was the program of work carried out by or stimulated by the ICRP which, over time, began to construct the knowledge base from which more scientifically defensible and detailed recommendations for radiological protection could be drawn. The steady progress towards robust definitions of dose and techniques for its measurement; the improved understanding of the effects of external radiation and of inhaled and ingested radionuclides; the work on standard man/reference man; the modelling of internal exposure; and the systemization of protection strategies involving constructs such as dose equivalent and effective dose equivalent all contributed to an increasingly coherent picture of radiation risk and protection.

2.2. From 1977 to 1990: ICRP26 By the mid-1970s, the ICRP was able to engage in a major review of its previous guidance and set out new recommendations on a fresh canvas. The result was ICRP Publication 26 [8]. In it can be recognized the essential features of the radiation protection practices of today, even though these have been subsequently refined following ICRP Publication 60.

Table 1. Evolution of the principal recommendations of the ICRP - 1950s and 1960s protection

Dose limitation for workers External exposure Internal exposure

1950 [1]

Avoiding the threshold for adverse effects. Judgement made by ICRP.

Maximum permissible dose of 0.3 r/week to whole body and to critical tissues*; 1.5 r/week to skin and forearms

Attention drawn to maximum permissible amounts in use in LISA, UK and Canada* *

1954 [2]

No appreciable bodily injury. Judgement made by ICRP on behalf of the individual .

For X rays: 300 mr/week to whole body and critical organs and 600 mr/weck to the skin; for all types: same values in mrem

300 mrem /week; maximum permissible body burdens given by radioisotope in u Ci

1958 [3] 1CRP1

Risk not unacceptable to the individual and to the population at large . Judgement made by ICRP.

1962 [4] ICRP6 (update of ICRP1)

1965 [5] ICRP9

Basis of

Year

Public

Precautionary guidance

Comments

'..strongly recommended that every effort be made to reduce exposure. . . to the lowest possible level'

* reduced from 1 r/week in earlier recommendations; reference to an early version of Standard Man

For large populations, reduce occupational values by a factor of 10 (concerns for genetic damage)

'..strongly recommended that every effort be made to reduce exposures. . . to the lowest possible level'

Increased attention to partial body exposure; first ICRP values for MPBB; MPCs given for air and water. ^an injury that a person 'would regard' as objectionable or that medical authorities 'would regard' as deleterious

Total accumulated dose (sum of external and internal) to the critical organs (gonads, blood-forming organs, lenses) less than 5(N-18) rems where N is age in years. Implies maximum of 100 mrem/ week on average for occupational exposure 1 . For other organs, between 4 and 20 rems/ 13 weeks depending on organ. MPCs still used, but adjustments to be made for total dose and mixtures of radioisotopes. Maximum over a year for special groups 11 : 1.5 rems. Doses from natural sources and medical procedures explicitly excluded.

Maximum permissible genetic dose111 (to a population): 5 rems/y.

'..recommends that all doses be kept as low as practicable, and that any unnecessary exposure be avoided'

' Prevent or minimise somatic injuries and minimize deterioration of the genetic constitution of the population. 1 Working in controlled areas. Working in the vicinity of controlled areas, but not classed as occupational exposure. 111 Genetically significant dose multiplied by the mean age of childbearing (30y).

as above

as above, but: 'special groups' replaced by 'adult workers not directly engaged in radiation work'; treat female workers such that dose to fetus would be less than 1 rem

as above, plus max. total dose to gonads and blood-forming organs: 0.5 rem/y. Other organs: 1/10 occupational value.

as above

First hint of LNT: 'It appears possible on some theoretical and experimental grounds that when either the total dose or the dose-rate is very low any [somatic] effects will be directly proportional to the total dose. . . '

Assumed risk from exposure deemed to be acceptable to the individual and to society. Judgement made by ICRP.

Annual dose limits: for whole body, gonads and red marrow - 5 rems; for skin, bone and thyroid - 30 rems; for hands and feet - 75 rems; other organs - 1 5 rems.

Annual dose limits: one tenth of the values for workers. Suggests using the concept of the critical group.

'..recommends that '. . . all doses be kept as low as readily achievable, economic and social considerations being taken into account.'

Introduces the concept of risk as directly proportional to accumulated dose. Makes the 'cautious assumption' that any exposure may carry some risk of somatic effects, such as leukaemia and other malignanacies.

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49

2.2.1. Principal features

The objective of radiation protectiona in ICRP26 is to protect people while allowing necessary activities that may give rise to radiation exposure. Despite the conservative assumption of a linear, no threshold (LNT) relationship between dose and effect, implying some small measure of risk down to very low doses, it is clear that some human activities that give rise to exposure to radiation have advantages that outweigh the risk of detriment resulting from the exposure. The ICRP had reached a mature understanding of risks and benefits by 1977 and how they could be incorporated into radiation protection policy. Further, the distinction between stochastic and 'non-stochastic' (deterministic) effects had become clearer and the ICRP was able to state the aim of protection as preventing the latter and limiting the risk of the former to acceptable levels. The principles of the system of protection were then expressed quite simply: • no practice shall be adopted unless it produces a net benefit, • all exposures shall be kept as low as reasonably achievable, economic and social factors being taken into account, and • doses to individuals shall not exceed the recommended dose limits. ICRP26 provided definitions of the quantities dose equivalent, collective dose equivalent and committed dose equivalent and it adopted metric units. It specified tissue weighting factors to put partial-body and whole-body exposure on the same footing from a risk perspective and came very close to defining effective dose equivalent, but technically this was not made formal until the ICRP Statement from its 1978 Stockholm meeting [included in [8]]. These definitions provided a common basis for estimation of doses and risks and, especially, for quantitative cost-benefit analyses in the context of keeping exposures as low as reasonably achievable (ALARA). ICRP26 clearly distinguished between occupational exposure, medical exposure and public exposure, providing guidance on protection in each case. It also used the concept of intervention, but essentially in the context of remedial action following accidents. For occupational exposure, recommended limits for non-stochastic effects were adjusted: 500 mSv/y for all tissues except the lens of the eye, for which the limit was 300 mSv/y. For stochastic effects the recommended limit for uniform irradiation of the whole body was set at 50 mSv/y, based on what the ICRP judged to be an acceptable risk for typical doses likely to be received if such a limit were applied, in comparison with occupational risks from other causes in industries regarded as having high standards of safety (roughly corresponding to an annual mortality risk of 10 -4 ). ICRP26 introduced the concept of working conditions to distinguish between groups of workers habitually and necessarily exposed in their work at relatively high levels for whom a 50 mSv/y limit was appropriate (Working Condition A), and those habitually less exposed (Working Condition B) where doses were most unlikely to exceed three-tenths of the limit. This allowed workplaces to be classified in a broadly corresponding fashion, as controlled areas or supervised areas, and appropriate measures taken in each case to control access and apply protection and monitoring strategies. ICRP26 recommended that for pregnant women, arrangements be made such that they did not work under Working Condition A. The rationale for the recommended dose limit for public exposure was a judgement by the ICRP, based on its understanding of public acceptability of other risks in everyday life, that an annual risk of fatality between 10-6 and 10 - 5 was likely to be acceptable to individual members of the public. Using the risk factor

a

ICRP26 uses the term 'radiation protection', whilst ICRP60 uses 'radiological protection'. Elsewhere, these terms seem to be used more or less interchangeably. The arguments in favour of one or the other promise to provide sport and amusement for radiation (radiological?) protection specialists for generations to come.

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of the time, about 10-2 Sv-1 , this led to a recommendation to continue using the existing whole-body doseequivalent limit of 5 mSv/y, noting that average doses were likely to be an order of magnitude lower than the limit. The ICRP stressed that the public limit was intended to apply to critical groups, groups of people broadly representative of those in the population expected to receive the highest doses. On the presumption that practices exposing the public were few and caused little exposure outside the critical group, typical doses to individuals in the population at large were expected to be much less than the limit. Nevertheless, the cautious manner in which this recommendation was expressed suggests the ICRP was a little concerned that it might not be sufficiently stringent and, by 1985, the ICRP felt confident in recommending a reduction in the public dose limit to 1 mSv/y [9]. ICRP26 also provided guidance on protection in the context of medical exposure and in accidents and emergencies. In a notable change of direction, it abandoned the use of genetic dose limits for populations, arguing that they were not useful in the light of better protection afforded through individual dose limits for members of the public. It should be noted that the ethical judgements implicit in the recommendations of ICRP26 were made by the ICRP on behalf of others, such as workers and members of the public, on the basis of what ICRP believed would be acceptable to them. Further, the focus of protection continued to be on human health. 2.2.2. Achievements and implementation

Among the achievements of ICRP26 that have had a lasting influence on radiation protection practice are:

• distinguishing stochastic and non-stochastic effects; • establishing the principles of justification, optimization (ALARA) and dose limitation; • defining the quantities dose equivalent and effective dose equivalent; • placing emphasis on ALARA rather than dose limits (including the use of collective dose); • re-enforcing the concept of the critical group in public dose assessments; and • providing a rationale for the recommended values of dose limits.

The recommendations of ICRP26 had a mixed reception. Some recognized the coherence brought about by the technical innovations and the logical merit of ALARA, while others expressed anxiety about the possibility of inappropriate use of ALARA to drive exposures down to very low levels at unnecessary cost, although this would seem to miss the point of ALARA entirely. Nonetheless, following a slow start, more widespread acceptance of the new recommendations was achieved, stimulated in part by the work of the International Atomic Energy Agency (IAEA) in updating its Basic Safety Standards for Radiation Protection [10]a. The ICRP also supported the concept of optimization with further guidance in 1983 [13] and, later, in 1988 [14]. In time, the international acceptance was such that during the 1980s most developed countries introduced new national standards based on ICRP26, and ALARA became an enduring paradigm.

a

From the very first publication in its Safety Series [11], the IAEA has adopted the recommendations of the ICRP through successive editions of Safety Series 9 on Basic Safety Standards for Radiation Protection up to the current international standards [12], cosponsored by FAO, ILO, OECD/NEA, PAHO and WHO.

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51

3. THE PRESENT: ICRP60 During the 1980s, evidence began to accumulate that the risk factors on which ICRP26 had been based needed to be updated. The principal motivation for change came from the continuing Life Span Study of the survivors of the 1945 atomic bomb blasts at Hiroshima and Nagasaki. ICRP26 risk factors were consistent with the UNSCEAR review of 1977 [15], but later assessments of the same Life Span Study cohort through to 1988 yielded risk factors that were significantly higher than had been derived previously. Several factors contributed to the change, including the longer followup period, which showed that the incidence of late effects was higher than observed earlier [16], improvements in retrospective dosimetry which suggested that the doses received were less than previously thought [17], improvements in age-specific risk calculations [18] and a preference for a multiplicative, rather than additive, projection model to predict future mortality from the observed data. As a consequence, the estimated overall risk per unit dose increased by a factor of about three. ICRP conducted a thorough review of these data and set out the detail in Annex B of Publication 60 [19]. Reviews were also made by UNSCEAR in 1988 [20] and by the Committee on the Biological Effects of Ionizing Radiations of the United States National Academy of Sciences [21]. The weight of evidence clearly supported a revision of ICRP recommendations. The ICRP took advantage of the need for revision to review all of the ICRP26 recommendations and the principles and assumptions on which they were based.

3.1. Principal features ICRP60 does more than merely provide recommendations for radiation protection. It is an information resource in its own right on quantities and dosimetry used in radiological protection, and on biological effects of radiation and predictive modelling of mortality risk. In ICRP60, the ICRP redefined the protection quantities dose equivalent and effective dose equivalent, using the new names 'equivalent dose' and 'effective dose' respectively. The subtle changes in name served to distinguish the new quantities, based on new radiation weighting factors and tissue weighting factors, from the old. Using its extensive review and analysis as a foundation, the ICRP set out a comprehensive system for radiological protection. ICRP60 continues the distinction between deterministic (non-stochastic) effects and stochastic effects, noting the objective of eliminating the former and controlling the risk of the latter. It also specifically recognizes that, in a world where natural and artificial sources of radiation are ubiquitous, there is a need to define the scope of the system of protection. To this end it discusses the concept of exclusion of exposure from the system of protection when it cannot realistically be controlled: for example, exposure from cosmic rays at ground level or from potassium-40 in the body. It also notes that regulatory authorities may exempt certain activities from specified regulatory requirements where these are not necessary. This situation may arise when doses are considered to be trivial or when the regulatory requirement will produce no substantial improvement in protection. It further recognizes that radiological protection needs to include social as well as scientific judgements. The ICRP makes clear in Publication 60 an important distinction between 'practices' and 'interventions'. Practices are human activities that have the effect of increasing exposure to radiation, and they include the generation of electricity by nuclear power, medical applications such as radiography, radiotherapy and nuclear medicine, and a broad spectrum of industrial and research applications. Such exposures are clearly controllable, and the purpose of radiological protection is to restrict the increase in exposure. Some human activities, however, are designed to reduce existing exposures, such as those arising from sites contaminated by accidents or those due to high levels of radiation from natural sources. These activities are identified in

52

Current Trends in Radiation Protection

ICRP60 as interventions, and since they are intended to have the effect of reducing rather than increasing exposure, the provisions for protection are different from those for practices. For practices, ICRP60 reinforces the three principles of justification of the practice, optimization of protection, and limitation of individual dose and risk. Justification and optimization both involve judgements of acceptability and reasonableness and an acknowledgement that social factors should be taken into account, although ICRP60 gives little guidance on how that might be achieved. The discussion of optimization introduces the concept of a 'dose constraint' as a mechanism for placing source-related restrictions on individual dose within optimization assessments in order to limit inequities in exposure that could otherwise occur. The intention was to use dose constraints as a prospective tool to establish an envelope within which optimization could take place - the dose limits often being regarded as too high for this purpose. In practice, there has been some confusion between the intended use of the term and the concept of prescriptive limits applied by a regulator. Following its review of risk factors, the ICRP decided to reduce the recommended dose limit for occupational exposure to 20 mSv/y as a long-term average. The adoption of this value was based on a combination of factors, not only the overall risk of fatal cancer. These included consideration of age specific risk and reduction in life expectancy. Taking all factors into account, the ICRP reached a judgement that the cumulative dose over a working life should not exceed about 1 Sv and that this figure should rarely be approached. An effective dose limit of 20 mSv/y averaged over 5- year periods should achieve that objective in practice, although the ICRP retained 50 mSv as the occupational dose limit for a single year in order to provide for some flexibility in particular circumstances. Limits for equivalent dose to prevent deterministic effects in the lens of the eye were set at 150 mSv/y and for the skin and the hands and feet at 500 mSv/y. For public exposure from practices, the ICRP found it even harder to settle on a foundation for the dose limit value for stochastic effects. It reviewed what information was available in the literature on acceptable risk and devoted a whole Annex in Publication 60 to bases for judging the significance of the effects of radiation. It drew attention to levels of exposure from natural background radiation, but stressed that such comparisons did not justify the choice of any particular value for a public dose limit, rather they merely provided a context in which to assess the significance of a small increase in exposure caused by practices. The ICRP made the judgement that a dose limit of 1 mSv in a year would be just short of an unacceptable value for continued exposure from practices. Again, however, it suggested that in special circumstances, a higher limit of 5 mSv could be allowed in a single year provided the 5-year average does not exceed 1 mSv/y. It also set equivalent dose limits of 15 mSv/y for the lens of the eye and 50 mSv/y for the skin —one tenth of the limits for occupational exposure in each case. In dealing with existing exposures, the ICRP introduced recommendations for radiological protection in intervention actions. By analogy with practices, the principles of justification of action and optimization of protection are both valid, but dose limits cannot apply as there is no increase in exposure to be restricted. Instead, practical guidance can be given through the use of 'intervention levels', usually expressed in terms of a measurable quantity, such that action to reduce total doses would be considered when intervention levels are exceeded. ICRP60 provided further guidance on potential exposures - exposures that may occur from events that were unplanned or unforeseen such as from accidents or, for example, from changes in land use or in the environment near a radioactive waste repository. The ICRP gave guidance on establishing risk limits and risk constraints but did not make numerical recommendations. ICRP60 elaborated on the comment made in ICRP26 that if humans are protected then other living things are likely to be protected. It noted that ICRP's interests were directed principally at protection of humans, but offered a view that the standard of environmental control needed to satisfy the recommendations

From Recommendations to Reality

53

on human exposure would ensure that other species would not be put at risk. While individual members of non-human species might be harmed, the species themselves would not be endangered nor the balance between species disturbed.

3.2. Achievements and implementation One of the principal achievements of ICRP60 is the logic of its approach. The separation of circumstances into practices and interventions makes the different strategies adopted in each case theoretically understandable. Similarly, the hierarchical application of the concepts of justification, optimization and dose limitation is a defensible and principled way to approach protection. Further, the separate recommendations for occupational, medical and public exposure, and for the treatment of potential exposure, allow the relevant parts of the recommendations to be brought bear as straightforwardly as possible in particular circumstances. A more unexpected achievement perhaps is the rapidity with which the recommendations of ICRP60 have become the international norm for radiation protection, being taken up in legislative instruments and regulatory practices in most countries of the world. One factor that has undoubtedly contributed to this success is the involvement of the IAEA in updating its Basic Safety Standards to take account of ICRP60 and in encouraging its Member States to adopt them. Another is the parallel adoption by the Council of the European Union of a Directive concerning Basic Safety Standards [22] based on ICRP60 recommendations. The IAEA process of development for the International Basic Safety Standards (BSS) [12], illustrated in Figure 1, highlights the different roles played by the ICRP and IAEA. As a matter of policy, the ICRP avoids making prescriptive recommendations because of the different approaches adopted in different countries. ICRP recommendations are usually descriptive and discursive in style; this allows for interpretation

Figure 1. From recommendations to reality

and adoption into as broad a range of styles as possible of national regulatory systems. However, it also means that ICRP recommendations are usually not amenable to simple conversion into regulatory instruments. The IAEA process, on the other hand, specifically sets out to prepare safety requirements that are, in essence, model regulatory instruments based on the ICRP recommendations. Furthermore, while ICRP recommendations are developed and published by the ICRP alone, the IAEA system for production of its Safety Standards Series involves all of its Member States and a number of international organizations in the development and approval process. This ensures a degree of ownership of the Basic Safety Standards by the countries and organizations that agreed to their publication. Furthermore, the IAEA has pursued and is continuing a major program of work to assist developing countries to upgrade their regulatory infrastructures to be consistent with the BSS and hence with ICRP60 [23].

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Current Trends in Radiation Protection

3-3. Unresolved problems Despite the overwhelming success of ICRP60 as a normative guide for radiation protection practices around the globe, there remain some problems of implementation and interpretation, as indicated below. 33.1. Practice or intervention? Difficult cases.

ICRP60 recommendations can work well for those human activities that are clearly practices and those that are clearly interventions. But there are many activities that are difficult to classify. Is the activity of building and living in homes a practice, for example? The initial reaction is usually to say that it is not: one would intervene in circumstances where indoor exposures were found to be high, in order to reduce them. But suppose a building material containing radium became available cheaply as a by product from an industry processing natural ores: does it become a practice to use that material to construct dwellings? If the concentration of radium were high, it might be reasonable to consider that this would indeed constitute a practice: it increases exposure (over the use of alternative materials) and the exposure is controllable (by regulating or, in the extreme, forbidding the practice). The problem arises in the more realistic situation when the concentration of radionuclides is neither very high nor very low. In the real world there is a grey scale in terms of radionuclide concentrations in building materials, but ICRP60 seems to require a binary decision - practice or intervention - in order to know which protection measures to apply. The problem extends in principle to all areas of activity involving naturally occurring radioactive materials (NORM). Either a greater consensus is required concerning criteria on which a decision can be based for categori2ing an activity as a practice, or the problem has to be solved at its root by not requiring a separation into practices and interventions. The ICRP has provided guidance on the first option in its Publication 82 [24]. It recommends treating situations involving building materials, commodities and the like through protection by intervention. This is consistent with the ICRP's guidance for dealing with radon in homes and workplaces [25], which seems to have met with broad endorsement. Intervention exemption levels could be established for building materials and commodities in terms of radionuclide concentration, which could then be used as criteria for deciding whether or not to intervene. It appears that the new ICRP proposals (see Section 4) favour the second option by avoiding making a distinction between practices and interventions, although the end result would still be to use a prescribed level as a reference for decision making. 3.3.2. Should protection measures be applied to everything? The problem of scope.

ICRP60 makes provision for some exposures to be excluded from the system of protection on the grounds that they are not controllable by reasonable means. It makes no sense to require controls on things that cannot be controlled. The classic, and uncontroversial, examples given are exposures to cosmic rays at ground level and exposures from potassium-40 in the body. There is, however, a grey scale of controllability of exposures to natural sources in various circumstances, whereas a binary decision is called for in excluding or not excluding exposure. Further guidance is needed to assist in decision making. One possibility is to use the general concept of optimization to compare the 'costs' of applying the system of protection to a particular circumstance of exposure with the benefits expected to be achieved in reduction of dose or risk. A similar problem of scope arises in the context of exemption. While ICRP60 explicitly leaves decisions on exemption to national authorities, many of those same authorities have been calling for international guidance. In a global economy, with huge numbers of goods and services being traded between nations, it can be most beneficial to have international uniformity concerning what should be regulated and what may be exempted. A case in point is international trade in commodities containing small quantities of radionuclides. Is there a level of radionuclide concentration below which trade in such commodities could be conducted freely; that is, free of regulatory controls for radiation protection purposes? The IAEA was asked at its

From Recommendations to Reality

55

General Conference in 2000 to develop consensus guidance on this issue; at the time of writing, over three years later, its Member States are still wrestling with the problem. While the concept and quantification of exemption appears to be accepted in terms of dose arising from practices involving 'artificial' radionuclides the BSS value of ('the order of) 10 /J,Sv in a year - there seem to be two major hurdles to overcome to achieve an international consensus on exemption of commodities. One of these is to reach agreement on the numerical values of radionuclide concentration, particularly for 'natural' radionuclides, that are unlikely under any realistic circumstances to lead to exposures requiring regulatory attention. The other is to satisfy two diametrically opposed styles of regulation: one which a priori encompasses all activities and exempts some of them through a regulatory decision, and another which defines a priori what lies outside the scope of regulation. Adherents to the former style argue that their approach allows them to retain regulatory control of any circumstance that requires it, in contrast to the latter style which lacks a legal instrument for dealing with activities that lie outside scope. Adherents to the second style use a de minimis non curat lex type of argument to avoid unnecessary regulatory activities concerned with trivia. And in any case, they argue, it is possible to include a 'catch-all' clause in regulations that allows the regulatory authority to regulate activities that would otherwise be out of scope, should it see a need to do so. Whether the ICRP can or should offer any advice on these matters is moot. 3.3.3. How useful are dose limits in a regulatory context? What is the role of the dose constraint? There is a general acceptance that the ICRP60 dose limits (20 mSv/y for occupational exposure and ImSv/y for public exposure) mark an upper boundary to what is acceptable for individual dose from practices. If everyone were exposed only to one source, for whom a legally responsible person could be identified, it would be a straightforward matter to apply regulatory controls to that person, requiring that the doses received be kept below the limits. Unfortunately, that is often not the case. The underlying problem is that dose limits are individual-related, whereas regulatory instruments are source-related; that is, related to the person responsible for the source. How is responsibility to observe individual dose limits to be apportioned when the individual is exposed to more than one source, each source being the responsibility of a different person? Many regulators seem to have opted for a 'target' maximum dose (a prescribed dose limit) or a 'dose constraint' applied to a specified practice or else have required the responsible person to demonstrate that protection has been optimized (below the limit). In some cases, owners and users of sources have set selfimposed maximum dose targets as part of their protection systems. While it is therefore possible to work around the problem, the solutions can be untidy and may not strictly adhere to the system that ICRP60 recommends. In this context, it should be noted that the intent of the ICRP was that dose constraint be used prospectively, as an upper bound to the individual dose assessed as likely to be delivered by a protection option, during the analysis of options within an optimization process. It was not intended to double as a prescribed dose limit and to be used retrospectively. It may be that one of the things that has been missing from international norms is a consensus on prescribed limits that are source related. This might have reduced the temptation to misapply the concept of dose constraint. Numerical values of dose constraint in use by regulatory authorities, whether purely prospectively or as prescribed limits, lie mostly in the range 0.1 to 0.3 mSv/y. The ICRP has recommended a generic dose constraint of 0.3 mSv/y for public exposure in the context of radioactive waste disposal [26]. 3.3.4. How are social and economicfactors to be taken into account? Justification and optimisation: who is the judge?

While the concepts of justification of practices and optimization of protection have become well established, the judgements made concerning benefit vs. detriment and what is reasonably achievable seem often to be

56

Current Trends in Radiation Protection

taken by the regulator. Day-to-day 'optimization' is typically managed within the organization carrying out the practice. The ICRP has published guidance on decision-aiding techniques for optimization [14], but decisions must be made justly, which includes being made by the appropriate persons. At the higher level - the regulatory level - the intention of balancing benefit and risk, and of taking 'economic and social factors' into account, was to recognize that decisions about how far social resources are to be expended on measures to reduce dose and risk are not the prerogative of radiation safety specialists. Such decisions require input from a range of affected and interested parties, ideally through some democratic and transparent procedure of review. The apparent lack of progress in establishing such procedures may indicate that the concept is still not fully mature in the minds of governments and national decision makers. It is likely that this will change through the ongoing social evolution in 'democratization of knowledge and of decision-making processes' [27], through which mechanisms are being devised to allow stakeholders some input into the regulatory process. It is quite reasonable for the ICRP to excuse itself from offering advice in this area, but this leaves something of a vacuum which many regulators would like to see filled. 3.3.5. Is collective dose useful in practice? Has it really been misused? Can very small doses received by large numbers of people be discounted: for example, in considering remote populations or future generations?

The early advice from ICRP on optimization of protection [6], [13] focused on collective dose as a measure of harm: optimization involved balancing the benefit of reduction in collective dose against the cost of achieving that reduction. Mathematically, it was possible to use the tools of monetary cost-benefit analysis to this end, once a value of the monetary equivalent of the person-sievert - the so called 'alpha value' had been decided upon. However, a simple, linear relationship between dose reduction and cost does not recognize society's preference for expending greater resources on unit reduction in risk when individual risks are high. That is, for doses close to the dose limits the monetary equivalent of the person-sievert is higher than for very small doses. ICRP37 introduced the idea of 'extended' cost-benefit analysis which gave greater weight to high individual doses through the use of a non-linear term involving a 'beta' value [13]. With time, it became evident that these analyses, while relatively straightforward, did not reflect the true complexity of decision making in regard to optimizing protection. ICRP55 gave some practical guidance on strategies for a multi-attribute approach to balancing benefit and harm, where collective dose might be one of several factors to take into account [14]. Each factor is assigned some kind of weighting, not necessarily in monetary terms, in order to find a balance that is acceptable overall, taking all factors into consideration in due measure. The potential of ICRP55 seems not to have been fully exploited. This may change as stakeholder involvement and the 'democratization' of regulatory decision-making (see above) gain hold. While formal techniques for optimizing protection may be seldom applied in practice, at an informal level the principle is thriving. It takes the operational form of continually asking whether the level of protection obtained is the best that can be achieved in the circumstances and then making adjustments accordingly. There have been ALARA conferences [28] and there are active ALARA networks [29] to demonstrate that the fundamental notion is sound and is endorsed by the radiation protection community. In contrast to the common-sense approach adopted operationally, criticisms have been voiced about inappropriate use of collective dose considerations in optimization on a larger scale. There seems to be concern that aggregating large numbers of very small individual doses, such as could occur for example following the release of radioactive material to the environment, might have an adverse effect on decision making. It is certainly possible that, if predicted doses from different options for a particular practice were to be aggregated over all space and all time, the result could be dominated by the large number of small doses received at distant times and in distant places. This might well adversely affect the discriminating power of the analysis, since many or all options might end up yielding much the same collective dose. Some of the

From Recommendations to Reality

57

suggestions made to solve this problem have been confronting to the mainstream paradigm of radiation protection, in particular the ground-swell of opinion in some quarters to abandon the presumption of the linear, no-threshold hypothesis relating doses and effects. While the presumption remains in force, however, the issue of whether very small doses predicted to be delivered to distant populations and to future generations should be discounted in some manner remains a controversial one. 'Out of sight, out of mind' is clearly an ethically indefensible position. These ethical implications are further addressed in Section 4. 3.3.6. Can the different dose limits for workers and for members of the public be explained?

Many people outside the radiation safety profession ask why the dose limits for workers are significantly higher than for members of the public. Indeed, some authors have called this a double standard [30]. Is the difference defensible? In the context of ICRP recommendations, the different annual limits for practices arise from different considerations of risk and acceptability. In ICRP26, this was clearly spelt out: the choice of dose limit for workers was based on considerations of what was thought to be an acceptable level of risk in 'safe' industries coupled with the observation that typical occupational doses would be expected to be an order of magnitude smaller than the limit, while the dose limit for members of the public involved judgements about the community's acceptance of risk in daily life, insofar as such information was available. It is generally acknowledged that, given the nature of industry in modern society, workplaces may involve some degree of risk not present in the home. Furthermore, the population at large includes infants and children who are more radiosensitive than the population of adult workers. ICRP60 continues to recognize this difference. While optimization of protection demands continual vigilance in reducing risk as far as is achievable, there would be little point in requiring adherence to a statistical risk of fatality at work that was unrealistically low. It is doubtful, for example, that many commonplace medical procedures would be allowed to continue if all medical staff were required to observe an occupational dose limit of 1 mSv per year. In practice the difference in outcomes is less stark than the difference in dose limits. The latter suggests a ratio of 20:1 (some authors, to emphasize their point, use 50:1 based on the single-year limit), but in practice typical occupational doses in most industries involving radiation exposure are a few mSv per year [31], while everyone is exposed to around 2 mSv per year on average from background radiation and medical practices. The difference in total doses, therefore, is no higher than a ratio of 2:1 or 3:1 for most workers, although clearly a minority will experience higher doses. This magnitude of difference in total doses could arise in principle for members of the public by moving from areas and homes where there is low natural background radiation to those where the background is higher. This is not an argument to justify a difference between worker exposures and public exposures, but it does put the magnitude of the difference in context. From an ethical perspective, the arguments for allowing higher doses to workers in industries involving exposure to radiation than to members of the public continue to need to be demonstrated on the basis of considerations such as social need for the work to be done, informed consent and free choice. 3.3.7. Should there be recommendations for the protection of species other the humans? There is now a clear expectation that specific consideration should be given to radiation protection of species other than humans. What is less clear is whether this should be done by the ICRP or by some other process. What is less clear still is whether such consideration will result in recommendations that differ from or augment those currently in place. In any event, the ICRP has decided to establish a new Committee to review the problem. As noted above, the presently valid recommendations of the ICRP [19] express a view that as long as humans are protected to the standard recommended other species will not be put at risk. This may be

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correct, but it has not been demonstrated. In particular, there are known to be some environmental niches where humans are absent but other species are not. In these circumstances, concern would necessarily focus on those species. For example, the existing ICRP position would not completely address the acceptability of a practice that introduced radioactive materials into the deep ocean. It seems unlikely that there will be many cases where additional protective measures will need to be provided over those necessary for humankind, but an open mind should be kept until the issue has been adequately studied.

4. THE FUTURE: NEW RECOMMENDATIONS FOR 2005? For some time, the ICRP has made it clear that it intends to make new recommendations for radiological protection that will supersede ICRP60. In contrast to the conventions of former times, the ICRP has been commendably open in its approach to the development of new recommendations, thinking aloud both in print [32], [33], [34] and at international conferences [35] and other meetings. A presentation of the proposed new recommendations is expected at the 11th International Congress of the International Radiation Protection Association in Madrid in May 2004, with publication anticipated in 2005 [34].

4.1. What is being proposed and why? How are the new recommendations expected to differ from the present system for protection? The main reasons given for proposing a change are: • an evolution in social attitudes from emphasizing utilitarian considerations towards greater concern for the individual; and • a belief that the present recommendations are too complex and often misunderstood, particularly with regard to: • the categorization of activities as practices and interventions, coupled with the apparently different treatment of artificial sources of exposure and natural sources, • possible inappropriate use of the collective dose concept and monetary cost-benefit analysis, and • too many different numerical values of limits, constraints and action levels. The ICRP has also indicated a need to revise its recommendations concerning radiation-weighting factors and tissue-weighting factors on the basis of recent scientific data. The first of these reasons relates to the recommendation to optimize protection. The ICRP believes that many have interpreted optimization in terms of a balance between reduction in collective dose, as the measure of benefit, and the cost of achieving that reduction. This results in emphasizing the interests of society as a whole over those of the individuals exposed. Consideration of collective dose alone would not deal with the possibility of doses being distributed inequitably among those exposed, and this is why the concept of the dose constraint was introduced to provide some bounds for individual doses within the context of optimization. It is not clear from the ICRP's discussion to date why this problem could not be solved through evolution of the multi attribute concepts developed in ICRP55. As will be discussed below, some authors argue that the ICRP is now headed too far in the other direction, by discounting collective dose too greatly. The second reason no doubt reflects an awareness that the public at large finds much of the radiation protection philosophy perplexing. However, the problems are complex and it should not be surprising that they require complex solutions. The difference between practices and interventions and problems related to

From Recommendations to Reality

59

the treatment of natural sources are indeed difficult, as discussed in 3.3.1 above. If some simplification of this situation could be achieved it would certainly be of great benefit. The issue of inappropriate use of collective dose has been addressed earlier, but the suggestion that there are presently too many numerical 'levels' in the recommendations merits further attention. The ICRP has identified around 30 such numbers in about 10 separate ICRP publications [34], and it has set itself the task of enquiring whether this number could be reduced for the sake of simplicity and improved understanding. The new proposals are expected to make some significant changes in approach [34]. • First, it is intended that the issue of justification of a practice be taken up by national governmental and social mechanisms so that the ICRP's system of protection would apply only to activities that have already been declared justified. • Second, for each source within a justified practice, a new definition of the concept of constraint would require doses to the most exposed individuals from that source to be restricted to values below the constraint. This would be regarded as a basic standard of protection for the individual. It is also suggested by the ICRP that this would provide protection for society from that source. • Third, there would be a further duty on those responsible for sources to achieve a higher level of protection when feasible — essentially the existing concept of optimization, but involving 'authorized levels' set by the regulatory authority. These levels correspond in a sense to the (current) use of dose constraints, except that they would be used retrospectively as well as prospectively. The basis of the ICRP's approach to the new constraint values is to explore the levels of concern that are felt to be held by people about the magnitude of exposure. Levels of concern can, in the ICRP's view, range from essentially none (trivial doses), through low (doses of the order of background levels) and raised (doses of several tens of mSv), to high (doses of over 100 mSv). The ICRP appears to intend to set maximum values of constraint on risk-based criteria, allowing national authorities to establish other (lower) values of constraint (authorized levels) related to this ranking of levels of concern and/or to input from affected parties or stakeholders. The ICRP also intends to clarify the use of the term 'exclusion' and to provide explicit recommendations concerning exposure to natural sources [34]. These are likely to include recommended exclusion levels for natural sources.

4.2. How have these proposals been received to date? The ICRP proposals for new recommendations have so far found a lukewarm and sometimes critical reception. Many in the radiation safety profession feel that the case for change has yet to be made: that it would be preferable to improve the existing system than to replace it. Some have noted with concern the apparent shift away from a risk-based approach to setting protection standards towards an approach that uses natural background radiation as a benchmark or comparator for perceived levels of concern. There has also been trenchant criticism of the ICRP for failing a number of ethical tests [36], although the ICRP would presumably contest some of the faults alleged (see also Section 4.3). The major change foreshadowed for the new recommendations is the setting up of a small number of source-related constraint values with the intent of simplifying the thirty or so numbers referred to above. As presently understood, the ICRP would recommend maximum values of constraint that continue to be risk based. It would propose that national authorities set authorized levels at values up to the maximum but probably lower for particular circumstances. These would be established by whatever process a country chooses,

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depending on its regulatory system. Without this fundamental shift in approach, the new recommendations would indeed amount to a fine tuning of ICRP60 and there would likely be much less controversy. A change of direction such as this needs careful scrutiny: are the alleged grounds for change real, are the proposed changes acceptable, will they be implementable, will they be effective and cost-effective, will they improve protection, will they improve understanding and reduce confusion, could the objectives of the change be met by an alternative and preferable method? It seems desirable that some degree of public scrutiny of the proposed changes should be allowed for by the ICRP; this is further discussed in Section 5. In what follows, some of the principal concerns and arguments relating to the new proposals, as far as they are known, are discussed.

4.3. Some issues of concern There have been concerns that the ICRP is proposing to abandon the principle of setting limits of exposure on the basis of acceptable risk and to turn instead to a system of reference levels based on perceived concern. This has been labelled a 'naturalistic fallacy' in one particularly critical article [36] the fallacy being to assume that what is natural is acceptable, when the notion of acceptable should really address what ought to be rather than what is the case. However, this criticism seems to be based on a misreading of what the ICRP actually intends. As indicated above, the ICRP plans to recommend maximum values of constraints that will be based on assessments of acceptability of risk. This will not satisfy those who argue that the ICRP has no authority to make judgements about what is an acceptable risk - that this should be done with the participation of those who bear the risks - but it does at least preserve the notion of setting a boundary beyond which exposures would be regarded as unacceptable and therefore to be prevented. This will need to be explained clearly and forcefully by the ICRP if it wishes to avoid this kind of criticism. The same article that posits the naturalistic fallacy suggests a number of shortcomings - ethical, logical and scientific - in the ICRP's proposed approach [36]. When analysed, however, the majority of alleged shortcomings are related to an objection to abandoning collective dose as a measure of harm. The real issue here concerns the presumption of a simple linear, no-threshold relationship between dose and risk. If the ICRP continues to hold to this premise, as it appears to do, then it follows as an unavoidable mathematical and logical consequence that collective dose cannot be ignored. This is because it does not matter in a statistical sense who receives the doses, provided they are below thresholds for deterministic effects: the number of predicted cases of radiation-induced cancer among those exposed is directly proportional to the collective dose. The shift towards individual-based criteria and away from optimization of protection that includes collective dose as a factor could then be seen both as an ethical shortcoming and a failure in logic. The way to resolve the conflicting concerns with collective dose - the logic of premise and consequence vs. the intuitive belief that merely adding together large numbers of small doses is too simplistic given the uncertainty involved - is probably to address the fundamental assumption. In experimental science, the weighting of results according to their precision of measurement is a commonplace statistical procedure: typically, a data set of repeated measurements is weighted in inverse proportion to the variance (the square of the standard deviation) of the data points in the set. In the context of LNT, the epidemiological data lose statistical significance below a level of dose around 100 mSv. Linear extrapolation to zero is a presumption, not a statistical procedure, but it may be reasonable to suppose that extrapolation immediately below 100 mSv carries less uncertainty than extrapolation further afield towards zero. Thus it may be possible, in optimization assessments, to defend a case for weighting the extrapolation by some function of dose; that is, in the aggregation process, giving low doses less weight than higher doses. Collective dose would not be not ignored, but taken it into account in a manner commensurate with the degree of confidence or belief in the LNT presumption at different levels of individual dose. This 'disggregration' is consistent with the suggestion of a 'matrix' approach by the ICRP [34] and very similar to the use of a 'beta' term, as discussed in ICRP55 [14]: it would have the effect of lessening the significance of the large number of doses close

From Recommendations to Reality

61

to zero. The details of such a procedure are beyond the scope of this paper, but it could offer a means of retaining a degree of logical and ethical validity while at the same time permitting a more intuitively realistic application of the optimization concept. Other concerns relate to whether the new recommendations will in fact be an improvement on the existing ones. Will they bring an improvement in safety? That seems unlikely to any significant degree. Will they lessen complexity and improve understanding? That cannot yet be assessed. Will they solve the problems that have been put forward as motivators for change? Again, that can only be judged when the recommendations become available in full detail. These concerns make most welcome the ICRP's intent to consider a period for review of its 'final' recommendations.

5. POSSIBLE BENEFITS OF A REVIEW PERIOD In the context of professional anxiety about the directions that the ICRP appears to be taking in its new proposals, which rests in part on doubt about the need for change in the near future, it seems desirable that the new recommendations should lie on the table for a period prior to final publication. This would allow the profession and other interested parties to fully analyse the proposals and their implications in order to satisfy themselves of the validity and merit of the recommendations from their perspective, or to suggest improvements, or both. There seems little need for urgency in moving to new recommendations, especially when many countries have only recently adopted, or are still in the process of adopting, national standards that are consistent with ICRP60. The new proposals are not being driven by new science that would require swift amendment to standards of protection. It is understood that the ICRP will make provision for a period of review, which would allow for a number of different types of assessments to be made by those who may be affected by the recommendations or who have an interest in radiological protection. Such reviews could include: • Impact assessment. Many countries now require that any proposed new regulation or change in regulation undergo a regulatory impact review process. The case for the regulation or the change has to be made in terms of the benefit it would bring in relation to what it would cost to implement it. How would the new recommendations fare under such a test? • Verification of a consensus concerning the assumptions and judgements made by the ICRP. Until the recommendations are known in detail, it is difficult to assess whether they will meet with consensus support from the international community. It is highly desirable that radiation safety professionals and international bodies such as the IAEA, ILO, WHO, PAHO and NEA agree with and endorse the new recommendations if they are to progress through the process outlined in Figure 1 above and be cast in regulatory form in a future edition of the BSS. • Regulatory road testing. Will the recommendations solve the problems they are intended to cure? It would be very useful to conduct analyses of the new recommendations against each of the issues identified as problematic with the existing recommendations. For example, will the new recommendations lead to practical and implementable solutions to the problems of regulating naturally occurring radioactive materials (NORM)? Or the problems of exclusion? Or the problems of equity of protection (both the distribution of individual doses and the concerns for distant populations and future generations)? • Simplicity and understanding. Will the new recommendations be seen as simpler than the existing ones and will they be better understood, especially by people who are not radiation safety professionals? Some adventurous persons or groups might try putting this to the test.

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Given the close marriage of ICRP recommendations with processes for establishing international regulatory norms, as indicated in Section 3.2 above, and the consensus-building approach of those processes, involving 'ownership' by a number of international organizations and their member states, the ICRP is to be commended for planning a period of consultation for its new recommendations. Issuing documents for consultation is consistent with the ICRP's policies and procedures [37]. And such a process may lead to improvements in the final publication — at least, in small measure, it could go some way towards alignment with the evolving democratization of standards setting and allow for independent consideration of policy issues involved in bridging science, ethics and protection practices [38]. It could, thereby, positively assist in the widespread acceptance of the ICRP's new recommendations and in the successful transition from recommendations to reality.

REFERENCES [1]

International Commission on Radiological Protection, International Recommendations on Radiological Protection, Br. J. Radiol. 24, 46-53 (1951).

[2]

International Commission on Radiological Protection, Recommendations of the International Commission on Radiological Protection, Br. J. Radiol. Suppl. 6 (1955).

[3]

International Commission on Radiological Protection, Recommendations of the International Commission on Radiological Protection, ICRP Publication 1 (Pergamon Press, London, 1959).

[4]

International Commission on Radiological Protection, Recommendations of the International Commission on Radiological Protection, ICRP Publication 6 (Pergamon Press, Oxford, 1964).

[5]

International Commission on Radiological Protection, Recommendations of the International Commission on Radiological Protection, ICRP Publication 9 (Pergamon Press, Oxford, 1966).

[6]

International Commission on Radiological Protection, Implications of Commission recommendations that doses be kept as low as readily achievable, ICRP Publication 22 (Pergamon Press, Oxford, 1973).

[7]

United Nations, Ionising Radiation: Levels and Effects—A. Report of the United Nations Scientific Committee on the Effects of Atomic Radiation, Volume I: Levels (United Nations, New York, 1972), pp. 173 -184.

[8]

International Commission on Radiological Protection, Recommendations of the International Commission on Radiological Protection, ICRP Publication 26 (Pergamon Press, Oxford, 1977).

[9]

International Commission on Radiological Protection, Statement from the 1985 Paris Meeting of the ICRP, in ICRP Publication 45, Annals of the ICRP 15(3) (Pergamon Press, Oxford, 1985).

[10]

International Atomic Energy Agency, Basic Safety Standards for Radiation Protection, 1982 Edition, Safety Series No.9 (IAEA, Vienna, 1982).

[11]

International Atomic Energy Agency, Safe Handling of Radioisotopes, Safety Series No.l (IAEA, Vienna, 1962).

[12]

Food and Agriculture Organization of the United Nations, International Atomic Energy Agency, International Labour Organisation, Nuclear Energy Agency of the Organisation for Economic Cooperation and Development, Pan American Health Organization and World Health Organization, International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources, Safety Series No.l15 (IAEA, Vienna, 1996).

[13]

International Commission on Radiological Protection, Cost Benefit Analysis in the Optimization of Radiation Protection, ICRP Publication 37, Annals of the ICRP 10(2/3) (Pergamon Press, Oxford, 1983).

[14]

International Commission on Radiological Protection, Optimization and Decision-Making in Radiological Protection, ICRP Publication 55, Annals of the ICRP 20(1) (Pergamon Press, Oxford, 1989).

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[15]

United Nations Scientific Committee on the Effects of Atomic Radiation, Sources and Effects of Ionising Radiation, 1977 Report (United Nations, New York, 1977).

[16]

Pierce, D. A., An Overview of the Cancer Mortality Data on the Atomic Bomb Survivors, RERF CR1-89 (Radiation Effects Research Foundation, Hiroshima, 1989).

[17]

Roesch, W. C. (ed.), Final Report on Reassessment of Atomic Bomb Radiation Dosimetry in Hiroshima and Nagasaki (Radiation Effects Research Foundation, Hiroshima, 1987).

[18]

Preston, D. L. and Pierce, D. A., The effects of changes in dosimetry on cancer mortality risk estimates in the atomic bomb survivors, Radiat. Res. 114, 437 - 466 (1988).

[19]

International Commission on Radiological Protection, 1990 Recommendations of the International Commission on Radiological Protection, ICRP Publication 60, Annals of the ICRP 21(1 — 3) (Pergamon Press, Oxford, 1990).

[20]

United Nations Scientific Committee on the Effects of Atomic Radiation, Sources, Affects and Risks of loni^ingRadiation, 1988 Report (United Nations, New York, 1988).

[21]

National Academy of Sciences, Health Effects of Exposure to Low Levels of Ionising Radiation, BEIR V Report (National Academy Press, Washington DC, 1990).

[22]

European Communities, Council Directive 96/ 29/Euratom of13 May 1996 laying down basic safety standards for the protection of the health of workers and the general public against the dangers arising from ionising radiation, Official Journal of the European Communities L159(39), 1 (1996).

[23]

Cetto, A. M., Strengthening control of radioactive sources: the IAEA Model Project as a Case Study, Proc. Int. Conf. on Security of Radioactive Sources, Vienna, 10-13 March 2003 (IAEA, Vienna, 2003), 219-244.

[24]

International Commission on Radiological Protection, Protection of the Public in Situations of Prolonged Radiation Exposure, ICRP Publication 82, Annals of the ICRP 29(1-2) (Pergamon Press, Oxford, 1999).

[25]

International Commission on Radiological Protection, Protection Against Radon-222 at Home and at Work, ICRP Publication 65, Annals of the ICRP 23(2) (Pergamon Press, Oxford, 1994).

[26]

International Commission on Radiological Protection, Radiological Protection Policyfor the Disposal of Eonglived Solid Radioactive Waste, ICRP Publication 77, Annals of the ICRP 27 suppl. (Pergamon Press, Oxford, 1998).

[27]

Nuclear Energy Agency, Policy Issues in Radiological Protection Decision Making— Summary of the 2 Workshop (OECD Publications, Paris, 2001), p. 8.

[28]

Lewins, J. D. (ed.), AEARA—As Eow As Reasonably Achievable Radiation Doses in Industry, Proc. of the ALARA-II Meeting, London, September 1990 (Research Studies Press, Taunton, 1991).

[29]

Croiiail, P., Lefaure, C., Croft, J., The European AEARA Network, in Proc. 10^.Int. Congress of the International Radiation Protection Association, Hiroshima, May 2000 (IRPA, Hiroshima, 2000), P6a-

Villigen

273. [30]

Shrader-Frechette, K., Persson, L., Ethical Problems in Radiation Protection, Swedish Radiation Protection Institute SSI Report 2001:11 (Statens stralskyddinstitut, Stockholm, 2001).

[31]

United Nations Scientific Committee on the Effects of Atomic Radiation, Sources and Effects of Ionising Radiation, 2000 Report, Vol I: Sources (United Nations, New York, 2000), p. 8.

[32]

Clarke, R. H., Control of low-level radiation exposure: time for a change?,]. Radiol. Prot. 19, 107 — 115 (1999).

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[33]

International Commission on Radiological Protection, A report on progress towards new recommendations: A Communication from the International Commission on Radiological Protection, J. Radiol. Prot. 21, 113 — 123 (2001).

[34]

International Commission on Radiological Protection, The evolution of the system of radiological protection: thejustification for new ICRP recommendations,J. Radiol. Prot. 23, 129-142 (2003).

[35]

Clarke, R. H., Progress Towards New Recommendations from the International Commission on Radiological Protection, in Proc. 10th. Int. Congress of the International Radiation Protection Association, Hiroshima, May 2000 (IRPA, Hiroshima, 2000), L-3-1.

[36]

Shrader-Frechette, K., Persson, L., Ethical, logical and scientific problems with the new ICRP proposals, J. Radiol. Prot. 22, 149-161 (2002).

[37]

International Commission on Radiological Protection, International Commission on Radiological Protection: History, policies and procedures (ICRP, Stockholm, 1999).

[38]

Mossman, K. L., de Planque, E. G., Goldman, M., Kase, K. R., Magnusson, S. M., Muntzing, L. M., Roessler, G. R., bridging Radiation Policy and Science, in Proc. 10 . Int. Congress of the International Radiation Protection Association, Hiroshima, May 2000 (IRPA, Hiroshima, 2000), S-4.

Current Trends in Radiation Protection H. Metivier, L. Arranz E. Gallego and A. Sugier (eds.)

Active Methods & Instruments for Personal Dosimetry of External Radiation: Present Situation in Europe and Future Needs Teresa Bolognese-Milsztajn*1, 1 Merce Ginjaume** , Filip Vanhavere*** *Institut de radioprotection et de surete nucleaire, F-92265 Fontenay-aux-Roses, France **Institut de Tecniques Energetiques. Universitat Politecnica de Catalunya, Barcelona, Spain *** S tudiecentrum voor Kernenergie- Centre d'etude nucleaire, B-2400 Mo/, Belgium

Abstract. Active personal dosemeters (APD) are progressively more and more used in radiation protection. Despite their success APDs are relatively new devices for individual monitoring of workers. Interesting characteristics of APDs compared to passive dosemeters are: instant or direct reading, data transfer to and from computer network, lower dose sensitivity, audible alarms and dose memory options for distant readout. A wide range of APDs for gamma and beta are commercially available, their performances are in general sufficient for radiation protection. Recently also commercial neutron devices appeared on the market. In modern radiation protection APDs are strictly necessary operational tool to satisfy the ALARA principle.

1. INTRODUCTION In this paper we will give an overview of the legal framework in Europe for the use of APDs. A description of different techniques used for APDs will show the state of the art of the devices. Calibration and testing of the APDs is important, and several national and international standards exist. An overview will be given, as well as an outline of the quantities to be used. Finally, some reflections are made concerning the use of APDs at the workplace by the end user.

1

E-mail: [email protected]

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Current Trends in Radiation Protection

1.1. Recommendations and Legal requirements Electronic and instant reading devices are extensively used in Europe for radiation protection of workers although the 96/29 European Union directive [1], based on the recommendations of ICRP 60 [2], does not specify the type of dosemeters to be used for individual monitoring. Substantial improvements on radiation protection programs and procedures, as required by European directives, were achieved using active devices APD. The 96/29 European Union directive reinforces basic recommendations previously established, namely: justification of exposure, optimisation of protection and dose limitation requiring the submission of certain practices involving ionising radiation to a system of reporting and prior authorisation. In the context of optimisation, all exposures shall be kept as low as reasonably achievable and dose constraints should be used for radiological protection purposes. This requires the implementation of control measures and monitoring relating to the different areas and working conditions including individual monitoring, which should be systematic for exposed category A workers. This monitoring shall be based on individual measurements that are established by an approved dosimetry service. A record containing the results of the individual monitoring shall be made for each exposed category A worker. In the case of an accidental or emergency exposure, the results of individual monitoring shall be submitted without delay. Legal dosimetry for dose record is mostly performed with passive dosemeters except for some pilot countries, such as the United Kingdom and Switzerland, where APDs are accepted if approved by accredited services. In other countries plans to accept some APD for legal dose record are being set up. APD systems present powerful capabilities for day-to-day and job-to-job processing of data, which will optimise the application of the ALARA principle. Several European countries considered that APDs are necessary for optimisation of radiation protection of special categories of workers (ex: A) or in special areas (ex controlled area). The recommendations of the European directive, in the field of operational external dosimetry, are widely spread in European countries even when a transcription to the national law is not yet realized. The concept of individual dosimetry for radiation protection of workers is applied wherever possible. In many sectors, though not in all, employers consider APDs as an efficient and reliable way to satisfy ALARA principle and management of doses for optimisation. In several European countries APD use is either considered as a license condition for some workplaces (nuclear power plants: NPP), fuel production and spent fuel reprocessing, some medical practices, industrial radiography .. .) or mandatory in special cases(in high dose level areas or for potential accidental situations, for itinerant workers) In many places they are used also on a voluntary base. Recommendations of the European directive are widely applied as regards individual dosimetry at work places. Nevertheless, progress must still be done in the industrial and medical sectors.

1.2. Calibrations and Standards According to the 96/29 European Union directive, the undertaking are responsible for assessing and implementing arrangements for the radiological protection of exposed workers. Member States shall require the undertaking to consult qualified experts or approved occupational health services on the examination and testing of protective devices and measuring instruments comprising in particular: • Regular checking of effectiveness of protective devices and techniques,

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• Regular calibration of measuring instruments and regular checking that they are serviceable and correctly used.

The directive does not specify requirements on calibration but these are established by member states. In most countries, APDs are calibrated and regularly tested following national directives. ISO Standard 17025 [3] for accredited services is progressively established in Europe. European or IEC standards for APD use are only applied in some countries: progress has still to be done to harmonize the use of international and European standards for calibration and testing procedures. In table 1 the relevant standards for APDs are summarized Table 1. Standards relevant for APDs IEC 61283 series.

IEC 1283: Radiation Protection Instrumentation - Direct readingpersonal 'dose equivalent (rate) monitors- X, gamma and high-energy beta radiation. IEC 61283 (1995) IEC 1525: Radiation protection instrumentation —X, gamma, high energy beta and neutron radiations -Direct reading personal dose equivalent and/ or dose equivalent rate monitors IEC 1525,1996

IEC 1323 IAEA

IEC: Radiation Protection Instrumentation. Measurement of Personal Dose Equivalent Hp (10) and Hp (0.07) for X, Gamma and Beta radiation: Direct Reading Personal Dose Equivalent and/ or Dose Equivalent Rate Dosemeters. IEC 61526 (1998) IEC 1323: Radiation Protection Instrumentation — Neutron radiation — Direct reading personal dose equivalent and/ or dose equivalent rate monitors IEC-1323 (1995) IAEA Safety Series: Safety Guide: Assessment of occupational exposures to external sources of radiation RS-G-1.3, 1999

2. INSTRUMENTS AND METHODS 2.1. Detectors Active personal dosemeters, commercially available, for gamma and beta are based mainly on Geiger-Miiller, silicon diodes and on direct ion storage (DIS) detectors. For neutrons personal dosimetry only silicon diodes and direct ion storage plus bubble devices [4] are used. Geiger-Miiller tube detectors are pulse type ion chambers operated in electron sensitive mode. Ion chambers have been used as reference devices for a long time and are described in many textbooks [5, 6]. The main difficulty to be overcome, in order to use them for personal dosimetry, is to maintain a high constant electric field to collect the ionisation charges before they recombine. Due to their higher mobility electrons have collection time shorter than ions. For that reason, commercially available personal dosemeters based on ion chambers are working on Geiger-Miiller electron sensitive mode. Silicon diodes have a much higher sensitivity to radiation than ionisation chambers. The mean energy spent by the charged particles to produce an electron-hole pair in silicon semiconductors is about ten times smaller than in gases. The ionisation process is than ten times more efficient in silicon diodes than in ionisation chambers [7].

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Figure 1. Photon sensitive ion chamber Wall Material: Graphite or Teflon

The DIS detector (Figure 1) is an hybrid between an ion chamber and a MOSFET data storage device [8]. It can be used simultaneously as a passive or an active dosemeter but it needs an initial reference voltage value. Integrated dose can be obtained by measuring the shift of the voltage from the initial value. Dose rates are obtained by measuring step by step the shift voltage. Silicon diodes and DIS are well-established detectors for gamma-beta dosimetry. Table 2 gives the main characteristics of 22 devices used in Europe [9]. Most devices are calibrated in units of personal dose equivalent, H p ( 1 0 ) or H p ( 1 0 ) and H p (0.07) when they are manufactured for the European market and fulfil some requirements stated in the IEC 61526 and IEC 61283 Standards. However, there still exist big differences between manufacturers as regards the standard and the type of testing procedure followed. This seems to be variable depending on the main users of the dosemeter and the country where it is used. Generally speaking, the overall radiological behaviour of active personal dosemeters compared to the behaviour of passive dosemeters is satisfactory in particularly as regards as accuracy for photon and beta radiation, measurement range and dose linearity. The poor performance at low photon energy described for earlier dosemeters is now overcome by a few APDs. Most APDs listed in table 2 have specific software for dose recording and can be connected to a centralised dosimetry system. Many new developments related to the transmission and handling of data are being implemented. Recent developments on dosemeters based on industrial diamond were reported in a review on solid state detectors [7]. The advantages of diamond are its equivalence to biological tissues and its resistance to high radiation doses; on the other hand its detection efficiency is low compared to that of silicon. This characteristic makes diamond more suitable for high doses measurements for radiotherapy. Some developments on CCD-based readout for silicon or caesium iodine detectors [10] and on metallicoxide-semiconductors (MOS) [11] are devoted to improving low doses measurements (down to the uSv region). Recently some electronic dosemeter for extremities have also been developed and commercialised. Several papers highlight the advantage of these devices compared to conventional skin and extremity TLDs [12],

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Table 2. Main Characteristics of a set of 22 photon APD (information provided by manufacturers) APD Reference AEATech. DoseGuard S10 Aloka PDM112 Automess ADOS Canberra Dosicard Comet APD (Panasonic Ind.Eur.) Dositec L36 Fuji Electroc NRY 20001 Graetz ED 150 MGP DMC 2000S MGP DMC 2000X MGP DMC 2000XB MGP SOR/R Mini instruments 6100 Polimaster PM1203 Rados DIS-1 Rados RAD-51/51T Rados RAD-60/62 Rados RDD-20/RDR-20 Saic PD-2i/PD-3i Saphydose Gamma Siemens EPD1, EPD2 (MK1) Siemens Mk2

Energy range (keV) Min Max % 137Cs 60 3000 40 1000 70 3000 15% 50 2000 20 1600 25% 60 6200 25% 50 6000 50 2000 50 20% 6000 30% 20 6000 30% 20 6000 50 6000 20% 30 1000 25% 60 1500 30% 15 9000 60 3000 25/35% 25% 60 3000 30% 50 1500 55 6000 25% 30% 50 1300 20% 20 10000 20% 15 7000

Angular response %137Cs

weight

0°-45°20% 0°-90°25%(Co-60) 0°-60°20%

190 65 109 77 100 160 70 70 70 55 125 90 20 90 80 24 90 165 170 95

0°-60°20% IEC 61283 IEC61526 IEC 61526 IEC 61283

0°-60°20% IEC 61283 IEC 61283 IEC 61283 IEC 61283 IEC 61526 IEC 61526

(g) 80 50

Volume (cm3) 115.0 52.2 133.9 83.3 93.5 57.1 85.0 92.5 70.6 70.6 70.6 37.0 118.8 126.0 16.2 115.0 115.0 14.0 58.8 167.3 162.3 101.7

mainly in the estimate of hand or finger doses during interventional radiology and radio pharmaceutical manipulation. At present these are still rarely used due to practical limitations. The latest developments consist of electronic dosemeters, which are made of a small sensor and a recording unit. The small sensor is positioned in the part of the body where the dose is to be measured, usually the fingertips. The recorder is bigger and it is usually kept in the wrist or in a pocket; unfortunately, at the moment, there does not exist a specific Standard for extremity electronic dosemeters, and there are not many published data related to the calibration and characterisation of such devices. For neutron a few silicon devices are commercially available since a few years and several prototypes are under development. State of the art of APDs for neutron are given in references [13]; the response functions presented in figure 2 show that only one of the devices, the SAPHYDOSE-n has an almost constant response from thermal to 14 MeV This device has also interesting spectrometric characteristics (Figure 3); it can roughly identify the energy range of the detected neutron [14] Its main drawback is its high cost due to the sophisticated detection technique based on an epitaxial silicon strip detector covered with several convertors. DIS detectors can also be used as neutron dosemeters [15]. The prototype detector, described in Figure 5, use a double chamber system to separate neutron from photons. The camber wall is a tissue equivalent material which convert neutrons into alpha particle and protons. The region between 1 eV to 100 keV is still under investigation for all devices since no mono-energetic reference data exist in this region but broad resonance; an extrapolation method to cover this region has been proposed in reference [16] Some APDs for neutrons are currently under test in the framework of the EC project EVIDOS [17].

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Figure 2. Response functions some commercial (a) and prototypes (b) APD for neutrons

Figure 3. Simulation of the energy deposits of the neutrons at 144 keV, 250 and 565 keV and of the photons of the Co in a depleted zone of 5/^m

60

Figure 4. Comparison of spectra in energy deposited, experimental and numerical

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Figure 5. Neutron/photon sensitive ion chamber Wall Material: A-150/PE containing 6Li

2.2. Measured quantities The ICRP60 publication (1991) [2] defines and recommends the use of the effective dose E for radiological protection purposes. However, this quantity cannot be directly measured; and in practice, the operational quantities, ambient dose equivalent (H*) and personal dose equivalent (Hp), as defined in the ICRU 51 report (1993) [18] are recommended to estimate the effective dose E. These operational quantities are related, through calculated conversion coefficients "h ", to the measurable function fluence by:

is the distribution of the fluence with respect to energy (energy E and direction ); h or hp , are the fluence to operational quantity conversion coefficients as defined by the ICRU 57 [19].The ambient dose equivalent H*(10) (defined in reference [19]) is an isotropic function independent of the angle which, if correctly measured, approximates with accepted accuracy the protection quantity E. Hp (10) (which is defined as the dose equivalent at 10 mm in the body at the location where the personal dosementer is worn) on the other hand, is a directional function, which depends not only on energy but also on the angle of the radiation field. The coefficients hp (E, ) are calculated [19] only for angles between 0° and 75°, for these reasons Hp (10) accurately approximates E only in certain field geometries and certain energies. In Figure 6 the ration of H p / E as function of photon energy for AP, ROT and PA field geometry fields present discrepancies at low energy [20]. This problem, as shown in Figure 7, is more important for neutron because in some energy range Hp underestimate E which should be avoided for radiation protection purposes. More calculations and developments have to be done in order to achieve a better approximation of the effective doses. Facilities simulating workplace conditions for calibration and studies are an important tool to improve

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Figure 6. Ratio personal dose equivalent Hp to effective dose equivalent as function of energy for photons at AP, ROT and PA field geometry

Figure 7. Ratio personal dose equivalent Hp to effective dose equivalent as function of energy for neutrons at AP, ROT and PA field geometry

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Figure 8. The IRSN CANEL Facility assembly(a), Neutron fluence energy distribution measured an MCNP calculated (b) and neutron fluence energy distribution in directional intervals from 0° to 50° in the calibration area (c)

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Current Trends in Radiation Protection

dosimetry instruments and methods. As an example, the CANEL facility of IRSN in Cadarache (Figure 8a shows the assembly), which produces neutron spectra encountered in the nuclear industry, has been fully characterised in fluence as function of energy (Figure 8b [21]), angular distribution have been calculated [22] and used to study the behaviour of APDs in the framework of EVIDOS [17]. Workplace studies using instrumented anthropomorphic [23] phantoms may also allow to foresee important information since introducing dosemeters at well-defined places, representing human organs, in the phantom will give directly the measurement of the effective dose. The comparison of these effective dose measurements to measurements of operational quantities using conventional instruments will evaluate the deviation of operational quantities from radiation protection quantities in several real workplace situations. APD can be useful in studying geometry considerations in workplaces because of their direct reading and resetting capabilities.

2.3. Calibration and testing As already mentioned compliance to standards is not always required for APDs but in several European countries APD approval is delivered by authorized services that apply international standards.

For instance in France a legal decree requires for APD:

• To be adapted to the type of radiation and follow the European or, failing this, French standards; • To be individual and personal, worn on the body trunk; • To present an instantaneous reading of personal dose equivalent and personal dose equivalent rate over one period of wearing; • To offer the possibility of adjusting the alarm levels.

European standards are often a transcription of international standards. For photon radiation the standard ISO 4037 [24] and specifications given in paragraph 8 of the IEC-61526 [25] standard apply for calibration. The reference photon radiation qualities are: filtered X-radiation in the energy range 12 keV-300 keV and radioactive gamma sources 137Cs (662 keV) and 60Co (1.25 MeV) defined in the ISO [24] standard from the International Organization for Standardization. For the purpose of personal dosemeter calibration and testing, the operational quantity Hp(d), is defined as the dose equivalent at a depth d in a phantom made of ICRU tissue [26]. For strongly penetrating radiation the depth d of 10 mm is used to approximate the effective dose; for weakly penetrating 0.07 mm is used for skin doses and 3 mm for the length of the eye. Three phantom types defined by ISO 4037-3 are used for calibration purposes: a slab water phantom, 300 mm X 300 mm X 150 mm in dimension to approximate the human torso, a pillar water phantom: 73 mm diameter X 300 mm length cylinder for calibration of wrist dosemeters; and a PMMA rod phantom: 19 mm diameter X 300 mm length cylinder for calibration of finger dosemeters. Table 3 lists the main radiological tests to be performed on the APDs according to ISO and IEC standards. Together with the listed requirements, IEC 61526 also includes several environmental tests (such as electromagnetic compatibility, temperature, humidity, etc.). These tests are expensive and constructors do not always perform all of them. Although manufacturers are required to comply with standards, sometimes they don't specify which tests have been performed with their instruments. For this reason, in several

Table 3. Tests performed and limits given by standards. Hp(10) has been determined using an ISO water slab phantom. Calibration Quantity Hp (10)

Name

Standard

Method

Reproducibility of the reading

ISO 4037

Repeatability of the reading Dose equivalent rate dependence

ISO 4037

Relative intrinsic error

8.1*

3 measurements done periodically, on each EPD, during all the study (1 year) 10 successive measurements on each EPD Irradiation of each EPD at different dose equivalent rate for different dose equivalents between 0,8 and 800 mSv. Test of EPD effective range (20, 40 and 80% of each decade) for dose equivalents and dose equivalent rates

Response as function of radiation energy

8.4*

5 measurements on each EPD with different filtered Xradiations and gamma sources

Hp (10)

Response as function of radiation angle of incidence

8.5*

Hp(10)

Retention of reading

8.6*

Accuracy of alarm levels

8.3*

Response time

8.2*

Neutron sensitivity Indication in overload

8.9*

3 measurements for each angle (0° to ± 75°, every 15°) in one horizontal and vertical plane with respect to the front face of the dosemeter Verification of the EPD reading each hour during 8 hours after irradiation Dose equivalent: Irradiation at the alarm level ±20 % Dose equivalent rate: Irradiation at the alarm level ±15% Time of stabilization of the reading after a factor 1 0 increase of the dose equivalent Irradiation with neutrons

8.7*

8.8*

Irradiation with dose equivalents and dose equivalent rates 10 times higher than the upper limit of the EPD * Paragraph in stasndard IEC 61526

Radiation

Dose equivalent rate 7mSv.h-1

Limits given bv standards ±2%

137

Cs 7mSv.h-1

Hp (10) 137

Cs

H* (10) 60

Co

H*(10) 137

1,10, 100 and 1000 mSv.h

< ±20%

< ImSv.h-1

Dose equivalent < ±20 + x% Dose equivalent rate < ±15 + x % X: uncertainty on H* (10)

~ l0mSv.h-1

< ±30 %

Cs

X- radiations (12 to 250 keV), 137 Cs (taken as reference), 60 Co

~

10mSv.h - 1

137

Cs and filtered X-radiations of 65 keV

Hp (10) 137

Cs

137

Cs

H* (10)

Hp(10)

Filtered Xradiations at 118 keV

Hp(10)

Am-Be with cadmium shield

H*(10) 60

Co

< ±20%(137Cs) < ±50% (65 keV)

(For angles at ±60°) 5 SmSv.h - 1

< ±2 %

Depends on the alarm levels

Lower levels: 10 min irradiation without alarm Upper Levels: Start of the alarm in less than 5 s Stabilization time lower than 5 s

> 10uSv.h -1

Reading due to neutrons < 5% Hp (10) of neutrons 10 times the upper limit of the EPD

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countries, comparisons of APDs have been performed to verify their compliance to standards, to offer constructors suggestions to improve their instruments, and to help users in choosing the APD best adapted to their own application. Dosemeters should be calibrated and tested on a phantom not only in laboratory conditions but also when their performances are investigated in workplaces. Nevertheless the reading of personal dosemeters on phantoms represent only on average the reading on a human body, which means that two personal dosemeters giving the same response in laboratory conditions may give different responses, in the same workplace, when worn by two workers which have different morphologies. To calibrate and test personal dosemeters, their reading has to be compared to reference values. In laboratory, reference values are well known while in work places they are not always easy to determine since they may vary in space and time. In some workplaces, measurements cannot be reproduced in exactly the same conditions. For all these reasons, if the accuracy of personal dosemeters can be of the order of 10 to 20% (at 95% confidence level) in laboratory conditions, it can be much larger in workplace conditions (a factor 1.5 or more for neutron or for low dose measurements). In order to improve the accuracies of personal dosemeters, studies can be performed using laboratory simulated workplaces facilities.

Intel-comparisons In the past 5 years, several comparisons of APDs have been performed based on IEC standard requirements [27-29]. As an example, Figure 9 shows the energy response of some APDs. It can be noticed that the energy response varies very much in the energy range indicated by the constructor and that there might be up to a factor of two between the response of two devices. Measurements showed a large variation of performance among the different tested electronic dosemeters. A few devices satisfied most of the IEC 61526 technical requirements and had only little minor noncompliance, whereas some other dosemeters presented important limitations that could imply the loss of dosimetry information or a misreading of the registered dose. The different studies agreed to outline as most critical parameters, the response at low energy photon and beta radiation and the mechanical resistance. Other limitations such as differences in background estimate, dead time corrections at high dose rates or spurious alarm signals were also reported. On the other hand, the behaviour of the tested dosemeters at temperatures from — 20° C to 40° C, as well as in the presence of external electromagnetic fields, was in general satisfactory. All referred papers pointed out the need to have a well-defined international standard, such as IEC 61526, and recommended to manufacturers to give technical specifications in accordance to such a standard, in order to allow users to make a proper selection, depending on their needs. An International APD comparison will be organized by AIEA starting in 2004. 2.4. APD use in workplaces Since several years, the use of active personal dosemeters became common practice in most nuclear installations. Also in smaller companies and hospitals, APDs are starting to find their way. So among the users, there is already a lot of experience on practical aspects of APDs. The use of an APD is likely to be different in a hospital than in a nuclear power plant. Because the radiation environment can be completely different, dosemeters adjusted for these specific fields might have to be used. The knowledge of on the one hand the real characteristics of the dosemeter, and on the other hand the radiological situation in the workplace, is not sufficient to ensure the correct use of the APDs. While passive dosemeters are often supplied by an external service, the APDs are used mostly completely in-house. This enhances the risk of wrong use and

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Figure 9- Response as function of radiation energy of the studied EPDs

misinterpretation of the easily retrievable results from an APD. It is very easy to get a result with electronic dosemeters, but the correct interpretation of the result is more difficult. Some users devote a lot of attention to the APD results, while for others it is just a tool for ALARA that is used occasionally. In most power plants with a strongly evolved radiation protection awareness and over a thousand APDs in use, much more attention is given to the correct use of the APDs, than in a small hospital with only a few occasionally used APDs. The situation will of course also change from country to country, reflecting the different legislations. It might be allowed to use the APD for dose record, there might be the obligation to use it as an alarm dosemeter, or there might be no requirement for APDs at all. Not in all countries the use of APDs is under regulator control. Most users still use both passive and electronic dosemeters in parallel. With a general tendency to reduce the costs, some users want to use only APDs as dosemeter instead of a double dosimetry system. Still, there is hardly any record on how many failures occur with the APDs, and what other practical difficulties are encountered with the use of APDs. In the framework of the European project EURADOS, a working group on Harmonization of individual dosimetry will publish by the end of 2004 a report on the status of APDs, which will contain among other information a catalogue of the APDs most frequently used in Europe and an image of the present usage of the APDs.

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Figure 10. X ray field measurements in workplaces

As an example the adequacy of APDs to the range of energy in several practical applications is reported. Photon energy spectra in some activities have already been reported in references : [30-32], and are shown in Figure 10. If one looks at the energy response of the most common APDs, there is usually no problem for photons in the range from 50 keV to a few MeV. This is the range encountered in most end-users from the fuel cycle NPPs, industrial companies and research institutes. Only some problems might arise for the 6 MeV photons in NPPs, or for some specific fields in research institutes (around high-energy accelerators). Some difficulties might also arise with the low and very high-energy photons and betas in hospitals, Figure 11, as well as with the measurement of pulsed radiation in medical linear accelerators. The number of APDs used in hospitals is of course still very low. In activities where both passive and active dosemeters are used, some comparisons of results are performed. In some nuclear power plants this is done in a systematic way, on a monthly base. The differences between both sets of data are generally reported to be between 3 and 8%, but some users report differences up to 20%. As soon as the differences are beyond a certain value (sometimes 10%, sometimes dependent on the dose value), the reason for the differences is investigated.

2.5. Users requirements In the framework of the program EURADOS, supported by the European commission, the working group "harmonisation of individual monitors" sent a questionnaire [9] to APD end users in order to identify what characteristics would be considered ideal for an electronic dosemeter. The best characteristic was considered to be a low price. Next, technical parameters such as energy response, together with mechanical characteristics (robustness, shock resistance...) were selected as second important, closely followed by the environmental characteristics (temperature, humidity resistance.. .). Much less attention was given to the

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Figure 11. Comparison of X-ray spectral distribution in medical sector with some APD response as function of energy

response to other radiation types like neutrons and betas. Clearly, gammas and X-rays are considered, by all types of users, to be the most important radiation. Many users find it important that a longer battery life could be attained. To the question what the major problems were, mechanical problems were reported to be the most important. However, better mechanical characteristics were not considered of high priority. This might mean that encountered mechanical problems are not solely attributed to the dosemeters, but partly to wrong and inattentive use. Improvements to the software were considered least important. Spurious alarms were also considered less important. Most end-users assume that the present dosemeters measure the radiation adequately. The wish for an electronic neutron dosemeter is not often expressed. In most workplaces in nuclear industry, neutron doses contribute only a small percentage of the total dose. But in some workplaces, like fuel production, spent fuel manipulation and transport action , neutrons are a very important contribution to the total dose. The project EVIDOS, supported by the European Commission, aims to evaluate the individual neutron dosimetry method in the European nuclear industry, including commercial and prototype APDs for neutrons. Some preliminary results are reported in ref [17].

3. CONCLUSIONS AND FUTURE NEEDS The analysis of the state of the art in APDs highlights the fact that present technology for photon APDs has reached a level of reliability comparable or even better then passive techniques for most radiological applications. In the case of nuclear power plants, there is now especially great experience in APD use and there are records of APD readings compared with conventional TLD measurements. These data confirm the advantages of APDs over conventional dosimetry, mainly related to alarm features, direct reading and optimisation of practices. Improvements related to low-energy photon response as well as immunity to a wide range of environmental conditions have been reported for the latest developments.

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Furthermore, within the framework of the EU 96/29 Directive in Europe, a wide consensus has now been reached regarding the operational quantity of external radiation for individual monitoring dosimetry for radiation protection purposes, which is the personal dose equivalent Hp(d) at depths of 0.07, 3 and 10 mm defined by ICRU. There is also a good agreement on calibration procedures and calibration standards. Nevertheless improvements on effective dose assessment will need developments and studies on angular response function of personal dosemeters. This is of primarily importance for neutrons but not negligible for photons [handbook spectro] Knowledge of the energy and of the geometry of neutron, and photon fields have to be taken into account to correctly measure fluence and dose equivalent energy distributions. Spectrometry results at workplaces may help users to adapt radiation protection instruments to their working conditions and to choose calibration sources and procedure [Thomas] Spectrometric method currently applied for nuclear industry measurements may be used also in other domains such as medical application for better patient treatment planning. Unfortunately, agreement is not as widespread with respect to APD performance requirements and the type testing standards. In this field, significant differences are observed among countries and manufacturers, as has been shown through independent intercomparisons. Standards for active extremity dosemeters and for photon pulsed radiation fields are not yet available. In the last decade great efforts have been devoted to the development of APDs for neutron dosimetry. At present there are several prototypes and some commercial APDs, which clearly improve passive dosimetry results. However, further work is still needed in this field to improve energy response of neutron dosemeters and to lower the price of available devices. Greater efforts are also needed to gather and analyse the experience of different types of APD users. There is very little knowledge about failures and workplace performance of APDs. Moreover, preliminary data show large differences among users. This information can be of great importance for improvements in APD design and use and for the development of new standards, in particular as regards the legal use of APDs for dose records.

REFERENCES [1]

EU. Council Directive 96/29/EURATOM of 13 may 1996.

[2]

ICRP (1991). International Commission on Radiological Protection, 1990 Recommendations of the International Commission on Radiological Protection, ICRP Publication 60, Annals of the ICRP 21, No. 1/3 (Pergamon Press, Oxford).

[3]

ISO (1999). General requirementsfor the competence of testing and calibration laboratories. International Standard ISO/IEC 17025, (ISO, Geneva) (1999).

[4]

Vanhavere F. and d'Errico F. Standardisation of superheated drop and bubble detectors, Radiat. Prot. Dosim. 101 (2002) 283 - 287.

[5]

Blanc D, The Ionising Radiation: Detection, Spectrometry and Dosimetry, Messon, Paris 1990.

[6]

Turner J.E, Atoms, Radiation, And Radiation Protection, Wiley, New York 1995.

[7]

Barthe J., Electronic dosimeters based on solid state detectors, NIM B 184 (2001) 158 -189.

[8]

Mathur V.K., Ion store dosimetry, NIM B 184 (2001) 190-206.

[9]

Bolognese-Milsztajn T, Ginjaume M., Luszik-Bhadra M, Vanhavere F., Weeks A.R. Reports by the EURADOS working group "Harmonisation in Individual Monitoring" 2001 -2004. To be published in Radiat. Prot. Dosim.

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[10]

Harris E.J. et al. ACCD-based y-ray dosimeter, NIM A 458 (2001) 227 - 232.

[11]

Sarrabayrouse G., Polischuk V., MOS ionizing radiation dosimeters from low to high dose measurement, Radiat. Phys. Chem. 61 (2001) 511-513.

[12]

Martin C.J., Whitby M., Hilditch T. and Anstee D. Use of an electronic finger dosimeter in optimisation of finger doses. Proceedings of 6th European ALARA Network Workshop on "Occupational Exposure Optimisation in the Medical Field and Radiopharmaceutical Industry", Madrid, October 2002.

[13]

d'Errico E, Luszik-Bhadra M., Lahaye T., State of the Art of Electronic Personal Dosemeters for Neutrons, Nuclear Instr. Meth. in Phys. Research A 505 (2003) 411 -414.

[14]

Lahaye T. et al., Numerical and Experimental results of the operational neutron dosemeter "Saphydose-n" NUDOS 9; Delft 2003: procedeeng to be published in Radiat. Prot. Dos.

[15]

Fiechtner A., Wernli C. and Kahlainen. A Prototype personal neutron dosemeter based on ion chamber, Radiat. Prot. Dosim. 96, (2001) 269-272.

[16]

Luszik-Bhadra M., Wendt,W. and Weierganz M., The electronic neutron I photon dosemeters PTB DOS-2002 NUDOS 9; Delft 2003 : proceeding to be published in Radiat. Prot. Dosim.

[17]

Bolognese-Milsztajn T. et al., Individual Monitoring in workplaces with Mixed Neutron I Photon Radiation NUDOS 9; Delft 2003 : proceeding to be published in Radiat. Prot. Dosim. (International Commission on Radiation Units and Measuerements, Bethesda, Maryland).Bolognese-

[18]

ICRU. Quantities and Units in Radiation Protection, ICRU Report 51 (International Commission on Radiation Units and Measurements, Bethesda, Maryland).Bolognese-

[19]

ICRU, Conversion Coefficients for use in Radiological Protection Against External Radiation, ICRU Report 57 (ICRU, Bethesda, Maryland).

[20]

Bartlett D.T., Chartier J-L., Matzke M., Rimpler A. and Thomas D.J., "A Handbook on: Neutron and Photon Spectrometry Techniques For Radiation Protection" Edited by DJ. Thomas and H. Klein , Chapter 2: Concepts and Quantities in Spectrometry and Radiation Protection. Radiat. Prot. Dosim. 107 (1-3) (2003).

[21]

Gressier V. et al., Characterisation of the IRSN Canel/T400 Facility Producing Realistic Neutron Fields for Calibration and Test Purposes, Nudos 9; Delft 2003: proceeding to be published in Radiat. Prot. Dosim.

[22]

Lacoste V., Gressier V., Monte-Carlo Simulation of the Irsn Canel/T400 Realistic Mixed Neutron-Photon Radiation Field, Nudos 9; Delft 2003: proceeding to be published in Radiat. Prot. Dosim.

[23]

Menard S. (scientific in charge) Design and development of an instrumented anthropomorphic phantom with the objective to evaluate the effective dose E at work places and give reference values for the individual operational quantity: feasibility study. IRSN Thesis in progress.

[24]

International Organization for Standardization. X and gamma reference radiations for calibrating dosimeters and dose rate meters and for determining their response as a function of photon energy -Part 3: Calibration of area and personal dosimeters and the determination of their response as a function and angle of incidence. International Standard ISO 4037-3 (ISO, Geneva) (1999).

[25]

IEC, Radiation protection instrumentation - Measurement of personal dose equivalents Hp(10) and Hp(0,07)forX, gamma and beta radiations - Direct reading personal dose equivalent and/'or dose equivalent rate dosemeters, IEC 61526(1998).

[26]

ICRU, Measurement of Dose Equivalents from external photon and electron Radiations. ICRU Report 47. (Bethesda, MD 20814-3095: ICRU Publication) (1992).

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[27]

Texier C, Itie C, Serviere H., Gressier V, Bolognese-Milsztajn T., Study of the photon radiation performances of electronic personal dosemeters. Radiat. Prot. Dosirn. 96 (2001) 245-249.

[28]

Ortega X., Ginjaume M., Hernandez A., Villanueva I. and Amor I., The outlook for application of electronic dosemeters as legal dosimetry. Radiat. Prot. Dosim. 96 (2001) 87-90.

[29]

Butterweck G, Zimmerly H.P. and Wenli c., Comparison test of Electronic Personal Dosemeters. Radiat. Prot. Dosim. 96(1-3) 109-112.

[30]

Burgess P.H., Bartlett D.T. and Ambrosi P., Workplace Photon Radiation Fields IAEA TECDOC in progress.

[31]

d'Errico, E, Bartlett, D.T, Ambrosi, P. and Burgess, P.H. "A Handbook on:Neutron And Photon Spectrometry Techniques For Radiation Protection" Edited by DJ. Thomas and H. Klein, Chapter 8, Determination of Direction and Energy Distributions. Radiat. Prot. Dosim. 107 (2003) 133 —154.

[32]

Ambrosi P., Hilgers G., Photonenstrahlung - Strahlungsfelder und Expositionsbedingungen an Arbeitsplatzen. Strahlenschutz PRAXIS, Organ des Fachverbandes fur Strahlenschutz e. V., 5, 4/99, 1999, Seite53-57.

[33]

Thomas D, "A Handbook on: Neutron And Photon Spectrometry Techniques For Radiation Protection" Edited by DJ. Thomas and H. Klein, Radiat. Prot. Dosim. 107 (2003) 13-21.

Current Trends in Radiation Protection H. Metivier, L. Arranz, E. Gallego and A. Sugier (eds.)

Training Users of Medical Radiation Fred A. Mettler Jr. M.D,1 M.P.H. Professor Emeritus, University of New Mexico, Department of Radiology, New Mexico Federal Regional Medical Center, 1501 San Pedro Blvd.. SE, Albuquerque, New Mexico 87108, USA

Abstract. Radiation has been used in medical practice for over a century. While hazards were recognized very early, radiation protection in medicine evolved over many subsequent decades. Current issues and problems of radiation protection in medicine are mainly the result of rapidly changing technology and lack of education. With the widespread application of computed tomography and digital radiography, use of high dose radiological equipment by non-radiologists and computerized high dose rate brachytherapy in radiation therapy there are new problems not envisioned before. Radiation protection in medicine is not likely to be significantly simply with the addition of more standards but it will require a different approach with the medical communities than has been used in the past.

1. INTRODUCTION Training in radiation protection receives little attention in most medical schools. It generally is included in medical specialty7 training. Even so, most radiologists and other physicians who use radiation in medicine do not have adequate training to appropriately protect patients. The speed of technological advances has been an additional problem. For example, currently many interventional cardiologists are performing long fluoroscopic interventional procedures due to very recent advances in coronary angioplasty, percutaneous stent placement and intravascular brachytherapy. These devices and techniques were developed long after many of these physicians had completed their formal medical specialty training. This clearly points to the need for continuing education throughout the professional career. In many countries, the main source of post-graduate training is the professional societies through their meeting and journals. Currently there are a number of efforts by international groups including but not Limited to the International Atomic Energy Agency (IAEA), International Commission on Radiological Protection (ICRP), and the World Health Organization (WHO) that provide the some materials and training in radiation protection.

1

E-mail: [email protected]

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Current Trends in Radiation Protection

One major hurdle in application of radiation protection and standards to the medical field is the sheer volume of procedures carried out annually. Worldwide, it is estimated that in the year 2000 there were about 2 billion diagnostic x-ray examinations, 32 million nuclear medicine examinations and 5.5 million patients treated with radiation therapy. While the exact number is not known, there are certainly in excess of several million persons who are administering radiation in one form or another. Reaching and educating these persons is essential. Accurate translation of the materials also has been a major problem. Probably, the most effective and cost efficient way to educate the medical community in radiation protection is through their professional organizations and journals.

2. BASIC ASPECTS OF RADIATION PROTECTON TRAINING IN MEDICINE Radiation protection of workers and the public seeks to minimize dose by a number of methodologies such as ALARA (as low as reasonable achievable allowing for social and economic considerations). Protection of patients in during medical exposures has been recognized as requiring a different operational philosophy [1]. The most obvious difference is that the patient (who receives the absorbed dose) receives a direct personal benefit and that the patient, in most circumstances, gives consent to have the exposure. One can question the degree of informed consent but generally with high doses in radiation therapy there is explicit written consent while with lower doses and lower risks the consent may be verbal and less explicit. Minimal patient dose is not necessarily good and may even be harmful. In medical diagnosis too small a dose will not provide adequate information for diagnosis and overexposure of a film can result in an uninterpretable image. In radiation therapy, too low a dose will result in lack of cure of a tumor while too high a dose may result in serious complications including death. Thus the "correct" (not the minimal) dose should be the goal. Radiation dose limits are not applicable to patients. Clearly, if a chest x-ray is indicated in a lifethreatening situation, it should not be denied, even if the equipment is older and provides a higher than average dose. The use of reference values in medicine allows abnormally high doses to be identified and corrected or justified. Radiation risks in medical exposure range from minimal to fatal depending upon the specific setting. As a result, standards and educational programs need to range from minimal to very specific depending upon the potential consequences. Any radiation protection system in medicine must be integrated with the practice of medicine if it is to be effective. The current philosophy of radiation protection in medicine includes the concepts of justification and optimization although they are applied somewhat differently than may occur in the case of occupational or public exposure. The initial idea is to justify a particular practice in medicine. Mammography may be though of as a practice and can be justified by the fact that has more benefit than risk with regard to detection versus induction of breast cancer. Although the practice of mammography is justified in general, that does not imply that it is justified for all women. Justification also needs to be performed on an individual basis. For example, mammography is justified in a 50-year old female with a family history of breast cancer but it is not appropriate as a screening tool in a 30-year old asymptomatic female. After general and individual justification, optimization needs to take place. An example of this in medicine this would mean doing only the essential number of images to obtain the desired information.

3. CURRENT STATUS OF INTERNATONAL RECOMMENDATIONS AND REQUIREMENTS FOR TRAINING Before embarking on an analysis of the educational issues associated with radiation protection in medicine, it is instructive to review current international guidance on the topic. It will become apparent that most recommendations or regulations are very general. This lack of specificity means that most users and organizations

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are free to provide whatever education they set fit. As we shall see in later sections, this has not always been done and the enthusiasm for using new technology has often eclipsed radiation protection concerns. The ICRP has discussed training as a theme in a number of documents. ICRP Publication 60 [2] only has one general statement in section 7.3 on regulatory requirements in paragraph 237 as follows: "One important national and international need is to provide adequate resources for the education and training of future professional and technical staff in radiological protection. These resources cannot be provided by the regulatory agencies alone". There is a similar paragraph related to medicine in ICRP Publication 73 [1] paragraph 128 which states: "One important need is to provide adequate resources for the education and training in radiological protection for future professional and technical staff in medical practice. The training program should include initial training for all incoming staff and regular updating and retraining." There are additional comments related to specific user oriented ICRP documents on computed tomography, fluoroscopically guided interventional procedures and radiation therapy. The IAEA has also long recognized training as a particular need in the medical field. In Safety Reports Series No. 20 [3] under section 2.5 related to health professionals it states; "The appropriate level of formal training for health professionals could, for example, be that corresponding to the practice and type of job, emphasizing the biological effects of ionizing radiation, together with specialized training in their field of work. Health professionals need to be acquainted with up to date information on the diagnosis and treatment of radiation injuries and have well developed communication, leadership, analytical and human-machine interface skills as part of their professional training. Further training in radiation protection and safety would enhance these skills. The duration and depth of the specialized training depends on the level of responsibility and the complexity of the job of the health professional." The IAEA also has addressed education issues of health professionals in the Basic Safety Standards (BSS) [4] in section 2.14 on authorization, registration or licensing where it states that :"The legal person responsible for a source to be used for medical exposure shall include in the application for authorization: (a) the qualifications in radiation protection of the medical practitioners who are to be so designated by name in the registration or license; or (b) a statement that only medical practitioners with the qualifications in radiation protection specified in the relevant regulations or to be specified in the registration or license will be permitted to prescribe medical exposure by means of the authorized source. Also in appendix II on medical exposure of the BSS it states that;"Registrants and licensees shall ensure that: - Medical practitioners be assigned the primary task and obligation of ensuring overall patient protection and safety in the prescription of, and during the delivery of, medical exposure; - Medical and paramedical personnel be available as needed, and either be health professionals or have appropriate training adequately to discharge assigned tasks in the conduct of the diagnostic or therapeutic procedure that the medical practitioner prescribes; — Training criteria be specified or be subject to approval as appropriate by the Regulatory Authority in consultation with relevant professional bodies. And registrants and licensees shall; (c) take all reasonable measures to prevent failures and errors, including the selection of suitable qualified personnel, the establishment of adequate procedures for the calibration, quality assurance and operation of diagnostic and therapeutic equipment, and the provision to personnel of appropriate training and periodic retraining in the procedures, including protection and safety aspects;

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2.64 Depending on the facility's complexity, the following staff should be trained in radiation protection and safety: radiation protection officers, appropriate senior administrators, embers of the radiation safety committee, radiographers, radiologists, radiation oncologists, nuclear medicine physicians, technologists, medical physicists, maintenance personnel and ancillary personnel, as appropriate. Nursing staff attending to patients undergoing medical exposures should be given appropriate training. The level of this training will depend on the specialization of the individuals, their academic background and previous experience. Examples of training recommendations in radiation protection and safety are given. Requirements for training criteria are given in the BSS. 2.65 Registrants and licensees should be able to demonstrate proof of such training to the regulatory authority, particularly when applying for an authorization for a facility. Some regulatory authorities may choose to issue personal authorizations to individual medical practitioners or other health professionals as a way of formally acknowledging adequate training in radiation protection and safety. 2.66. If registrants and licensees cannot demonstrate that their staff are adequately trained, the regulatory authority may consider requesting applicants to take an examination or attend a supplementary training course provided by an appropriate educational institution or professional body. However, the implications of time off work and financial costs should be taken into consideration especially when several persons at one facility are involved in administering medical exposures. Further guidance on training in diagnostic radiology as follows: 3.31. Training is required for all persons involved in the use of X-rays on humans for diagnostic purposes. The degree of training depends on the type of work and degree of responsibility, and should be provided to the following persons: — The physicians who are responsible for individual justification and conducting the exposures - Physicians in training who perform procedures under the supervision and responsibility of such physicians; — Radiation technologists or equivalent staff. The regulatory authority should encourage health authorities, universities and professional associations to design and implement education and training programmes in radiation protection and safety for professional staff involved in diagnostic and interventional radiology. 3.32. The extent of medical knowledge required of persons involved in X-ray procedures varies and may include the whole field of X-ray diagnosis (e.g. radiologists) or a subspecialization (e.g. orthopedic surgeons, traumatologists and cardiologists). The training of health professionals in relation to diagnostic radiology should include specific medical and radiation protection topics. 3.33. Specific training in radiation protection should be planned for specialists performing special procedures such as fluoroscopy, pediatric radiology or interventional radiology. Guidance on training in nuclear medicine appears as follows: 4.24. The regulatory authority should encourage health authorities, universities and professional organizations to design, implement continuing education and training programs in radiation protection and safety

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for nuclear medicine specialists, physicists, technologists and other professional staff involved in the practice of nuclear medicine. Such programs for nuclear medicine should include radiopharmaceutical biokinetics and dosimetry, elution of generators, contamination control, waste management, waste prevention and the management of incidents and accidents. Guidance on training in radiation therapy is given in 3 paragraphs as follows: 5.23 The regulatory authority should encourage health authorities, universities and professional organizations to design, implement training programs on radiation safety aspects for radiation oncologists, qualified experts in radiotherapy physics, radiotherapy technologists, dosimetrists and maintenance personnel. Training curricula can be found in several references [6,7] Hospital administrators who allocate resources should be trained on the implications of their decisions on protection and safety in medical exposure. 5.24. To meet provisions of the BSS, training criteria should be specified or approved by the regulatory authority in consultation with professional bodies, for example the professional bodies for radiation oncology and medical physics. Radiation safety aspects should cover radiation modalities, facility design, the characteristics of the safety features of sources and source related equipment, dosimetry, instrument calibration, treatment planning, radioactive waste disposal, accident prevention and emergency (including medical) procedures to deal with general and medical emergencies. The training should include lessons learned from past accidental exposures. 5.25. Basic education should be followed by continuing education, particularly when a new treatment modality or a different type of equipment is considered.

The European community has addressed the issue of training and education in EURATOM Council Directive 97/43 [8] on health protection of individuals against the dangers of ionizing radiation in relation to medical exposures has requirements for training in Article 7 that states: 1. Member states shall ensure that practitioners and those individuals mentioned in Articles 5 (3) and 6(3) have adequate theoretical and practical training for the purpose of radiological practices, as well as relevant competence in radiation protection. For this purpose Member States shall ensure that appropriate curricula are established and shall recognize the corresponding diplomas, certificates or formal qualifications. 2. Individuals undergoing relevant training programmes may participate in practical aspects of the procedures mentioned in Article 5 (3) 3. Member States shall ensure that continuing education and training after qualification is provided and, in the special case of the clinical use of new techniques, the organization and training related to these techniques and the relevant radiation protection requirements 4. Member States shall encourage the introduction of a course on radiation protection in the basic curriculum of medical and dental schools. Also in article 9 of the same directive it states that:' Member States shall ensure that appropriate radiological equipment, practical techniques and ancillary equipment are used for the medical exposure — of children — as part of health screening program — involving high doses to the patient, such as interventional radiology, computed tomography or radiotherapy.

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4. ANALYSIS OF ROOT CAUSES OF SOME CURRENT ISSUES The real question is "What is wrong with the current educational process and what are the problems that need to be fixed?" If there truly are problems, it is important to answer the question whether the educational materials were not required, not available or inadequately distributed or even whether something else was responsible. A useful exercise is to examine radiation protection problems that have arisen in medicine over the last several years to see the root causes. A major issue has been rapid development of new technologies, lack of integration of radiation protection issues with training in the use of new technologies and the lack of regulations and standards to keep up. During the last decade there has been rapid expansion of complex interventional procedures using fluoroscopy. A classic example of such a procedure is percutaneous transluminal coronary angioplasty (PTCA) with dilatation of a narrowed coronary artery using a balloon catheter and then placement of a wire stent to keep the artery open. Almost a decade ago, the U.S. Food and Drug administration issued a warning that due to the high dose rates and long procedure times there was a very real possibility of injuries to the patient in the form of skin burns [9]. In spite of this, there have been continued injuries with large areas of ulceration and necrosis requiring surgical grafting (figure 1). The cause of these

Figure 1. Areas of ulceration and necrosis requiring surgical grafting

injuries is not a lack of standards but rather a lack of education and understanding of radiation effects and radiation protection by physicians who are performing these procedures [10-13]. Computed tomography (CT) has been recognized as a relatively high dose procedure for over a decade. The doses to tissues from computed tomography (10 — 100 mSv) can often approach or exceed the levels known to increase the probability of cancer. This was not regarded as a major problem because the high cost, slow scan times and other factors limited the CT use to patients who were quite ill and exposure to limited parts of the body. In the last decade, however, there have been major advances in equipment design that has reduced scan times from 30 minutes to seconds. As a result, more patients can be scanned and physicians faced with a patient who has major trauma will often order a CT scan of the head, neck, chest, abdomen and pelvis. The patient is rapidly and effectively treated but there has been little regard on the part of the manufacturers and physicians to dose reduction. Currently, in some radiology departments, CT scans

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have grown to 11% of the total procedures but contribute over 70% of the dose [14]. Newer CT techniques have often increased doses when compared to standard CT. Many practical possibilities currently exist to manage dose the most important of which is reduction in mA. Automatic exposure control would be the most helpful improvement in CT equipment for dose management. Only recently, with public attention to the matter, have manufacturers begun to include automatic exposure control and other devices that have the potential to reduce doses. In the last 2 years, there has been another new use for CT, the annual screening examination. This use is becoming widespread although the efficacy is in question. Referring physicians and radiologists should make sure that the examination is indicated. [15]. The CT dose and use problem has been highlighted by uses in pediatric radiology. Often adult exposure factors have been used on children with no regard to increased sensitivity of children to radiation carcinogenesis [16,17]. The problem has existed for years even when children get typical radiographs. Pediatric patients should have specific protocols with lower exposure factors (especially mAs). If there are dedicated pediatric protocols and trained pediatric x-ray technologists doses are often much lower than when a routine technologist is faced with a child. Often there is little or no collimation employed and repeat examinations may be necessary due to improper exposure factors. The radiation protection problems with CT are primarily due to lack of education and training ad lack of customer demands on the manufacturers to produce acceptable images at lower patient doses. In many radiology departments, film is being replaced by digital techniques with images being stored and displayed on a picture archiving system. Basic training in managing image quality and patient dose in digital radiology is necessary for radiologists, medical physicists and radiographers involved in the use of digital techniques [18]. Unfortunately, most digital systems are installed with little or no training in radiation protection aspects. In digital radiology, higher patient dose per image usually means improved image quality. However, there is a tendency with digital systems to use higher patient doses than necessary This increase should be avoided. With film radiography and under or overexposed film is easy to recognize. With digital systems, the parameters are often set higher than necessary and overexposures are immediately compensated by "windowing" the image. Thus, there is the distinct possibility of increased dose (up to a factor of ten or more) with no added benefit to the patient and the problem not being recognized. Many of the current digital image displays give no indication of the patient dose or exposure factors. Even when some "dose index" is displayed the value is often not linearly related to the actual dose and the quantities provided are not standardized between manufacturers. Patient dose parameters should be displayed at the operator console (and inside the x-ray room for interventional procedures) to allow radiographers and medical specialists to manage patient doses better. Local diagnostic reference levels (DRLs) are useful tools to manage patient doses in medical imaging tasks. DRLs for non-digital imaging tasks are not necessarily applicable to specific, similar digital imaging procedures. With digital fluoroscopy systems it is very easy to obtain (and delete) images and there may be a tendency to obtain more images than necessary. This would irradiate the patient more than is clinically necessary. Procedure protocols should be agreed to manage this problem. There are other potential problems with digital techniques. The number of pulses or exposures is not evident when viewing the final images. One can easily set a sequence that provides much more exposure than is necessary. In addition, the radiologist now often interprets the images from a remote location and is not on hand to supervise the technical portions of the examinations. The possibility of overexposures may potentially be controlled by regulations requiring some assessment of reference values for a specific set of examinations. In the United States this was effective for film screen mammography but even those standards and regulations have been outdated by the recent development of digital mammography. An additional issue related to digital radiography has also just become apparent. The convenience with which the referring clinicians can view the image and the radiologists report on their office or desktop computer appears to have substantially increased the incidence of examinations being performed of a given

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set of patients. This raises the question of whether all the examinations are truly justified. Justification criteria should be one of the key components considered in the update of a quality assurance program when a facility converts to digital imaging. As with CT, the issues in digital radiology are primarily related to a rapidly expanding technology and lack of training. There are some current radiation protection issues in nuclear medicine as well. For many years there have been standards (limits or constraints) that related to exposure of the public or family members when patients who have received radionuclide therapy are released. The regulations and suggested restrictions in many countries and states are distressingly variable. In some countries in Europe, patients are required to be hospitalized for days, but not in other European countries. This has resulted in what some have termed "nuclear therapy tourism" where patients go to the country with least restrictions for their treatment. In the United States, most cooperative patients are not hospitalized at all. What is the cause of this variation? It certainly is not lack of a clear standard, but rather use of models that are ultraconservative and societal misunderstanding about radiation effects, rather that using actual measurements to demonstrate compliance with standards [19]. Radiation oncology also has had its share of problems. In spite of a plethora of standards there have been continuing radiation therapy accidents, resulting in the deaths of a number of patients [20]. A recent accident in Costa Rica was due to a manual miscalculation of the beam output. There was no secondary calculation as suggested by international standards. In fact, the root cause was multi-factorial with lack of adequate training of the physicist, lack of application of existing international standards/recommendations and physicians and technologists who were trying to treat too many patients with too little equipment [21]. Another accident in Panama was due to treatment planners using a computerized planning system in a way that was different from that defined in the manual. In fact there were trying to use it in a way that they though would provide additional patient protection.

5. CURRENT EFFORTS AND POSSIBILITIES FOR THE FUTURE The IAEA has recently published a Safety Series Report (No. 20) [3] on training in radiation protection and the safe use of radiation sources. The report discusses classroom, distance learning and on the job training as the major types of training. It also covers development of training objectives, syllabus development, training schedules, lesson plans, materials, practical sessions, assessment procedures, training facilities, selection of participants and selection of trainers and supervisors. While this type of training pertains to nuclear power plants and other types of regulated facilities, it is not likely to work well in most medical settings. Justification and optimization are part of the normal practice of medicine and pose no conceptual or real problems. One difficulty is that "recommendations" of organizations such as the ICRP rarely if ever find their way to a physician's desk. In addition, the medical community generally has little interest or time to spend attending courses on radiation protection. Reference, action and investigation levels and their implementation is usually relegated to the medical physicist at the institution. Unfortunately, there are many physician's offices that have medical x-ray equipment and are visited rarely, if ever, by a medical physicist. Recently, there was an international conference on the radiological protection of patients in diagnostic radiology and interventional radiology, nuclear medicine and radiotherapy [22]. The findings of the conference were incorporated into an international action plan for radiation protection of patients. The plan has training and education actions common to diagnostic and interventional radiology, nuclear medicine and radiotherapy as follows: — to complete the development of a standard syllabus and packages for training in the application of safety standards.

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— To train the trainers involved in national training programmes using the above mentioned packages. — To arrange for a review of the syllabus for the Agency training courses in medical radiation physics by appropriate professional bodies and to publish the results. - To explore the potential uses of information technology and distance learning, identifying application areas and types of information technology. — To explore mechanisms for widely disseminating information related to the protection of the patient. - To collect and disseminate, using the IAEA's International Reporting System for unusual radiation events, information about accidental medical exposures, including, as far as possible, information about events that did not have clinical consequences but from which prevention-relevant lessons can be drawn. — To support Member States in the gradual transition from the basic to advanced stages of implementation of the BSS. - To promote the formal recognition of medical physicists responsible for the radiological protection of patients as health professionals. — To promote - through the provision of advice about the functions, responsibilities and training of technologists - recognition of the impact of technologists involved in day-to-day procedures on the radiological protection of patients. — To continue current activities in radiotherapy concerned with the traceability of dose measurements and with audit services, including the development of local expertise, and to extend these services to diagnostic radiology and nuclear medicine. — To finalize the existing draft practice-specific guidance documents, seeking input from professional bodies, international organizations and national authorities responsible for the radiological protection and medical care of patients. — To provide guidance to donors, recipients and NGOs on the safety issues related to the transfer of second-hand equipment. The ICRP, through Committee 3, has developed a new philosophy and approach relative to training of specific aspects of radiation protection in medicine. It was realized that most physicians would not want or read a text on radiation protection per se but that they would read short documents related to specific issues, particularly in areas of new technology. As a result, documents have been recently published on - Pregnancy and medical radiation - Management of dose in transition from film screen to digital radiography - Dose management in computed tomography - Release of patients after therapy with both sealed and unsealed radionuclides - Prevention of accidents in radiotherapy - Special aspects of high dose rate brachytherapy In spite of current educational efforts there remain significant problems. Many current international recommendations do not adequately stress the importance of training in radiation protection and many countries continue to allow physicians to use high dose rate equipment simply by virtue of their credentials as a physician. Currently, the ICRP has a task group examining the issue of training and possibly certification for some groups of medical users. One must remember that training the physician users of medical radiation

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equipment alone is not adequate. There also must be adequate training of the radiographers and other technologists who often are the actual operators of the equipment. In addition to international efforts, there also are a number of national efforts regarding radiation protection training in medicine. One very successful national program is in Spain [23,24]. In 1999, a Royal Decree was published for criteria for quality in radiodiagnosis which complemented an earlier decree dealing with medical radiation exposure [25,26]. These decrees require that professionals who perform interventional practices guided by fluoroscopy be accredited at a "second level" of training in matters of radiological safety. Toward this end a 20 hour course was developed by the Spanish Society of Vascular and Interventional Radiology to meet the requirements of the European Guidelines [27,28].

6. SUMMARY AND CONCLUSION There are a number of current concerns regarding radiation protection in medicine. Quite a number of these issues have arisen due to rapidly advancing technology and the pressure to get new techniques into clinical practice. Unfortunately, the clinical pressure has often eclipsed appropriate training in the radiation protection aspects. While there are some educational materials available, there dissemination is often poor unless they were developed with and distributed by professional societies. At the present the most successful strategy appears to be to develop concise and technique specific user related documents and have them published in medical journals. There are current international efforts to examine whether there should be training and educational recommendations/standards for individual authorization that might be required for medical staff to use new (and particularly high dose) equipment.

REFERENCES [1]

International Commission on Radiological Protection, Radiological Protection and Safety in Medicine, Oxford, Pergamon Press, ICRP Publication 73. Ann. ICRP 26(2), 1996

[2]

International Commission on Radiological Protection, 1990 Recommendations of the International Commission on Radiological Protection, Publication No. 60, Annals of ICRP 27(1 -3) 1991

[3]

International Atomic Energy Agency, Training in Radiation Protection and the Safe Use of Radiation Sources, Safety Reports Series, No.20, International Atomic Energy Agency Vienna 2001

[4]

International Atomic Energy Agency, International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources, Safety Series, No.115, International Atomic Energy Agency Vienna 1996

[5]

International Atomic Energy Agency, Radiological Protection for Medical Exposure to Ionizing Radiation, Safety Guide, No.RS-G-1.5, International Atomic Energy Agency Vienna 2002

[6]

Leer J, Overgaard J, Heeren G, The European core curriculum on radiotherapy, Radiother. Oncol. 22: 153-155,1991

[7]

Coffey M, et. al. The European core curriculum for radiotherapy technologists. Radiother. Oncol. 43:97-101,1997

[8]

European Council Directive 97/43, June 30, 1997, h t t p : / / w w w . E u r o p a . e u . i n t / c o m m . /energy/nuclear/radioprotection/doc/legislation/9743

[9]

U.S. Food and Drug Administration (FDA) Avoidance of Serious X-ray induced Skin Injuries to Patients during Fluoroscopically Guided Procedures. Med Bull. 24:7- 17, 1994

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[10]

Koenig T, Wolff D, Mettler F and Wagner L, Skin Injuries from Fluoroscopically Guided Procedures: Parti, Characteristics of Radiation Injury, Am. J. Roentgenol. 177(3): 3-11, 2001

[11]

Koenig T, Mettler F and Wagner L, Skin Injuries from Fluoroscopically Guided Procedures: Part II, Review of 73 Cases and Recommendations for Minimizing Dose Delivered to the Patient, Am. J. Roentgenol. 177(3) 13-20, 2001

[12]

Vano E, Goicolea J, Galvan C, et. al. Skin radiation injuries in patients following repeated coronary angioplasty procedures, BritJ. Radiol. 74: 1023-1031, 2001

[13]

International Commission on Radiological Protection, Avoidance of Radiation Injuries from Medical Interventional Procedures, Oxford, Pergamon Press, ICRP Publication 85. Ann. ICRP 30 (2), 2000

[14]

International Commission on Radiological Protection, Managing Patient Dose in Computed Tomograph}', Oxford, Pergamon Press, ICRP Publication Ann. ICRP 30(4), 2000

[15]

Linton O., Mettler FA, National Conference on Dose Reduction in CT, with an Emphasis on Pediatric Patients, Am. J. Roentgenol. 181:321-329, 2003

[16]

Brenner D, Elliston C, Hall E and Berdon W. Estimated Risks of Radiation-Induced Fatal Cancer from Pediatric CT, Am. J. Roentgenol. 176:289-296, 2001

[17]

Frush D, Soden B, Frush K and Lowry C. Improved Pediatric Multidetector Body CT Using a SizeBased Color-Coded Format. Am J. of Roentgenol. 178:721-726, 2002

[18]

International Commission on Radiological Protection, Managing Dose in Digital Radiology, Oxford, Pergamon Press, Annals of ICRP (in press)

[19]

International Commission on Radiological Protection, Release of Patients after Therapy with Unsealed Radionuclides, Oxford, Pergamon Press, Annals of. ICRP (in press)

[20]

International Commission on Radiological Protection, Prevention of Accidental Exposures to Patients Undergoing Radiation Therapy, Oxford, Pergamon Press, ICRP Publication Ann. ICRP 30(3), 2000

[21]

International Atomic Energy Agency, Accidental Overexposure of Radiotherapy Patients in San Jose, Costa Rica, International Atomic Energy Agency ,Vienna 1998

[22]

International Conference on the Radiological Protection of Patients in Diagnostic and Interventional Radiology, Nuclear Medicine and Radiotherapy, Malaga, Spain 26-30 March 2001. IAEA-CN-85-196 and IAEA-CSP-7/CD. 2001

[23]

Vano E, Gonzalez L. Canis M and Hernandez-Lezana A, Training in radiological Protection of Interventionalists: Initial Spanish Experience, Brit. J. Radiol. 76:217-219, 2003

[24]

Vano E, Vargas F, Training in Radiological Protection for Interventional Cardiology, Rev. Esp.Cardiol. 56(1)111-112,2002

[25]

Real Decreto 1976/1999 por el que se establecen los criterios de calidad en radiodiagnostico. Boletin Oficial del Estado de 29 enero de 1999; 45891-900

[26]

Real Decreto 1891/1991 sobre instalacion y utilizacion de aparatos de rayos X con fines de diagnostico medico. Boletin Ofical del Estado de 3 de enero de 1992; 138-48

[27]

DIMOND. Measures for optimizing radiological information and dose in digital imaging and interventional radiology. European Commission. Fifth Framework Programme, 1998 — 2002. Program Acroynm FP5-EAECTP C. Project reference FIGM-2000-00061. Project Acronym DIMOND III. http://dbs.cordis.lu

94 [28]

Current Trends in Radiation Protection MARTIR (Multimedia and Audiovisual Radiation Protection Training in Interventional Radiology), CD-ROM. Radiation Protection 119, European Commission. Directorate General Environment, Nuclear Safety and Civil Protection. Luxembourg, 2002 (free availability from the Publication Department of the European Commission, Office for Official Publications of the European Communities, Luxembourg, e-mail: [email protected])

Current Trends in Radiation Protection H. Metivier, L. Arranz E. Gallego and A. Sugier (eds.)

Occupational Radiation Protection in the European Union: Achievements, Opportunities and Challenges Klaus Schnuer*1, Augustin Janssens*2, Jochen Naegele*3, Pascal Deboodt** *'Radiation Protection Unit, European Commission, Wagner building, WAG C/320, L-29 20 Luxembourg **SCK/CEN, Boeretang 200, B-2400 Mol, Belgium

Abstract. a The Treaty establishing the European Atomic Energy Community places an obligation on the Community to establish basic safety standards for the protection of the general public and workers against the dangers arising from ionising radiation. Since its establishment in 1957, Euratom has regularly legislated and issued guidance in many areas driven by scientific developments, by experience with former legislation or by the identification of regulatory gaps. Most recently, the Community issued two major pieces of radiation protection legislation. In May 1996, the new Basic Safety Standards Directive was issued followed by the Directive on medical exposures in June 1997. The EU Basic Safety Standards improve the protection of workers in particular by the reduction of annual dose limits and the extension of the scope to natural radiation sources. This paper gives consideration to whether the protection of workers against the dangers arising from ionising radiation should be seen as an isolated subject or integrated into the wider aspects of workplace saftey and worker health policy. Examples are presented of situations where radiological and non-radiological safety considerations led to unbalanced situations and to accidents.

1. INTRODUCTION During the last four decades the European Atomic Energy Community has placed high emphasis on legislative and research activities aimed at creating best conditions for the protection of workers and the general public against dangers arising from ionising radiation. The starting point of this particular European health

a

This paper reflects the authors' personal viewpoints and should not be regarded as an official document of the European Commission. 1 E-mail: [email protected] 2 E-mail: [email protected] 3 E-mail: [email protected] 4 E-mail: [email protected]

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policy was the 1957 Euratom Treaty [1]. This treaty established the European Atomic Energy Community and vested it with far-reaching competencies. Since 1959, the Community has issued at regular intervals basic safety standards for the radiological protection of workers and the general public. Repeated updates have improved and strengthened the provisions and have led to protection standards for all categories of workers, as well as for members of the general public.

2. THE LEGISLATIVE PROCEDURE In order to meet the obligation under Article 2b of the Euratom Treaty, the legislative procedure laid down in Article 31 of the Treaty must be followed. The Treaty requires the Commission to obtain the opinion of a group of radiation protection experts on any legislative initiative. Following this step, the Treaty7 foresees the consultation of the Social and Economic Committee of the European Parliament once the Commission has submitted its proposal to the Council. The European Council adopts new legislation by a qualified majority. Since the first Basic Safety Standards, Council Directives addressed to the Member States have been considered to be the most appropriate legal instrument, to facilitate transposition into national legislation. According to Article 161 of the Treaty, a Directive is binding on the Member States with regard to the results to be achieved but leaves the national authorities the choice of the form and methods. Article 33 of the Treaty foresees that Member States shall communicate to the Commission all draft legislation implementing EU radiation protection legislation. In order to ensure a harmonised approach within the EU, the Commission may issue recommendations on Member States' draft provisions.

3. THE BASIC SAFETY STANDARDS The major reason for initiating the revision of the 1980 Basic Safety Standards [2] was to bring European radiation protection legislation into line with the 1990 ICRP Recommendations No 60 [3]. Important new features of the ICRP No 60 Recommendations made it necessary to develop a new structure for the Directive. Therefore, the latest BSS Directive (96/29/EURATOM) [4] does not simply amend the former legislation but it repeals the 1980 and 1984 Basic Safety Standards Directives [5].

3.1. Extended Scope of the Standards The ICRP had introduced a fundamental distinction between practices and intervention. Practices are defined as human activities that can increase the exposure of individuals to radiation from a source, and interventions are to be seen as human activities aimed at preventing or decreasing the exposure of individuals. An important feature of the 1996 Basic Safety Standards Directive is that, unlike ICRP, a distinction is made between three situations: practices, work activities and interventions. Work activities are activities involving the presence of natural radiation sources. 3.1.1. Practices By definition of the Directive, practices relate to artificial radiation sources or to natural radiation sources where radioactive substances are processed for their radioactive, fissile or fertile properties. 3.1.2. Interventions Intervention situations are now dealt with much more explicitly than before. Intervention situations account for radiological emergencies and for lasting radioactive contamination resulting from past practices or work activities.

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3.1.3. Work activities The extended scope of the Directive now includes human activities involving natural radiation sources. The structure of the Directive is such that, a priori, all work activities are within the scope of the Directive. It is up to Member States to identify, by specific surveys, which work activities are of concern and may require appropriate forms of regulatory control. Such flexibility is necessary in view of industrial or geological particularities of the different Member States. Most of them must set up a new legal framework for this purpose and have little experience with the regulation of natural radiation sources. The Directive specifies that consideration has to be given to terrestrial natural radiation sources, including exposure to radon gas, to work activities involving ores or residues containing enhanced levels of natural radioactivity and to cosmic radiation during the operation of aircraft. It is for the Member States to decide whether a particular human activity is fully or partially covered by the scope of the Directive.

3.2. General Principles 3.2.1. justification The Directive requires that all practices shall be justified in advance and existing practices may be examined again. Justification is a complex issue and may include factors that are wider than those directly related to radiological protection. 3.2.2. Optimisation If the practice is justified, the optimisation principle is of primary importance for radiological protection whether at design or at the operational stage. The operational application of the ALARA principle has lead to the introduction of the concept of dose constraints. The key to successful implementation of the optimisation principle is a strong commitment at the management and operational level. This commitment has to be translated into the allocation of responsibilities among key personnel and into training and education programmes. The application of the ALARA principle requires judgement based on common sense and experience. 3.2.3. Dose Umits An important new feature of the BSS Directive is the reduction of annual dose limits. The Directive introduces the ICRP concept of effective dose and requires uniform methodologies for the estimation of doses to be applied. The new concept of a 5-year average dose limit of 100 mSv and a limit of 50 mSv in one single year within this period is reflected in the BSS Directive. However, the Directive leaves the freedom to Member States to introduce an annual dose limit. About half of the Member States have made use of this option and introduced a 20 mSv annual dose limit.

3-3. Operational Protection of Workers The BSS Directive requires for any practice involving ionising radiation that operational control should follow a structured approach. In Title VI, the Directive gives the individual steps of the procedure. It stipulates that the routine and reasonably foreseeable potential sources of exposure are to be identified. The realistic magnitude of expected doses shall be estimated and subsequently the radiological protection measures necessary to satisfy the optimisation principle shall be determined. In order to meet the ALARA principle, the creation of an operational radiation protection programme, commensurate with the radiological risk, is necessary to ensure effective management of the protection measures. This also requires periodical

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appraisals of the programme with the aim of identifying overlaps and room for improvements. The intervals should be dependent on the practice and the magnitude of doses and associated risks. Maintaining the control of the radiation source and of the occupationally exposed workers is an essential function of the management. There are two major mechanisms that help to achieve this goal: the classification of workplaces and the categorisation of workers. 33.1. Classification of Workplaces

One well established mechanism is the use of designated areas. The ICRP Recommendations describe the concept of designated areas, which is broadly reflected by the Directive. The Directive requires the classification of workplaces into controlled and supervised areas based on estimates of possible radiation doses, the expected frequency and possible consequences of incidents including the spread of contamination. It is important to note that the Directive now places reduced emphasis on the level of dose and on any derived dose rate for the definition of the boundaries of supervised or controlled areas, and rather puts responsibility on the operator for the classification and delineation of working areas. According to Article 18 of the Directive, it is not necessary to make special arrangements where the annual dose is not liable to exceed 1 mSv per year. 3.3.1.1 Controlled areas: Controlled areas are locally limited zones subject to specific procedures and working rules to which access is controlled and only permitted to workers who have received appropriate instructions. Specific arrangements and procedures shall be made for the purpose of preventing the spread of radioactive contamination. The Directive requires that competent authorities shall establish guidance on the criteria for classification of areas and that operators shall keep the working conditions under review. 3.3.1.2 Supervised areas: Workers may receive doses above 1 mSv outside controlled areas and therefore working conditions shall be kept under surveillance. For this purpose, the Directive lays down specific provisions for areas within which a worker is liable to receive an annual dose in excess of 1 mSv. This area shall be designated as supervised and the working arrangements and conditions shall be kept under review. 3.3.2. Categorisation of Workers

The BSS Directive requires that for purposes of monitoring and surveillance a distinction shall be made between two categories of workers on the basis of possible exposures. ICRP 60 Recommendations and the BSS Directive identify three major grounds for the decision to provide individual monitoring. The primary factor is the expected level of doses or intakes, secondly the likely variation in the doses or incorporation of radioactivity and finally the complexity of the measurement techniques. In this context, the assessment of internal doses is more difficult than that of external exposures. The distinction between categories of workers as laid down in the Euratom BSS is not shared by the ICRP or by the International Basic Safety Standards (IAEA, Vienna). It is not recommended by the International Labour Organisation either (Convention No 115, the Recommendation No 114) [6]. However, the concept of the EU Basic Safety Standards does not introduce any discrimination in terms of the level of protection afforded to workers and is highly effective in connection with the classification of workplaces. 3.3.2.1 Category A Workers: The concept of category A and B workers is thus maintained by all Member States of the EU as the basis for the purposes of monitoring and surveillance. Individual monitoring should be systematic for category A workers who, by definition, are liable to receive annual doses exceeding 6 mSv or 3/10 of equivalent dose limits for extremities. 3.3.2.2 Category B Workers: Category B workers should be subject to systematic assessment of individual doses based either on individual monitoring or the results of workplace monitoring. It is also appropriate to make generic assessments for groups of workers.

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3.4. Record Keeping The BSS Directive requires record keeping of individual exposures for both categories of workers during their working life and retained afterwards until the worker would have attained the age of 75 years but not less than for 30 calendar years from the termination of work as a classified worker. Also required is the record keeping of results of workplace monitoring used for the estimation or assessment of individual doses.

3.5. Medical Surveillance Regular medical surveillance of the workforce forms part of the general occupational health policy and related national rules and regulations. Supplementary to these general rules, the medical surveillance of workers occupationally exposed to ionising radiation requires specific examinations in relation to working conditions. On that basis, the medical practitioner has to decide for each category A worker on his fitness for the tasks assigned to him. The Directive provides that workers shall have access to their medical records including dosimetric results. The BSS Directive provides specific requirements for occupational radiation protection of women. While the risks associated with exposures to ionising radiation are similar for women and men, there is a particular risk for the unborn child. The BSS Directive therefore recognises special radiation protection requirements for pregnant and nursing women.

4. OUTSIDE WORKERS DIRECTIVE Council Directive 90/641/Euratom [7], on the operational protection of outside workers exposed to ionising radiation during their activities in controlled areas provides for a binding set of rules aimed at supplementing the Basic Safety Standards Directive (80/836/EURATOM). The purpose of this Directive is to ensure at European Union level that the radiological protection situation for temporary contract workers is equivalent to that offered to those workers permanently employed by the operators of the controlled areas. The Outside Workers Directive requires prior reporting and authorisation for outside undertakings and introduces requirements additional to the fundamental principles for the operational radiological protection of workers. It is important to underline that the Directive is not only applicable to the nuclear industry, but covers all work sectors where controlled areas are operated in the sense of the Basic Safety Standards Directive. Since the adoption of the Outside Workers Directive, the working arrangements for workers in all sectors have considerably changed. As a consequence of the completion of the internal market, an ever-increasing number of workers perform their activity consecutively in Member States other than the one where their employer is legally registered. Self-employment is another form of employment situation that allows more flexibility and is therefore attractive to specialists and experts in specific work sectors. For these and other reasons (reference to Directive 96/29 rather than 80/836) a revision of the Outside Workers Directive is currently being considered.

5. IMPLEMENTATION The Euratom Treaty provides specific instruments for ensuring the correct transposition of measures into national legislation (Article 33 requires Member States to transmit legislation in draft, so that the Commission can make appropriate recommendations). A key element in the successful implementation of the EU radiation protection policy is the additional guidance provided by the Commission to stakeholders at all levels. In order to provide guidance for the implementation of the Basic Safety Standards Directive, the Commission published a Communication [8] and specific recommendations for the implementation of Title VII of the Directive on natural radiation at workplaces [9]. Under the Euratom Treaty, the European Commission also sponsors a considerable research programme. Furthermore, the European Commission has launched several projects directly linked to the operational implementation of the BSS Directive.

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5.1. Transposition Within the European Union, the Member States were obliged to complete the transposition of the 1996 Basic Safety Standards before May 2000. The full implementation and integration of the new radiation protection concepts into national regulations is now finalised to a great extent. Additional to the ongoing activities in the current Member States, ten Central and Eastern European countries will join the EU in 2004 and have to demonstrate to the European Union that they have correctly adopted all EU radiation protection legislation at the foreseen date of entry.

5.2. Operational Projects 5.2.1. ALARA Projects The implementation of the optimisation principle has been the central point of the activities of the Radiation Protection Unit for more than two decades. The ALARA network [10], conferences on radiation protection optimisation, ALARA workshops and a series of ALARA training courses were initiated. The results of dose assessments to workers in particular sectors identified a considerable number of opportunities for improvement of practices. The EC has recently initiated the creation of a European ALARA Network in the non-destructive testing sector. Apart from the radiation protection sector, the European federation of non-destructive testing EFNDT and representatives from non-destructive testing utilities are represented on the steering committee. 5.2.2. Job-related Doses in NPP

During the late 1970s, the European Commission received information about a considerable increase in radiation doses to workers in Nuclear Power Plants during operation and in particular during shutdown for refuelling and maintenance. In order to help the operators to implement the ALARA principle, the Radiation Protection Unit initiated a project aimed at promoting the exchange of information and experience between the operators and to provide them with feedback and information on good practice [11]. The radiation protection departments returned annually a commonly agreed questionnaire containing detailed information on collective and individual doses to workers assigned to defined jobs or departments during operation and shutdown periods. The Commission evaluated and analysed the data and discussed the results during an annual meeting with all contributors. According to the participating nuclear power plant operators, this project was of great value for the operational implementation of the ALARA concept and the reduction of doses to workers. In 1989, the Commission offered its co-operation with the NEA of the OCDE. This cooperation lead directly to the creation of the ISOE (Information System on Occupational Exposure: network co-sponsored by OECD and IAEA) project. Now, after 20 years of operation, the Radiation Protection Unit will finalise this project and publish the collected data, the analysis and statistics. 5.2.3. Occupational Exposure ESOREX In order to identify the particular sectors where radiation protection of workers can be improved, the European Commission initiated the European Survey on Occupational radiation exposure, the ESOREX project. The aim of this multi-annual activity is to assist radiation protection competent bodies in Europe in the design and operation of national dose registers. Furthermore the individual dose data monitored, registered and recorded provides an excellent tool to identify trends and developments in occupational exposures of all classified workers in Europe [12]. The project also assists the member States authorities in the implementation of the requirement, laid down in Article 38(5) of the BSS Directive, that Member States shall facilitate the exchange of dosimetric and medical data of workers between involved departments and services.

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5.2.4. Accidents and Incidents EURAIDE

In the same context, the increasing number of registered mishaps or incidents involving radioactive sources initiated another important project. The Commission awarded a contract for a study on the feasibility of a European data and information exchange system on incidents and accidents involving radiation sources or substances in the industrial sector. The EURAIDE study showed there is a need for feedback and the exchange of lessons learned in this sector. There is room for harmonisation of recording and reporting procedures in European countries [13].

5.2.5. Protection of Aircrew, EPCARD

Radiation exposure of aircrew is one of the most complex occupational radiation protection areas. This multidisciplinary activity required considerable research before it was possible to identify the most appropriate methodology for the operational implementation of protection measures. Existing international conventions, multinational regulations and agreements as well as national air safety and transport rules had to be respected and incorporated into a final approach for the radiological protection of air crew. The Commission supported the development of a computer code for the assessment of generic route dose data based on the most recent scientific findings. The EPCARD programme [14] is an excellent tool for the air industry and competent radiation protection authorities for the implementation of Article 42 of the BSS Directive on protection of aircrew.

5.2.6. Training and Education

Another important aspect of radiation protection is the role of the qualified expert. The BSS Directive makes many references to the role, the responsibilities and the tasks of these particular important actors. Therefore, the training and education is of great importance for the operational implementation of radiation protection. In this context, the Commission has recently commissioned a study assessing the Status of the Radiation Protection Qualified Expert in the EU Member, Accession and Candidate States. The study resulted in a fairly comprehensive overview of the present situation. It identified requirements to move forward to mutual recognition of qualifications and diplomas and revealed a wide interest in the establishment of a European Discussion Platform. Therefore, the Commission will initiate the creation of a European radiation protection training and education platform. This platform should form the basis for defining a methodology aimed at harmonising national radiation protection training and education and for a system of mutual recognition of diplomas and qualifications. Pursuant to Article 3(c) of the EC Treaty, the abolition of obstacles to freedom of movement between Member States of persons and services implies the possibility of pursuing a profession in a Member State other than the one where these persons have acquired their professional qualifications. For those professions for which the European Union has not laid down minimum levels of qualification, Member States reserve the option of fixing their own levels with a view to guaranteeing the quality of services provided in their country. Currently the mobility of qualified radiation protection experts is very limited, due to restrictive national rules and regulations. The expert group established under Article 31 of the Euratom treaty supervises this activity and provides for recommendations and advice for the creation of the planned European radiation protection training and education platform.

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6. COMMON HEALTH AND SAFETY POLICY Radiation protection is an integral part of sound and comprehensive health and safety management. There are important general work place safety and public health concepts equally applicable to any field of endeavour. Involved stakeholders already cope with health and safety policies that address all hazards, with radiation protection being part of the whole.

6.1. Conventional Health and Safety at Work In 1989 the European Union issued the European Framework Directive on health and safety at the workplace [15]. The scope of this directive covers all forms of occupational hazards, and is also applicable to general work conditions of workers involved with ionising radiation. This Framework Directive was relevant to the revision of the radiation protection Basic Safety Standards Directive. A number of requirements of the Framework Directive overlay or directly overlap the scope of the BSS Directive, such as general risk assessments, engaging qualified experts and occupational medical surveillance. Systematically, Member States regulate at national level activities involving ionising radiation by regulations dealing mainly with non-nuclear practices. Frequently, the scope of national transport regulations, social law, workplace safety requirements, norms and safety standards for industrial activities and products cover activities involving ionising radiation. The protection of workers against the dangers arising from ionising radiation is not an isolated subject in workplace safety and worker health policy. It is part of a package of regulatory measures and actions taken in the industrial, social and health policy sector. Therefore, radiation protection in industry, education, research and medicine has to follow these changes. Radiation protection in the future will be multidisciplinary, involving different interest groups and specialised services. In order to improve the overall health situation of workers exposed to ionising radiation, it is necessary to establish procedures both for management decisions and for technical advice, including training and information for workers.

6.2. Overlapping Safety Requirements: some examples Mutual influence between radiological and non-radiological risks can be illustrated by some practical examples [16-19]. The request to minimise exposure and to reduce radioactive waste may highlight ignorance of other regulations for safety at workplace. A worker who has to use special tools may decide to protect his tools against radioactive contamination. This change in the design of tools may be a cause of severe accidents. Another example highlights the need, in some circumstances, for defining priorities and for managing simultaneously two risks, for instance the radiological one and an asbestos problem. During the decommissioning of a nuclear power plant it was found that the asbestos concentration in a controlled area was above the legal limiting value. Applying the regulations for asbestos removal and the implementation of radiological protection requirements may not be fully compatible. An in-depth analysis and ALARA procedure for reducing both the radiological risk and the risk from inhalation of asbestos requires a multidisciplinary approach involving players from different health and safety disciplines. There are several fields in industry where operational radiation protection measures may increase risks due to other physical or chemical agents'. On the other hand, workers' health may be considerably improved if radiation protection measures are included in overall workplace safety regulations. In this context, protection measures aimed at preventing inhalation of exhaust gas during arc welding using Thorium electrodes will protect against inhalation of radioactivity as well as the inhalation of chemical agents. Similar approaches may count for handling Zircon

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sand. Radiation protection measures for preventing permanent body contact with sand sacks and protection against inhalation of radioactive dust also protects against orthopaedic lumbar disease as well as against hazards to the pulmonary tract of the workers. Another example is the protection of aircrew. The requested change of working schedules of highly exposed aircrew may have a positive influence on overall safety because it may reduce health impacts due to stressful working hours. One of the most discussed areas is Radon at workplaces. Protection measures against inhalation of Radon at workplaces may create a considerable economic burden on companies and are therefore sometimes not seen as justified. However, the ventilation of underground mines reduces not only the exposure to Radon gas but improves considerably the working atmosphere and consequently the health protection of the miners. Other working sectors such as spas or mineral water springs or drinking water supply facilities need careful examination of the Radon concentration and the subsequent protection measures to be put in place.

7. CONCLUSIONS It is not an overstatement to say that the European radiation protection policy has contributed significantly to the achievement of the current high standard of radiological protection of workers and the general public within the European Union. The harmonised implementation of the EU Basic Safety Standards and the other radiation protection related Directives into national regulations is the result of continuous efforts of the European Union. In this context, the radiation protection policy of the European Union always followed promptly the recommendations of the ICRP. Further pursuing international harmonisation and to make effective use of the available resources, the Commission co-operates closely with international organisations such as the IAEA, the NEA, as well as the ILO, ISO, IRPA and national radiation protection associations and organisations. It must be emphasised that most workers are exposed to a wide variety of other risks. Consequently, the radiological protection issue will no longer be seen as isolated and disconnected from other developments in society, which is undergoing deep-rooted changes. One of these important developments in the industrial sector is the integration process of areas that have been historically separated from each other. Therefore, the subject of radiation protection in industry, education, research and medicine has to follow these changes. Radiation protection in the future will be a more multidisciplinary initiative involving different interest groups and specialised services. Natural radiation sources at workplaces are an excellent example for these developments. Another problem for future radiation protection is changing working conditions. Mobility of workers, temporary work as well as self-employment may prompt a need for additional requirements for operational radiation protection. In this context, education, vocational training and information of workers and the role of the qualified radiation protection experts have to be carefully reconsidered. The Commission, together with the other European institutions, will continue to co-ordinate scientific, social, economical and legal activities in support of future concepts aimed at maintaining and improving the already remarkable level of radiological protection for workers.

REFERENCES [1]

EURATOM, Treaty establishing the European Atomic Energy Community, Rome 1957 Office for official publications of the European Communities, Luxembourg, 1999

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[2]

EURATOM, Council Directive of 15 July 1980, 80/836/Euratom, amending the Directives laying down the basic safety standards for the protection of workers and the general public against the dangers arising from ionising radiation. Official Journal of the European Communities No L 246 of 17 September 1980, Luxembourg 1980

[3]

ICRP, 1990 Recommendations of the International Commission on Radiological Protection, Publication No 60, Pergamon Press, Oxford 1991

[4]

EURATOM, Council Directive of 13 May 1996, 96/29/Euratom, laying down the basic safety standards for the protection of workers and the general public against the dangers arisingfrom ionising radiation. Official Journal of the European Communities No L 195 of 29 June 1996, Luxembourg 1996

[5]

EURATOM, Council Directive of 3 September 1984, 84/467/Euratom, amendingDirective 8018361 Euratom as regards the basic safety standards for the health protection of workers and the general public against the dangers of ionising radiation. Official Journal of the European Communities No L 265 of 5 October 1984, Luxembourg 1984

[6]

ILO, Convention C115 of 17June 1962 concerning the Protection of Workers against Ionising Radiations and Recommendation Rl 14 concerning the Protection of Workers against Ionising Radiations, International Labour Organization, Geneva, Conference 44, of 22:06:1960

[7]

EURATOM, Council Directive of 4 December 1990, 90/641/Euratom, on the operational protection of outside workers exposed to the risk of ionising radiation during their activities in controlled areas. Official Journal of the European Communities No L 349 of 13 December 1990, Luxembourg 1990

[8]

EUROPEAN COMMISSION, Communication from the Commission concerning the implementation of Council Directive 96/' 29/Euratom. Official Journal of the European Communities No L 133 of 30 April 1998, page 3, Luxembourg 1998

[9]

EUROPEAN COMMISSION, Radiation Protection 88, Recommendation for the implementation of Title VII of the European Basic Safety Standards Directive (BSS) concerning significant increase in exposure due to natural radiation sources. Office for official publications of the European Communities, Luxembourg, 1997

[10]

CEPN, European network for the implementation of the radiation protection optimisation principle. Centre d'etude sur 1'evaluation de la protection dans le domaine nucleaire, F-92263 Fontenay aux Roses, France

[11]

EUROPEAN COMMISSION, Radiation Protection 56, Occupational radiation exposure in European water power reactors 1981 — 1991. Publication No. EUR 14685 of the Commission of the European Communities, Luxembourg, 1994

[12]

SONS, BfS, Study on occupational radiation exposure of workers in Europe 1995-2000 Website: http : // www.esorex.cz

[13]

EUROPEAN COMMISSION, Pilot study for the creation of a European Union radiation accident and incident data exchange, (in the process of publication)

[14]

GSF, EC, Computer based tool for the assessment of radiation dose to air crew, European Program Packagefor the Calculation of Aviation Route Doses, EPCARD. National Research Center for Environment and Health, Institute of Radiation Protection, D-85758 Neuherberg. Website: h t t p : / / w w w . gsf . de/epcard

[15]

EUROPEAN ECONOMIC COMMUNITY, Council Directive 89/391/EEC of 12 June 1989 on the introduction of measures to encourage improvements in the safety and health of workers at work Official Journal of the European Communities No L 183, 29 June 1989, Luxembourg 1989

[16]

P. DEBOODT, The place of radiological protection in the global management of the risks on the workplaces, Proceedings of the Radiation Protection Symposium of the North West European RP Societies, Utrecht, the Netherlands, 2-5 June 2003

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[17]

P. DEBOODT, Radiological and non-radiological risks: the search for a global approach, Proceedings of an International Conference on "Occupational Radiation Protection: Protecting Workers against Exposure to Ionizing Radiation", Geneva, 26 — 30 August 2002

[18]

P. DEBOODT, The ALARA approach and related classical safety factors, Proceedings of the Second EC/ISOE Workshop on Occupational Exposure Management at NPPs, Tarragona, April 2000

[19]

P. DEBOODT, Management of radiological and non-radiological risks in a decommissioningproject, 4' European ALARA Network Workshop on "Management of Occupational Radiological and Non-Radiological Risks: Lessons to be Learnt, Antwerp, 20-22 November 2000

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Current Trends in Radiation Protection H. Metivier, L. Arranz E. Gallego and A. Sugier (eds.)

Education and Training Needs in Radiation Protection Agustin Alonso1 Chair of Nuclear Technology. Nuclear Engineering Department, Madrid Polytechnic University, Jose Gutierrez Abascal, 2. 28006 Madrid, Spain

Abstract. Education and training needs in radiation protection increase worldwide with expanding uses of ionizing radiation, more strict requirements and new fields of interest, such as environmental protection and natural radioactivity. Professional education and training is regulated and controlled by international recommendations and national standards, but there are still practices, such as dismantling, remediation and disposal, which are not specifically covered; moreover harmonization has not yet been reached. Vocational education is practiced in high-level learning institutions, but the stagnation of nuclear power in many countries and the phobia of society for radiation are reducing the number of applicants. Social education and information is a basic human right difficult to achieve. The use of modern teaching tools and distance learning will increase the efficiency of education and training. Recent international conferences on education and training have analyzed in depth the needs and deeds of such endeavour. The IAEA has been making efforts to produce advanced teaching materials and has introduced the concept of teaching the teachers to multiply efficiency, it also has recognized the importance of native languages. The European Union is in the process of introducing harmonization among the member countries in the educational requirements for the qualified expert.

1. INTRODUCTION The needs for education and training on radiation protection comes from the increasing range of applications of ionizing radiation in medicine, research and industry; from the increasing radiation safety and security requirements on the use of such radiation sources, and from new fields of interest such as the present concerns for the protection of the environment and natural radiation. Education and training on radiation protection is needed, inter alia, in regulatory organizations, operating nuclear power plants and fuel cycle installations, in facilities where radiation sources and radiation producing devices are used, in the transport of radiation sources, in the management of radioactive waste and in dismantling nuclear installations or cleaning old research and production facilities.

1

E-mail: [email protected]

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The education and training requirements vary considerably from practitioners requiring only elementary knowledge, to high-level educators and researchers, in need of the highest possible educational level. Radiation protection or radiation safety is considered an applied chapter of atomic and nuclear physics. In that sense it covers from the complicated concepts of quantum mechanics to simple descriptions on how radiation is produced and interacts with inert and biological matter. It also goes from the complicated technical aspects imbedded into radiation shielding of large sources of radiation to the most elementary protection procedures in the handling of small radiation sources. But radiation protection is also founded on some basic principles — justification, optimization and limitation — that have become part of the legislative and legal framework. In particular, the optimization principle brings about concepts such as risk-benefit analysis, which introduces economics and ethics into education and training. The new movement towards protecting the environment and the non-human species against the harmful effects of ionizing radiation includes a new field of research and ethical conduct. The increasing radio phobia in our societies also invites to create activities aimed at educating the general public on the risks and benefits of ionizing radiation and in producing transparent information on the use and applications of such radiation. Education and training in radiation protection can be accomplished for different purposes in different ways. The professional education and training has the main objective of obtaining recognition for work, generally under prescriptive requirements. The vocational education aims at gaining knowledge to obtain academic titles. Finally, social education and information is the way to increase the knowledge level of the society as a whole. Each country should analyse the education and training needs for each one of the existing modalities and take actions to satisfy such needs. This presentation will cover the education and training needs on radiation protection, and how to fulfil such needs, in different fields of activities, including regulation; power applications; medical, research and industrial users; in the management of radioactive waste; in dismantling of installations and remediation of contaminated sites, and in natural radiation and protection of the environment, as well as on social education and communication. In recent times two international events of a large significance for education and training have taken place: The International Conference on National Infrastructures for Radiation Safety: Towards Effective and Sustainable Systems (Rabat, Morocco 1-5 September 2003) and The II International Conference on Radiation Protection Training: Future Strategies (Madrid, 17-19 September 2003). The main findings and recommendations produced in these two events will also be included.

2. EDUCATION AND TRAINING NEEDS AND REQUIREMENTS As said in the Introduction, education and training in radiation protection can have different objectives and can be obtained in different ways. The objectives can be divided into three major categories: professional, vocational and social. Professional education and training is pursued by those individuals searching for working positions in licensed or registered practices and activities requiring recognized regulatory positions, such the qualified experts. In general the education and training programmes are well defined in regulatory documents and such individuals need to prove their levels of education and training. Licensees or registrants through in-house training programmes or through service companies generally deliver professional education and training. In occasion's university departments, research institutions and other learning establishments offer ad hoc courses to cover at least part of such education and training. In some countries professional societies are also very active in this field.

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Education and training of radiation protection experts is well established and defined in the IAEA Basic Safety Standards. The IAEA has also developed appropriate training material and has conducted pilot courses covering a large range of applications. Nevertheless, these recommendations could be interpreted in different ways, likewise the supporting training material used in different countries has not reached and appropriate level of harmonization. The qualified expert on radiation protection is well defined in the 96/29 Euratom Directive, as well as its level of education and training. Nevertheless the details of such training and, most importantly, the accreditation system is left to the individual member countries, which have not yet reached a consensus on that important subject, neither agreements have been reached, nor even fully discussed on the mutual recognition of such experts. Those individuals interested in gaining knowledge and obtaining academic degrees search for vocational education and training. They may or not end up working as professionals in radiation protection; in the first case they will have an advantage in obtaining the required recognition. Vocational education and training is offered in university' departments, vocational schools and other recognized educational organizations, through under-graduated and graduated courses, as well as high-level doctoral courses. University chairs and departments in national or private institutions can provide a wide variety of education and information activities, from high level doctoral courses to customized information courses in accordance with given syllabi to professionals at different levels, from industry executives to fire brigades. In fact, radiation protection has been part of the curricula in the Catalonian and Madrid Polytechnic Universities since the early sixties, valid texts and other teaching materials have also been published. Social education and communication is a basic human right that must be properly fulfilled. The present social phobia to radiation, irrational in many respects, makes social education and communication an urgent issue; it includes many peculiarities and involves a set of abilities difficult to find together in single individuals and organizations. Communicating facts to the public requires knowledge, training and expertise. Those experts on communications are generally no knowledgeable enough in science and technology; on the other side, good scientists are rarely experts in communication. Many professional societies and organizations, such as the Spanish Society on Radiation Protection, have established fora and other activities to inform the public. Even the IAEA has produced a handbook on how to communicate with the public. So far, in most cases, these activities have not produced significant results and the phobia to certain uses of radiation, mainly nuclear power, has not abated. This human dimension of the radiation protection specialist should not be forgotten. The creation of Codes of Ethics in many professional societies, including IRPA, is a step forward in gaining the confidence of the public. Professional education and training may by pursue by thousands of individuals in a given country at different levels. Statistics are difficult to produce and compare. In Spain, for example, up to 76 thousand professionally exposed individuals are registered. In a worldwide basis a few million persons will require some radiation protection education and training. As a consequence, international organizations, such as the IAEA are recommending that countries should be prepared to provide such services. Likewise, vocational education and training, and a well-designed programme on social education and information must also cover many individuals. International and supranational organizations are also recommending to member countries that the necessary infrastructures be created to cope with such needs and demands.

3. EDUCATION AND TRAINING NEEDS AND DEEDS IN REGULATORY ACTIVITIES Regulatory education and training is actually needed to create experts in radiation protection to serve both the regulatory organizations and their counterparts, that is the responsible licensees and registrants. The IAEA

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guide RS-G-1.4 "Building Competence in Radiation Protection and the Safe Use of Radiation Sources" clearly indicates the responsibilities of the different actors. Governments and regulatory authorities are the key players in introducing professional education and training on radiation protection in the respective countries, but such authorities themselves need to be highly competent on the matter. The three major responsibilities of regulatory organizations are closely related to: Drafting regulations, verifying compliance with such regulations and exercising enforcement to prevent and correct deviations from the rules. Therefore, the education and training of persons performing such activities goes beyond the technical knowledge and enter into legislation and judgement. The competence of the regulatory personnel on radiation protection has been termed by the International Nuclear Safety Advisory Group, INSAG, in a soon to be published report, as one of the main attributes for independence of regulatory decisions. Regulatory education and training demands high level and well-coordinated educational activities. Writing legislation, requirements, guides, instructions and procedures demands deep knowledge of the scientific and technical aspects supporting the subject matter, a long accumulated experience and some legal skills. Moreover, such requirements need to be wide in scope to cover from complicated technical operations to simple activities and from elementary protection measures to complex emergency situations. Verifying compliance with regulations in analysing justifications in license applications and in performing inspections demands a deep knowledge of the activity to be licensed and on the applicable rules and standards. Inspecting installations or documentary information requires a deep knowledge of the installations proper and on what to look for when reviewing documentary evidences. Enforcement is a very delicate subject, as it normally includes subjective interpretation on how to grade the offences committed. The ethical need of being just in the interpretation requires a good understanding of the rules and the technicalities involved in the case. Within the regulated organizations about the same type of knowledge should be required. Radiation protection aspects have to be incorporated into any application for a license in full compliance with the applicable regulations. Verification of compliance — both evaluation and inspection — is generally contained in written documents, which are presented to the responsible operating organization before the findings are made official. It is for the benefit of the responsible operator to have sufficient knowledge to debate about the correctness of such findings. The same comments apply also to any enforcement activity. High-level educational institutions may provide for such education but not in a coordinated manner. Nuclear law, nuclear physics and nuclear technology, basic and applied radiation protection for a multitude of applications can be taught in the universities at different levels. The coordination of such knowledge with that of the installation specifics and procedures has to be managed by the regulatory institution itself. The Nuclear Safety Council of Spain, for instance, has in place a substantial internal training programme for its own personnel and sustains a number of scholarships for young graduates who receive on the job training on some radiation protection matters. The Council also maintains an Expert Group to analyze the enforcement activities.

4. EDUCATION AND TRAINING NEEDS AND DEEDS IN OPERATING INSTALLATIONS The education and training of operating personnel is well considered in the IAEA Basic Safety Standards 115. Of particular importance is the introduction of the terms qualified expert and radiation protection officer, which have also been introduced in 96/29Euratom Directive, although with slightly different definitions, and therefore adopted in the national legislation of the member countries. The figure of the qualified expert is receiving a great deal of attention within the European Union. As required in the definition, those individuals have to be technically competent and be designated as such.

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The Union is looking for the minimum requirements for technical competence and the formal designation process for that to be accepted in all countries across the Union. The survey performed clearly indicates that there is a large diversity of requirements and recognitions. In the case of Spain, the figure was formally introduced in Decree 2869/72, enacted in 1972, and it has been honoured in the recent Royal Decree 783/2001. The Nuclear Safety Council has the power to include in the operating license whether or not a given installation should have a Radiation Protection Service of its own or count for that purpose on an external Technical Unit for Radiation Protection. In both cases, the head of the Service, or that of the Unit, is considered as the qualified expert, who has to be formally recognized by the Council under a proposal for the responsible owner/operator of the installation. The Council, in 1986, published a Safety Guide 7.2 establishing the minimum education and training requirements for obtaining the needed recognition. But education and training needs in installations where practices are conducted is not limited to the qualified expert, it also includes other personnel related to the installation and also to outsiders working temporarily in the installations. The degree of education and training depends upon the risk associated to the practice.

4.1. Education and Training in Nuclear Power Plants, Fuel Cycle Installations and Industry Radiation protection activities in nuclear power plants are of a large variety, going from performing radiation surveys to planning for emergency interventions. In most cases each power plant will have a qualified expert and several radiation protection officers and practitioners. In the case of Spain, such plants will require a Radiation Protection Service as part of the operation team. One typical characteristic of the radiation protection activities in operating nuclear power plants is the preventive nature of such activities and the dependence from the specificities of the given plant. All this makes the ALARA principle to be heavily applied in operating nuclear power plants and applicable in the corresponding degrees to all types of operating personnel. Radiation protection education and training in Spanish nuclear power plants is mainly performed inhouse, in accordance with the specific regulatory requirements, but also attending the needs of the plant itself. The Spanish operating nuclear power plants have developed a common standard on plant personnel education and training, which has been accepted by the Nuclear Safety Council. This standard covers all types of operating personnel. In general, following such standard, each power plant has an in-house service that provides such training. The power plant management may contract with external organizations, generally reactor suppliers and service companies, to deliver such training, but always within the umbrella of the inhouse training service. Deregulation of the electricity market has fostered the economical aspects of reactor operation, that, together with the lack of short and medium term perspectives in the nuclear sector, are causing a loss of expertise and so it has created the risk of loosing the know-how acquired through many years of experience on radiation protection. Therefore there is the need for urgent action. The use of radiation sources in the industry may be confronted with a similar problem. Radiation protection activities in fuel cycle installations have their own specificities. Activities in the first part of the cycle mainly include natural and enriched uranium. The use of MOX fuel introduces plutonium into the system. Radiation protection in reprocessing plants includes added difficulties. The experience in Spain is limited to the first kind and the licensee is a national company covering mining, milling, conversion and fuel manufacturing and transport. In any case, requirements and how to comply with them are generally well established.

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The education and training in the safe use of radiation sources for industrial purposes, mainly radiography, is regulated in most countries. Nevertheless, the mobility of such sources and the economic incentives behind their use produce, in general, the highest doses to personnel. This is of concern in many countries and actions are been taken to increase the safety of such operations and the radiation protection of the workers.

4.2. Education and Training in the Medical Field Specific radiation protection education and training needs and deeds in the medical field are well covered in most countries by present standards. In Spain, Royal Decree 1132/1990 requires that appropriate radiation protection education and training is needed for any responsible person using ionizing radiation in medicine. Later on, to assure compliance with 97/43/ Euratom Directive, Royal Decree 815/2001 further establishes that radiation protection should be included in the teaching curricula and practices in University Faculties and Schools of Medicine. But harmonization is far from been achieved. This seems to be also the case in other countries. The Spanish State Faculties for Medicine and Dentistry have been working in the development of a common education curricula, either compulsory or optional, to avoid the present differences and to reach an acceptable level of harmonization. The harmonization process should continue until it reaches the appropriate level, taken into account the peculiarities of each institution. In all cases, it is recommended that such training and education should be provided in close cooperation with the radiation protection services in the attached hospitals. More recently, a group of high level professionals from several universities, radiation protection officers and representatives from research centres and the Nuclear Safety Council have proposed a basic radiation protection curricula for the Faculties of Medicine and Dentistry and other Medical Schools in the country. This course, with duration from 20 to 40 hours, is based on the recommendations coming from the European Union in publication Radiation Protection 116. A pilot course has already been conducted at the Faculty of Medicine in the Madrid Complutense University. To contribute and help on the harmonisation process, the exchange of information among worldwide professionals and regulatory bodies should be reinforced. As a consequence, in the Rabat and Madrid International Conferences, it has already been proposed to create a network to circulate information. For the moment, this network could be simply based on a list of electronic mail addresses of all concerned persons and will allow the circulation of information of common interest, on a voluntary basis.

4.3. Education and Training in Radioactive Waste Management Specific education and training is needed for the correct management of radioactive waste. The handling of low and intermediate level radioactive waste has been covered by several IAEA standards, but the final disposal of highly radioactive long life waste is still under consideration. Education and training on radiation protection for such activities has not been specifically considered, although general education and training in radiation protection may suffice for some given cases. Waste is produced and treated in nuclear power plants, fuel cycle installations, medical applications, research institutions and industry. Low and intermediate waste is generally solidified, conditioned and transported to and stored in near surface installations. Highly radioactive waste is recycled or stored in preparation for the final disposal. Of special concern are the long-term storage and the final disposal of irradiated nuclear fuel. The first steps of the process, up to transportation to the disposal facility, are generally under the responsibility of the waste producer; transport and store are mainly under the responsibility of dedicated

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national institutions or waste operators. In all these operations the needs for experts on radiation protection is growing due to increasing number of practices using radiation sources and producing waste, but also because of the accumulation of waste due to the absence of disposal facilities in many countries and the lack of appropriate or incomplete legislation on the matter. It is believed that such demands for education and training have not been properly analyzed in many countries. In Spain the national Radioactive Waste Disposal Agency, Enresa, is sponsoring a certain number of training courses in several Spanish universities on how to manage radioactive waste in a safe manner and within the radiation protection standards. One of the most dedicated courses is the post grade course offered by the School of Industrial Engineering, Madrid Polytechnic University, in cooperation with the Institute of Energy Studies from Ciemat. In that 50 hours course, which is now in its XV edition, the scientific background, the technical aspects and the legal requirements for the safe handling, transport and disposal of all types of waste are presented and discussed. One point of observation in this type of activities is related to the safety and security of the disposal facilities. At the end, such facilities are left in place, but it has to be demonstrated that they will not pose any radiological risk to future generations, so creating a point of direct contact with society and ethical conduct. The final disposal of highly radioactive waste is a major endeavour requiring especial completely developed and validated techniques. It is believed that education and training for professionals on the matter and clear information to the society are highly in need.

4.4. Education and Training in Dismantling and Remediation Specific education and training needs in dismantling and remediation operations have not been formally established. Dismantling of old nuclear power plants has already started and it will be increasing as old plants are put out of service for any reason. When a nuclear power plant, or any other fuel cycle installation, is dismantled, the early concerns with nuclear safety diminish, but there is a relative increase in the importance of radiation protection. Remediation of old nuclear research centres is becoming an increasing activity. This is due to the obsolescence of some of the old establishments or to the non-permissible contamination levels in some of these establishments when they operated to less strict requirements or malpractices. A recent standard on remediation has been approved by the IAEA, but not specific requirements are formulated on the education and training of those professionals who will be responsible for such operations. There is an increasing amount of experience on dismantling nuclear power plants. From the radiation protection side there is a continuous change in the risk level. The radiation sources diminish as a consequence, but some of the protection and mitigation systems of the old installation disappear as they are removed; the amounts and types of waste become enormous and they should be classified for a better management; finally the dismantling workers, when they belong to the old operating staff, are not used to such operations, but if they come from outside they will not know the peculiarities and details of the installation to be dismantled. In Spain, the dismantling, up to level 2, of the Vandellos I nuclear power plant has produced a valuable experience on the radiological protection aspects of such operations. The plant radiation protection service had to be increased up to more than 40 individuals and reorganized to cope with the increase in personal dosimetry, including internal dosimetry through the analysis of biological samples; the radiological control of the dismantling operations, which was performed within the ALARA principle, and the radiological control of the many materials to determine the exemption levels or the final destination of such materials. The IAEA safety standard on "Remediation of Areas Contaminated by Past Activities and Accidents" is the first of its kind on the subject. Remediation is considered as an intervention "to reduce prolonged exposure, to avert prolonged potential exposure, or to reduce the likelihood of the occurrence of such exposure due to contamination".

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In this sense, the document treats at length radiation protection in such remediation situations. Spain has accumulated some experience in such interventions; mainly through remediation activities in abandoned uranium mining and milling operations and in the intervention that took place in a large area contaminated with plutonium as a consequence of the Palomares air accident. At present there is a large intervention plan to clean up some contaminated parts in the premises of Ciemat as a consequence of activities taken place in the old Nuclear Energy Board.

4.5. Education and Training on Natural Radioactivity and the Protection of Non-human Species The fact that electro magnetic energy and that associated to nuclear particles is the most natural form of energy introduces a new dimension on education and training on radiation protection. Natural radiation should be recognized and how such radiation has intervened, and it is still intervening, in human evolution. These facts should be included into any educational activity regarding radiation protection. Apart from that, the complete and detailed knowledge of the natural radiation background will serve to understand radiation protection and to make comparisons with artificial sources. The presence of radon in dwellings has been a serious concern in many countries since the early seventies. Radon measurements have been performed and remedial actions taken. From the scientific point of view the understanding of radon risk has some difficulties, moreover reliable mitigation measures take some advanced technical developments. From the social point of view the radon presence affects everybody and it is present in air and water within our living space. Therefore education and training on the radon risks is a necessary endeavour. In the recent Madrid II International Conference on radiation protection training, the Swedish Radiation Protection Authority presented a series of radon courses they have been maintaining in the country and attended by a large variety of health professionals. The question of naturally occurring radioactive materials and its potentiality to produce occupational doses of concern has been recently recognized. In accordance with 96/29 Euratom Directive, the question has been formally introduced in the corresponding national regulations, nevertheless very few training activities in this matter seem to be offered so far. In recognition of the hazards associated to natural radiation and naturally occurring radioactive materials, it is to be recommended that such aspects be also treated in training courses as appropriate. The International Commission on Radiation Protection in the year 2000 created a working group to study the protection of the environment against the harmful effects of ionizing radiation. A report has been produced and accepted by the Commission. As a follow up of such activities, the Commission has recently created a new working group to define reference animals and plants and so creating the scientific bases for a systematic approach to the protection of non-human species. All these activities will create certain needs for education and training in protecting the environment against ionizing radiation.

5. THE RABAT AND MADRID INTERNATIONAL CONFERENCES The International Conference on National Infrastructures for Radiation Safety: Towards Effective and Sustainable Systems, held in Rabat 1-5 September 2003, was organized by the IAEA with the cooperation of WHO, ILO, EU and OECD/NEA. It included two topical sessions and a round table discussion on education and training. Topical session 5: Sustainable Education and Training. Developing Skills (National Systems and Regional Solutions), included a dozen presentations from developed and developing countries and international organizations. Topical session 6: Needs for Education and Training at the International Level (Including IAEA Programmes Assisting in Establishing Adequate Infrastructures) included eight presentations from a variety of countries, the European

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Union and the IAEA itself. The conference was very well attended, as non IAEA Member States were invited and received support. As it is common in the IAEA conferences, the final proceedings will be published, together with the conclusions and recommendations proposed by the chairs of the different sessions and round tables, from which specific actions may later be taken. The needs and requirements for education and training on radioprotection were amply recognized worldwide and in the individual countries. Although the mood of the Conference was optimistic, several proposals were formulated to improve the situation in the less developed countries and to increase harmonization in the developed countries. The activities of the IAEA on education and training were also widely recognized; such activities have materialized in guides and technical documents as well as on advanced teaching material. The representatives of the Agency clearly indicated the determination of the Agency on being more pro-active in education and training and they introduced the concept of training the trainers to make education wider and more effective. As radiation protection education and training covers a wide range of subjects and educational levels, the problem of the education and training language was brought about; it was recognized that the training, to be effective, has to be conducted in the mother tongue of the individuals. In this context, the Conference strongly recommended the IAEA to translate all relevant education and training documents, as well as related standards, to the official languages of the Agency. The II International Conference on Radiation Protection Training: Future Strategies, held in Madrid, 17 — 19 September 2003, was organized by Ciemat, the Spanish National Centre for Research on Energy, the Environment and Technology, under the auspices of the IAEA and the European Union and with the cooperation of several Spanish high level organizations and concerned professional societies. An official account of the Conference is being produced. The I International Conference on Radiation Protection Training was celebrated in Saclay (France) under the slogan "Radiation Protection: What are the future training needs?". This first conference constituted a forum for discussion, in a general framework, on the problems associated with radiation protection training. The principal path at that time was the implementation of the IAEA Basic Safety Standards. During that conference exhaustive analyses were undertaken on education and training in different countries as well as on the establishment of responsibilities and competences related to the risks associated to the different practices. The objective of this second conference was to analyse results and to discuss future strategies, mainly within the European framework, but with a significant representation from Ibero American countries. It may be considered as a continuation of the one celebrated in Saclay. In this sense, it is important to take account of several new entries: 1) the coming into effect of the VI Framework Euratom Research Programme in which all aspects related to education are reinforced, 2) the European Union has undertaken work on the situation of qualified experts on radiation protection in its different member countries, 3) advances have taken place in the incorporation of new teaching technologies. All this implies to optimise efforts, work as a group and strengthen national and supranational educational networks. A session was specifically dedicated to future activities. Participants from international organisations discussed their views on the matter, including the European training platform and activities based on electronic distant learning. Specific presentations included the activities of the working party on education and training of the expert group on article 31 of the EURATOM treaty, as well as the IAEA and UE radiation protection training programmes. The vision and role of IRPA in the field of education and training of radiation protection professionals was also discussed. All speakers transmitted an optimistic impression on the future of education and training on radiation protection.

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6. CONCLUSIONS 1 st . There is a general agreement on the need for increasing the level of education of our societies on the risks and benefits of using ionising radiation, even starting at the secondary schools. There is equally a general agreement that the professional practitioners and the experts controlling such uses acquire an acceptable training in radiation protection principles and practices. There is also a need for information on the basic aspects of radiation protection to related managers and ancillary workers. 2nd. There is a general appreciation for the requirements established in the IAEA Basic Safety Standards and the corresponding Safety Guides and Technical Documents, as well as for the Euratom Directives, dealing with training qualified experts and radiation protection officers. Nevertheless, there is a common feeling that in some countries these basic documents have not been fully translated into a complete set of regulatory requirements. Moreover, there is also the appreciation that education and training for some basic practices, such as dismantling, remediation and radioactive waste management and disposal, are not well covered by requirements. 3rd. It is widely recognized that radiation protection is a multidisciplinary subject, with its basic roots in nuclear and modern physics, as well as on biology and physiology, among other sciences. Moreover, it includes modern technologies such as shielding, filtration, robotics and others. At the same time, it is also recognized that a large number of stakeholders need to know about radiation protection principles and practices, including regulators, research personnel, all type of users and practitioners, designers, operators, ancillary service personnel and civil protection officers, inter alia. 5th. A recent survey on the status of radiation protection experts in the Member States and applicant countries of the EU showed a broad range of education and training systems; it was concluded that international agreement criteria and qualifications of radiation protection experts, in accordance with the definition of the qualified expert in the directive 96/29/EURATOM, is a pre-requisite for harmonization of education, training and mutual recognition. 6 th . There is also the sentiment that the IAEA should maintain its proactive attitude in radiation protection training and help to create interconnected centres of training excellence and good quality training material in the official languages of the Agency.

Current Trends in Radiation Protection H. Metivier, L. Arranz E. Gallego and A. Sugier (eds.)

Realistic Retrospective Dose Assessment Jane Simmonds1 National Radiological Protection Board, Chilton, Didcot, Oxfordshire, OX 11 ORQ, United Kingdom

Abstract. Retrospective dose assessments may be carried out for a number of purposes such as demonstrating compliance with dose limits or investigating possible health implications of past events that led to releases of radioactive materials to the environment. The purpose of the assessment has a major impact on what is assessed and how the assessment is carried out. Any dose assessment requires information about the sources of radioactive material, the way in which they behave in the environment and hence how people will be exposed to the radiation before doses can be estimated. Such doses may also be used to estimate the risks of radiation induced health effects. For a dose assessment to be realistic then there needs to be good understanding of local conditions and the use of any measurements can improve realism. It is important to use the correct dosimetry for the particular assessment which depends on its purpose. It is also important to recognise the uncertainty and variability associated with any dose assessment.

1. INTRODUCTION Retrospective dose assessments are carried out for a number of different purposes. When planning such an assessment it is important to think carefully about what you are trying to achieve, particularly what radiation doses you are trying to estimate as this has a major bearing on how you carry out the assessment and what tools and data you use. This paper is concerned with estimating doses to people from releases of radionuclides to the environment and other factors would need to be taken into account if the aim was to estimate the effect on biota of such releases. One of the main purposes of retrospective dose assessments is to demonstrate compliance with the dose limit for members of the public for the normal operations of nuclear facilities. Here you are interested in the annual effective dose for external irradiation received in a year plus the internal irradiation from intake by inhalation and ingestion in a year. The dose will be assessed for the critical (or reference group) as representative of those people in the population who are most exposed, as the International Commission

1 E-mail: [email protected]

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on Radiological Protection (ICRP) has recommended that this is the dose that should be estimated for demonstrating compliance with the dose limit [I]. The purpose of the dose assessment could be to consider a pattern of individual or collective doses as a function of time, say over the operating lifetime of a nuclear facility. This might be to see the effects of reductions in discharges to the environment over time or to compare current discharges with what happened in the past. Such an assessment might consider critical group or 'average individuals' and could be based on effective doses or doses to particular organs. If collective doses are required then information is required to a greater spatial and temporal extent than for individual doses. Another possible purpose of a retrospective dose assessment is to look again at the radiological impact of past events such as the accidental release in the 1957 Windscale fire or the discharge of radioactive waste to the Techa River in the early 1950s. There are many possibilities for what doses should be estimated for such assessments and this is discussed further later in the paper. Another significant reason for carrying out a retrospective dose assessment is to investigate the possibility of radiation induced health effects in a particular population probably with a related epidemiological study. There is then a defined population group to be considered and it will be necessary to consider relevant organ or tissue doses allowing for intakes and exposures over a defined period. One of the difficulties in carrying out a dose assessment is how you take account of the variation in exposure with time. When a radionuclide is released to the environment it may continue to lead to the exposure of people for some time depending on its physical half-life and its behaviour in the environment. Also radionuclides taken into the body by ingestion or inhalation may continue to irradiate different organs and tissues for many years after intake. One approach is to take a standard time for integrating the exposure, say 30 years for environmental contamination [2] or to age 70 for dose coefficients for ingestion and inhalation [3]. However, this will not always be appropriate for retrospective dose assessments and the time dependence may need to be considered more explicitly.

1.1. Steps in a radiological assessment For any release of radioactive material into the environment the same basic approach is used to assess the radiological impact; this involves the following steps:

• Identify and quantify the source. The type and amount of each radionuclide being discharged is required together with the nature and location of the release. Where the chemical or physical form is likely to have a significant effect on doses this should also be determined. • Determine activity concentrations in environmental materials. The transfer of radionuclides in the environment is considered to predict concentrations of radionuclides in relevant materials, such as air, water and food. If available, measurements can also form an input to the assessment at this stage. • Determine the exposure pathways. People can be exposed to radiation in a number of. different ways depending on the chemical properties of the element concerned and the physical properties of the emitted radiation. • Identification of the exposed group. This may be the critical group, a representative individual or the population as a whole, if estimating collective doses. • Estimation of doses. Appropriate dosimetric models are needed to estimate radiation doses.

If required a final step would be to estimate the risks of radiation induced health effects.

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2. SOURCE TERMS It is important to determine what radionuclides have been released to different parts of the environment. To do a realistic dose assessment it is essential to have as much information as possible. For retrospective dose assessments it may be necessary to consider both routine, continuous discharges and any short term releases, including accidents and incidents. It may also be necessary to take account of any disposals of radioactive waste say by burial. The information required is: • Type and amount of the radionuclides released, e.g. 10 TBq of iodine-131. • Type of release e.g. vapours, particles, liquid. • Location of release e.g. atmospheric release from stack of height 80 m, river or coastal area to which liquid releases are being discharged. • Duration of release and timing of release. Often routine discharges are reported for groups of radionuclides with the same type of activity (e.g. total alpha or total beta activity). Assessments of doses can only be carried out on a radionuclide specific basis and so where groups of radionuclides have been reported either the discharges have to be split between the radionuclides known to be included in the group, or a 'representative' radionuclide has to be used. For example, it might be assumed that plutonium-239 is representative of total alpha activity and caesium-137 is representative of total beta activity. In order to perform a realistic assessment the assumptions should be as site-specific as possible based on the radionuclides known to be discharged from the site. In some cases the chemical form of the discharged radionuclide can have a significant effect on radiation doses, e.g. for tritium, carbon-14, sulphur-35 and information on chemical forms should be sought. Similarly physical form can have a bearing on the resulting radiation doses; for example, the particle size of releases to atmosphere can affect the subsequent doses from the discharges. Knowledge of the time variation of any discharges is also important for retrospective dose assessments. The purpose of the assessment will determine whether it is sufficient to have annual discharges or whether more detailed information is required, e.g. daily or monthly discharges. Short term discharges can either be considered independently or could be added to the annual routine discharge. However, short term discharges can have a significantly different impact than the equivalent discharge spread over a year [4] and a more realistic assessment would take them into account separately. For short term releases it can be particularly important to take account of seasonal effects as a release in summer may have a different effect than a release in winter.

3. ACTIVITY CONCENTRATIONS IN ENVIRONMENTAL MATERIALS It is obviously preferable, and usually more accurate, to base estimates of doses on measured dose rates or on measurements of radionuclide concentrations in environmental materials. However, in many circumstances this is not possible and mathematical models of radionuclide behaviour in the environment have to be used. The types of situations where models are usually required are where no measurement data are available or the available data are not sufficiently comprehensive and when a possible future practice that may release radionuclides into the environment is being evaluated. Also levels in environmental media may be below limits of detection. Furthermore, doses to populations (collective doses) invariably have to be calculated using mathematical models as the doses are often delivered over large temporal and spatial scales. Typically a retrospective dose assessment would use a combination of measurement and modelled data with either, the modelled data providing information where the measured data are at the limit of analytical detection, or the measured data being used to verify the modelled data. Measurement data can also be valuable for

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both prospective and retrospective dose assessments in determining the accuracy of the models for local conditions. However, it should be remembered that measurement data could include contributions from sources other than the site being considered, e.g. natural radionuclides, fallout from atmospheric weapons testing, the Chernobyl accident and other sites discharging radionuclides to the environment. A number of models are available to estimate radiation doses, e.g. see references [5, 6], including models provided by the IAEA [2]. However, such models are often designed for prospective dose assessments, e.g. to show that a proposed discharge will meet the appropriate dose criterion and they may not be suitable for retrospective dose assessments. Also care has to be taken in using the generic default parameter values provided with such models as they may not be appropriate for the situation of interest. It is important that any models used are robust and fit for purpose. Measures should have been taken to ensure that the models are valid. This means that the models should have been tested to ensure that they are behaving as intended and where possible should have been compared with measurement data to ensure that they are an adequate representation of reality. The International Atomic Energy Agency (IAEA) has run a number of programmes to validate models (VAMP, BIOMASS and currently EMRAS), which can be a source of information [7,8]. Some radionuclides due to their long radioactive half-lives and their behaviour in the environment, may become globally dispersed and act as long-term sources of exposure of large populations. This is commonly termed global circulation. The principal radionuclides in this regard are tritium, carbon-14, iodine-129 and krypton-85. Models for estimating collective doses from the global circulation of these radionuclides are available these range from the relatively simple approach adopted by UNSCEAR [9] to compartmental models used in Europe [5] and the USA [6].

4. EXPOSURE PATHWAYS Radioactive effluents may be released to either the atmospheric or the aquatic environment and models are required to describe the transfer of radionuclides through the relevant parts of the biosphere to people. Radionuclides discharged to the atmosphere are dispersed due to normal atmospheric mixing processes. Airborne radionuclides can give rise to exposure by two principal routes: external irradiation by photons and electrons emitted as a result of the radioactive decay process and internal irradiation following inhalation of radionuclides. During their transport downwind radionuclides may be deposited from the atmosphere by impaction with the underlying surface or due to rainfall. This transfer onto land surfaces may lead to further irradiation of people by three important routes: external irradiation from deposited activity; internal irradiation from inhalation of resuspended activity; internal irradiation from ingestion of contaminated food and inadvertent ingestion of soil. A list of exposure pathways for discharges of radionuclides to atmosphere is given in Table 1. The relative importance of these pathways depends on the radionuclide and the nature of the surface onto which the deposition occurs. For example, alpha emitters such as plutonium-239 do not give significant external irradiation and are relatively immobile in the environment so the most important exposure pathway for releases to atmosphere is internal irradiation following inhalation of radionuclides in the atmosphere. For noble gases such as krypton-85 the most important exposure pathway is external irradiation from activity in the atmosphere as they do not deposit on the ground and do not get appreciably absorbed into the body. Gamma emitting radionuclides such as caesium-137 with its daughter barium-137m, can be mobile in the environment and both external irradiation and internal irradiation following ingestion can be important; the relative importance of the different pathways depending on local conditions. The exposure pathways in Table 1 are based on information for northern temperate environments [4]; different exposure pathways may be important in other situations.

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Table 1. Exposure pathways for radionuclides released to atmosphere.

Inhalation Ingestion

External

Air Resuspended deposits Beef Cow liver Milk Sheep liver Sheep meat Grain Green vegetables Root vegetables Milk products Plume Deposited radionuclides

Liquid radioactive effluents may be discharged to freshwater (particularly rivers), estuaries or the marine environment. Radionuclides discharged to rivers are dispersed due to general water movements and sedimentation processes. The principal routes leading to the irradiation of people are: external irradiation from sediments; ingestion of foods derived from the river; drinking water taken from the river; water used for irrigation of crops and pasture. The local features of the environment, in particular tidal currents and the degree of sedimentation, initially determine the dispersion of radionuclides discharged into the marine environment. General water movements and sedimentation processes in the larger sea and ocean masses influence subsequent dispersion. There are again a number of pathways leading to the irradiation of people including: ingestion of marine foodstuffs; external irradiation from activity on beaches; inhalation of seaspray. Again the relative importance of the different exposure pathways depends on the radionuclide and the particular circumstances. For radionuclides such as plutonium-239 internal irradiation following ingestion or inhalation is more important than external irradiation. For radionuclides such as caesium-137 both external irradiation and internal irradiation following ingestion of marine or freshwater foodstuffs may be important. Radionuclides with a significant beta emission may give rise to contact doses to the skin through handling fishing nets or being on contaminated sediments. Table 2 gives some information on the important exposure pathways for liquid discharges to the freshwater or marine environments.

5. IDENTIFICATION OF THE EXPOSED GROUP The population of interest will depend on the purpose of the study. Possibilities include the critical group, typical individuals living in the locality of interest, a subset of the population for which the risks of radiation induced health effects are required and the population of the whole country, continent or even world for collective doses.

5.1. The critical group The critical group (sometimes referred to as a reference group) is intended to be representative of those people in the population who receive the highest doses. The mean dose to the critical group is compared with the dose limit and dose constraint for members of the public. People form part of the critical group due to where they live, where they spend their time or what they eat. When characterising the critical group an important point is that the chosen habits should be those that would be expected to apply on a continuing

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Table 2. Exposure pathways for radionuclides released to an aquatic environment

Inhalation

Ingestion

Inadvertent ingestion

External

Resuspended soil following deposition of radionuclides in seaspray Resuspended beach material Seaspray Drinking water Freshwater fish Marine Fish Crustaceans Molluscs Seaweed Terrestrial foodstuffs2: Beef, Cow liver, Milk, Sheep liver Sheep meat, Grain, Green vegetables Root vegetables Soil following deposition of radionuclides in seaspray Beach material Land following deposition of radionuclides in seaspray Beaches Fishing gear

'Following deposition of radionuclides in seaspray or irrigation water

basis, rather than those that depend on, say, one or two people with particularly extreme habits that might stop if the individuals concerned moved on. ICRP gives some guidance on the selection of critical groups in Publication 43 [10]. In summary, in cases where assessed doses are likely to approach the relevant dose criterion (dose constraint or dose limit), the difference between the highest and lowest member of the critical group, in terms of the important habits, should be no more than a factor of three. In other cases, where the assessed doses are likely to be much less than the dose criterion, a wider range of up to ten can be taken. The group should be small enough to have relatively similar habits and will usually be up to a few tens of persons. It is not appropriate to use extreme habits. However, where the normal behaviour of one or two individuals results in them being significantly more highly exposed than any other individuals, then the critical group can be deemed to comprise of only those individuals. In specifying critical groups two broad approaches are possible. The first involves carrying out surveys of the local population to determine their habits, where they live etc. From these surveys the people who are receiving or who received the highest doses can be identified. The second approach involves using more generalised data to establish generic groups of people who are likely to receive the highest doses. The two approaches can be used separately or a combination of both used for example local surveys of consumption of seafood used in conjunction with consumption rates of terrestrial food based on more generic data. Detailed site-specific data on critical group habits will give a more realistic assessment but it is costly both in monetary terms and in time to obtain such data. Therefore, when assessed doses are low compared to the criteria of interest it is often adequate to use information taken from country specific or regional information on, say, food consumption. Some information has been published in connection with past radiological assessments, e.g., the European Project MARINA II study [11], although of course information from one geographical region should be interpreted with caution in another region. Representative habits data are available [2,4-6,12] but should be used with caution for particular studies.

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5.2. Age groups It is also necessary to consider the ages of the exposed population. If assessing critical group doses it may be important to assess doses to different age groups to see which are the most restrictive. ICRP has published dose coefficients for the intake of radionuclides by ingestion and inhalation for six age groups [3] and has also published dose coefficients for the embryo and fetus from intakes by the mother [13]. In practice it is not necessary to assess dose to all these age groups but it is sufficient to just estimate doses to 1 year olds, 10 year olds and adults. The exposure of the fetus may also need to be considered for some radionuclides where the exposure of the fetus will be greater than the exposure of the mother [14] (tritium, carbon-14, phosphorus-32, phosphorus-33, sulphur-35, calcium-45, calcium-47, selenium-75, strontium-89, strontium90, iodine-131, radium-224, radium-226). However, it should not automatically be assumed that a critical group contains pregnant women; there should be a reasonable basis for such an assumption. For some retrospective dose assessments it might be necessary to assess radiation doses and risks for a cohort of people, say those born between 1950 and 2000 (e.g. see reference [15]). In this case the assessment is complicated by the need to take account of the exposure of individuals from the time they are a fetus until they reach adulthood. When assessing collective doses it is usually sufficient to consider adults, e.g. in estimating collective doses from ingestion and inhalation of radionuclides the whole population is assumed to have the same adult intakes and metabolism. Incorporating age related factors is likely to have little effect on the resulting collective dose due to the large proportion of the population that are adults [5].

6. ESTIMATION OF RADIATION DOSES Various dosimetric, habit and other information are required to estimate radiation doses given the estimated or measured concentrations of radionuclides in environmental media and foods. The concentrations in air, water and food are combined with intake rates to obtain an estimate of the total intake of radionuclides in a period. This total intake is then multiplied by the appropriate dose coefficient to estimate the dose from inhalation or ingestion. Similarly, the concentrations of radionuclides in shoreline sediments and surface soils are used with appropriate dose coefficients to estimate the dose from external irradiation, taking account where appropriate of the amount of time an individual is exposed and the shielding effects of buildings during the time spent indoors. The dose from immersion in a cloud containing radionuclides may be estimated by multiplying the concentration in air by the appropriate external dose coefficient. The total dose is then the sum of the doses from all radionuclides and exposure pathways.

6.1. The use of effective dose Effective dose is an extremely useful quantity that was introduced by ICRP some time ago [1]. Through the use of tissue weighting factors it enables the effects of different radionuclides to be combined and as it is based on equivalent dose it takes into account the relative biological effectiveness of different types of radiation compared to each other. However, ICRP have stated that 'Both equivalent dose and effective dose are quantities intended for use in radiological protection, including the assessment of risks in general terms. They provide a basis for estimating the probability of stochastic effects only for absorbed doses well below thresholds for deterministic effects.' [1] Effective dose is based on a population averaged risk factor and is an average for male and female exposure. Whether it is appropriate to use it in a retrospective dose assessment depends on the purpose of the study and the levels of dose assessed. Many retrospective dose assessments are carried out to demonstrate compliance with the dose limit for members of the public. As this limit is based on effective dose then it is entirely appropriate to use

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effective dose for this purpose. In some limited situations you will also need to consider doses to the lens of the eye and skin, where separate limits are given [1]. Effective dose can also be useful for looking at the doses from discharges as a function of time, provided that the estimated doses are well below thresholds for deterministic effects. It can also form part of a re-investigation of past events but here needs to be used with more caution depending on the level of the estimated doses and also which radionuclides are involved. If considering a release with significant quantities of iodine radioisotopes for example, it is important to consider doses to the thyroid. It is generally not appropriate to use effective dose when assessing the risks of radiation induced health effects in particular populations. Here the doses to the relevant organs should be considered, for example the red bone marrow when considering radiation induced leukaemia [15]. It may also be appropriate to estimate absorbed doses to body tissues and consider different types of radiation separately rather than use equivalent dose [15]. This gives a greater degree of flexibility in carrying out such studies and enables different values for the relative biological effectiveness to be investigated. The International Commission on Radiological Protection has published dose coefficients for a wide range of radionuclides for different age groups [3,16]. The compilation on the CD-ROM [16] gives data for 6 age groups, members of the public and workers for a variety of tissues and integration times after intake. These data will be valuable for many retrospective dose assessments. However, additional information may be required when estimating radiation induced health effects, particularly if following a cohort of the population over a long time period [15].

7. ISSUES IN ACHIEVING REALISTIC ASSESSMENTS A realistic assessment must reflect the transfer of radionuclides through the environment to man. Discrepancies can occur at many stages for example, if the model for the transfer of radionuclides in the environment is not a true representation of reality7, or measurement data are not an accurate reflection of the real environment. Significant exposure pathways might have been omitted and the assumptions relating to the habit data for the population of interest might not be representative. The realism of an assessment can be improved through a good understanding of the local conditions in the area where doses are being assessed. In any assessment it is a good idea to investigate possible discrepancies but the extent to which this should be done will probably depend on the level of radiation exposure found. It is unlikely to be worth spending a lot of time and money on site specific surveys to refine an assessment that estimates individual doses of a few micro Sievert.

7.1. Variability and uncertainty Assessments of doses necessarily entail a series of assumptions about the behaviour of the population group of interest and about the transfer of radionuclides in the environment. The estimated mean dose to the group is therefore within a distribution of possible doses. There are two aspects to this distribution referred to as the uncertainty and the variability. The uncertainty reflects the amount of knowledge about the system being investigated and relates to how accurately the dose can be estimated; for example, how well are all of the parameter values in the calculation of doses known? The variability refers to the actual differences that occur both in transfer in different environments and between individuals within a group; for example, differences in how much of a particular food is eaten or where individuals spend their time. This topic is discussed in more detail in [17] and a number of studies have been carried out to investigate uncertainty and variability (e.g. [18,19]). In addition this subject has been examined in France by the Nord-Cotentin Radioecology Group [20].

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When performing an uncertainty/variability analysis one of the important first steps is to estimate the dose using 'best estimates' of the parameter values. This will indicate whether it is worthwhile proceeding with the work e.g. if doses are of order of 10 Sv y-1 which is considered a trivial dose [21] then it may not be effective continuing with the work. The 'best estimate' dose is also a useful benchmark against which to compare any results from the uncertainty/variability analysis e.g. if 'best estimate' dose is 200 Sv y-l but the uncertainty/variability analysis indicates a distribution of doses from 200 Sv y-1 to 600 Sv y-1 with the mean being 400 Sv y-1 then it would advisable to re-examine the distribution associated with the input parameters. Another useful exercise is to identify the input parameters which have the greatest influence on the doses, through performing a sensitivity analysis. For this various parameters and assumptions are varied and the effects of these changes on the estimated doses are studied.

8. SUMMARY The way in which a retrospective dose assessment is carried out depends on the purpose of the assessment. This effects what radiation doses are estimated, the methods and data used and the type of results obtained. In order to perform a realistic assessment then as much site-specific information as possible should be obtained. The type and amount of radionuclides being released to the environment together with the type and location of the release must be determined. A range of exposure pathways needs to be considered with the main focus of the assessment being on the pathways giving the greatest radiation doses. The most realistic method for assessing dose is by the extensive monitoring of the main exposure pathways. However, this is time-consuming, costly and levels in the environment may be below the analytical limits of detection. Typically a retrospective dose assessment will involve a combination of measurement and modelled data. The population group considered will depend on the purpose of the assessment. Critical groups are intended to be representative of individuals likely to receive the highest doses. The group should be small enough to relatively similar habits and will usually be up to a few tens of individuals. Critical groups will need to have a combination of habits, both high and average, based on local knowledge and plausible assumptions. These combinations of habits will need to be realistic and not lead to implausible situations, for example someone having an excessive intake of calories. Where different age groups need to be considered in an assessment then it is often sufficient to consider 3 age groups (1 and 10 year olds and adults). Fetal doses may also need to be estimated for some radionuclides, noticeably for elements such as phosphorus and calcium which are used by the fetus for skeletal growth.

REFERENCES [1]

International Commission on Radiological Protection, 1990 Recommendations of the International Commission on Radiological Protection. ICRP publication 60. Ann ICRP 21 (1 -3) (1991).

[2]

International Atomic Energy Agency, Generic models for use in assessing the impact of discharges of radioactive substances to the environment. Safety Reports Series No. 19, IAEA, Vienna, Austria (2001).

[3] International Commission on Radiological Protection, Age-dependent Doses to Members of the Public from Intake of Radionuclides: Part 5 Compilation of Ingestion and Inhalation Dose Coefficients. ICRP Publication 72. Ann ICRP, 26 (1). (1996). [4] Jones K, Walsh C, Bexon A, Simmonds J, Jones A, Harvey MP, Artmann A and Martens M. Guidance on the realistic assessment of doses to members of the public from nuclear installations operating under normal conditions. Luxembourg, European Commission, (2002).

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[5]

Simmonds, J R, Lawson, G and Mayall, A Methodology for assessing the radiological consequences of routine releases of radionuclides to the environment. Radiation Protection 72, EUR 15760, Luxembourg EC. (1995).

[6]

National Council on Radiation Protection and Measurements, Screening models for releases of radionuclides to atmosphere, surface water and ground. Rep. 123 II, NCRP, Bethsada, MD (1996).

[7]

International Atomic Energy Agency, Intercomparison and biokinetic model validation of radionuclide intake assessment. Report of a co-ordinated research project 1996-1998, IAEA-TECDOC1071, (1999). Linsley G., The international biosphere modelling and assessment programme (BIOMASS): an overview. In Proceedings from the International Conference on radioactivity in the environment, Monaco, 2002, edited by P Borretzen, T Jolle and P Strand.

[8]

[9]

United Nations Scientific Committee on the Effects of Atomic Radiation, UNSCEAR 2000 Report to the General Assembly, with scientific annexes, United Nations, New York (2000).

[10]

International Commission on Radiological Protection. Principles of monitoring for the radiation protection of the population. ICRP Publication 43. Ann ICRP 5 (1) (1985).

[11]

Simmonds JR, Bexon AP, Lepicard S, Jones AL, Harvey MP, Sihra K and Neilsen SP. Annex D: Radiological impact on EU member states of radioactivity in northern European waters. In MARINA II. Update on the MARINA Project on Radiological Exposure of the European Community from Radioactivity in North European Marine Waters. Luxembourg, European Commission, Radiation Protection 132. (2002)

[12]

Smith K R and Jones A L., Generalised habit data for radiological assessments. National Radiological Protection Board, Chilton, NRPB-W41 (2003).

[13]

International Commission on Radiological Protection. Doses to the Embryo and Fetus from Intakes of Radionuclides by the Mother. ICRP Publication 88. Ann ICRP, 31 (1-3), (2001)

[14]

National Radiological Protection Board. Guidance on the application of dose coefficients for the embryo and fetus from intakes of radionuclides by the mother. Docs of the NRPB (to be published).

[15]

Simmonds J R, Robinson C A, Phipps A W, Muirhead C R and Fry F A, Risks of leukaemia and other cancers from all sources of ionising radiation exposure. National Radiological Protection Board, Chilton, NRPB-R276 (1995).

[16]

International Commission on Radiological Protection. The ICRP Database of Dose Coefficients: Workers and Members of the Public. Version 2.01. Distributed by Elsevier Science Ltd, Oxford. ISBN number: 0-08-043876-8 (2001).

[17]

International Atomic Energy Agency, Evaluating the reliability of predictions made using environmental transfer models. IAEA Safety Series 100, IAEA Vienna. (1989).

[18]

Jones, J A, Ehrhardt, J, Goossens, L H J, Brown, J, Cooke, R M, Fischer, F, Hasemann, I and Kraan, B C P, Probabilistic accident consequence uncertainty assessment using COSYMA: Overall uncertainty analysis. EUR 18826, Luxembourg EC. (2000).

[19]

Jones K A, Bexon A P, Walsh C, Haywood S M, Jones A L, Payers C A, Haylock R G E and Phipps A W, Distributions of risk in exposed groups from routine realeases of radionuclides to the environment. National Radiological Protection Board, Chilton, NRPB-W45 (2003).

[20]

Groupe Radioecologie Nord Cotentin, Analyse de sensibilite et d'incertitude sur le risque de leucemie attribuable aux installations nucleaires du Nord-Cotentin (2002).

[21]

International Atomic Energy Agency, Principles for the exemption of radiation sources and practices from regulatory control. Vienna (1988).

Current Trends in Radiation Protection H. Metivier, L. Arranz E. Gallego and A. Sugier (eds.)

Quality assurance and the Evaluation of Uncertainties in Environmental Measurements Lourdes Romero Gonzalez1 CIEMAT, Av. Complutense, 22, 28040 Madrid (Spain)

Abstract. Radioactivity environmental monitoring programmes have been established to provide relevant information on radioactivity levels in all compartments of the biosphere; compliance against regulatory limits involves that large numbers of results from environmental radioactive determinations be compared to basic standards, to make important decisions on the potential risk to humans or the environment itself. The reliability of the assessment obtained from these programmes implies that laboratories producing the analytical data be able to provide results of the required quality. The confidence to be placed in results is possible only if a quantitative and reliable expression of their relative quality, the associated uncertainty, is assessed, obviously it has implications for decision purposes. The environmental measurements are frequently performed at levels where the radionuclide of interest cannot be distinguished from natural background levels and the relative uncertainty associated with the result tends to increase. This is a "conflicting domain" where some confusion exists due not only to the difficulty of establishing decision/ detection levels, but also due to the numerous existing criteria, terminology and formulation. The necessary comparability of the results from laboratories at international level involves, further to the implementation of a quality assurance program, the harmonisation of criteria, sampling procedures, calculations, or the reporting of results, agreed upon fundamental principles and international standards. This paper reviews and describes concepts relevant to uncertainty measurement and criteria at the "conflicting domain", based on recent international standards. Some recommendations are outlined, aiming to contribute to the achievement of international harmonization of criteria and terminology for stating formally the results of (environmental) radioactive determinations.

1. INTRODUCTION The radiological protection of the environment and the population involves the establishment of "the facilities necessary to carry out continuous monitoring of the level of radioactivity in the air, water and soil and to ensure compliance with the basic safety standards" EURATOM Treaty art.35 [1]. The Basic Safety

1

E-mail: [email protected]

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Standards establish the maximum permissible levels of exposure and contamination to which environmental measurements are to be compared daily, weekly, monthly or annually to make important decisions on the potential risk to humans or the environment itself. Radioactivity Environmental Monitoring (REM) programmes have been established in the EU Member States to comply with these requirements, they provide the relevant information on radioactivity levels in all compartments of the biosphere to the European Commission (EC). To ensure that potential impacts are detected and reviewed these programs must guarantee that the adequate network sampling is selected, representative types of samples are collected, the correct radiochemical techniques are employed, reliable measurements are made (even at the lowest activity levels found in the environment, close to detection limits of the detection systems), and that the "best quality laboratories" are selected for performing analytical determinations and measurements. The reliability of the assessment obtained from these programmes requires that laboratories producing the analytical data be able to provide accurate results, traceable to internationally recognised standards, and for their quality to be adequately demonstrated and documented. The necessary comparability of their results among different Member States laboratories would also have need of harmonising criteria, sampling procedures, calculations (uncertainty detection/decision limits), reporting of results, agreed upon fundamental principles. In the case of the monitoring regarding the Emergency preparedness, the EC develops several activities that require the harmonization of data provided by different countries i.e.: the ECURIE (European Community Urgent Radiological Information Exchange) system to ensure a rapid early warning in case of nuclear accident or a radiological emergency, the EURDEP (EUropean Radiological Data Exchange Platform) is both a standard data format and a network for the exchange of environmental radiological monitoring data from most European countries in real-time. The ENSEMBLE project, addresses the issue of harmonisation and coherence of emergency management and decision-making in relation to long range atmospheric dispersion modelling by providing a website tool to view and compare national dispersion forecasts [2]. Besides the above considerations, there are multiple areas where important decisions are based on the results of radioactive measurements: dose assessment models (accurate parameters influencing the transfer among different compartments), intervention levels, waste management, decommissioning of nuclear installations, clearance of materials, transport of radioactive material, the import of foodstuffs, ... Medical applications are an important area not only because they are the major source of exposure of the population to artificial sources but also measurements in this case have a direct influence on our lives when being part of medical diagnoses or therapy. Finally, the growing public concern over radioactivity levels in both terrestrial and marine environments, as well the potential risk of future accidents or terrorist actions involving radioactive material, present at an international level imperative demands for accuracy of measurements and traceability to international standards. To meet these requirements laboratories must establish quality assurance programmes to ensure that can produce data of the required quality. In general, this includes all activities concerned with determining that relevant requirements in standards or regulations is fulfilled: the use of validated methods of analysis, internal quality control procedures, participation in external proficiency tests schemes, accreditation (ISO 17025) [3], and establishing traceability of the measurements to a given standard. The user of the data reported by a laboratory should be aware that the information provided by measurement can rarely assumed to be complete. Confidence in the result of a measurement is only possible if a quantitative and reliable expression of its relative quality is assessed; the measurement uncertainty.

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Different uncertainty evaluation procedures have been developed over the years, it was the publication in 1993 of the ISO Guide to the Expression of Uncertainty in Measurement (GUM) [4], which formally established general rules for evaluating and expressing uncertainty in measurement. This document promoted the achievement of the international harmonization for stating formally measurement results, and makes possible international comparability. In 1995, the EURACHEM "Quantifying uncertainty in analytical measurement" [5] document was published and describes how the concepts in the ISO Guide may be applied in analytical measurement. A short review of the principles and recommendations from these documents applied to radioactive measurements is given below. The methods, terms, and symbols used in this document are described in the GUM and EURACHEM documents, criteria and recommendations for radioactive determinations are in compliance with MAR LAP [6] ISO 11843 [7] and ISO 11929 series [8]. The lack of harmonization still existing on different criteria, terminology, etc., is actually under study in the GTINC (National Working Group for the study of Uncertainties in REM) [9] from which the author is the coordinator. Many of the opinions and recommendations expressed in this article are the outcome of multiple review and discussions within the working group.

2. MEASUREMENT UNCERTAINTY Any measurement result is in general a point estimate of the measured quantity (measurand), the true value of which remains unknown. Therefore, the dispersion of the values about the estimate that could as well be attributed to the measurand should be appraised; this parameter is the measurement uncertainty; when stated the user of the result can asses the confidence to be placed on it.

2.1. Concepts and definitions Uncertainty: The definition of the term uncertainty of measurement (taken from the International Vocabulary of Basic and General Terms in Metrology (VIM) [10] is: "A parameter associated with the result of a measurement, that characterises the dispersion of the values that could reasonably be attributed to the measurand". The measured result may vary with each repetition of the measurement and should therefore be considered a random variable. Uncertainty and measurement error are quite often taken as synonymous. The difference between the measured result and the actual value of the measurand is the error of the measurement, which is also a random variable. Measurement error may be caused by random effects or systematic effects in the measurement process. Random effects cause the measured result to vary randomly when the measurement is repeated. Systematic effects cause the result to tend to differ from the value of the measurand by a constant absolute or relative amount, or to vary in a non random manner. Generally, both random and systematic effects are present in a measurement process. The error of a measurement is primarily a theoretical concept, because its value is unknowable. The uncertainty of a measurement, however, is a concept with practical uses. According to the definition of uncertainty, it is a parameter that characterises the dispersion of the values that could reasonably be attributed to the measurand; thus gives a bound for the likely size of the measurement error. In practice, there is seldom a need to refer to the error of a measurement, but an estimate of the uncertainty is required for every measured result. Also exists certain confusion involving the related concepts of accuracy and precision. Accuracy is the closeness of the agreement between the result of a measurement and a true value of the measurand: a measurement is accurate if its error is small. The term precision is not defined in the VIM [10], probably because many

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Figure 1. Accuracy and precision

meanings may be attributed depending on the context; in this document we take the definition as "a quantitative indication of the variability of a series of repeatable measurement results" [11]. Measurements of the same sample with a large standard deviation are not very precise, lack of precision is caused by random errors. In Figure 1, two cases of a series of results illustrate accuracy and precision. The measurement model: In a measurement process, to estimate the values of measurands subject to an indirect measurement, a proper measurement model should be established. The model can be described as a box that takes in input quantities and produces output quantities. In general, the mensurand Y, the output quantity depends upon a number N, of input quantities, (Xi,X2,... XN) according to the functional relationship:

(i) An estimate of the mensurand Y, the output estimate denoted by y, is obtained from (1) using input estimates X|, for the values of the input quantities Xj.

The standard deviation is used as a measure of the dispersion of values. The standard uncertainty of measurement associated with the output estimate (measurement result y), denoted by uc(y), is the standard deviation of the measurand Y. It is to be determined from the input estimates Xi, and their associated standard uncertainties u(Xi). For a measurement result y, the total uncertainty, termed combined standard uncertainty uc(y), is an estimated standard deviation equal to the positive square root of the total variance obtained by combining all the uncertainty components, evaluated using the law of propagation of uncertainty. When the input quantities are uncorrelated Xj, the combined uncertainty uc(y), is given by:

where u(Xj) can be uncertainties evaluated by a Type A or Type B methods. The partial derivates d f / d x j , are denoted sensitive coefficients (Ci) and describe the extent to which the output estimate y, is influenced by variations of the input estimate Xf.

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When the input quantities are correlated to some degree, the covariance also has to be considered as a contribution to the uncertainty. The expanded uncertainty U, provides an interval within which the value of the measurand is believed to lie with a higher level of confidence. U is obtained by multiplying uc(y), the combined standard uncertainty, by a coverage factor k. The choice of the factor k is based on the level of confidence desired, i.e.: for an approximate level of confidence of 95%, the value of k is 2. The coverage factor k should always be stated so that the combined standard uncertainty of the measured quantity7 can be recovered for use in calculating the combined standard uncertainty of other measurement results that may depend on that quantity.

2.2. Uncertainty sources The uncertainty on the result of a measurement or determination may arise from many possible sources, some of them are common to any analytical determinations such as: incomplete definition of the measurand, sampling, sub-sampling, storage conditions, matrix effects and interferences, environmental conditions, uncertainties of masses and volumetric equipment, reference values, approximations incorporated in the measurement method, digital displays and rounding, etc. In the case of radioactive determinations, many analytical techniques are to be used before measuring and the measurement involves sophisticated instrumentation. Besides some specific sources have to be considered due to the random nature of radioactive decay and radiation counting. The predominant source of uncertainty is the counting uncertainty, particularly at the low activity levels encountered in environmental samples, other possible causes of uncertainty include: radioactive standards, radionuclide halflife, counting efficiency, background, radioactive decay, source geometry and placement, variable instrument backgrounds and efficiencies, time measurements used in decay and ingrowth calculations, instrument dead-time corrections, approximation errors in simplified mathematical models, impurities in reagents, and uncertainties in the published values for halflives and radiation emission probabilities. In particular for gamma spectrometry also should be considered the Compton baseline determination, background peak subtraction, multiplets and interference corrections, peak-fitting model, efficiency calibration model, summing, density correction factors, etc. After all conceivable sources of uncertainty are listed, they should be categorized as either potentially significant or negligible. Uncertainties potentially significant should be evaluated quantitatively.

2.3. Uncertainty components In estimating the overall uncertainty, it may be necessary to take each source of uncertainty and treat it separately to obtain the contribution from that source. Each of the separate contributions to uncertainty, the input estimates, is referred to as an uncertainty component. When expressed as a standard deviation, an uncertainty component is the standard uncertainty u(Xi). These components are grouped into two categories according to the way in which their numerical value is estimated: Type A or a Type B method of evaluation. "Type A": Uncertainty that is evaluated from the statistical distribution of the results of series of measurements and can be characterised by standard deviations, Si : Sj = | y' s\ The associated number of degrees of freedom is Vf, being the standard uncertainty7 Ui = Si "Type B": Uncertainty that is evaluated by means other than the statistical analysis of a series of observations. In this case the standard uncertainty7 is evaluated by scientific judgement based on all available information

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Rectangular distribution Use when: • A certificate or other specification gives limits without specifying a level of confidence (eg.: 25 mL ± 0.05 mL) • An estimate is made in the form of a maximum range (± a) with no knowledge of the shape of the distribution.

Triangular distribution • The available information concerning x is less limited than for a rectangular distribution Values close to x are more likely than near the bounds. • An estimate is made in the form of a maximum range (± a) described by a symmetric distribution.

Normal distribution • An estimate is made from repeated observations of a randomly varying process. • An uncertainty is given in the form of a standard deviation s/x or, a relative standard deviation, or a coefficient of variance CV% without specifying the distribution. • An uncertainty is given in the form of a 95% (or other) confidence interval I without specifying the distribution.

Figure 2. Frequent Distributions used for Type B evaluation method, from [5].

on the possible variability of the input quantity; assumed probability distributions based on experience or other information (Figure 2), represented by a quantity, Uj , which can be characterized by a corresponding standard deviation: Uj =

Since the quantity uj like a standard deviation, the standard uncertainty is Uj.

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2.4. Process of evaluating uncertainty The steps for evaluating and reporting the uncertainty of a radioactive determination may be summarized as follows (adapted from [5] and [6], additional description on each step can be found in these references: Step 1. Specify measurand. Identify the measurand Y and all the input quantities Xi for the mathematical model. Include all quantities whose variability or uncertainty could have a potentially significant effect on the result. Express the mathematical relationship Y = f(X 1 ,X 2 ,... ,XN) between the measurand and the input quantities. Step 2. Identify uncertainty sources. List the possible sources of uncertainty; determine an estimate Xi of the value of each input quantity Xi Step 3. Quantify uncertainty components. Measure or estimate the size of the uncertainty component associated with each potential source of uncertainty identified. Evaluate the standard uncertainty u(Xi) for each input estimate Xi, using either a Type A or Type B method of evaluation Step 4. Calculate combined uncertainty. The information obtained in step 3 will consist of a number of quantified contributions to overall uncertainty, whether associated with individual sources or with the combined effects of several sources. The contributions have to be combined according to the appropriate rules, to give a combined standard uncertainty, Uc(y) of the estimate, y. Step 5. Determine expanded uncertainty. Multiply uc(y) by a coverage factor k to obtain the expanded uncertainty U such that the interval [y ±U] can be expected to contain the value of the measurand with a specified probability. Step 6. Expression of the result. Report the result as y ± U with the unit of measure, and, at a minimum, state the coverage factor used to compute U and the estimated coverage probability

2.5. Reporting uncertainty The information necessary to report the result of a measurement depends on its intended use. The guiding principle is to present sufficient information to allow the result to be re-evaluated if new information or data become available References [4], [5] and [6], recommend that the result of the measurement or determination should be reported as expanded uncertainty U, with the following format: Result: ( y ± U ) (stating the units) The value of k must always be reported and the confidence level associated to the y ± U interval. Example: The activity concentration of a radionuclide (A) in a water sample,

* The reported uncertainty is an expanded uncertainty calculated using a coverage factor of 2 which gives a level of confidence of approximately 95%. Rounding. The number of significant figures that should be reported for the result of a measurement depends on the uncertainty of the result. A common convention is to round the uncertainty (standard uncertainty7 or expanded uncertainty) to either one or two significant figures and to report both the measured value and

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the uncertainty to the resulting number of decimal places. This convention is recommended by [5], [6] and suggests that uncertainties be rounded to two figures, when possible. These rules for rounding should only be applied to final results. Intermediate results in a series of calculation steps should be carried through all steps with additional figures to prevent unnecessary round off errors. In radioactive environmental measurements it is possible to calculate results that are less than zero, although negative radioactivity is physically impossible. Negative values may occur when the measured result is less than a pre-established average background level for the particular system and procedure used. Laboratories sometimes choose not to report negative results or results that are near zero. Such censoring of results is not recommended, as these values should de reported to better enable statistical analyses and to observe trends in the data. All results, whether positive, negative, or %ero, should be reported as obtained, together with their uncertainties [5], [6].

Compliance against regulatory limits in REM involves that large numbers of results from environmental radioactive determinations be compared to basic standards or to be within specific limits. The uncertainty associated to the result has obviously implications for interpretation of analytical data in this context. According to section 9.6 of EURACHEM [5]: "The uncertainty in the analytical result may need to be taken into account when assessing compliance. The limits may have been set with some allowance for measurement uncertainties. Consideration should be given to both factors in any assessment".

3. CLOSE TO DETECTION/DECISION LEVELS As described above, the environmental measurements are frequently performed at levels where the radionuclide of interest, cannot be distinguished from natural background levels. The relative uncertainty associated with the result tends to increase to the point where the (symmetric) uncertainty interval includes zero. This region is typically associated with the practical limit of detection for a given method. This is a conflicting region where exists some confusion due not only to the difficulty of establishing a decision threshold ("does the sample contain a positive amount of the radionuclide?"), but also due to the numerous criteria, terminology and formulation developed since the first articles on making a detection decision for radioactive measurements were published [12], [13], [14]. All these methodologies involve the principles of statistical hypothesis testing, and this section would resume the latest harmonized international criteria, terminology and definitions based on [7], [8]. The application of more advanced statistical techniques i.e.: Bayesian inference, can be found in references [11], [15] -to- [22]. The terminology and definitions adopted by ISO are presented below for the basic concepts and criteria; to allow an easy reading, the classical names assigned by Currie are indicated in brackets. The complete definitions, terminology, equations, and explanations on when/how to apply, are described in the referenced ISO 1 1843 and ISO 1 1929. Curiously, it should be stressed that in spite of the aimed harmonization, symbols utilized for the same terminology (same physical concepts) are different in ISO 11843 and ISO 11929. Decision threshold, Rn* (Critical Level (Lc) Currie's}: "which allows a decision to be made for each measurement with a given probability of error as to whether the registered pulses include a contribution by the sample". Definition: "Critical value of a statistical test for the decision between the hypothesis p s =po and the alternative hypothesis ps> Po. PS = Expectation value of RS (gross effect counting rate quotient of the number pulses Ns counted during the preselected duration of measurement ts and the duration of measurement ts: RS = Ns / ts

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Po = Expectation value of R0 (background effect counting rate, quotient of the pulses NO counted during the preselected duration of measurement to and the duration of measurement to: R0 = N0/ t0 Rn = net effect counting rate, Rn = Rs -Ro pn — Expectation value of Rn For operational purposes, the statistical concept of Decision threshold is the lowest useable action level. Results of Rn are compared with the Decision threshold, which is a value chosen so that results above it are unlikely to be false positive, with a probability a fixed prior to commencement of the measurement. A smaller value of a makes type I errors (false positives) less likely, but also makes type II errors (false negatives) more likely when the sample concentration is near the blank. Frequently the results of radioactive determinations must meet certain reference-guide values established by the user of the results. With reference to the monitoring of the environmental radioactivity, a minimum value for the so-called Detection Limit for a method is required by the Regulatory body. The European Union REM sparse network (implemented within the Member States to obtain data on actual levels of radioactivity) requires that laboratories provide data with the highest achievable accuracy and high sensitivity measurements, in order to allow comparison of data sets for extended time periods. In this case an important performance characteristic of a radioanalytical procedure is the detection capability or Detection U,mit. The ISO 11929definitionis: Detection Limit, pn* Detection capability (Detection Limit, Ld Currie's}: "which specifies the minimum sample contribution which can be detected with a given probability of error using the measuring procedure in question. This consequently allows a decision to be made as to whether a measuring method satisfies certain requirements and is consequently suitable for the given purpose of measurement." "The difference between using the decision threshold and using the detection limit is that measured values are to be compared with the decision threshold, while the detection limit is to be compared with ti\z guideline value" Guideline Value : "Value constituted by requirements on measuring procedures arising for scientific, legal or other reasons which are specified, for example, as activity, specific activity surface activity, dose rate, etc.". In the case of the REM programmes this value is fixed by the Regulatory body for specific activity in the different types of samples analysed in the program. An important area of application of the detection capability for a radiochemical procedure is in fulfilling the safeguard agreements pursuant to the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). The verification activities include monitoring systems to detect the flow of nuclear material past key points (detection of very small amounts of specific radionuclides), to ensure that the nuclear material and other items placed under safeguards remain in peaceful nuclear activities. It should also be addressed the expense and consequences of making incorrect decisions; reporting false positive in environmental samples, can produce unnecessary costly cleanup, unnecessarily alarm public, spend money on unneeded resampling, analyses and further investigations. In the case of reporting a false negative, the consequences could affect directly the population, as not protective actions of public and environment would be taken, and if later discovered can destroy trust and communication, having obviously political consequences [23]. Other areas involving radioactive determinations such a exemption levels, clearance of materials, cleanup of contaminated areas, waste management or bioassay excreta radioanalyses in internal dosimetry [24], stress the significance of producing reliable measurements together with adequate uncertainty evaluation and having the "conflicting region" well characterized.

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As for the reporting of results at the "conflicting region", the value (and its uncertainty) should always be reported, if it does not exceed the decision threshold the comment "no detected" should be added; censoring data means changing measured results from numbers to some other form that cannot be averaged or analyzed numerically.

4. FINAL RECOMMENDATIONS The uncertainty associated to the result should be taken into account when comparing data against regulatory limits or among results of laboratories from other countries. At the environmental radioactivity levels, the relative uncertainty associated with the measurement result tends to increase and therefore uncertainties should be correctly assessed and the detection/decision levels in this conflicting region must be carefully characterized, being thus necessary further harmonization of criteria and terminology. The radiological protection of the environment and the population requires from all states to have laboratories with internationally comparable quality7 levels. Adequate management of any eventual situation of nuclear emergency can only be assured on the basis of reliable and traceable measurements to international standards. Therefore, laboratories should establish uniform quality assurance programmes to ensure that they can produce data of the required quality. Other recommendations extracted from ISO references, aiming to contribute to the international harmonization of criteria for stating formally the results of (environmental) radioactive determinations, are outlined: Measurement uncertainty

Laboratory measurements always involve uncertainty, which must be considered when analytical results are used as part of a basis for making decisions. Every measured value obtained by a radioanalytical procedure should be accompanied by an explicit uncertainty estimate. All results, whether positive, negative, or zero, should be reported as obtained, together with their uncertainties. The coverage factor and approximate coverage probability should be stated whenever an expanded uncertainty is reported. Assessment of measuring procedure

The decision as to whether a measuring method satisfies certain requirements with respect to the detection limit shall be made by comparing the detection limit (which has been determined) with the specified guideline value.

If the detection limit thus determined is greater than the guideline value, the measuring procedure is not suitable for the purpose of the measurement. Assessment of measured results

A measurement result shall be compared with the decision threshold thus obtained. If a result is greater than the decision threshold, it is assumed to be a real sample contribution. Documentation

A report on measurements shall be accompanied by details on the probabilities of error, the decision threshold and the detection limit. For established sample contributions, in addition to the measured value, confidence intervals and the confidence level shall be reported. The value (and its uncertainty) should always be reported, if it does not exceed the decision threshold the comment "no detected" should be added. To conclude, efforts should be made by the scientific community to have all involved laboratories in closer collaboration for an international harmonization of criteria and terminology, and to diffuse this information among the users of the results.

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REFERENCES [1]

European Atomic Energy Community. EURATOM Treaty. Rome (1957)

[2] Europa. European Commission. Energy. Radiation Protection c o m m / e n e r g y / n u c l e a r ) (2003)

(http://europa.eu.int/

[3]

International Organization for Standardization (ISO) General Requirements for the Competence of Calibration andTestingEaboratories. ISO/IEC 17025. ISO, Geneva. Switzerland. (1999)

[4]

International Organization for Standardization (ISO). Guide to the 'Expression of Uncertainty in Measurement. ISO, Geneva, Switzerland. (1995)

[5]

EURACHEM. E URACHEM/ CITAC Guide: Quantifying Uncertainty in Analytical Measurement, 2nd ed. EURACHEM. (2000)

[6]

U.S. Environmental Protection Agency (EPA); Department of Energy (DOE); Department of Defense (DOD); Nuclear Regulatory Commission (NRC); National Institute of Standards and Technology (NIST); Geological Survey (USGS), and Food and Drug Administration (FDA). Multi-Agency Radiological Laboratory Analytical Protocols (MAREAP) draft (2003)

[7]

International Organization for Standardization (ISO). Capability of Detection - Part 1-2:. ISO 11843-1 y -2. ISO, Geneva, Switzerland (1997-2000)

[8]

International Organization for Standardization (ISO). Determination of the Detection Eimit and Decision Threshold for loni^ingRadiation Measurements -Part 1-2-3-4: ISO 11929. ISO, Geneva, Switzerland. (2000)

[9]

GTINC, Ea evaluation de incertidumbres en la determination de la radiactividadambiental. Consejo de Seguridad Nuclear (CSN). Coleccion Informes Tecnicos. Serie Vigilancia Radiologica. CSN (in press)

[10]

International Organization for Standardization (ISO). International Vocabulary of Basic and General Terms in Metrology. ISO, Geneva, Switzerland. (1993)

[11]

Lira, I., Evaluating the measurement uncertainty. Fundamentals and practical guidance. Institute of Physics Publishing. Bristol and Philadelphia (2002)

[12]

Altshuler, B.; Pasternack, B. Statistical Measures of the Lower Limit of Detection of a Radioactivity Counter. Health Physics 9:293-298, (1963)

[13]

Nicholson, WL. Statistics of Net-Counting-Rate Estimation with Dominant Background Corrections. Nucleonics 24(8):118-121, (1966)

[14]

Currie, L.A. Eimits for Qualitative Detection and Quantitative Determination. Application to Radiochemistry. Analytical Chemistry 40:587 - 593 (1968)

[15]

Strom, D.J., Introduction to Bajesian Statistics. PNNL-SA-31527. Health Physics Society Annual Meeting, June 27-July 1, 1999. Richland, Washington: Pacific Northwest National Laboratory (1999)

[16]

Bayes, T. An Essay Towards Solving a Problem in the Doctrine of Chances. The Philosophical Transactions 53:370-418; 1763. Reproduced in. Biometrika 45:293-315; (1958)

[17]

Berry, DA. Statistics: A Bajesian Perspective. Belmont, California: Wadsworth Publishing Company; (1996)

[18]

Little, R.J.A. The Statistical Analysis of Eow-Eevel Radioactivity in the Presence of background Counts. Health Physics 43(5):693-703; (1982)

[19]

Miller, G; Inkret, W.C.; Martz, H.F. Bayesian Detection Analysis for Radiation Exposure. Radiation Protection Dosimetry 48(3):251 -256; (1993)

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[20]

Miller, G.; Inkret, WC; Martz, H.F. Bayesian Detection Analysis for Radiation Exposure, II. Radiation Protection Dosimetry 58(2):115-125; (1995)

[21]

Miller, G.; Martz, H.F.; Schillaci, M.E.; Berry, D.A.; Inkret, WC.; Little, T. Support for Bayesian Statistics. Health Physics Society Newsletter 26(3):28-29; (1998)

[22]

International Organization for Standardization (ISO). Determination of the Detection Limit and Decision Threshold for Ionising Radiation Measurements - Part 7. Fundamentals and general applications: ISO/DIS [6 11929-7. ISO, Geneva, Switzerland. (2003)

[23]

Strom, D.J., False Alarms, True Alarms, and Statistics: Correct Usage of Decision Level and Minimum Detectable Amount. Handout for Continuing Education Lecture, Health Physics Society Annual Meeting, Minneapolis, Minnesota. Richland, Washington: Pacific Northwest National Laboratory. (1998)

[24]

Strom, D.J., MacLellan, J.A., Evaluation of eight decision rulesfor low-level radioactivity counting. Health Physics, 81(l):27-34, (2001)

Current Trends in Radiation Protection H. Metivier, L. Arranz E. Gallego and A. Sugier (eds.)

Site Restoration and Cleanup of Contaminated Areas Gordon Linsley1 International Atomic Energy Agency, P.O. Box 100, A-1400 Vienna, Austria

Abstract. In this paper some of the recent developments related to the remediation of areas contaminated with radioactive materials are reviewed. Specifically, the current situation at the nuclear weapons test sites and some of the recent efforts to remediate them are described. A brief account is given of the international assessment work carried out in recent years in relation to depleted uranium residues in the environment from military conflicts in the Persian Gulf and the Balkans. Progress in establishing regulatory conditions for managing the decommissioning of nuclear facilities and the release of materials, buildings and sites from regulatory control is described. Finally, essential elements of the ongoing discussion on the role of radiation protection in decision making for the management of contaminated sites are set out.

1. INTRODUCTION From the beginning of the twentieth century radioactive materials have been deposited on the earth's surface as a result of the mining and processing of uranium and thorium, then, the use and testing of nuclear weapons and, then, through normal operations and accidents in the civil nuclear power industry and, most recently, through the use of depleted uranium in conventional military weapons. The presence of these radioactive residues on terrestrial surfaces can cause the exposure of humans and other plant and animal species to the potentially harmful effects of ionizing radiation. In view of these potential hazards it is clearly desirable to remove the residues, where it is feasible, or at least to reduce them to acceptable levels. Of late, and in particular since the ending of the "cold war", there has been an increased effort globally to address the problem of contaminated areas and several international conferences have been devoted to the subject [1-5]. The most well known events which have led to terrestrial contamination have been those associated with nuclear weapons testing and with accidents at nuclear facilities. The normal operation of the nuclear fuel cycle, with the exception of uranium mining and milling, has not generally caused significant environmental contamination but, of late, there has been interest in this area because of the increasing numbers of nuclear

1

E-mail: [email protected]

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facilities reaching the end of their productive lifetimes and of the need for them to be decommissioned. At the end of the decommissioning process, consideration has to be given to the future of the sites and of any remaining buildings and of the possible need to remediate. The policies and criteria governing this last step in the life of nuclear facilities have been the subject of recent international conferences [6,7]. Exploration for, and then the mining and milling of, uranium and thorium ores took place in many countries and, as a result, there are more than 300 sites at which tailings from these operations exist. Many of them have not been properly stabilized and pose potential hazards to persons living in their vicinity [8, 9]. Some radioactive contamination of the environment has also resulted from the extractive industries, such as, those for phosphorus, oil, iron, coal, and mineral sands. The potential radiological problems associated with environmental contamination due to naturally occurring radioactive materials, so-called, NORM, from these sources have also received greater attention in recent years [10]. The recent military actions in the Balkans and in the Middle East have led to localised contamination of areas with depleted uranium. Subsequent claims of health effects in some of the soldiers who were operating in the environments where the depleted uranium tipped weapons were used has excited considerable concern and interest and has prompted various related scientific investigations, including radiological surveys of the areas in which the weapons were used [11-14]. This review is not comprehensive in its coverage of the various types of contamination situation but rather it addresses some recent events and developments in the following areas: a) sites contaminated due to nuclear weapons testing b) areas affected by residues from the military use of depleted uranium c) site release at the termination of practices d) decision making for site cleanup and release

2. THE RADIOLOGICAL SITUATION AT SITES CONTAMINATED DUE TO NUCLEAR WEAPONS TESTING The main nuclear weapons test sites are listed in Table 1 and some indication is given of their restoration status [15-24]. The extent to which the various sites were used for weapons testing is variable; some, such as the Monte Bello Islands and the Algerian sites, were used for comparatively few tests. The nature of the testing also varied; at some, the testing was limited to atmospheric tests of nuclear devices; at others, the testing included atmospheric and underground testing of nuclear devices and also so-called "safety tests" involving only conventional explosions of devices containing radioactive materials. All of these factors determine the extent to which the sites are contaminated. It seems that the "safety tests" often gave rise to the most significant contamination problems since they resulted in the spread of plutonium isotopes over significant surface areas. Some sites were affected by accidents or unplanned events during the testing programmes, again leading to significant surface contamination. Remediation programmes have been instituted mainly at sites which are outside the present territories of the nations responsible for conducting the testing; examples are: Maralinga and Emu, (Australia), Bikini and Enewetak (Marshall Islands), Christmas Island (Republic of Kiribati). Several of the non-remediated sites remain under military control and access is restricted for military as well as radiological reasons.

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Table 1. Main nuclear test sites and their remediation status

Site Maralinga and Emu (Australia) Monte Bello Islands (Australia) Enewetak Atoll (Marshall Islands) Bikini Atoll (Marshall Islands)

Remediaton status Remediated Not remediated Remediated Remediated

Johnston Island (USA) Christmas Island (Republic of Kiribati) Reggane and In-Ekker (Algeria) Mururoa and Fangataufa (France) Semipalatinsk (Kazakhstan) Novaya Zemlya (Russian Federation) Lop Nor (China) Nevada (USA)

Remediated Remediated Partly remediated Remediated Not remediated Not remediated Not known Not remediated

Access/use restrictions Use restrictions No access or use restrictions Resettled Eneu island is now resettled Use restrictions at Bikini island Access restrictions Resettled Some access restrictions No use restrictions but access controlled Some access and use restrictions Access restrictions Access restrictions Access restrictions

There has been little commonality in the radiological protection criteria used as a basis for decision making on site clean-up at those sites at which remediation has been undertaken. In the early phases of the site clean-up, the strategy seems to have been to remediate the most highly contaminated parts, if practicable. At later stages, and with the objective of de-restricting the sites, the aim became to bring the radiological conditions, for anyone living on the site, close to those in uncontaminated areas. This is a difficult objective to attain and, at those sites where there is a local population, that population has been involved in determining what is acceptable as a final condition for the site. Radiological protection information has played its part in helping to establish what is acceptable. For example, it is necessary for all concerned to know the risks associated with particular levels of contamination. This information helps in determining what is unacceptably high as a residual contamination level. However, the difficulty is always in deciding what is acceptably low and what could be tolerated by a population living on a former test site. In this and other environmental contamination situations, existing international radiological protection guidance [25] helps by providing a framework within which decisions can be made, but the decisions are often likely to be made based mainly on social and political grounds. The nuclear test sites are all located in remote regions often in areas where there were few inhabitants. However, for several of the sites, the final decisions on the conditions of the sites have been made with the involvement of local population groups. At Maralinga, where several attempts at clean up have been made since nuclear weapons testing ended in 1957, the target of the most recent remediation was to reduce the residual dose to as low as reasonably achievable [19].The boundaries for soil removal were based on an individual dose of 5 mSv per year in a region restricted to hunters and persons in transit and 1 mSv per year in an area where it is possible for a person to live continuously (excluding the dose rate from natural background radiation). In each case, the doses were estimated on the conservative assumption that there is permanent residence and that exposure due to inhalation and radionuclide ingress through wound contamination can occur. Actual doses received by persons hunting, in transit or living in the areas are expected to be very much less than the boundary radiological criteria. These access restrictions were agreed to by the local aboriginal community subject to a financial settlement. In the case of Bikini Atoll, again, several attempts at remediation have been made since weapons testing ceased in 1958. At the time of the IAEA assessment in 1995-96 consideration was being given to

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remediating the soils of Bikini Island mainly to prevent the uptake of caesium-137 into foodstuffs [20]. The assessment had shown that, without remedial measures, the radiation doses that would be received assuming a diet of entirely locally derived foodstuffs (although not likely) could lead to annual effective doses of about 15 mSv. It may be noted that this is in excess of the international reference level for aiding intervention decisions (an annual effective dose of 10 mSv including the contribution from natural radiation) [25,26]. The remedial measures favoured by the international Advisory Group consisted principally of administering a potassium containing fertiliser to the island soils and removing soil from around and beneath dwelling areas and replacing it with crushed coral. This treatment was estimated to reduce the maximum annual dose to around 1 mSv (above natural background levels) [20]. Negotiations have continued between the Governments of the Marshall Islands and the United States of America on this subject but the current situation is that the proposed remediation has not been fully implemented and Bikini Island has not been resettled. However, one of the smaller of the islands, Eneu, is now inhabited by former islanders sustained mainly by imported foodstuffs. A similar pattern of events seems to have occurred in relation to the remediation of Rongelop Atoll which was affected by fallout from testing at Bikini. The local population evacuated their atoll in 1986 because of concerns over the residual radioactive contamination and is still in dispute with the US Government. At Enewetak Atoll, the local people returned in 1980 after an extensive cleanup operation on behalf of the US Government [17]. In the case of the nuclear weapons test sites at Mururoa and Fangataufa Atolls in French Polynesia, there are no records of any permanent habitation of the Atolls. However, after the remediation programme conducted by the French Government, an assessment of the radiation doses that would be received by hypothetical inhabitants obtaining their diet entirely locally was performed, as part of an international assessment of the radiological conditions at the Atolls in 1996 — 98 [21]. The doses that could be received in this way were found to be negligibly small. Small areas with surface contamination from plutonium exist but it was regarded as only remotely conceivable that a plutonium-containing particle could enter the body of an individual, e.g. through a cut in the skin. Plutonium, tritium and caesium in the sediments of the lagoons were considered unlikely to cause significant exposures at present or in the future to any repopulated individuals or to residents of other islands throughout the Pacific region. The Atolls continue to be uninhabited except for a continuing military presence.

3. SITES AFFECTED BY RESIDUES FROM THE MILITARY USE OF DEPLETED URANIUM The Gulf War in 1991 was the first conflict in which extensive use was made of Depleted Uranium (DU) in anti-tank munitions and missiles. It is estimated that around 300 tonnes of DU was used in this war [14]. Subsequently DU has been employed in munitions in the Balkans conflicts where around 10 tonnes of DU were fired [11-13]. DU poses a radiological hazard at the time at which the munitions are used, mainly due to airborne particles created in the vicinity of the target. Subsequently, any hazard arises due to possible exposure from deposited particles and fragments in soils in the neighbourhood of the sites of conflict. The reports of assessments carried out by international teams (Table 2) confirm that any hazard associated with residues of depleted uranium is localized to within a few hundred metres of the target rather than being widespread throughout the region. The long-term hazard from DU in soil can arise through resuspension of the particles due to wind action or local disturbance, followed by inhalation of the particles. Transfer to humans via the foodchain or via drinking water is also possible. The transfer to food occurs mainly due to surface deposits of dust on food rather than by root uptake. About ten years after the Gulf War, these pathways were explored by an

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Table 2. International assessments of DU in the environment Site Kosovo Serbia and Montenegro Bosnia and Herzegovina Kuwait

Information source UNEP[11] UNEP [12] UNEP [13] IAEA [14]

IAEA led team of experts at various locations in Kuwait where it was known that military actions had taken place or where damaged military vehicles had been stored [14]. In all cases examined, the estimated annual effective radiation doses that could arise from exposure to DU residues were of the order of a few microsieverts or less, well below the annual doses received by the population of Kuwait from natural sources of radiation in the environment. However, it was noted that complete DU penetrators or fragments can still be found at some locations where these weapons were used in the Gulf War. Prolonged contact with these DU residues is the only exposure pathway that could result in exposures of radiological significance. Access to a few areas is restricted; one example is a military base where a fire resulted in the spread of DU from stored munitions. Parts of this area have been remediated by soil removal and covering with fresh soil and the long-term effectiveness of this remediation approach is being monitored. The assessment team recommended that the Kuwait authorities arrange for the removal of penetrators and fragments from sites where they are known to be present and to consider informing local residents and workers at such sites of the possible hazards associated with collecting DU munitions or fragments. Similar advice has been given to the authorities in the Balkans states affected by DU munitions.

4. SITE RELEASE AT THE TERMINATION OF PRACTICES The number of nuclear facilities which have reached the end of their useful lives is increasing. It is estimated that more than 100 nuclear power plants and more than 200 nuclear research reactors have been "shut down" awaiting decommissioning or are currently undergoing decommissioning [15]. In the USA, where most experience of nuclear power reactor decommissioning has been obtained, the currently most favoured strategy consists of immediate dismantlement (DECON) in which equipment, structures and portions of the facility containing radioactive contaminants are removed or decontaminated to a level that permits release of property and termination of the regulatory licence. Already operators of 11 power reactors in USA have elected to use this approach, [Orlando in [7]]. To facilitate the expected increase in decommissioning, countries need to have in place appropriate regulatory policies and criteria [6]. These should include criteria for the release of materials, buildings and sites from regulatory control. In many countries, policies for releasing sites from regulatory control are being influenced by an increased public and political concern for the environment and its protection, as exemplified at the international level by the Rio Declaration of 1992. This emphasised the need for "sustainable" industries that have no long-term adverse affect on the environment. It has prompted a desire for returning sites to a "green field" condition after their industrial use has ended.

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Such targets are attainable for many parts of the nuclear fuel cycle especially in relation to civil nuclear power plant sites. However, for some parts of the nuclear fuel cycle and for some of the 'historic' nuclear sites, this target may prove to be difficult to reach. Furthermore, in most countries, solutions still have to be found for the management and disposal of the radioactive waste that results from the decommissioning of nuclear facilities. International meetings and conferences such as those organized by the IAEA in Berlin [6] and by the NEA in Tarragona [7] have shown that national decommissioning strategies vary and that a wide variety of radiological criteria are being used as conditions for site release. In Germany, a basic criterion of 10 /iSv per year is being used to determine the contamination level below which sites must be cleaned up before being released for public use [Schattke in [7]]. In Spain, a criterion of 100 //Sv per year has been used for the same purpose for the decommissioning of the Vandellos I nuclear power station [Lentijo in [7]]. In the USA, the Nuclear Regulatory Commission has established a policy for unrestricted site release which requires that radiation doses to the average member of a critical group do not exceed 250 /uSv per year and that doses are reduced to be as low as reasonably achievable [Greeves in [6]]. An interesting element in the discussion of these criteria is the issue of whether the radiological criteria for the release of sites should be the same as those for the removal of materials from regulatory control (clearance). In the light of these wide divergences it was concluded, by the President of the Berlin Conference, that "the international community should make concerted efforts to resolve these issues" [6]. In the ongoing international discussions on this subject there is concern to preserve coherence with other elements of international radiation protection policy, for example, policies for the discharge of radionuclides to the environment and those for the clearance of materials. Schemes are being developed which allow for national flexibility through the optimization process while at the same time maintaining the basic logic of radiation protection principles for the control of exposures to members of the public [Linsley in [6]].

5. DECISION MAKING FOR SITE CLEANUP AND RELEASE In recent years, this subject has proved to be controversial and has stimulated argument and discussion at several international conferences [3-5]. Radiation protection specialists have established a framework and criteria for guiding decisions on remediating areas affected by radioactive contamination [25]. The guidance is based mainly on risk considerations; the risks associated with living in the contaminated area, and consideration of the costs of remediation. Judgements are made on when remediation is needed on this basis. However, the evidence presented at international conferences shows that, in situations where decisions have had to be made related to contaminated environments, e.g. in the vicinity of the Chernobyl NPP, in the vicinity of operating nuclear facilities, at nuclear weapons test sites, the international radiation protection advice has usually not been followed [3,4]. In all of these cases, there has been strong involvement of the affected groups in the population in decisions on the future of the affected areas. It is evident that those involved are very unwilling to accept anything less than "normal living conditions". Often, well established radiological criteria, such as the dose limit for members of the public, established for other radiological protection purposes, have been used as a basis for decisions on site access restriction or remediation. This has prompted a discussion on the role of radiation protection in this context [[27] and Kelly in [5]]. It seems clear that radiation protection is only one of the factors that have to be taken into account in

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making decisions on the future of contaminated sites. The many political and societal issues that influence any decision in a community will usually dominate over the radiation protection concerns. Some of the lessons learned from past experiences include the recognition that: (i) the concepts of "practice" and 'intervention" are not readily understood by non-radiation protection professionals. It is not easy to explain why a contaminated area should be treated differently depending on whether it was contaminated as a result of a controlled operation or as a result of an uncontrolled event; (ii) decisions will tend to be made for site specific reasons. Each situation and the circumstances affecting the local people will be different and so the decisions made and the associated radiological end-points can also be expected to be different. It is nevertheless clear that there is a role for radiation protection in aiding decision making in relation to determining the future of contaminated areas. Radiation protection experts are able to provide advice and information as an aid to those concerned in decision making, at least, on the following aspects: (i) Information on the risks to health of living in the affected areas or using them for different purposes. (ii) Perspectives on the risks in relation to other radiation exposure situations, in particular associated with natural background radiation, and other risks in life. The "bounding" guidance of the international radiation protection experts in this context may also be useful to decision makers, that is, advice on the upper levels of dose at which remediation or access restriction should be imposed under almost all circumstances, and also the lower bounds of dose, below which the effort of further clean-up would bring negligible benefit in terms of risk reduction.

6. SUMMARY AND CONCLUSIONS a) There has been progress in remediating the former nuclear weapons test sites, especially those located outside the territories of the weapons states responsible for the testing. However, many of the major test sites are unremediated and not generally accessible, mainly because they are still under military control. b) Sites affected by the previous military use of depleted uranium are generally only slightly contaminated and the associated radiation doses to persons living in the areas are exceedingly small. The main remaining hazard comes from the penetrators and fragments of munitions still present in the environment. c) With the increasing numbers of nuclear facilities becoming candidate for decommissioning, Governments need to have appropriate regulatory frameworks in place to provide for safe decommissioning and for the release of materials, buildings and sites from regulatory control. At present, the criteria being used by countries in which such decommissioning is being implemented vary widely. It seems desirable to improve the coherence of radiation protection policies governing the termination of such practices. d) There is increasing recognition that the role of radiation protection in relation to decisions on the future of areas contaminated with radioactive materials is limited to aiding decisions. Radiation protection considerations are only one of the many elements which must be considered in the decision making process, which will often be dominated by social and political considerations. However, such decisions should not be made in the absence of radiation protection based information and there is, therefore, a real and important role for appropriate and sound technical and scientific guidance.

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ACKNOWLEDGMENTS The author wishes to acknowledge the information and advice kindly provided by D. Reisenweaver and T. Cabianca (IAEA Vienna), S. Simon (NCI Bethesda, MD), K. Lokan (Australia), A. McEwan (New Zealand) and T. Hamilton (LLL California).

REFERENCES [1] European Commission, Remediation and restoration of radioactive-contaminated sites in Europe, Proceedings of a symposium, Antwerp, 1993, Luxembourg, DOC Xi-5027/94 (1994). [2] European Commission, Restoration strategies for contaminated territories resulting from the Chernobyl accident, Proceedings of a workshop, Brussels, 1998, Compiled by L. Cecille, Luxembourg, EUR 18193, (2000). [3] International Atomic Energy Agency, Restoration of Environments with Radioactive Residues, Proceedings of an international symposium, Arlington, Virginia, 1999, IAEA, STI/PUB/1092, (2000). [4] International Atomic Energy Agency, Radiation legacy of the 20th century: Environmental restoration, Proceedings of an international conference, Moscow, 2000, IAEA-TECDOC-1280, (2002). [5]

Radioactive Pollutants, Impact on the environment, edited by Francois Brechignac and Brenda J. Howard, based on invited papers at the ECORAD 2001 International Conference, EDP Sciences (2001).

[6]

International Atomic Energy Agency, Safe decommissioning for nuclear facilities, Proceedings of an international conference, Berlin, 2002, IAEA, STI/PUB/1154, (2003).

[7] OECD/Nuclear Energy Agency, Strategy selection for the decommissioning of nuclear facilities, Proceedings of an international seminar, Tarragona, 2003. [8] International Atomic Energy Agency, Planning for environmental restoration of radioactively contaminated sites in central and eastern Europe, Proceedings of workshops held in Budapest, Hungary 1993, Piestany, Slovakia, 1994 and Rez, Czech Republic, 1994, (in 3 volumes) IAEA-TECDOC-865 (1996). [9] International Atomic Energy Agency, Planning for environmental restoration of uranium mining and milling sites in central and eastern Europe, Proceedings of a workshop held in Felix, Romania, 1996, IAEA-TECDOC-982, (1997). [10]

International Atomic Energy Agency, Technology enhanced natural radiation (TENRII), Proceedings of an International Symposium, Rio de Janeiro, Brazil, 1999, IAEA-TECDOC-1271, (2002).

[11]

United Nations Environment Programme, Depleted Uranium in Kosovo, Post-conflict environmental assessment, UNEP, (2001).

[12]

United Nations Environment Programme, Depleted Uranium on Serbia and Montenegro, Postconflict environmental assessment in the Federal Republic of Yogoslavia, UNEP, (2002).

[13]

United Nations Environment Programme, Depleted Uranium in Bosnia and Herzegovina, UNEP, (2003).

[14]

International Atomic Energy Agency, Radiological Conditions in Areas of Kuwait with Residues of Depleted Uranium, IAEA, STI/PUB/1164, (2003).

[15]

International Atomic Energy Agency, Status of the decommissioning of nuclear facilities around the World, IAEA-TECDOC (to be published).

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[16]

United Nations Scientific Committee on the Effects of Atomic Radiation, UNSCEAR 2000 Report to the General Assembly, Sources and Effects of Ionizing Radiation, Volume 1: Sources, UN, New York, (2000).

[17]

Simon, S.L., A brief history of people and events related to atomic weapons testing in the Marshall Islands, Health Physics, 73, July 1997.

[18]

S. Simon and A. Bouville, Radiation doses to local populations near nuclear weapons test sites worldwide, Health Physics, 82, 5 May 2002.

[19]

Maralinga Rehabilitation Technical Advisory Committee, Rehabilitation of former nuclear test sites at Emu and Maralinga, Commonwealth of Australia, (2002). (See http : : / /www . rasanet. iaea . org/apprai sals/waste-appraisals . htm).

[20]

International Atomic Energy Agency, Radiological Conditions at Bikini Atoll: Prospects for Resettlement, IAEA, STI/PUB/1054, (1998).

[21]

International Atomic Energy Agency, The Radiological Situation at the Atolls of Mururoa and Fangataufa, IAEA, STI/PUB/1028, (1998).

[22]

International Atomic Energy Agency, Nuclear Explosions in the USSR: The North Test Site, Reference material, see h t t p : / / w w w - r a s a n e t . i a e a . o r g / a p p r a i s a l s / waste-appraisals.htm

[23]

International Atomic Energy Agency, Radiological Conditions at the Semipalatinsk Test Site, Kazakhstan, Preliminary assessment and recommendations for further study, IAEA, STI/PUB/1063 (1998)

[24]

North Atlantic Treaty Organization, Investigation of the Radiological Situation in the Sarzhal Region of the Semipalatinsk Nuclear Test Site, N. Priest et. al., NATO, SfP-976046(99) (2003).

[25]

International Commission on Radiological; Protection, Protection of the Public in Situations of Prolonged Exposure, Annals of the ICRP, Publication 82, Vol. 29, Nosl-2, 1999, Pergamon Press, (1999).

[26]

International Atomic Energy Agency, Remediation of Areas Contaminated by Past Activities and Accidents, IAEA Safety Standards Series, Safety Requirements, WS-R-3 (2003).

[27]

P. Hedemann Jensen, Radiation protection and decision-making on cleanup of contaminated urban environments, NKS Conference on Radioactive Contamination in Urban Areas, Ris0 National Laboratory, May, 2003.

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Current Trends in Radiation Protection H. Metivier, L. A.rran^ E. Gallego and A.. Sugier (eds.)

The Lessons to be Learned from Incidents and Accidents John Croft1 National Radiological Protection Board, Chilton, Didcot, Oxon, OX11 0RQ,, United Kingdom

Abstract. The paper emphasises the important role that learning the lesson from accidents and incidents play in the cyclical process of improving operational safety and security of sources and emergency response arrangements. It reviews events that have provided "awakenings" and the initiatives that have stemmed from them particularly in respect of orphan sources, source security and emergency preparedness. It is noted that whilst terrorist driven issues are receiving well merited attention, conventionally failures in safety and security of radiation sources still regularly occur, sometimes with severe consequences. The paper reviews mechanisms for capturing the lessons to be learned, some common causes of accidents, with examples tracked through the life cycle of sources.

1. INTRODUCTION Learning the lessons from accidents and incidents should be a fundamental element of all radiological protection programmes, both in respect of improving controls to prevent accidents and in improving emergency preparedness to respond to them should they occur. It feeds into the cyclical process of risk assessment, implementing controls and emergency arrangements, training, review and back to risk assessment. There are a number of dimensions to this. One is the level at which the learning process is taking place; from international and national levels down to the individual level. Other important dimensions are — the extent of sophistication of the radiological protection infrastructure; — the different sectors of use, eg, nuclear, industrial, medical, research etc and their respective safety cultures; — the mechanisms for capturing information on accidents and incidents; assessment, analysis and dissemination. This paper reviews some of the initiatives to improve the process of learning the lessons from accidents and incidents. It primarily focuses on the non nuclear sector. By its nature it cannot be exhaustive and is very much a personal view. 1

E-mail: [email protected]

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2. AWAKENINGS The radiological accident in Goiania, Brazil in 1987 [1] provided something of a wake-up call on the potential serious consequences that can arise from the loss of control of radioactive sources. One of the positive outcomes from that accident was the start of a series of International Atomic Energy Agency (IAEA) Accident Investigation publications that identified lessons to be learned [1-11]. Sadly many accidents are still either not reported in the open literature - or in some cases not even recognised. Over the subsequent years there was an increasing stream of reports of sources either ending up in the metals recycling industry with serious economic consequences from smelting of the sources [12]; or in the public domain resulting in serious deterministic effects, environmental and socio-economic impacts. IAEA identified that globally a key root cause was the lack in many countries of an effective regulatory infrastructure and a critical mass of appropriate radiological protection expertise. To address this IAEA developed the Model Project [13]; and whilst there is clear progress, there is much to do. The various issues were brought into focus in the International Conference on the Safety of Radiation Sources and Security of Radioactive Materials in Dijon in 1998 [14]. Arising from this was the development of IAEA's Action Plan to address the issues [15]. This was subsequently revised in 2000 and 2003 [16]. The term Orphan Source came into common usage being defined as "a source which poses sufficient radiological hazard to warrant regulatory control but is not under regulatory control, either because it never has been under regulatory control or because it has been abandoned, lost, misplaced, stolen or transferred without proper authorization". A major element of IAEA's Action Plan was the development of an international "Code of Conduct on the Safety and Security of Radioactive Sources" [17]. Whilst not legally binding as an International Convention would be, it provided a vehicle for an 'international undertaking' that countries could commit to at a political level. Within the European Union (EU) the orphan source problem was also being addressed with the development of a (legally binding) High Activity Sealed Source (HASS) Directive [18]. Both these initiatives are examples of the international community learning the lessons from previous accidents and incidents, and seeking to improve controls over radioactive sources. However one has to say that the overall timescale for change and the pace in moving towards these international undertakings was not breath-takingnot for the want of effort by IAEA, EU and many others. The tragic act of terrorism of 11 September 2001 in New York and Washington, gave a wake-up call to the world in more ways than one. It has impacted on all our lives in some way. This was followed by the distribution of Anthrax spores through the US postal service, which claimed 5 lives, caused significant disruption and spawned ongoing "white powder" incidents around the world. These events together with the earlier terrorist attack on the Tokyo underground in 1995 using the nerve agent Sarin, have fundamentally changed the credibility of a spectrum terrorist driven scenarios using different agents. To date there has been no serious attempt to utilise radiological or nuclear agents, however the global lessons from the terrorist events were recognised by the radiological protection community and, importantly, by governments and international bodies. The net result has been a significant focus of effort and political commitment to improve our collective ability to prevent, and if necessary, respond to Chemical, Biological, Radiological and Nuclear (CBRN) incidents.

3. IMPACT 3.1. Source security and orphan sources The above had a significant impact on the various initiatives to improve the safety and security of radioactive sources worldwide and to address the issue of orphan sources. To the latter we now have to overlay the

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serious potential for terrorists to maliciously acquire radioactive sources and use them in some form of improvised radiological device. This is a significant change in that historically the emphasis in respect of source security has been on preventing inadvertent access or loss of control. Whereas now there is the added dimension of deliberate challenges to source security7 by terrorists. Getting the balance correct between security measures and maintaining the functionality and usefulness of radiological sources is not without problems. This issue is developed in the subsequent paper by Dodd [19] and it is anticipated that the solution to the issue will evolve, probably on a timescale of years rather than months. Another impact of the global lessons, has been an acceleration of actions to address orphan source issues. The net effect has been that inter alia the IAEA Code of Conduct and the EU HASS Directive have been formally agreed faster than they would have otherwise have done. However there is still much to be done and lessons to be learned in the practical implementation of these documents. This acceleration has stemmed from the issue rising up the political agenda. In turn this is due to a recognition not only of the need to improve source security, but the need to bring back under control the many orphan sources that are either already lost from control and in the public domain or just one stage removed. This latter group is the large volume of disused sources, that are nominally still under control, but have been disused for many years and the record or knowledge of their existence is diminishing (see Section 8).

3.2. Emergency preparedness As identified earlier the range of the credible has shifted dramatically and this provides an opportunity and a positive need for 'Getting Ahead of the Curve' - or ahead of the changing threat profile. As yet there has been no real example of the use of a terrorist driven Improvised Radiological Device (IRD), but it is known that terrorists have shown interest in these. This has caused emergency planners to ponder long and hard over how to plan for a radiological attack at an unknown location(s), with an unknown source term and an unknown dispersion/deployment mode. The latter could vary from the classical dirty bomb giving rise to plume dispersion and/or fragments, to a radiological emplacement device that is not announced and only becomes apparent when deterministic health effects are recognised. In essence the emergency planners are pondering the question of "how long is a piece of string". Here it is suggested that there is much to be learned from the lessons of dealing with previous accidents. In particular the accident in Goiania, Brazil in 1987 [1] has much to commend it as a design basis consequence to plan for. It has the elements of • unrecognised health effects from external exposure to source fragments (as may be the case for an implacement device); • widespread dispersion of radioactive contamination across an urban environment; • a large range of intakes of radioactive material; • disruption, fear and trauma (as may be associated with a terrorist attack); • the production of a large volume of radioactive waste (3,500 m3)-very few countries have addressed this lesson. An attack resulting in an end effect such as Goiania would challenge even the most well developed national radiological protection infrastructures. To this we also have to add the lesson that recent experience has shown a predilection of the terrorists to coordinate multiple events. There are international assistance mechanisms in place that would help, for example (a) the IAEA administered International Convention on Assistance in the Case of a Nuclear Accident or Radiological Emergency [20]

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(b) the WHO Radiation Emergency Medical Preparedness and Assistance Network (REMPAN) [21]. Perhaps the immediate lesson is that there is an ongoing need for review and exercising of national and international arrangements. A further conclusion to be drawn from the recent past is that terrorists may not just use one agent in an attack or a series of coordinated attacks. This has led a number of national authorities to look towards a coherent approach to CBRN issues, which also has implications for more routine aspects of radiological protection. For example, in the UK, the Chief Medical Officer for England, published in January 2002 a document entitled "Getting Ahead of the Curve" [22]. This was primarily targeted at improving the strategy for combating infectious diseases but "In its development the strategy has been shaped by experience and opinion which strongly supports the need for a broad based approach to health protection as a whole — infectious disease control as well as measures to address the risks posed by chemical and radiation hazards". This led to the establishment of the Health Protection Agency (HPA) which NRPB is working in partnership with and under a Bill currently going through Parliament, NRPB will become part of HPA. There have already been a number of positive elements to this; for example, collaboration with our chemical colleagues on dispersion modelling for radioisotopes and chemicals; and coordination of emergency response measures, one aspect of which is the development of a broader surge capacity base. It will be interesting to see at the IRPA12 meeting in 2008 what effects this and other coordination of public health issues will have had on the radiological protection community.

3.3. Other lessons continue The current focus on CBRN issues is well merited, and has had a beneficial effect in dealing with some preexisting issues such as those from orphan sources. However conventionally driven accidents and incidents still regularly occur, sometimes with severe consequences. It is important that we continue to investigate these and learn the lessons from them. The following sections concentrate on this ongoing aspect.

4. FEEDBACK MECHANISMS The IAEA's reports of accident investigations have contributed significantly to the process of learning from accidents. By their very nature they have concentrated on the more important accidents that need to be reported in depth, often having many facets such as regulatory control, system failures, emergency response and medical treatment of the radiation casualties. However it is not only the big accidents from which we can learn, we can also learn from the smaller accidents and near misses. This feedback is relevant to suppliers in improving the safety aspects of design, the management in developing radiation protection measures and the training of their staff, and to national and international authorities in helping them prioritise issues and resources to deal with them. Some examples of feedback mechanisms are given in the following subsections.

4.1. IRID In 1996 in the UK, NRPB, the Health and Safety Executive (HSE) and the Environment Agency (EA) jointly established the Ionising Radiations Incident Database (IRID) and published its specifications [23]. The database has 23 alphanumeric fields which categorise the incidents and allow navigation through the database. However the 24th field is the most important field being a text description of the incident, the causes, the consequences and the lessons to be learned. The description is anonymous and is designed to be used as training material. In 1999 a first review of cases reported was published [24] and it is accessible on the web, http://www.irid.org.uk.

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4.2. RELIR The Qualified Expert Group of the French Radiological Protection Society has created an arrangement known as Retours d'Experience sur Les Incidents Radiologiques (RELIR) or in English, Feedback Experience on Radiological Accidents. This has now been undertaken in collaboration with CEPN and the case reports can be found on their website http: / / w w w . relir .cepn . asso. f r.

4.3. EURAIDE A pilot study is nearing completion for the creation of a European Union Radiation Accident and Incident Data Exchange (EURAIDE) system. The objectives of the study are (i) facilitating the establishment of national radiation accident and incident databases where there are none, and to encourage the compatibility of such databases; (ii) establishing a European network to exchange radiological protection feedback from accidents and incidents; (iii) establishing summary reports of relevant accidents and incidents with the aim of identifying lessons to be learned, so that they can be included in radiation protection training programmes; (iv) upgrading the radiological safety in the countries applying to join the EU by integrating them into the above feedback exchange system. 4.4. RADEV The IAEA is informed of radiation accidents and incidents by a variety' of routes. In order to bring these inputs together in a database to facilitate feedback it has developed the RADiation EVent (RADEV) database. This provides for the categorisation of accidents and provides summary descriptions of events, with lessons to be learned that can be used as training material. There has been significant international consultation on the design of the database and the software. It is currently in its final stages of international trialing and will be made available on the IAEA website. Importantly the software has been designed so that Member States can have their own copy and use it as the basis of their national database.

5. COMMON CAUSES OF ACCIDENTS The causes for the loss of control of a source are many and varied. It may be due to a single catastrophic failure or more commonly a combination of events. Table 1 provides a list of some of the more common causes. Here 'loss of control of a source' is taken to include failure of safety systems to control exposures, as well as the physical loss of a radioactive source. An effective regulatory infrastructure will incorporate measures to eliminate or minimize the above problems. However it has to be recognised that it is not just a case of having an appropriate set of regulations. The regulators have to have an appropriate knowledge and skills base (in short be trained) and need the support of a radiation protection infrastructure with a critical mass. By their regulatory enforcement programme, the regulators can set the tone of user compliance. Together with input from Qualified Experts (from the radiation protection infrastructure) this strongly influences the development of the safety culture amongst users. Safety culture is an intangible but readily recognisable characteristic that takes time to develop. The consequence is that although many countries are making significant steps forward to develop a regulatory infrastructure, the development of a safety culture will lag behind and threats to the safety and security of sources will remain an issue for some time to come.

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Table 1. Common causes of loss of control of radioactive sources

Root causes •

Lack of, or ineffective regulatory bodies — regulations — regulatory enforcement • Lack of — national radiation protection services — awareness or training of management and workers commitment by management to safety — an effective radiological protection programme in the organization Specific causes • Lack of, or inadequate — prior risk assessment — security during storage, transport and use radiation surveys, e.g. failure to monitor after a -radiography exposure — supervision emergency preparedness plans • Design or manufacturing fault • Inappropriate maintenance procedures • Human error • Deliberate avoidance of regulatory requirements • Abandonment • Catastrophic event, e.g. fire, explosion, flood • Theft • Malicious act • Loss of corporate knowledge, due to: — loss or transfer of key personnel bankruptcy long term storage of sources decommissioning of plant and facilities • Death of owner • Inhibitions to legal disposal, such as: — no disposal route available — export not possible high costs of disposal

Even mature regulatory infrastructures cannot completely eliminate the threats. Periodically the effectiveness of the arrangements needs to be reviewed in the light of accidents and incidents that have occurred or might occur. One aspect of this might be to look at the possible threats through the life patterns of use of sources. Figure 1 provides a schematic representation of one such approach. In Section 6 examples are given of incidents and accidents that have arisen from the listed shortcomings.

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Good practice with effective control

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Possible shortcomings leading to increased risk and possible loss of control

Figure 1. Challenges to good practice

6. EXAMPLES OF FAILURES IN SOURCE SECURITY 6.1. llegal importation/purchase In 1977 a 37 TBq 60Co teletherapy unit was bought from a hospital in the USA by a hospital in Juarez, Mexico [25]. It was not imported legally and the authorities were unaware of it. The hospital did not have the resources to use it immediately and it was put into storage in a commercial facility without a clear indication of the hazards. The relevant senior staff left the hospital. In 1983 a junior member of staff who knew of its existence, but had no knowledge of the hazard, removed it to sell as scrap metal. During transport of the source it was ruptured and some small source pellets scattered along the road. The source was smelted in a foundry and was only discovered when a lorry carrying contaminated products set off the alarms at the Los Alamos nuclear facility. Some 75 people received doses between 0.25 and 7.0 Gy: 814 houses with activity in the steel reinforcing bars had to be demolished, several foundries required extensive decontamination and the waste generated amounted to 16,000 m3 of soil and 4,500 tonnes of metal. This accident provides an example of a combination of causes: illegal importation preventing regulatory oversight together with long term insecure storage before use and loss of key staff. Had regulatory oversight

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been possible from the start ie, legal importation and authorisation, the other causes of the accident could have been prevented.

6.2. Normal usage Table 1 includes many possible causes of loss of control of radioactive sources that provide challenges to source security during the normal usage of radioactive sources. Management commitment, training and overall safety culture are key elements in ensuring appropriate safety and security measures throughout the useful life of radioactive sources. However there are many instances of good systems being introduced at the beginning of usage, but not being maintained throughout the useful life of sources. 6.2.1. Brachytherapy sources in hospitals There are different types of brachytherapy radioactive sources ranging from 50 - 500 MBq 137Cs sources, used in interstitial manual techniques, to 400 GBq 192Ir sources used in remote afterloading techniques. A major radiotherapy unit could have several hundred brachytherapy sources that are continually being moved and manipulated. This provides an increased potential for failures in following procedures and sources to be lost. There have been many reported instances of such sources leaving hospitals in refuse, still implanted in patients or cadavers. To address this countries often require hospitals to have installed radiation detectors at relevant exit points. Even so there are still reported instances of sources being lost. Typically this comes about from a combination of (i) complacency by those manipulating the sources — "familiarity breeds contempt" — leading to failure to follow procedures, (ii) poor maintenance of detector systems, either of the equipment itself or its positioning in what may be a changing environment, and (iii) lack of management oversight to recognise and address the problems. 6.2.2. Radioactive sources in the nuclear industry Within a nuclear fuel cycle facility a high profile is given to the security of nuclear material and fission products. The same may not always be the case for radioactive sources. Following a minor incident at a nuclear facility in the UK involving the security of a conventional radioactive source, the company carried out a review of the security arrangements for such sources. They found that for the over 2000 sources they had on site these arrangements needed improving, particularly in respect of keeping inventories up to date. Although all the sources were accounted for, many were in different locations than the records showed; having been moved from one location to another for operational reasons. In locating all the sources they realised that a visual image of each source or device was important. As a result they now have a policy of having an electronic image of all their sources to supplement the inventory record and to facilitate finding a source were it to be lost.

6.3. Increased risk modalities Some types of use provide increased challenges to source security. Whilst maintenance of equipment is often an essential element of a radiation safety programme, it can also provide greater scope than normal usage for mishaps. This is because maintenance work often requires the overriding of installed safety systems or working in an environment where the operators may not be fully familiar with the local arrangements or

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hazards. If the work is not properly planned by well trained staff the net effect has in some cases been that the radioactive source has been left in an insecure manner. Another increased risk modality is that of mobile sources. Common examples are sources used for industrial radiography (see Section 6.4) and those used in the oil exploration, mining industry and construction work for the determination of density, porosity and moisture or hydrocarbon content of geological structures or building materials. The sources in their containers are transported from site to site in cars or vans and may be left overnight in the vehicle or temporary storage facilities that may not be secure. There have been instances of the vehicles (with the device in them) being stolen. The thieves may or may not recognise the significance of the contents and often the devices with the radioactive sources in them are abandoned in the public domain.

6.4. Industrial radiography accidents Industrial radiography is in wide spread use, and has a high hazard potential. The construction of petrochemical installations, for example, will involve the use of portable radiographic sources of up to 5 TBq for testing welds in pipes and tanks. Some years ago 137Cs sources were used and some of these may still exist Currently, sources will most often be 192Ir or 60Co, but 169Yb, 170Tm or 75Se may also be used. The housings for these portable sources contain several tens of kilograms of shielding material, such as depleted uranium, lead or tungsten, which may be perceived as being potentially valuable. Also relevant is the fact that the portable nature of this equipment allows it to be used almost anywhere. Often this is in remote locations or under extreme working conditions. Couple this with often limited or non-existent supervision and there is a real potential for entire containers with their sources to be lost or stolen. They can end up in the metals recycling industry or lay dormant in random locations in the public domain. However, perhaps the most significant threat comes from loss of the source on its own. Most remoteexposure radiography source containers have the same general design. The source capsule is physically attached to a short flexible unit often known as a 'source pigtail'. This is designed to be coupled, often with a spring assisted ball and socket joint, to a flexible drive cable. When not in use the source is located in the center of the source container. In use, a guide tube is attached to the front of the container and the source is pushed down it to the required position by winding out the drive cable. Poor maintenance, incorrect coupling, obstructions in the guide tube or kinking it can all lead to extreme pressures being placed on the various linkages and eventually to the source becoming decoupled from the drive cable. This poses an immediate threat to the radiographer who must monitor after every exposure to ensure the source has fully returned to the safe shielded position. Failure to do so has lead to serious exposure of the radiographer and the source dropping out of the equipment unnoticed. To members of the public who find such radiography sources, they look like intriguing items and can easily be picked up and carried back to the family home; often with lethal effects as illustrated below. 6.4.1. Morocco, 1984

In this serious accident, eight members of the public died from overexposure to radiation from a radiography source. A 1.1 TBq (30 Ci) 192Ir source became disconnected from its drive cable and was not properly returned to its shielded container. Later the guide tube was disconnected from the exposure device and the source eventually dropped to the ground, where a passer-by picked up the tiny metal cylinder and took it home. The source was lost from March to June, and a total of 8 persons (the passer-by, members of his family and some relatives) died; the clinical diagnosis was 'lung haemorrhages'. It was initially assumed that the deaths were the result of poisoning. Only after the last family member had died was it suspected that the deaths might have been caused by radiation. The source was recovered in June 1984.

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6.4.2. Yanango, Peru, 1999 In this accident [10] gamma radiography using a 1.37 TBq 192Ir source in a remote exposure container, was being carried out at the Yanango hydroelectric power plant. At some stage the 'source pigtail' became detached from its drive cable. A welder picked up the source, placed it in his pocket and took it home. The loss of the source was noticed the same day and it was recovered within 24 hours. However the dose received in this period was such that despite heroic medical treatment the welder lost one leg and had other major radiation burns. His wife and children were also exposed, but to a lesser extent. 6.4.3. Cairo, Egypt, 2000 This was a very similar incident to the one above. A farmer picked up a 3 TBq 192Ir source, thinking it valuable and took it home. On 6 May 2000 the farmer and his 9-year-old son went to their local doctor complaining of skin burns. The doctor prescribed medication for a viral or bacterial infection. The youngest son died on 5 June 2000 and the farmer on 16 June. On 26 June a blood test was done on other family members who were showing similar symptoms. The blood test showed severe depression of the white blood cell count and radiation exposure was suspected. The source was located and recovered. Other family members were hospitalized. Four men were charged with gross negligence, manslaughter, and unintentional injury because they had failed to notify authorities that the source, used to inspect natural gas pipeline welds, was not recovered after the job.

6.5. Challenging events During the life of some sources there may be some events that challenge the safety and security measures through abnormal situations, eg, fires, flood, explosions, transport accidents etc. The first requirement is recognition that an event may have a source security implication. This should then lead to the triggering of appropriate emergency preparedness plans. The greater the delay in implementing the emergency preparedness plan the longer there will be uncontrolled exposure and the greater area over which there may need to be searches for lost sources. 6.5.1. Accident in San Salvador, 1989 This accident [6] occurred in an industrial irradiation facility containing 0.66 PBq of 60Co in the form of a source rack of two modules each containing a number of source pencils. At the time of the accident there was no relevant regulatory or radiation safety infrastructure and the country had been in a civil war for 10 years. The net effect was a degradation of the safety systems and the operators' understanding of radiation hazards. In the accident in 1989, three people gained entry to an irradiation chamber to free the source rack, whose movement to the safety of the water pit had been impeded by distorted product boxes. One person died and another had a leg amputated. The occurrence was not recognised for two weeks, and during this time damage to the source rack from the accident caused the source pencils to drop out. Most fell into the water pit, but one fell onto the floor of the irradiation chamber. It is pure chance that none fell into one of the product boxes that could have transferred them out of the facility. The installed monitor on the product exit, designed to detect such an event, had long since failed. Some 6 months after the accident an IAEA team visited the plant to carry out an accident investigation. By that time the source pencil from the irradiation chamber had been recovered and shielded by the supplier, but the other source pencils were still at the bottom of the water pit awaiting recovery. Importantly no one had confirmed that the total inventory of source pencils had been accounted for and that none had left the plant. At the insistence of the IAEA team an underwater photograph was taken to confirm that all the source pencils were accounted for.

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6.5.2. Tammiku, Estonia, 1994 In this accident [2] a cylindrical radioactive source in a metal frame was found in a consignment of scrap metal imported to Tallin, Estonia. The source, with an activity of up to 7.4 TBq 137Cs was thought to be part, just a small part, of a seed irradiator (leaving the open question of where the rest of it was?). In this case the first part of the emergency preparedness plans worked and the source was successfully recovered and taken to the national waste disposal facility. Unfortunately this was just an underground concrete bunker with poor security. Three brothers broke into the facility and stole the source for resale as scrap metal. As a result one brother died from radiation exposure and the other two brothers, plus two other family members suffered significant deterministic effects. The original find of the source in scrap metal imports had raised queries about other possible orphan sources being in Estonia and a Government Commission to assess the situation was set up. During its work it found a 1.6 TBq 137Cs source in a container that had been abandoned close to a main road in the countryside.

7. MAINTAINING KNOWLEDGE AND PRECAUTIONS Over the useful life of a radioactive source, which may be decades, there can be challenges to keeping the corporate knowledge of the source security requirements or even of the existence of the sources. For example (i) The knowledge of the source security arrangements may be vested in one or two key staff, without it being properly covered in safety documentation or covered by management oversight. When those key staff leave the source security arrangements will degrade. (ii) A sudden change in ownership can remove all corporate knowledge of the need for source security requirements. The accident described in 6.5.1 below provides an example of the change of ownership of a facility between nations where knowledge was not passed on. (iii) Bankruptcy can also remove corporate knowledge. This can happen very suddenly with in some cases everybody walking away from the problem and leaving a derelict facility. Although the accident in Goiania described in 6.5.2 is not a case of bankruptcy it has the same characteristics eg, abandonment of responsibility.

7.1. Lilo, Georgia In 1992, with the break up of the former USSR, the Soviet Army abandoned its former facilities in Georgia. One of these was a training camp in Lilo, which was taken over by the Georgian Army. In October 1997, eleven soldiers developed radiation induced skin lesions. A radiation-monitoring search of the facility revealed 12 abandoned Cs sources ranging from a few MBq to 164 GBq [3]. These had been used by the previous occupants in Civil Defence Training; with the sources being hidden about the site and trainees having to find them. Many were still where they had been hidden. In addition, one 60Co source and 200 small Ra sources used on gun sights were also found on the site.

7.2. Goiania, Brazil In 1987 in Goiania [1], a private medical partnership specialising in radiotherapy broke up acrimoniously. No one took responsibility for a 50 TBq 137Cs teletherapy unit that was left abandoned in the partially demolished building of the former clinic. After two years some local people dismantled the source and its

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housing and removed it for scrap metal value. In the process the source was ruptured. The radioactive material was in the form of compacted caesium chloride, which is highly soluble and readily dispersible. For over two weeks the radioactivity was spread over parts of the city by contact contamination and resuspension. Contaminated items (and people) went to other parts of the country. The recognition of the existence of the problem was triggered by an increasing number of health effects. Overall some 249 people were externally contaminated, 129 internally, 21 people received in excess of 1 Gy and were hospitalized, of which 10 needed specialized medical treatment with 4 of these dying. The decontamination and clean up of the environment took 6 months of intensive effort and produced 3,500 tonnes of active waste. In passing it is worth noting that although not an example of terrorism the Goiania accident provides a good example of the possible consequences of the use by terrorists of an improvised radiation dispersal device.

8. DISUSED SOURCES There are a number of similarities between the issues identified in the previous section and the problem of disused or "spent sources". Both involve the loss of corporate knowledge or awareness of source security issues, but this section very much focuses on the end of life issues of radioactive sources. Perhaps the main characteristic here is that at some stage there has been a recognition that the sources, or the equipment they are in, have come to the end of their useful life or there is no clear future use for them. This can manifest itself in many ways. (i) The sources can simply be removed to storage on site and through lack of management are not disposed of but simply left. Over time the safety and security arrangements degrade until eventually control is lost and the source may end up in the public domain, especially the metals recycling industry. The accidents described in 6.1 and 6.2 provide significant examples of this. (ii) A variation on the above theme is that the sources are left in situ, eg, in level gauges on a disused part of a petrochemical facility. Eventually when that part of the plant is demolished, all the metal, including the sources, ends up in the metals recycling industry and the source may be smelted. There are many such recorded events which can be very costly: in the range US$ 1 to 100 M [12]. (iii) In many cases the management takes a conscious decision not to dispose of the source, simply because the costs of disposal are very high. Whilst security arrangements may be maintained to a degree, the effect of this practice is to increase the potential for security to fail over time. It has been estimated that in the USA 500,000 of the two million sources may no longer be needed and thus could be susceptible to being orphan [26]-or a target for malicious intent. In the European Union some 30,000 sources are in a similar position [27].

8.1. Istanbul, Turkey In 1993 a licenced operator loaded three spent radiotherapy sources into transport packages for their return to the original supplier in the USA [4]. However the packages were not sent and were stored in Ankara until 1998. Two were then transported to Istanbul and stored in a general-purpose warehouse. After some time the warehouse became full and the packages were moved to empty adjoining premises. After 9 months these premises were transferred to new ownership, and the new owners not knowing the nature of the packages, sold them as scrap metal. The family of scrap merchants broke open the source container and unwittingly

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exposed themselves to the unshielded 3.3 TBq 60Co source. Ten people received doses between 1.0 and 3.1 Gy and showed signs of the acute radiation syndrome. Fortunately no one died. The second source, 23.5 TBq 60Co remains unaccounted for, despite an extensive search and monitoring programme.

8.2. Samut Prakarn, Thailand One company in Bangkok possessed several teletherapy devices without authorization from the Thailand Office of Atomic Energy for Peace [5]. In the autumn of 1999, the company relocated the teletherapy heads from a warehouse it had leased to an unsecured storage location. In late January 2000, several individuals obtained access to this location and partially disassembled a teletherapy head containing 15.7 TBq of Co. They took the unit to the residence of one of the individuals, where four people attempted to disassemble it further. Although the head displayed a radiation trefoil and warning label, the individuals did not recognize the symbol or understand the language. On 1 February 2000, two of the individuals took the partially disassembled device to a junkyard in Samut Prakarn. While a worker at the junkyard was disassembling the device using an oxyacetylene torch, the source fell out of its housing unobserved. By the middle of February 2000, several of the individuals involved began to feel ill and sought assistance. Physicians recognized the signs and symptoms and alerted the authorities. After some searching through the scrap metal pile, the source was found and recovered. Altogether, ten people received high doses from the source. Three of those people, all workers at the junkyard, died within two months of the accident as a consequence of their exposure.

9. CONCLUSIONS It is clear that there are many lessons to be learned from accidents and incidents which can help improve our control of radiation sources and in responding to radiation accidents. During the 1980's and 1990's there was a growing awareness of a major issue over Orphan Sources and source security. As a result the international radiation protection community set in motion a number of initiatives to address the issue. These are now starting to bear fruit, but there is still much to do. The tragic act of terrorism on 11 September 2001 in the USA fundamentally changed the credibility of terrorist driven scenarios that might include radiation sources. In particular it indicated that source security must now not only protect against inadvertent access to radiation sources but also the deliberate access challenge from terrorists trying to aquire radiation sources. Getting the correct balance between source security and maintaining the functionality and usefulness of radiation sources will be a challenge. The current focus on CBRN issues is well merited, and has had a beneficial effect in dealing with some pre-existing issues such as those from orphan sources. However conventionally driven accidents and incidents still regularly occur, sometimes with severe consequences. It is important that we continue to investigate these and learn the lessons from them.

REFERENCES [1] International Atomic Energy Agency, The Radiological Accident in Goiania, IAEA, Vienna (1988). [2]

International Atomic Energy Agency, The Radiological Accident in Tammiku, IAEA, Vienna (1998).

[3] International Atomic Energy Agency, The Radiological Accident in Lilo, IAEA, Vienna (2000).

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[4] International Atomic Energy Agency, The Radiological Accident in Istanbul, IAEA, Vienna (2000). [5] International Atomic Energy Agency, The Radiological Accident in Samut Prakarn, IAEA, Vienna (2002). [6]

International Atomic Energy Agency, The Radiological Accident in San Salvador, IAEA, Vienna (1990).

[7] International Atomic Energy Agency, The Radiological Accident in Soreq, IAEA, Vienna (1993). [8] International Atomic Energy Agency, The Radiological Accident at the Irradiation Facility in Nesvizh, IAEA, Vienna (1996). [9] International Atomic Energy Agency, An Electron Accelerator Accident in Hanoi, IAEA, Vienna (1996). [10]

International Atomic Energy Agency, The Radiological Accident in Yanango, IAEA, Vienna (2000).

[11]

International Atomic Energy Agency, The Radiological Accident in Gilan, IAEA, Vienna (2002).

[12] J. O. Lubenau, J. G. Yusko, "Radioactive Materials in Recycled Metals-An Update", Health Physics, 74 (3), 293-299(1998). [13]

International Atomic Energy Agency, Organization and Implementation of a National Regulatory Infrastructure Governing Protection against Ionizing Radiation and the Safety of Radiation Sources, IAEA-TECDOC-1067, IAEA, Vienna (1999).

[14]

Safety of Radiation Sources and Security of Radioactive Materials, (Proc. Int. Conf., Dijon, 1998), IAEA, Vienna (1999).

[15]

Action Plan for the Safety of Radiation Sources and Security of Radioactive Materials, GOV/1999/46GC(43)/10, IAEA, Vienna (1999).

[16]

Action Plan for the Safety of Radiation Sources and Security of Radioactive Materials, GOV/2003/47GC, IAEA, Vienna (2003).

[17]

International Atomic Energy Agency, The Code of Conduct on the Safety and Security of Radioactive Sources, IAEA-CODEOC/2003, IAEA, Vienna (2003).

[18]

Commission of the European Communities. Council Directive 2003/122/Euratom of 22 December 2003 on the control of high activity sealed sources. Official Journal of the European Union L346, 31 December 2003.

[19]

B. Dodd, Safety and Security of Radioactive Sources: Conflicts, Commonalties and Control (these proceedings).

[20]

International Atomic Energy Agency, Convention on Early Notification of a Nuclear Accident, and Convention on Assistance in the Case of a Nuclear Accident or Radiological Emergency, Legal Series No. 14, IAEA, Vienna (1987).

[21]

M. Repacholi, G. Souchkevitch, I. Turai: Proceedings of the 8th Coordination meeting of WHO Collaborating Centres in Radiation Emergency Medical Preparedness and Assistance Network, REMPAN, 4-7 June 2000, NRPB, Chilton, UK. WHO/SDE/RAD/02.08, pp!45, WHO, Geneva, Nov 2002.

[22]

Department of Health. Getting Ahead of the Curve-A strategy for infectious diseases (including other aspects of health protection). A report by the Chief Medical Officer. Department of Health, 2001.

[23]

G. O. Thomas, J. R. Croft, M. K. Williams, J. O. McHugh. IRID: Specifications for the Ionising Radiations Incident Database, Chilton, NRPB/HSE/EA (1996).

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[24] J. R. Croft, G. O. Thomas, S. Walker, C.R. Williams. IRID: First Review of Cases Reported and Operation of the Database, Chilton, NRPB/HSE/EA (1999). [25]

Comision Nacional De Seguridad Nuclear Y Salvaguardias, Accidente por contaminacion con cobalto60. Mexico, Rep. CNSNS-IT-001, CNSNS, Mexico City (1984).

[26]

R. A. Meserve, "Effective Regulatory Control of Radioactive Sources", National Regulatory Authorities with Competence in the Safety of Radiation Sources and the Security of Radioactive Materials (Proc. Int. Conf., Buenos Aires, 2000), IAEA-CN-84/2, IAEA, Vienna (2001).

[27]

M. J. Angus, C. Crumpton, Et Al, "Management and Disposal of Disused Sealed Radioactive Sources in the European Union", EUR1886 (2000).

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Current Trends in Radiation Protection H. Metivier, L. Arranz E. Gallego and A. Sugier (eds.)

Safety and Security of Radioactive Sources: Conflicts, Commonalities and Control Brian Dodd1

ED Consulting, 10313 Cogswell Avenue, Las Vegas, NV89134-5209, USA

Abstract. The events of 11 September 2001 required radiation safety professionals to rethink the basis of security for radioactive materials. This brought them into conflict with nuclear security professionals who expanded their degree of interest in other radioactive materials. Being forced to work together was like an arranged marriage. Problems arose because of different cultures, mindsets and language. The relationship between the safety of radioactive sources and the security of radioactive sources was hotly debated with the aim of establishing areas of responsibility and authority. Some models of the possible relationship between safety and security are presented and discussed along with a new model that highlights the commonalities yet acknowledges the differences in purpose of the two disciplines. The implications of this model and the possible emergence of a new discipline are addressed.

1. INTRODUCTION Without glorifying the events of 11 September 2001, it must be recognized that they have awakened a dormant and fascinating dilemma. Exactly how do, or should, safety and security interact? Which should take the lead? How can safety and security efforts be managed efficiently without duplication or conflict? The safety and security paradox has caused professionals throughout the nuclear and radiation disciplines to scratch their heads, argue and debate in ways not seen before. In no area has this been more so than in the safety and security of radioactive sources.

1

E-mail: [email protected]

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2. BACKGROUND Historically, with regard to radioactive sources, safety was the primary focus. A radiation protection officer's responsibility was to ensure that sources could be used for their intended beneficial purposes without harming either the user or the public. Security was an integral, but a relatively minor, part of safety in that it was used to prevent people being unintentionally exposed to the source, either by them being able to get to the source or by the radioactive material getting to them. The drafters of the International Basic Safety Standards [1] wisely addressed the issue in paragraph 2.34 by stating, "Sources shall be kept secure so as to prevent theft or damage and to prevent any unauthorized legal person from carrying out any of the actions specified in the General Obligations for practices of the Standards..." However, in the late 1980s and 1990s, it became clear to some in the health physics profession that our controls were not sufficient. A pattern was observed of members of the public being seriously injured and killed by orphan radioactive sources, often in developing countries. The world's consciousness of the problem was raised at the landmark Dijon conference on Safety of Radioactive Sources and Security of Radioactive Materials in September 1998 [2] and was reinforced at the regulator's conference in Buenos Aires in December 2000 [3]. Efforts to address orphan source problems were begun in earnest by the International Atomic Energy Agency (IAEA) in their 1999 Action Plan for the Safety of Radioactive Sources and Security of Radioactive Materials [4]. This included actions for the development of a Categorization of Radiation Sources [5] and "an international undertaking" that eventually took the form of a Code of Conduct for the Safety and Security of Radioactive Sources [6]. Security of sources, especially through strengthening infrastructures, was a component in all of these activities. And then came the tragic and watershed events of 11 September 2001, and every professional in every scientific and technical field started thinking differently. "What if someone tried to use this technology in a deliberately malicious or malevolent way?" Naturally, those involved with nuclear power became concerned with airplanes being flown into plants, owners of large irradiators started worrying about saboteurs forcing their way in and blowing them up, and health physicists started brainstorming about what malicious things can be done with radioactive sources. Once some of the more likely scenarios had been postulated, the concerns soon moved on to determining which sources were the 'best' for these malevolent purposes. Then the questions became: "Where were these sources located?" and "How can we stop them getting into the hands of terrorists?" Suddenly, security of sources took on a completely new emphasis.

3. SAFETY AND SECURITY PROFESSIONALS This new perspective on the security aspects of radioactive materials immediately required two separate, but related groups of professionals to begin to figure out how to work with each other. "Discussions" took place as to which was the more important, safety of sources or security of sources. Who should do what? In particular, who should take the lead? Is it the security person's job to ensure sources are under better control or the safety person's job? In the more nuclear-developed countries that have separate groups of safety and security professionals, these people are working in different departments often in different ministries and almost certainly for different bosses. The natural human tendency to want to be involved with, and in charge of, high-profile work caused rivalries to develop. Altruistically, everyone wanted to do their part to fight the terrorists, but on a more selfish level (especially when the money began to flow), everyone wanted a piece of the pie. So, to establish our viewpoint and illustrate why the radiation safety staff should be responsible for this area rather than the nuclear security staff we started trying to carefully define safety and security and to delineate lines of work, responsibility and authority accordingly. And immediately we were confronted with

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linguistic difficulties. Look up the word safety in a dictionary and it uses the word security to describe it and vice-versa. In the international arena, the situation was worse. In a large number of languages, one word is used for both meanings, or there is one word for safety and security, and another that just means security. To talk about safety and security as distinctive concepts in most languages requires the use of further qualifying adjectives and it cannot be done with simple, single words. Trying to use physical protection to separate out security did not help because security employs analysis and administrative measures as well. So then we stated that the difference was obvious. Fire fighters deal with safety and the police deal with security It is intuitively clear. One deals with attempting to prevent harm and the other deals with attempting to prevent illegal acquisition and use. But if so, does this door lock meet a safety concern or a security concern? Part of the problem lies in the fact that safety and security professionals tend to have different mindsets. This is not unreasonable since in many instances safety and security tend to run counter to each other. This is best illustrated with regard to information management and dissemination. The requirements of safety demand open communication, the sharing of data and transparency about problems found. On the other hand, security demands secrecy, confidentiality and sharing only on a need-to-know basis. The socalled 'coastal states' want to be notified of ships carrying casks of high-activity spent nuclear fuel going past because of safety concerns. The 'shipping states' do not want to make such notifications because of security concerns. The information and safety signs in a hospital tell the terrorist exactly how to get to the radiotherapy therapy department that houses some of the 'best' radioactive material. But the opposite demands of safety and security are not only limited to information. For safety and emergency preparedness, it is important to keep exit doors unlocked. From a security viewpoint, the use of crash bars that anyone can open is unacceptable. Not only do safety and security professionals think differently, but in the back of our minds, we also do not trust each other. On the surface, we are professional and polite, but we are suspicious. Each thinks that the other does not know their subject well enough to dabble in it. The fear of the safety folks is that the security folks will want to increase security to the point that they will shut down the legitimate and beneficial uses of the radioactive sources. Safety people think that security people really do not know anything about what the sources are used for and how much good they do. Frankly, they wonder if the security folks even know what the sources look like and how they are used. Safety people think that left to their own devices, security folks are quite likely to specify that you cannot let a member of the public, such as a patient, into a radiotherapy treatment facility ... or at least not without a background check. Then there is the perception that security are the new "boys on the block" encroaching into the safety person's territory. Heretofore, most of the security professionals in the nuclear arena were only dealing with nuclear material and nuclear weapons, and now it seems that they want to move in and take over traditional safety responsibilities. In addition, safety people worry that the mentality of nuclear weapons material security will result in such an emphasis on security that safety issues are ignored. The fact that there have been events where an obsession with security resulted in unsafe situations serves to reinforce the perception and to generalize it. Conversely, the security professionals believe that safety folks really do not understand what security is all about. Safety folks think that a lock is a lock, and that it actually stops people. A lock might, perhaps, stop a teenager from stealing a bike, but most locks are not going to stop a professional for very long. A car thief can be inside the vehicle within minutes, if not seconds. Most safety people are ignorant enough to even think that a fence increases security and do not realise that a fence only causes a 30 second delay for a knowledgeable, trained person or assault group. The safety folks do not understand that the security requirements have to be matched to threats, risks and consequences. Security has no meaning in a vacuum. Asking, "Is this secure?" is as meaningless, or as meaningful, as asking "Is this safe?" In addition, the safety folks primarily only care about human health impacts and sometimes only about the short-term health

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impacts. The fact that a dirty bomb in the downtown area of a major city could have an enormous social and economic impact is pushed aside as not being that important as long as no-one is hurt. Finally, there is a mindset on both sides that one person cannot do both; that the degree of speciality is such that if a person is in a security role, he or she cannot take care of safety and vice versa. As a personal example, despite the fact that I had written the security plan for a research reactor facility with highly enriched fuel, I was looked upon as a safety person, not a security person because of the title of my job and my being in a Radiation Safety Section. However, this specialist mentality is usually only prevalent in those establishments or countries that are large enough to have specialists. These are usually the nuclear power countries. In the majority of countries and the facilities within them, there is just one person who controls the source(s). This person is responsible for both safety and security as traditionally defined. This is a fact of life for most of the world and we need to acknowledge it in the advice we give with regard to safety and security of radioactive sources. Where there are different groups of professionals, we have to recognize that while some of our objectives and priorities are different, there is common ground. Therefore, we have to learn to co-operate and work together. Many countries, institutions and agencies, including the IAEA, are struggling with exactly how to do this, and particularly with the organizational changes necessary. I have characterized the safety and security professional having to work together as an arranged marriage. It might not be what we would have both desired, but it is a reality of life that we have to live with in the future and so we might as well make the best of it that we can. We must learn to understand each other's language, viewpoint, thinking, objectives and objections... and be committed to see the common goal achieved. I am heartened by the analogy, in that my colleagues from countries where arranged marriages are the norm, say that they are almost always lasting and successful, and certainly much more so than in the West where we rely on that fickle feeling of love.

4. LANGUAGE PROBLEMS A marriage between those who speak different languages has extra challenges. The problem regarding the words safety and security has already been mentioned, but there are others that seem to cause us as much grief. For example, is malicious the same as malevolent, and if not, which should be used in the safety and security of sources context? A careful study of the words seems to allow a slight difference. Malicious, related to persons or their dispositions, means "given to malice, addicted to sentiments or acts of ill-will" as in "malicious damage, mischief, slander, striking..." whereas malevolent means "desirous of evil to others... exercising an evil influence". So the distinctives seem to be that malevolent has a sense of evil associated with it and seems better applied to threats or intents, while malicious is better applied to acts. To clarity, one could have a malicious act that is not malevolent. Most vandalism or graffiti would fall into this category in that it is an act of ill will without evil intent. The use of a key to scratch the paint of a random selection of cars would be malicious, while the intent to use a key to scratch the paint of a hated rival's car is likely to be malevolent. Then one has to be very careful about use of the word terrorist, especially in the international agencies. In fact, this is such a sensitive subject, fraught with all sorts of political implications that the IAEA, for example, will try to avoid the use of the term in anything but a generic context and talk about 'those with malevolent intent' or 'sub-national groups' instead. The problem is that one man's terrorist is another man's freedom fighter. It can be argued that whether people are terrorists or not depends upon what one thinks of their motivation and which side of the fence one is standing. History is replete with examples of 'terrorists' who would be considered 'successful' in that they have overthrown one government and eventually formed recognized legitimate governments of their own. However, whether one can define a terrorist in absolute terms or not will be left to those who are better qualified to answer.

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One of the terminological confusions that is more straightforward, however, is that of the blossoming misuse of the adjective 'radiological' as used in such expressions as 'radiological materials' and 'radiological dispersal devices' (RDDs). There are no such things, and it is a misuse of the English language by those who are new to the subject or on the fringes of it. There are two accepted uses of the adjective in the field of radiation protection. When it is desired to encompass the hazards from both sealed and unsealed radioactive material (radiation, contamination, inhalation, ingestion), one can talk about radiological hazards, or radiological protection. The only other proper use is related to radiology. A colleague ably and humorously illustrated this issue, by asking whether an HDD was a device to scatter radiologists around. However, even here, one has to recognize that English is a living language and the sheer weight of force of the United States' usage of the terms is such that the 'purists' have already lost the battle. Unfortunately, RDDs at least have entered into common usage and are probably here to stay. An additional point of terminology clarification that has to be made to some of the incoming security staff is the distinction between radiation sources and radioactive sources. In IAEA documents, great care is taken to use the correct term in the correct place. Radiation sources are any source that emits radiation, including machine-generated radiation sources such as X-ray devices. Radioactive sources are those incorporating radioactive materials and are therefore a sub-set of radiation sources. Then there are all sorts of problems with differing use of such terms as threat, risk, consequence and response between safety, emergency response and security professionals. For example, when radiation safety and emergency response people talk about response to an event they mean all of the actions that subsequently follow an event. So for a transportation accident involving radioactive materials, for example, this would include the initial actions by police, fire and ambulance as well as subsequent actions by radiation safety staff with their associated surveys, monitoring and clean up. In other words, response would include all necessary actions to restore normality. On the other hand, those working in security7 have a more limited use of the term response. It is primarily the initial actions that a security force takes when notified of a security breach, for example. However, it can include subsequent law enforcement follow-up actions. Further confusion arises from the fact that emergency response professionals use the term threat to mean what the security professionals call a consequence. From a safety viewpoint, the threat from a lost Category 1 radioactive source is that it will get into the hands of an innocent member of the public, become unshielded and cause serious injuries. However, from a security person's perspective, a threat is the actual intruder or group attempting to gain entry or access along with their resources such as information, money and weapons. They would say that the potential injuries from an RDD are the consequences of a threat being carried out successfully. This leads to a discussion of the different types of analyses that safety and security professionals undertake. Security assessments largely have a deterministic basis whereas safety assessments often use probabilistic methods. Design basis threats and risk-based threat assessments are essential to security considerations, since there is universal acceptance within security circles that security must be based on a specified threat. At first, this is difficult for those working in safety to understand, but it becomes clearer when examples are used. Consider locks on doors. If the threat is a toddler getting into the cupboard under the sink, then a 'childproof latch is sufficient security. However, anyone above the age of four can figure out how to get in, and so an increased threat needs a commensurate increase in security. Therefore, a house or apartment has a front door with a lock, which requires a specific key to open. However, having seen televised police raids, there can be no doubt that those who want to get in and do not care about damaging the door can easily do so. But then again, a police battering ram will not do the job on a bank vault. Nonetheless, given enough time and the right equipment, such as a thermic lance, a determined group of robbers could probably manage to get inside. So, in order to answer the question as to what sort of lock and door provides sufficient security, one has to consider the likely threat and the consequences of them being successful. This

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process is called a risk-based threat assessment. The decision as to what threat one will specifically protect against (child, burglar, bank robber) is deterministic and becomes the design basis threat. Risk is another term, which has caused difficulties for a number of years and is not new to the current safety and security dilemma. Part of the problem is that in general conversation it is often used carelessly. However, even its technical use by safety and security professionals is different enough to add to the poor communication between them. Most professionals concur with the definition that risk is equal to the probability of an event multiplied by the consequence of the event. In safety circles, a great effort is made to quantify the probability, usually in terms of some small fraction (10~x) so that it can be used in probabilistic safety assessments. While it might be difficult, for example, to determine the probability of a transport container failing under certain accident conditions, at least it is theoretically possible and methodologies are available. In security, the situation is much more difficult because probabilities are related to human actions. Quantifying the risk of an HDD requires knowing such things as the probability of a person or persons wanting to develop and use such a device, the probability of their being able to acquire the necessary materials and so on. These probabilities are almost impossible to quantify, and this drives the security folks to use the more deterministic conditional risk. In this case, it is assumed that the attack will occur (probability = 1), and the conditional risk becomes the probability of it being successful multiplied by the consequences.

5. THE RELATIONSHIP BETWEEN SAFETY AND SECURITY OF SOURCES Recognizing that we have an arranged marriage between professionals with different cultures and language and that there is a some reluctance and mistrust between us, but also recognizing that we have a common goal, the question becomes: Is it possible to derive a philosophy that links safety and security to the satisfaction of both parties? The reasons for doing so must rise above the baser motivations of budget, power and prestige, because there is a desperate need for a model that will clarify roles and responsibilities and enable the important work on safety and security to be managed efficiently and effectively, without duplication or conflict.

5.1. Various models One conference participant described the relationship thus: "Safety is keeping sources away from the people, while security is keeping people away from the sources." If it is understood that the 'people' in each instance are different, then this is quite a catchy and succinct summary. (In the first instance, the people are the innocent public, while in the second they are those with malevolent intentions.) Others would explain that there are four possible alternatives with regard to the relationship between safety and security as illustrated in Figure 1. Which is correct? Most people would agree that the first is not valid. Safety and security are not independent and separate, but somehow connected. A large group of people, feeling uncomfortable with options 3 or 4 would opt for number 2. The argument is that with regard to radioactive sources there are aspects of safety, such as personnel dosimetry, that have nothing to do with security, and there are aspects of security, such as threats assessment, that have nothing to do with safety. However, there are areas, such as access control, where there is clear overlap. Putting a high-activity source in a locked, shielded storage container in a locked, thick concrete storage room addresses some of the concerns of both safety and security. Some respected safety professionals argue strongly for alternative 3, saying that a large source cannot be safe unless it is secure but a source can be secure without being safe, e.g. a source could be well guarded, but it could be leaking radioactive material or not properly shielded. So that for radioactive sources, security is a necessary, but not sufficient, element of source safety. Therefore, security is a subsidiary to source safety.

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Figure 1. Options for the relationship between safety and security of radioactive sources

However, security professionals object to the logic that prerequisites are by definition subsidiaries. On the contrary, they say, if security is a prerequisite or an essential element then it is a dominant or controlling factor because safety cannot be achieved without first achieving security. This leads to alternative 4. Security professionals would state that keeping sources safe from harming people is only one small part of security. The purpose of security is much broader in that it also tries to prevent the social, economic and political impacts of malevolent use. Yet another model is a development of alternative 2, which recognizes that there are not sharp boundaries, but indistinct or variable boundaries between the overlap of safety and security. It also broadens the discussion to include all radiation sources. This is illustrated in Figure 2 where it can be seen that electrically generated sources of radiation, such as X-ray machines, are largely a safety' issue with just a small security component. While the malevolent use of a portable generator to beam radiation to an innocent victim should not be ruled out, it is probably not very attractive to terrorists because of its localized nature. At the other end of the spectrum, the security' component of nuclear materials control, especially weapons-grade material, is much greater than any human health and safety concerns. Radioactive sources span the gap between, with the more 'desirable' sources from a malevolent use perspective, such as Categories 1 and 2 [8], having a greater security component than the lesser ones. However, this model does not present the complete picture, since some sources are so innocuous (Category 5) that their safety and security components are both quite small.

Figure 2. The safety and security of radiation sources continuum

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Figure 3. Model for the relationship between safety and security of radioactive sources

The problem again is that most of these discussions relating to the interface between safety and security have not taken place from a pure academic or philosophical perspective. They have come about as a result of arguments about such things as to who should take the lead in developing policies, procedures, regulations and guidance. Is this job in my health physics programme or is it in your physical security programme? The decisions have implications for human and financial resources, for power, prestige and visibility.

5.2. A proposed new model There is a great need for a satisfactory solution, and so the following model of the relationship between safety and security is offered as one that identifies a single commonality while recognizing a variety of purposes. It is believed that the model, which is diagrammed in Figure 3, and focuses on the prevention aspects of safety and security, provides a way forward. The primary objective of radioactive source safety, and safety professionals, is to prevent adverse human health impacts, whatever the cause, whether they are from inadvertent or intentional events. Inasmuch as the other adverse impacts, such as environmental impacts also affect human health and safety, then prevention of these also becomes a goal, but the focus is still primarily on human health. However, as reluctant as the safety professional might be to admit it, the purposes of radioactive source security are more evenly aimed at preventing all five adverse impacts. Perhaps the main emphasis for security is on prevention of political and human health impacts, but social-psychological, economic, and environmental consequences are also significant factors. The common cause of these adverse impacts is the lack of, or loss of control (Figure 3) of the radioactive sources (or the radioactive material within them). Therefore, the single, common objective of both safety

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and security, which is necessary to achieve their ultimate goals, is the prevention of loss of control. This is the common ground upon which a successful arranged marriage can be built. The significance of this simple statement should not be underestimated. A new discipline called 'Radioactive Material Control' is in the process of being created that encompasses the common components of both radioactive material safety and security (See Table 1). Within the IAEA, in addition to the International Basic Safety Standards [1], the standard references for this discipline would include documents such as the requirements on Legal and Governmental Infrastructure for Nuclear, Radiation, Radioactive Waste and Transport Safety [7], the revised Categorization of Radioactive Sources [8], the interim guidance on Security of Radioactive Sources [9], the revised Code of Conduct for the Safety and Security of Radioactive Sources [10] and the Technical Document on Improving Control over Radioactive Sources [11]. Immediately, it should be recognized that loss of control could be caused by either inadvertent or intentional events. Inadvertent loss of control usually results from: negligence, when sources are misplaced, lost, or forgotten; through accidents, when a source is lost or damaged with a release of its radioactive material; or through collateral theft. Collateral theft occurs when the theft of the source is not the objective but is incidental, for example, to the theft of the vehicle or shielding material containing the source. As shown in Figure 3, the two motivations for deliberately violating control over sources are financial or malevolent and can be promulgated by licensees already in possession of radioactive sources or by those who would like to acquire them for such purposes. Acquisition of radioactive sources can be via theft, illegal purchase, legal purchase or possibly finding an orphan source. Incidentally, it should be noted that deliberate loss of control events did not originate post 11 September 2001. In the past, source owners have been known to throw them away to avoid the costs of proper disposal, and there have also been a few malevolent attempts by source owners to hurt other individuals by secretly irradiating them. However, it is true to say that the magnitude and range of the intentional loss of control possibilities has increased. Financial motives for loss of control of sources can involve: — illegal sale for profit of possessed or acquired materials; — attempts to extort money via blackmail; — avoidance of the burdens of the cost of ownership, such as dumping to avoid disposal costs, or licensing fees. The malevolent motives include: — terrorism; — attempts to gain political power by persuading governments to capitulate on issues, such as releasing prisoners; — an individual's intent to injure another person for non-terrorist reasons, such as hate, or jealously. Malevolent objectives can be achieved by dispersion of the radioactive material, by direct irradiation or by sabotage of a facility or consignment (which may result in these) or by just threatening to do these things. Any instance of loss of control (inadvertent, or deliberate malevolent or financial) can produce any of the five main adverse impacts given on the right hand side of Figure 3; however, their significance varies in

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each situation. For example, the dominant concern with inadvertent loss of control is its potential for adverse human health impacts, such as injury or death. This was the key motivator for the first international efforts to control orphan sources in the late 1990s. However, the other impacts are also possible, as demonstrated in the Goiania event [12], which not only killed four people, but also had significant adverse socio-psychological, political, economic and environmental impacts on the region. Interestingly, the driving motivation for some US regulatory rule changes on certain devices at one point was the economic impact of orphan sources on US steel mills. The prime concerns with regard to the malevolent use of radioactive sources, such as in RDDs are socio-psychological (panic) and economic disruption impacts. However, the malevolent use has to have at least some potential, or perceived potential, for human harm otherwise it would have minimal impact. (No one would get too concerned with a threat to spray water everywhere.) Clearly, a malevolent dispersion is also likely to have a political impact and an environmental impact. The prime impact for those with a financial motive is clearly economic, but there could also be environmental impacts if material is dumped as well as possible long-term human health impacts.

6. IMPLICATIONS This new model illustrates a number of points. First, it clarifies that safety professionals do not just care about inadvertent loss of control, as has been argued, but that they have a legitimate interest in deliberate and malevolent loss of control events, since these too can result in human harm. However, it does acknowledge that their primary interest is in preventing adverse health impacts. Second, it shows that security professionals generally have a wider gamut of adverse impacts that they are trying to prevent. The model also illustrates that 'loss of control' is the common ground between safety and security as well as describing the routes that lead to the five adverse impacts. Knowledge of the routes enables us to identify and group the potential prevention, detection and response measures. To completely prevent any of these adverse impacts requires all of the pathways to be broken. This may be impossible to achieve; however, one should not be disheartened, because measures that address and attack the individual pathways can significantly reduce the probability and magnitude of the ultimate impacts. However, the most important benefit of the model is that it achieves the goal stated earlier of "clarifying roles and responsibilities and enabling the important work on safety and security to be managed efficiently and effectively, without duplication or conflict". It does this by recognizing that there are aspects of the problem that are 'pure' safety and 'pure' security, but that control of radioactive materials is the common ground of importance for both safety and security purposes. Therefore, management of the work on the safety and security of radioactive sources can be based on where the core competencies are, with the creation of a new group covering the common ground. This group should be drawn from professionals who have experience in the topics given in the center column of Table 1. They should be people who understand the different mindsets, cultures and languages of both safety and security, and who are desirous of building bridges and achieving the common goal. A key part of the process for effective management of safety and security is to define and agree upon the core and common competencies, or the areas of interest of the three disciplines. Table 1 contains an unranked list of some suggestions as to what these might be. The safety of radioactive sources covers the topics in the first and second columns, and the security of radioactive sources covers the topics in the second and third columns. Once agreed upon, such a table becomes the arbitrator of areas of work, roles, responsibilities and budgets. A further pragmatic implication is that it demonstrates that funds allocated solely for security purposes can legitimately be spent on tasks within the new discipline of radioactive materials control.

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Table 1. Table of suggested competencies

Core Competencies3 in Safety of Radioactive Materials and Facilities

Common Competencies1* in Radioactive Materials Control

Core Competencies0 in Security of Radioactive Materials and Facilities

Safe handling of radioactive materials and devices

Regulatory oversight of sources: e.g. authorizations (licenses, registrations) Inspections, evaluations, compliance appraisals, and enforcement Inventories and accounting of materials Import/export controls on radioactive sources 'Routine' access control measures, e.g. authorization of personnel, keys, doors, locks, interlocks, casks Design and use of radiation detectors and alarms Administrative or physical (active or passive) searches for lost, stolen or illicitly trafficked materials Proper disposition of disused sources Categorization of sources

Gathering and use of intelligence and other information Personnel security management, assessment of insider threat, background checks Threats assessment, design basis threats Security force requirements and their response

Assessments of doses from radiation, contamination, inhalation, ingestion Dispersion models and calculations Shielding calculations and assessments Health impacts of events involving radioactive materials Radiological emergency planning and response Restoration and clean-up of radioactive material Management of irradiated or contaminated persons

More 'severe' security measures, e.g. guards, guns, concrete road blocks Confidentiality of information

Design and implementation of security systems

a+b= Safety Competencies b+C= Security Competencies

7. CONCLUSIONS A new model has been presented that aims to resolve conflicts and enable the successful management of safety and security issues, particularly with regard to radioactive sources. It is hoped that this model will help safety and security professionals to recognize each other's individual purposes while still emphasizing the common concern regarding the control of radioactive sources. The turbulent early years of the arranged marriage between safety and security professionals has given birth to a new being, the radioactive material control professional. To answer a question posed earlier, the locks on the shielded source container and storage room are not there for safety or for security reasons, they are there for radioactive material control purposes. This paradigm shift is as profound as it is simple.

ACKNOWLEDGMENTS The philosophy and model expounded here are the result of many stimulating interactions with colleagues at the IAEA, who freely shared their ideas, thoughts and comments. Special thanks are due to Richard Hoskins

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(Security), Tony Wrixon and Abel Gonzalez (Safety). However, this does not imply their agreement with the views expressed, which remain the sole responsibility of the author.

REFERENCES [1] Food and Agriculture Organization of the United Nations, International Atomic Energy Agency, International Labour Organisation, OECD Nuclear Energy Agency, Pan American Health Organization, World Health Organization, International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources, Safety Series No. 115, IAEA, Vienna (1996). [2] International Atomic Energy Agency, Safety of Radiation Sources and Security of Radioactive Materials, (Proc. Conf. Dijon, 1998), IAEA, Vienna (1999). [3] International Atomic Energy Agency, National Regulatory Authorities with Competencies in the Safety of Radiation Sources and the Security of Radioactive Materials, (Proc. Conf. Buenos Aires, 2000), C&S Papers Series No. 9/P, IAEA, Vienna (2001). [4] International Atomic Energy Agency, Action Plan for the Safety of Radiation Sources and Security of Radioactive Materials, GOV/1999/46-GC(43)/10, IAEA, Vienna (1999). [5] International Atomic Energy Agency, Categorization of Radiation Sources, IAEA-TECDOC-1191, Vienna (2000). [6]

International Atomic Energy Agency, The Code of Conduct on the Safety and Security of Radioactive Sources, IAEA/CODEOC/2001, IAEA, Vienna (2001).

[7]

International Atomic Energy Agency, Legal and Governmental Infrastructure for Nuclear, Radiation, Radioactive Waste and Transport Safety, IAEA Safety Standards Series No. GS-R-1, Vienna (2000).

[8]

International Atomic Energy Agency, Categorization of Radioactive Sources, IAEA-TECDOC-1344, Vienna (2003).

[9] International Atomic Energy Agency, Security of Radioactive Sources: Interim Guidance for Comment, IAEA-TECDOC-1355, IAEA, Vienna (2003). [10]

International Atomic Energy Agency, The Code of Conduct on the Safety and Security of Radioactive Sources, IAEA/CODEOC/2003, IAEA, Vienna (2003).

[11]

Improving Control over Radioactive Sources: National Strategies for Strengthening Control over Sources in Authorized Use and Regaining Control over Orphan Sources, IAEA-TECDOC (In Press), Vienna (2004).

[12]

International Atomic Energy Agency, The Radiological Accident in Goiania, IAEA, Vienna (1998).

Current Trends in Radiation Protection H. Metivier, L. Arranz E. Gallego and A. Sugier (eds.)

Mobile Telephony: Evidence of Harm? Bernard Veyret1 PIOM laboratory, ENSCPB/EPHE,

University of Bordeaux, France

Abstract. Mobile telephony has developed rapidly over the past ten years and it has led to concerns about health effects caused by exposure to the microwaves emitted by mobile telephones and base stations. Research on biological effects of mobile telephone signals has been very active. Epidemiological research so far has been inconclusive. In the laboratory, no evidence has been obtained of well-established effects in human, animal, and cellular models. Major research projects are ongoing worldwide and the findings will help evaluate health risks by 2005.

1. INTRODUCTION Mobile (or cellular) telephony has developed very rapidly over the past ten years. It is now part of the basic equipment of modern life and over 1.3 billion phones are in use worldwide. Concerns about health effects caused by exposure to the microwaves emitted by mobile telephones and base stations have increased over the last few years becoming a major societal issue in some countries, or at least among part of the population. This short chapter reviews the scientific knowledge acquired on the biological effects associated with mobile telephony signals, together with conclusions about related health hazards. Stories about health risks from radio frequency radiation (RFR) from mobile phones and base stations have become common in the media over the past five years. In the United Kingdom for example, one early infamous headline warned that cell phones might "fry" the brain!* In contrast, the media do not often communicate on official scientific reports firmly concluding that there is no evidence of a health hazard from mobile phones.

1

E-mail: [email protected] * Sunday Times, 4 April 1996

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1.1. Mobile telephony Several systems are used in mobile telephony worldwide, all based on the same principle, i.e. "cellular" mapping of the territory. In each cell, a base station (BTS) emits towards and receives signals from the mobile telephones active in that cell (up to around 50). There are, for example, 30,000 BTS in France used by three networks. The carrier frequency varies from 400 to 2100 MHz and the voice or data information is coded digitally either by frequency or phase modulation. /. /. /. Mobile telephones

Mobile telephones are two-way radio transmitters operating in the 400 — 2100 MHz frequency range. In the GSM system, for example, the peak power emitted is 2 W, but the time-averaged power is always below 1/8 of this value, as power control reduces emission to the lowest level required. About half of the emitted power is absorbed by the user's head, i.e. a maximum of 125 mW. Power absorption is expressed as the specific absorption rate (SAR) in W/kg. Major improvements have been achieved in measuring the SAR in liquid phantoms and calculating power distribution in the head using numerical phantoms over the last ten years. Today, the worst-case SAR associated with the average GSM phone on the market is ca. 0.5 W/kg, i.e. 1/4 of the recommended localexposure limit value [1]. It is now known with certainty that temperature increases in the brain periphery caused by the waves emitted by mobile telephones does not exceed 0.1 °C. As a result of current changes in usage — increasing use of text and image messages and hands-free kits — mobile telephones are less frequently placed against the ear. This dramatically reduces exposure of the tissues in the head. 1.1.2. Base stations

GSM base-station antennas have an emitting power of ca. 20 W They are usually placed on rooftops and the emission beam is disc-shaped. Maximum exposure occurs on the ground, approximately 200 m from the BTS and it is almost zero at the bottom of the building or mast on which the antenna is mounted. Exposure of the public to the RFR emitted by base stations is typically 1/10000 of the recommended limit in terms of incident power. There is a consensus in the scientific community that base stations do not represent a health hazard. Therefore, in spite of the concerns of part of the public about antennas, they will not be mentioned further in this review.

1.2. Scientific approach to heath risk assessment The scientific approaches to health risk assessment related to non-ionizing electromagnetic fields are the same as in the ionizing range, i.e. epidemiology, experimental studies on humans, animals, and cells in culture. The experimental protocols are also similar but the choice of exposure systems and biological models are different. There is much scientific evidence, based on existing research, that warrants limiting exposure to highlevel RFR due to the "thermal effects" caused by heating of the tissues at SAR levels that correspond to a temperature elevation of a few degrees. However, this does not occur with mobile telephones. The search is thus for "non-thermal" effects and most of the research activity has been aimed at defining the thresholds for these effects, with respect to existing exposure guidelines [1] based on acute effects known to be due to heating [2]. Health risk assessment associated with RFR benefits from a database spanning over 50 years and including more than 350 studies specifically related to mobile telephony. Half of these studies relate to cancer and have been overwhelming in finding no evidence that RFR exposure initiates or promotes cancer.

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2. MAIN RESULTS The WHO and IEEE databases list about 1,300 peer-reviewed publications, from biophysical theoretical analyses to human epidemiological studies [3]. Recently, 11 review papers have been published on cancer, reproduction, calcium efflux, behaviour, thermoregulation, the nervous system, ocular and auditory effects, homeostasis and metabolism, longevity, epidemiology, and in vitro studies [3]. About half of the published studies are directly relevant to the issue of whether low-level exposure to RFR initiates or promotes cancer. The table below gives an update on completed and ongoing studies [4].

Type of study Cancer relevant or related Epidemiological studies Standard bioassays Sensitized in vivo studies Acute in vivo studies In vitro studies Total cancer studies Non-cancer studies Epidemiological studies Human studies Acute in vivo studies In vitro studies Total non-cancer studies

Grand totals

Completed

Ongoing

Total

12 8 13 23 57

24 7 7 8 25

113

71

36 15 20 31 82 184

10 50 37 15

1 21 10 7

11 71 47 22

112 225

39 110

151

335

2.1. Epidemiology Several epidemiological studies of mobile phone users have been performed worldwide, with mainly negative findings. However, they are not very informative, either due to poor exposure assessment or an insufficient statistical basis [5]. Overall, while occasional significant associations between various brain tumours and analogue mobile phone use have emerged, no single association has been consistently reported across population-based studies. The most recent study dealt with acoustic neurinomas and was again negative [6]. In view of the fact that the health of a huge population of mobile telephone users is potentially at stake, and the inconclusive findings of the published studies, a major multinational epidemiological study has been initiated, including 13 countries. It is led by IARCa and deals with three types of cancer of the head and neck. The results of this "Interphone" project will be known at the end of 2004 in some of the countries and a final conclusion will be drawn in 2005. In the mean time, parallel studies have shed some light on the association between mobile telephone development and increased cancer incidence. One of these studies showed no such association between the trend in incidence of adult primary intracerebral tumours and mobile telephone use in four Nordic countries [7]. WHO recommendations for short-term epidemiological projects are: '"Exposure surveys (in contrast to simple source evaluations) to assess an individual's total exposure. This includes, for instance, the relative contribution of occupational and residential exposures, and the impact of age, gender and mobility. Regional variations also need to be assessed. Future epidemiology study design and interpretation depend on data from studies started now. Additional exposure assessment research to permit the proper design of residential and occupational epidemiological studies."

a

International Agency for Research on Cancer

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2.2. Laboratory studies 2.2.1. Humans In spite of the obvious limitations of human experiments in terms of endpoints and exposure characterization, several investigations have been performed using various models. Findings have either been negative or difficult to replicate (sleep, EEG, cognitive functions, etc.). Today, there is no conclusive evidence from human studies of the detrimental health effects of mobile telephones. However, a report from a Dutch laboratory has drawn a lot of attention from the media and the scientific community as it reported minor effects on the well-being and cognitive functions of volunteers exposed to weak base-station signals [8]. This work, which is not yet published, has been heavily criticized but its protocol may serve as the basis of some more-refined work. However, it is not directly relevant to mobile telephone exposure. Clearly, the main issue today is the potential greater sensitivity of children to mobile telephone RFR. Their lifetime exposure, the fact that their CNS is still developing, and, possibly, increased RFR absorption in the head, have led to concerns that cannot be easily resolved through laboratory investigations and numerical modelling. A WHO scientific meeting, to be held in Istanbul in June 2004, will be devoted to this issue. WHO recommendations for short-term projects on humans are: "Replication and extension of the studies which demonstrated effects on sleep. Studies ofRF exposure and headaches in a controlled laboratory setting. Studies of memory performance should be expanded to include children" 2.2.2. Animals A large number of animal experiments have been performed over the past forty years, using various RFR frequencies and modulations. It is clear from these data that the vast majority of the reported biological effects are due to heating. These effects result either from a rise in tissue or body temperature exceeding 1 °C or in physiological and behavioural responses aimed at minimising the total heat load. Major improvements in exposure system design have made it possible to better characterize the SAR within the organism, and allow for either local exposure that mimics mobile telephone use (e.g. loop antenna, carousel) or whole-body exposure related to base-stations (e.g. Ferry's wheel, reverberation chamber, circular waveguide). Results on most of the non-cancer endpoints have been negative (memory, EEG, hearing, etc.) except for data on the permeability of the blood-brain-barrier, which was found to be increased by two research groups but not by several others [9]. Therefore, most of the major ongoing studies deal with cancer models. All of the long-term bioassays or sensitized studies have given negative results except for one using transgenic mice, [10] genetically modified to increase the background incidence of lymphomas, an increased tumour incidence was found following GSM exposure. No such finding emerged from a recent confirmation study, using a different design [11]. While awaiting the results of a further replication study, there is no convincing evidence from animal investigations that the incidence of lymphomas and other types of tumours is influenced by lifetime, daily exposure to mobile telephony RFR. WHO recommendations for short-term projects on animals are: "Follow-up studies to immune system studies that suggest an effect ofRF exposure (i.e., Russian publications from severalyears ago). Studies to assess the accuracy and reproducibility of published RF effects on the permeability of the blood-brain barrier and other neuropathologies (e.g., dura mater inflammation, dark neurones). Additional studies of the effect ofRF exposure on sleep are recommended. More quantitative studies on the effects of heat on the development of the central nervous system, particularly the cortex, in the embryo and foetus using morphological and functional endpoints"

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2.2.3. Cells In spite of their inherent limitations related to the lack of cell-to-cell interactions and altered genetic characteristics, in vitro investigations on cells have provided some useful information at a fast rate and moderate cost. A number of replication studies that addressed some positive findings on enzyme activity, gene expression, and DNA alteration have all proven negative so far. Research is currently very actively investigating possible alterations of heat shock proteins, seen as potential markers for RFR exposure and/or leading to physiological alterations in cells. A wide range of short-term, low-level in vitro experiments have shown that exposure did not cause cell death, implying that RFR is not a toxic agent. Furthermore, the weight of evidence available today (induction of DNA strand breaks, chromosome aberrations, micronuclei formation, DNA repair synthesis, sister chromatid exchange, and phenotypic mutation) supports the conclusion that RFR is not genotoxic. However, a major international study is being planned to finally resolve this issue in terms of low-level biological effects. Moreover, the synergy of RFR with chemical agents or other physical agents still needs further investigation. WHO recommendations for short-term projects on cellular systems are: "The expression of stress (heat shock) proteins in mammalian cells exposed to RF should be studied experimentally to follow-up recently published data, biologically relevant hypotheses, if supported by experimental data (in particular if related to the function of the central nervous system), should be tested to explore the utility of such data in risk assessment"

3. HEALTH RISK ASSESSMENT The process of health risk assessment by bodies such as ICNIRP, IEEE, IARC, and WHO relies heavily on judging the quality of investigations. As stated above, the quality of exposure systems has greatly improved and can now be considered adequate. The use of well-grounded experimental protocols (sham-exposure, blinding of exposure and biological tests, positive controls) has become generalized. Moreover, it is now common practice in the field of bioelectromagnetics to ascertain that any positive results are replicated in at least one independent laboratory [11]. In spite of these improvements, it should be noted that only a few top-level biology laboratories have engaged in this type of research, partly due to interferences created by societal and media pressure. Within its EMF International Programme, WHO has reviewed the science and issued the research recommendations quoted above [12]. The main conclusion from these reviews is that EMF exposures below the limits recommended in the ICNIRP guidelines do not appear to have any known impact on health. However, there are still some key gaps in knowledge requiring further research to provide definitive health risk assessments: IARC will issue a cancer classification of RFR in 2005 and WHO and ICNIRP's evaluations on RFR and health are due in 2006. Remaining uncertainties in the science database have led to pressure to introduce precautionary measures until gaps in knowledge are filled. If precautionary measures are introduced to reduce RFR levels, it is recommended that they should be voluntary and that health-based exposure limits be mandated to protect public health.

4. CONCLUSIONS Following the very rapid development of mobile telephony, a major research effort has been carried out worldwide (tens of millions of euros per year). Europe is most active (UK, Germany, Italy, and Finland, in particular), but many research groups are contributing in Japan, US, and Australasia.

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Most governments have addressed the issue of mobile telephony and health and several international and national expert committees have written accurate summaries of current knowledge (see the list of the most recent reports in the reference section). Their conclusions converge towards an absence of health effects related to mobile telephones, but all encourage continuing research in some areas. The CSTEE* was asked to prepare a revision of the 1999 European Commission recommendation and its conclusion in 2002 was that: "The additional information which has become available on carcinogenic and other nonthermal effects of radiofrequency and microwave radiation frequencies in the lastyears does not justify a revision of exposure limits set by the Commission on the basis of the conclusions of the 1998 opinion of the Steering Scientific Committee". In answer to the question: "mobile telephony: evidence of harm?" one must conclude that the weight of scientific evidence does not support health concerns or indicate any health risks from mobile phones in normal use, nor that there is any accepted mechanism for potential health effects at the low levels associated with these devices. Findings to date, including epidemiological studies and laboratory studies of animals exposed both short-term and for their entire lifetimes, have not provided evidence that exposure causes cancer, or affects biological tissues in a manner that might lead to, or augment, any disease. However, there are still some issues pending, in particular those related to the potentially greater sensitivity of children. The many ongoing research projects should help clarify these issues by the end of 2005.

REFERENCES [1] ICNIRP. Guidelines for limiting exposure to electric, magnetic and electromagnetic fields (up to 300 GHz). Health Physics 74 (1998) 494-522. [2]

ICNIRP Statement: General approach to protection against non-ionizing radiation. Health Physics 82 (2002)540-548.

[3]

Reviews of Effects of RF Fields on Various Aspects of Human Health, in Bioelectromagnetics as Supplement 6 (2003), (www3 . interscience . wiley . com/).

[4] www. who . int/peh-emf/research/database/en/ [5]

Boice J. D and McLaughlin J. K., Epidemiologic Studies of Cellular Telephones and Cancer Risk, - A Review. SSI report: 2002:16 September 2002, ISSN 0282-4434.

[6]

Christensen H. C., Schiiz J., Kosteljanetz M., Poulsen H.S., Thomsen J., and Johansen C, A.m J Epzdemiol 159 (2004) 277-283.

[7]

Lonn S, Klaeboe L, Hall P, Mathiesen T, Auvinen A, Christensen HC, Johansen C, Salminen T, Tynes T, Feychting M. Int J Cancer 108 (2004) 450-455.

[8]

Zwamborn A. P. M., Dr. ir. Vossen S. H. J. A., Ir. van Leersum B. J. A. M, Ing. Ouwens M. A., Makel W N., Effects of global communication system radio-frequency fields on well being and cognitive functions of human subjects with and without subjective complaints. Sept 30, 2003, TNO-report FEL-03-C148 www. tno . nl.

[9]

Hossmann K. A. and Hermann D. M., Bioelectromagnetics 24 (2003) 49 - 62.

[10]

Repacholi M., Basten A., Gebski V., Noonan D., Finni J., Harris A.W, Rad. Res 147 (1997) 631-640.

[11]

Utteridge T. D., Gebski V, Finnic J. W, Vernon-Roberts B. and Kuchel T. R.,. Radiat Res 158 (2002) 357-64.

* Scientific Committee on Toxicity, Ecotoxicity and the Environment

Mobile Telephony: Evidence of Harm? [12]

Repacholi M. H., Toxicol Lett 120 (2001) 323 - 331

[13]

WHO research recommendations: www. who . i n t / p e h - e m f / r e s e a r c h / r f 0 3 / e n / .

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Useful Websites: COST Action 281: w w w . c o s t 2 8 1 . o r g / UK research programme: www. mthr . org . uk/ National Radiological Protection Board: www . nrpb .org/ Swedish Radiological Protection Board: www. ssi . s e / e n g l i s h / C o n t a c t _ S S I .html European Bioelectromagnetics Association: www. ebea . org/ Bioelectromagnec Society: www. bioelectromagnetics . org International Commission on Non Ionizing Radiation Protection: www . icnirp . de IEEE subcommittee: grouper . ieee . o r g / g r o u p s / s c c 2 8 / s c 4 / WHO EMF International Programme: www. who . int/peh-emf /

Recent national reports: - Proposal for limiting exposure to electromagnetic fields (0-300 GHz), (in press, consultation diocument at www. nrpb . org). - Health Council of the Netherlands. Electromagnetic Fields: Annual Update 2003. The Hague: Health Council of the Netherlands, 2004; publication no. 2004/01. (www . h e a l t h c o u n c i l . nl). - AGNIR. Documents of the NRPB: Health effects from radio frequency electromagnetic fields volume 14, no2, 2003. (www. nrpb . org). - Recent Research on Mobile Telephony and Cancer and Other Selected Biological Effects: First annual report from SSI's Independent Expert Group on Electromagnetic Fields. SSI's Independent Expert Group on Electromagnetic Fields, 2003 (www .ssi.se). - Rapport a 1'Agence Fran9aise de Securite Sanitaire Environnementale : Telephonic mobile et sante. March 2003 ( w w w . a f s s e . fr). - IEGMP. Independent Expert Group On Mobile Phones (Chairman: Sir William Stewart). Mobile phones and health. Chilton, Didcot: Independent Expert Group On Mobile Phones, 2000 (www . iegmp . org . u k / r e p o r t / i n d e x . htm).

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Current Trends in Radiation Protection H. Metivier, L. Arran^ E. Gallego and A. Sugier (eds.)

Laser Radiation Protection David H. Sliney Laser/ Optical Radiation Program, US Army, Centerfor Health Promotion and Preventive Medicine, Aberdeen,Proving Ground, MD 21010-5422, USA

Abstract. Lasers have found widespread use in industry, science and medicine. In consumer products, they are engineered to be completely safe, and are placed in a no-risk hazard category referred to as Class 1. Class 2 lasers are generally safe when properly used as alignment devices and pointers. Class 3 laser products pose an eye hazard and Class 4 lasers may pose additional hazards, such as a fire hazard or a significant hazard to the skin. In recent years, two new hazard classes have been developed to better cite the potential hazards from optically aided viewing. Laser hazard controls must be employed by the user for Class 3 and 4 laser products and become more stringent for the higher class. Special controls are required in several application areas, such as laser material processing and surgery. Eye protection is required when laser beams are accessible in the open.

1. INTRODUCTION A laser produces coherent optical radiation. To date, lasers have been developed which emit monochromatic radiant energy having wavelengths ranging from the extreme ultraviolet to the far infrared (sub-millimeter) part of the electromagnetic spectrum. The term "laser" is an acronym for Light Amplification by Stimulated Emission of Radiation. Despite the fact that stimulated emission is a process that was theoretically predicted by Albert Einstein in 1916, the first successful laser was not demonstrated until 1960 (UNEP/WHO/IRPA, 1982). Lasers have many applications in the research laboratory, in industry, medicine and surgery, and even in office settings, construction sites and even households. For many applications, such as video disk players, laser printers, computers and optical fiber communication systems, the laser's radiant energy output is enclosed, the user faces no safety hazard or health risk. In such applications, the presence of a laser embedded in the product may not be obvious to the user. However, in some medical, industrial or research applications, the laser's emitted radiant energy is accessible and may pose a potential hazard to the eye and skin. Because the laser process (sometimes referred to as "lasing") can produce a highly collimated beam of optical radiation (i.e., ultraviolet, visible or infrared radiant energy), a laser can pose a hazard at a considerable

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distance-quite unlike most hazards encountered in the workplace. Perhaps it is this characteristic more than any other that has led to special concerns expressed by workers and by radiological and occupational health and safety experts. Nevertheless, lasers can be used safely when appropriate hazard controls are applied. Guidelines for safe exposure (ACGIH, 2003, ICNIRP, 2000; Sliney, 2003) and safety standards (ANSI, 2000; IEC, 2001) for lasers exist world-wide, and are currently quite similar or "harmonized." All of the safety standards make use of a hazard classification system, which groups laser products into one of four broad hazard classes according to the laser's output power or energy and its ability to cause harm. Safety measures are then applied commensurate to the hazard classification (ANSI, 2000; IEC, 2001; Henderson and Schulmeister, 2003; Sliney and Trokel, 1992; Sliney and Wolbarsht, 1980) Lasers operate at discrete wavelengths within the optical spectrum, and although most lasers are monochromatic (emitting one wavelength, or single color), it is not uncommon for one laser to emit several discrete wavelengths. For example, the argon laser emits several different lines within the near ultraviolet and visible spectrum, but is generally designed to emit only one green "line" (wavelength) at 514.5 nm and/or a blue line at 488 nm. When considering potential health hazards, it is always crucial to establish the output wavelength and wavelengths (Sliney and Wolbarsht, 1980). One can simply place a prism at the output aperture of the laser and look for indications of secondary beams on a white target card. UV laser lines would be visible by fluorescence, but infrared lines would be visible only with very special phosphor cards or and infrared image converter.

2. LASER CHARACTERISTICS All lasers have at least three fundamental aspects: (1) an active medium (a solid, liquid or gas) that defines the possible emission wavelengths, (2) an energy source (e.g., electric current, pump lamp or chemical reaction ), and (3) a resonant cavity with output coupler (generally two mirrors with one partially transmitting).

Most practical laser systems outside of the research laboratory also have a beam delivery system with lenses and mirrors to direct the beam, or a flexible delivery system, such as an optical fiber or articulated arm with mirrors to direct the beam. In most surgical and material processing applications, a focusing lens concentrates the beam on to the target tissue or the material to be welded, etched or cut. Figure 1 illustrates the three basic elements of a laser. Identical atoms or molecules are brought to an excited state by energy delivered from the pump lamp. When the atoms or molecules are in an excited state, a photon ("particle" of light energy) can stimulate an excited atom or molecule to emit a second photon of the same energy (wavelength) traveling in phase (coherent) and in the same direction as the stimulating photon. Thus light amplification by a factor of two has taken place. This same process repeated in a cascade causes a light beam to develop that travels along one axis (generally reflecting back and forth between two mirrors that form a resonant cavity. This has been a very brief description of the process of laser action: Light Amplification occurring by the Stimulated Emission of Radiation. In actual practice, this amplification process usually requires a long path length for the light to travel and it is not practical to build a laser as a very long tube. Instead, the long path length for the generation of the laser beam is created by forcing the light to travel between mirrors. These mirrors are placed at both ends of a short cylinder and send the photons bouncing back and forth within the energized medium. The space formed by the optical medium bounded by the two mirrors is

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Figure 1. A laser with an energy source, active medium and resonant cavity.

a special optical space called a resonant cavity (Figure 1). One of the mirrors is only partially silvered to allow some of the light to leave the cavity and to escape as a collimated beam. The laser is designed so that enough light reflects back into the cavity to maintain the laser action. In practice the mirrors usually have a certain curvature to better control the reflections of light within the cavity and produce a stable output. This has the effect of altering the distribution of light within the laser output beam. As we shall learn later, the beam profile is important in medical applications. Sometimes the optical gain within one pass through the cavity is so great, that the output mirror is not needed, but in this instance, the laser may only operate in a "superadiance" condition. Although the two parallel mirrors shown in Figure 1 are generally curved in larger cavities they may be nearly parallel at a semiconductor junction for a diode laser. In any case the source must have gain for the device to be termed a "laser," and the basic principle holds for all lasers. Light Emitting Diodes (LEDs) do not have gain and cannot be considered lasers as a few publications seem to suggest. All laser action originates in an active medium bounded by the two mirrors. Both mirrors reflect photons but the output mirror, is semi-transparent to allow laser light to leave the cavity. An energy source is required to excite the active medium and initiate laser action, e.g., light from a flash lamp or an electric discharge, or a semiconductor diode. Other components that may be within the cavity include apertures to shape the beam, and shutters to control laser action. Although several thousand different laser lines (i.e., discrete laser wavelengths characteristic of different active media) have been demonstrated in the physics laboratory, perhaps only 20 — 30 have been developed commercially to the point where they are routinely applied in everyday technology. Guidelines for human laser have been developed and published which basically cover all wavelengths of the optical spectrum in order to allow for currently known laser lines and future lasers (ICNIRP, 2000).

3. PROPERTIES OF LASER LIGHT The special properties of the light beam, produced by stimulated emission during this multiple passage of light between the mirrors of the resonant cavity, arise because the characteristics of each stimulating photon are maintained in the emitted photons. The laser light is highly monochromatic, coherent, directional, and extremely bright.

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3.1. Directionality Directionality is an unusual property of laser light and is not found in regular light sources. It means that little divergence is present (Figure 2) in the beam output and the laser light beam will travel considerable distances with little widening or spreading. This is one of the reasons why laser light is so hazardous. Unlike

Figure 2. Directionality is possible because of the low divergence of a laser beam. A typical laser divergence is of the order of 1 milliradian, which means that a beam spreads by one meter in each kilometer.

light from regular lamp sources which rapidly spreads from the source, laser light maintains its brightness by having very little beam spread or divergence. The measure of beam spreading is called "divergence," and usually measured in units of milliradians. A beam with a divergence of 1 milliradian expands one meter every kilometer. Low divergence arises from the long path length created by the multiple photon reflections within the cavity. Very small laser cavities, e.g., diode lasers have initially high divergences. Ordinary light sources emit photons in many directions; a laser produces a collimated beam of high brightness. This collimation and brightness is why a laser beam is hazardous over long distances.

3.2. Coherence Coherence describes the uniform spatial relationship between all portions of the electromagnetic wave. Monochromatic refers to the highly purified color (i.e., one wavelength) produced by most lasers and the extremely narrow spectral band of radiation. Both of these concepts are illustrated in Figure 3.

3.3. Radiance Since the rays emitted from a laser are relatively parallel and do not diverge as the laser moves through space, the light energy remains concentrated and retains its characteristic brightness. This concentration of the beam causes the laser brightness to be very much greater than the brightness of any other man-made light source. A small 1.0-milliwatt (mW) helium-neon laser or diode laser pointer used in a lecture hall is typically ten times brighter than the sun. The high brightness means that high concentrations of energy can be achieved when the laser beam is focused to a small spot. The resulting concentration of light energy, if

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COHERENCE

Figure 3. Coherence. The coherent nature of laser light relates to both spatial and temporal coherence. Spatial coherence means that the light waves are in phase.

absorbed, (Figure 4) can elevate the temperature at the focus to extremely high levels which can burn or melt materials. It is this phenomenon that makes the laser both a useful surgical or material processing device and a hazardous source of light. Under certain circumstances, when the laser light is concentrated to an extremely high level, the atoms in the focal zone of the laser beam can be ionized because the electromagnetic energy field is sufficiently intense to strip the electrons from outer atomic shells and directly ionize matter. This forms a spark referred to as an "optical plasma" which can be used to cut normally transparent structures including biological tissues (e.g., as used in the Nd:YAG ophthalmic laser photodisruptor for eye surgery).

3.4. Wavelength The optical radiation emitted by a laser can be in the ultraviolet (UV), the visible, or the infrared (IR) portion of the optical spectrum. Because of the quantum nature of the stimulated emission from the active state within the population inversion, only one or, in some cases, a few wavelength(s) of light are emitted. For example, the familiar argon laser emits most of its light in two wavelengths: 488 nm (blue) and 514 nm (green). The Nd:YAG laser emits most of its energy in the near-infrared portion of the spectrum at 1,064 nm (1.064 yum) and a slightly weaker output at 1,334 nm (1.334 /im). The mirrors and other optical components of the laser's resonant cavity are designed to favor a certain wavelength to enhance output power and suppress other wavelengths to aid in the production of a truly monochromatic output beam. Thus, it is always essential to specify the wavelengths at which a given laser is operating rather than to rely on naming the active medium to identify the laser system.

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LASER BRIGHTNESS (RADIANCE)

Figure 4. Radiance. The light from a laser can be totally collected by a lens and focused to a far smaller spot than can the light from a conventional optical source. This smaller focal spot of the laser contains far more concentrated light (a higher irradiance) than the focal spot of a conventional light source. Laser materiel processing and surgical applications, as well as fiber communications rely on this property.

3.5. Pulsed and CW Operation Many types of lasers have been produced that vary in their wavelengths and patterns of output. Hundreds if not thousands of different active laser media have been discovered, but only a few types have the characteristics and properties which favor widespread use and have properties suitable for industrial, scientific or medical applications. Depending upon how the excitation energy is applied and the laser cavity is configured, the output beam of a laser will be either pulsed or continuous-wave (CW). Some lasers, such as the solid-state ruby laser or any glass laser, cannot normally be operated as a continuous-wave laser because of problems with overheating and resulting damage to the laser crystal and adjacent components. The output of pulsed lasers can vary greatly in the duration and energy of individual pulses as well as their repetition frequency. This performance depends upon many factors including among others, the nature of the stimulation process, the duration of the exciting energy, the optical configuration and temperature of the laser cavity. The laser may be designed so that its output consists of pulses as short as a few femtoseconds (1 fs — 10~15 second) to many milliseconds. The pulses may be delivered individually, in groups or continuously over a broad range of frequencies. A laser with an output emission lasting more than 0.25 second is considered a CW laser for safety purposes. Let us consider the operation of pulsed lasers whose output pulse energy is concentrated into very short times. This compression in time causes the laser light to be delivered more rapidly. The rate of energy delivery is termed power and is measured in watts (W). Power in watts is equal to the energy measured in joules (J) divided by the pulse duration in seconds (s), i.e., W = J/s. This means that short pulses can compress small energies into high powers. A very small amount of energy delivered in an extremely short

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pulse duration can achieve very high peak powers for a brief period of time. The absorption of such high peak powers can result in effects other than simple heating, i.e., optical non-linear phenomena. These short pulses may be required for laser surface ablation with minimal heat dispersion or for optical breakdown and plasma production. Pulses may be produced so the laser energy is delivered over a wide variety of durations. A flashlamp driven laser will produce laser light which follows the output of the flash-lamp and will have a pulsed output of about 0.1 — 2 milliseconds. Further compression or shortening of pulses can be done with special techniques. Two ways to achieve this are "Q-switching" and "mode-locking." Q-switching is an optical technique to compress the laser output into 10 to 20 nanoseconds (ns = 10~9s, = billionths of a second, = thousandths of a microsecond). Mode-locking is a technique which further compresses the light into shorter pulses of 10 to 40 picoseconds (ps = 10 -12s5 = trillionths of a second, = millionth of a microsecond). Still shorter ultra-short pulses are measured in femtoseconds, and the shortest pulse for which we have currently exposure guidelines is 100 fs. The failure of laser eye protectors when irradiated by ultra-short pulses has been an issue in recent years; this phenomenon has been termed "saturable absorption."

3.6. Q-Switching The name Q-Switching is derived from an electrical engineering term used to describe the resonant quality of an electronic circuit. Some of the first laser designers were electrical engineers and they used electronic circuit terminology to describe the operation of the laser's resonant cavity, and referred to laser technology as "quantum electronics." The "Q" term was originally used to describe the resonant quality of a circuit, and came to be used by these engineers to describe the analogous change in resonant quality of a laser cavity which forces short pulses. These changes involve either one mirror's position (active Q-switching) or an interruption of light traveling throughout the laser cavity by an electro-optic shutter (active Q-switching) or by a saturable dye (passive Q-switching). All of these techniques block the passage of light in the laser cavity in a controllable manner. A number of engineering techniques have been developed for Q-switching. They all, in common, interrupt the light beam in a controllable manner so that laser action is delayed until maximal population inversion has been achieved in the active medium. A dye-cell Q-switch will remain opaque to transmitted light until the light concentration builds up to a certain threshold level. The bleaching of the dye then corresponds to the mechanical movement of a shutter or mirror as it opens the optical path to the passage of light. The most commonly used active Q-switches are electro-optic shutters known as Kerr Cells or the more typical Pockel Cells which change polarization very rapidly with an applied high-voltage pulse. With an adjacent fixed polarizer, an electric pulse will suddenly change the polarization of the Kerr Cell. This aligns the Kerr Cell to the adjacent fixed polarizer to permit light transmission and laser action. The most commonly used passive switch is a saturable dye which may be either in a solution in an optical cell or dispersed throughout a plastic film. In this method, the dye cell or film is placed between the laser medium and one mirror. When the dye is exposed to a very intense beam of light above a certain threshold irradiance (Watts/cm2), the absorbing dye bleaches and suddenly becomes nearly transparent. This bleaching abruptly makes the two mirrors of the resonant cavity available to the free passage of light and the beam can reflect back and forth. A very short, giant pulse results.

3.7. Mode-Locking Unfortunately, the term "mode" is confusing as it has many different meanings in optics and laser technology. It may refer to the time distribution or "temporal mode" of the output. That is, a pulsed or continuous wave

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laser can be described as being a "pulsed mode" or "CW mode" laser. Similarly, a burst of laser pulses can be described as a "burst mode." It may also refer to the spatial distribution of light within the laser beam. These are called the transverse or longitudinal modes of the laser beam and will be discussed later. The term "mode-locking" describes a method which fixes the way the photons bounce back and forth in the resonant cavity. Technically, mode-locking controls the number of longitudinal modes in a cavity. The net result is that a train (i.e., group) of evenly-spaced pulses is produced, where each individual pulse has an extremely short duration; such pulses are sometimes referred to as "ultra-short pulses". One can visualize longitudinal modes by imagining several groups of photons separated in space along the longitudinal or long axis of the cavity. These groups of photons are racing separately at the speed of light (c) between the two mirrors which are separated by the cavity length (L). The transit time between mirrors is c/L seconds and the time for a complete round trip to the starting point is 2 c/L seconds. If only one bundle of photons move back and forth between mirrors, a short pulse of light will leave the cavity through the partially silvered mirror every 2 c/L seconds. For example, since light travels about 30 cm (1 foot) in one nanosecond, a onefoot long cavity would have ultra-short pulses being emitted every 2 nanoseconds. This allows control of the light in the laser so the light energy bunches into a very concentrated short packet, delivered in a time determined by the length of the laser cavity. Characteristically mode-locking produces light pulses of higher power than does Q-switching because the pulses are very much shorter.

3.8. Beam Profiles Transverse Modes describe the energy distribution across the beam profile and determine the spatial distribution of the laser light in the beam and the nature of the laser focus. This description of the radiant power or energy in the beam's cross-section is one way to know if the laser will focus into a clean circular pattern or form several patches of light distributed over a larger area. A "single mode", or "fundamental mode" (noted as TEMoo), has a Gaussian (normal) distribution of power in the beam profile. This is desirable in many circumstances, since it can be focused to the smallest possible spot of any transverse mode. On the other hand, the fundamental mode can represent only a small fraction of the laser's output and may not be desirable where extremely high energy levels are required for a given task. Most laser designers attempt to achieve a single transverse mode of operation when possible, since the beam of a single-mode laser can be focused to the smallest theoretical spot for that wavelength. However, single-mode operation is not always possible and the beam profile may be irregular in shape. This irregular profile is referred to as "multimode."

3-9. Delivery Systems All industrial and medical laser systems require a beam delivery system which is responsible for directing the power output of the laser to its target site of action. The application requirements and design of a laser's delivery system will, to a great extent, determine its hazards. It is quite apparent that a fixed delivery system that is incorporated into another instrument or machine will be safer than delivery systems that can be freely moved in space. A CO2 laser beam directed downward by a focusing lens is fixed in space and even if directed by a joystick or similar control generally allows very limited movement of the beam. In many material processing systems the laser beam is fixed (or with very limited movement) and is directed downward, and the work-piece is moved under it. Fixed delivery systems are also typically found in many medical lasers (e.g., in ophthalmology) and may be connected to a microscope which permits the surgeon to both view the operative site and deliver the laser energy to the desired treatment site. Examples of more hazardous systems are hand-held laser rangefinders, high-power Class 3B laser pointers, and hand-held surgical lasers which employ a freely moveable handpiece.

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Delivery systems which are available to carry the laser beam's output from the laser cavity to the point of application may use either fiber optics or a conventional optical path which is either fixed or articulated. The fiber optic delivery system is generally favored because of ease of use and its great flexibility for directing the beam to the work site. There are very real and practical limits to the use of fiber optics. Suitable fiber optic materials capable of transmitting the laser beam are not available for all wavelengths. For example, the 10.6 /im output wavelength of the CC>2 laser does not pass through conventional quartz or glass fiber optics. Because of this, CC>2 lasers, which are in widespread use in surgical laser systems, are limited to situations for which an articulated arm can be used. There have been frequent efforts to extend the applications of the CC>2 laser by developing fiber optic materials that transmit its output. These efforts have been only partly successful. An articulated arm contains a series of mirrors which are mounted on pivots to allow the laser beam to be guided from its source in the laser cavity to its point of application. Typical delivery systems available today for the carbon-dioxide laser employ hollow tubes to form an articulated arm. The laser energy may be transmitted through a fixed optical system as is commonly done in laboratory instruments or in excimer laser material processing equipment.

4. LASER SYSTEM CONTROL In commercial laser products, the laser operation is controlled by the operator through the use of a series of electronic and optical controls on the laser and its delivery system. First, there is the main power switch which energizes the laser system, a control which varies the output power, and a firing or operation switch which triggers the laser output. This may be in the form of a foot or hand switch. In some recently described systems, the laser output may be under microprocessor control for some or all of its exposure. Stand-by or ready switches are frequently encountered to enable the user to place the equipment in a stand-by status to avoid accidental or unintentional firing of the laser. The standby function maintains power to the laser during workpiece preparation and allows rapid start up of the laser as application is needed. Continuous-wave lasers may be interrupted by a shutter to provide predetermined exposure duration. Further controls which are frequently present are a timer and a time interval or pulse duration control switch.

5. HAZARD EVALUATION MEASUREMENTS AND CLASSIFICATION Current laser safety standard throughout the world follow the practice of categorizing all laser products into several hazard classes, and control measures are specified for each class, based upon the actual hazards posed by the laser beam. Generally, the scheme follows a grouping of four broad hazards classes: 1 through 4. Class 1 laser products cannot emit potentially hazardous laser radiation and poses no health hazard. Classes 2 through 4 pose an increasing hazard to the eye and skin. The classification system is useful, since safety measures are prescribed for each class of laser. More stringent safety measures are required for the highest classes. The laser safety classification system greatly facilitates the determination of appropriate safety measures. Laser safety standards and codes of practice routinely require the use of increasingly more restrictive control measures for each higher classification. Hence routine measurements are normally not required.

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5.1. Class 1 Class 1 is considered an "eye-safe," no-risk grouping. Most lasers that are totally enclosed (for example, laser compact disc recorders) are Class 1. No safety measures are required for a Class 1 laser. Class 1 lasers are frequently referred to as "eye-safe" lasers. In the past few years, a new, conditional class has been introduced: Class 1M, which is effectively "eye-safe" unless the beam is directly viewed with optical instruments. Two conditions exist whereby optical instruments can collect more energy and increase the ocular hazard. Condition 1 is the most obvious and the most serious case: where a telescope or binocular is placed in the collimated laser beam and can introduce far more energy into the eye if there is a retinal hazard, or concentrate the energy on the cornea for laser wavelengths outside the retinal hazard region. The second condition is where a hand magnifier or jeweler's eye loupe is used to examine a highly diverging laser beam (generally emitted from an optical fiber) and recollimate the beam so that it can be concentrated on the cornea or focused on the retina. This is a rather unrealistic viewing condition except when service technicians examine the tip of an optical fiber. The safety criteria for this second viewing condition are now being re-examined by standards committees, such as IEC TC76 with a plan to either restrict the applicability or to relax the currently over-stated risks in the current edition of IEC 60825-1.

5.2. Class 2 Class 2 refers to visible lasers that emit within the 400 - 700 nm spectral band with a very low power (less than 1 mW) that would not be hazardous even if the entire beam power entered the human eye and was focus sed on the retina. The eye's natural aversion response to viewing very bright light sources protects the eye against retinal injury if the energy entering the eye is insufficient to damage the retina within the aversion response. The aversion response is composed of the blink reflex (approximately 0.16 — 0.18 second) and a rotation of the eye and movement of the head when exposed to such bright light. Current safety standards define the aversion response as lasting 0.25 s. Thus, Class 2 lasers have an output power of 1 milliwatt (mW) or less that corresponds to the permissible exposure limit for 0.25 s. Examples of Class 2 lasers are laser pointers and some alignment lasers. Another conditional sub-class, Class 2 M is analogous to Class I'M, but the optical hazard is applicable only for visible lasers that would be Class 2 if measured only with a 7 mm collecting aperture. As a note, at one time, US safety standards also incorporated a sub-category of Class 2, referred to as "Class 2A." Class 2A lasers, which were not hazardous to stare into for up to 1,000 s (16.7 minutes). Most laser scanners used in point-of-sales (super-market checkout) and small inventory scanners are Class 2A, but this class was no longer required when the exposure limits were adjusted (ICNIRP, 2000) such that a point-source laser was no more hazardous if viewed for any duration greater than 10 — 100 s.

5.3. Class 3 Class 3 lasers pose a hazard to the eye, since the aversion response is insufficiently fast to limit retinal exposure to a momentarily safe level, or if damage to other structures of the eye (e.g., cornea and lens) could take place. Skin hazards normally do not exist for incidental exposure. Examples of Class 3 lasers are many research lasers and military laser rangefinders. A special subcategory of Class 3 is termed "Class 3R" (once termed Class 3A in US standards). The remaining Class 3 lasers are termed "Class 3B." Class 3A lasers are those with an output power between one and five times the AEL for the Class 1 or Class 2. Class 3R should be thought of as a transitional class, since the laser beam irradiance exceeds the applicable exposure limit (EL), referred to as the "maximum permissible exposure (MPE), but injury is unlikely from a standpoint of probabilistic risk assessment, i.e., the likelihood that the eye will be perfectly positioned, focused for worst-case viewing (retinal hazards) and

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the person unusually sensitive become very small. The "R" in Class 3R refers to "reduced requirements" for product safety standards and very limited control measures are required for the user. Examples are many laser alignment and surveying instruments. In the 1.2 — 1.4 //m spectral band the Class 3R may not exist for some CW lasers where the range between Class 1 and Class 4 becomes very small.

5.4. Class 4 Class 4 lasers may pose a potential fire hazard, a significant skin hazard, or a diffuse-reflection hazard. Virtually all surgical lasers and material processing lasers used for welding and cutting are Class 4 if not enclosed. All lasers with an average power output exceeding 0.5 W are Class 4. If a higher power class 3 or class 4 is totally enclosed so that hazardous radiant energy is not accessible, the total laser system could be class 1. The more hazardous laser inside the enclosure is termed an "embedded laser."

5.5. Conditional Classes and the Possibility of Change In 2000, the world safety community recognized a need to make some minor revisions in the traditional laser classification systems, with the creation of a Class IM and Class 2M and expand Class 3R for greater consistency in dealing with the potential for optically aided viewing. This effort recognized the value of having conditional classes. It is hoped that there will be no further changes in classification to avoid confusion; however, the subject of further refinements sometimes arise in standards committees. From time to time there have been efforts in laser standards committees to "update" or "improve" the classification Class 3 eye-hazardous lasers and the most hazardous lasers (Class 4). Proposals are normally to insert additional classes based upon a concept that hazards increase gradually and the dynamic range of Class 3B can be a factor of 100-fold. However, past efforts to refine and sophisticate the classification system have been voted down because they added complexity, where simplicity was desired. The value could only be if they indicated different control measures. For the user, the class achieves the first step of hazard evaluation with the indication of appropriate control measures without the need to consult a laser safety advisor (LSA) or Laser Safety Officer (LSO). If a high-power, Class 4 laser is partially enclosed such that the risk of occupational exposure is very low, the level of control can be greatly reduced, but it is not necessary to invent another "conditionally safe" class. It is best to try to educate people that Class 4 does not necessarily imply a serious risk, and that the controls adopted should be appropriate to the circumstances, rather than defining a new class for "conditionally safe" products. The current system of classification is based on the level of hazard with only an implication for the degree of risk, and this is the basis of the recommendations given in the revised user guidelines. The Class indicates the potential hazard of the product, but the actual risk is not fully defined by the class, since it depends on the environment in which it is located and the people potentially exposed. For example, a high-power, Class 4 industrial, material-processing laser that is Class 4 because the enclosure does not have a fully light-tight enclosure, and perhaps does not have a roof could be quite acceptable in locations were the ceiling is close to the enclosure, but not in another location where there are walkways at a higher level that provide a direct view into the enclosure. In a user safety standard, the laser safety expert might classify the enclosure adequate for Class 1, but the manufacturer might have to retain the Class 4 label, since the system could be installed in any location.

6. LASER MEASUREMENTS To those in radiation protection, it is at first somewhat surprising to learn that instrumentation and measurements are not the focus of laser safety7. Laser measurements often require sophisticated equipment and fortunately are seldom essential for laser hazard evaluation, since the manufacturer must classify the laser

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Figure 5. The absurdity of testing laser eye protectors to withstand kilowatt laser beams.

product, and as noted above, actual use of the MPEs (ELs) is infrequent (Lyon, 1993; Sliney and Wolbarsht, 1980). Unlike some workplace hazards, there is generally no need to perform measurements for workplace monitoring of hazardous levels of laser radiation. Because of the highly confined beam dimensions of most laser beams, the likelihood of changing beam paths and the difficulty and expense of laser radiometers, current safety standards emphasize control measures based upon hazard class and not workplace measurement (monitoring). Measurements must be performed by the manufacturer to assure compliance with laser safety standards to assure proper hazard classification. Indeed, one of the original justifications for laser hazard classification related to the great difficulty of performing proper measurements for hazard evaluation. In this regard, MPEs are exposure limits measured at the points in space where individuals are potentially exposed and are used for occupational safety and health assessments. These originate from ICNIRP. The product-safety committee, IEC TC76, has gone on record on a number of occasions over the last 20 — 30 years that it recognizes WHO and ICNIRP as the source of the MPEs. IEC develops product safety standards that regulate emission and employ Accessible Emission Limits, AELs, which are derived by IEC from the MPEs and other considerations.

7. LASER EYE PROTECTION Laser eye protection becomes of great importance when engineering controls such as enclosures, baffles and barriers are inadequate to assure that persons will not enter the nominal hazard zone (NHZ), where a potential ocular exposure will exceed the applicable MPE. There are many commercial laser eye protectors available and standards have been written to test them. Issues remain as to whether some of the tests related to filter damage are realistic and are not just a costly added expense. Some existing testing standards require the eye protection to withstand levels far in excess of skin injury thresholds, with the result that many are critical of these requirements (Figure 5). Efforts are underway in the US to prepare a more realistic standard for eyewear (ANSI Z136.7), but this has not been published. On the international scene, ISO TC 94 is examining the same issue. The protective factor is normally expressed as a logarithmic quantity referred to as the optical density (OD). The OD is the negative logio of the transmittance.

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8. CONCLUSIONS Laser technology has become mature in the past three decades and is ubiquitous throughout industry, science and medicine. Laser safety programs are encountered in a large variety of workplaces. The keys to the safe use of lasers are firstly: enclose the laser radiant energy if possible; and if not possible, control measures become essential and training of those working with laser becomes paramount for safe use.

REFERENCES [1]

Bass M (ed.): Laser Materials Processing, (New York, Elsevier, 1983).

[2] Goldmann L (ed.): The Biomedical Laser. New York, Springer-Verlag, 1981. [3] HechtJ: UnderstandingLasers. (New York, Sams Publishing, 1988). [4] Henderson, R., and Schulmeister, K.,, Laser Safety, (Institute of Physics Publishing, Bristol, 2003). [5]

International Electro technical Commission, 2001, Radiation Safety of Laser Products, Equipment Classification, Requirements and User's Guide, IEC, Geneva, Switzerland, IEC Publ. 60825-1.

[6] International Commission on Non-Ionizing Radiation Protection (ICNIRP), 2000, Revision of guidelines on limits of exposure to laser radiation of wavelengths between 400 nm and 1.4//m, Health Physics, 79(4): 431-440. [7] Johnson J: Lasers. Milwaukee, Raintree Publishers, 1985. [8] Lyon T. L., 1993, Laser measurement techniques guide for hazard evaluation, / Laser Appl, [in two parts] 5(1): 53-58 and 5(2):37-42. [9] Sinclair DC, Bell WE: Gas Laser Technology, (New York, Holt, Rinehart, and Wilson, 1969). [10]

Shimoda K: Introduction to Laser Physics. New York, Springer-Verlag, 1986.

[11]

Sliney DH, Wolbarsht ML: Safety with Lasers and other Optical Sources, a Comprehensive Handbook (New York, Plenum Publishing Corp, 1980).

[12]

Sliney D. H. and Trokel S. L., 1992, Medical Lasers and Their Safe Use (New York: Springer-Verlag).

[13]

Svelto O: Principles of lasers, (New York, Plenum Publishing, 4th ed, 1998).

[14]

United Nations Environment Programme/World Health Organization/ International Radiation Protection Association, 1982, Environmental Health Criteria 23, Lasers and Optical Radiation (Geneva:WHO).

[15]

Weber MJ (ed.): CRC Handbook of Laser Science and Technology, vols. 1—5. (Boca Raton, FLorida, CRC Press Inc, 1982-1994).

[16]

Young M: Optics and Lasers, Including Fibers and Optical Waveguides, (New York, Springer-Verlag, 2000).

[17]

Laser Institute of America (LIA), LIA Laser Eye Protection Guide (LI A, Orlando, 2000).

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Current Trends in Radiation Protection H. Metivier, L. Arranz E. Gallego and A. Sugier (eds.)

What Policy Makers Need for Radiation Protection? Junko Matsubara1 Nuclear Safety Commission, The Cabinet Office, Kasumigaseki 3-1-1, Chiyoda-ku, Tokyo, Japan 100-8970

Abstract. Reviewing the history of governmental regulations of hazardous substances including radiation/ radioisotopes in the process of policy-making, standard settings, regulations and compliance, it is recognized that we are facing a new facet, greatly in need of confidence and risk literacy in the public at present. Roles of regulators and current problems in radiation protection are pointed out according to the author's experiences as a nuclear safety commissioner in Japan. The principles of ALARA and the LNT-hypothesis are very significant in the frame work of radiation protection. They have double-edged significance for the public. As accountability of the regulator, it is necessary to discriminate the LNT-hypothesis for the purpose of radiation protection from the reality of an effect from very low doses of radiation. A stiff use of LNT-hypothesis deteriorates public understanding about low dose effects of radiation. It also suppresses original contributions by minorities of experts who examine the hypothesis with laboring efforts. The author proposes how to break through the mechanical uses of LNT-hypothesis, by indicating examples in our academic sector in order to promote active discussions and investigations to approach biological reality in the whole body of man.

1. INTRODUCTION Risks of radiation and the principles of radiation protection we have been discussed at international level based on experiences since the early twentieth century. The established strategy of radiation control is one of the pioneering examples for the regulation of other toxic substances in our society. The more materialistic needs are fulfilled, the less the public accepts various types of risks. It means that people appreciate the value of the safety more seriously than the value of materials. Moreover, many people think that to feel secure is more important than the safety itself. With the increase of risk perception in public, the importance of risk communication and risk governance is widely acknowledged in the present world.

1

E-mail: [email protected]

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Figure 1. Shift of Mortality Rates of Tuberculosis in the United States during 1860-1960

In the use of nuclear energy and radiation regulators are also required to promote transparency in the process of regulations, by stimulating risk-communications, and to exchange dialogues among experts and stakeholders. Particularly, the public has strong and sensitive concerns on the effect of low dose of radiation. The government and experts have responsibility to answer a question of what is the effect of milli- or microSievert levels of radiation on man in reality with easy and accountable words. I would like to point out current problems in radiation protection and raise proposals bringing the application of LNT hypothesis into focus for policy makers based on my experience as a nuclear safety commissioner and an expert of radiation biology. Firstly, I summarize the evolution of governmental regulations in Japan.

2. EVOLUTION OF REGULATION 2.1. Establishment of safety policy and regulatory laws and rules We know that the level of life-standard in a nation is very significant to determine levels of health risks. Historically the mortality has been reduced continuously according to the improvement of levels of the standard of life in general, which was not particularly related to a certain scientific discovery [1] (See Figure 1[2]). Nevertheless, a decision of a policy maker is very significant. We have a typical episode in the late nineteenth century. Before the discovery of Vitamin BI by Drs. Suzuki and Ikeda beriberi was very common in Japan. Many soldier died in troops due to malnutrition. However, in the navy a naval officer decided

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to supply unpolished rice because the officer knew by experience that beriberi was more frequent among polished-white rice eaters. While in the army polished rice was supplied because the chief medical officer thought that beriberi was an infectious disease. Only a few died in the navy while 4000 soldiers died due to beriberi in the army in 1880s. It manifests the importance of the exact eyes of policy makers to watch the reality.

2.2. Standard settings In 1925 the International Congress of Radiology (ICR) was formed and started to establish protection standards for radiation workers in 1928 , nearly thirty years after the discovery of X-rays by Roentgen in 1895. It evolved into the present ICRP which has issued already nearly a hundred publications. Historically if a hazard of a toxic substance among workers is found, the government starts to regulate the toxic substance by setting regulatory criteria not to exceed TDI (tolerable daily intake of man). For control of chemicals a TDI or ADI( acceptable daily intake) can be set by the minimum body burden in the doseresponse curve of animal or man with defining VSD(virtually safe dose). Criteria (maximum levels) for foods or environmentals are set not to overcome the exposure which results TDIs in man. The regulatory criteria or standards are considered of uncertainty factor due to variations with species (3), animal to human(X10), and individual sensitivity(X10), and in overall it is set about 100. Yet, TDIs are getting lower with increase of the knowledge. Besides, policy makers should have comprehensive view-points for the prevention of hazards. For instance, the low-fat diet is more effective to reduce Dioxin in the body than regulations with severe criteria in food, if dilution of food toxicity by diversity of the food habit is considered. The mechanical use of safety factor or stiff use of the precautionary principle in the setting standards may result in overestimation of the risk on the effect. For the control of radiation a hypothesis of linear no threshold is set for the dose-response curve. I shall discuss about problems relating to LNT-issues later in detail.

2.3. Regulations and compliance A remarkable success in quick improvement of hygiene and public health in Japan was obviously a result from strong interventions on isolation, disinfection and inoculation by the government for the control of pathogens. A drastic decrease of infantile mortality rate in Japan as seen in Figure 2, [3] can be regarded due to the following reasons (1) strong regulation with help of the police before the World War II and (2)background of wide-spread school education. In 1937 a regulation of radiation protection started by the ministry of interior for the control of diagnostic X-ray operations. In 1957 regulations under the law of radiation/radioisotope control were enacted and intensively implemented. We think the regulators' role to check compliance according to laws /regulations and to find out violations or keeping records is very significant.

2.4. Collection of information and promotion of safety studies For ensuring nuclear and radiation safety the promotion of safety research is indispensable. Essentially safety studies are to deal with prediction of risks through examinations of nuclear related facilities. The know-how helps to establish effective regulations. The public expects that the government is neutral and scientific in promoting safety studies. The government should answer to expectations of the public. Policy makers must always harmonize current advance of new knowledge and social demands. The Nuclear Safety Commission should plan, deliberate and select research-subjects of importance and evaluate those results periodically.

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Figure 2. Yearly shifts of Infantile Mortality Rates in Various Countries

Figure 3. Disclosure on Public homepage

2.5. Promotion of transparency and public risk literacy Nowadays in Japan, openness or transparency is one of the key words to reconstruct or to acquire public confidence. Not only our government but utility companies open data even on trivial troubles or abnormal events at commercial nuclear operations. KEPCO started the disclosure of real-time display of monitoring spatial dose-rates around a nuclear power station as shown in Figure 3.

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The government should promote risk literacy of people to fulfill accountability for the public. When people have sound risk-consciousness they will participate in self-imposed actions to avoid risks. We are facing an era in need of a new thinking as post-normal science where knowledge is shared with not only experts but stakeholders with motive of problem-solving. [4]. New concepts of post-normal science are listed in comparison to positive normal science (See Table 1 [5]). My image for the future regulatory process is as follows:

Level 0

Promotion of safety studies and risk-literacy

Level 1

Promotion of dialogue between stakeholders

Level 2

Standard settings

Level 3

Regulation and compliance

Level 4

Promotion of transparency

Level 5

Self-motivated action and construction of safety culture

3. CURRENT PROBLEMS 3.1. Accident control Annually 20 billion X-ray examinations and 5.5 million cases of radiation therapies are performed worldwide (according to Dr. Mettler, 3rd Committee of ICRP). Uses of medical accelerators are widely spreading. With the increase of medical exposures, over-exposure accidents in hospitals are increasing. Digital safety measures are urgently needed.

3.2. Keeping compliance Source management is necessary to reduce orphan sources. Majorities of orphan sources are released when regulatory levels were not clear. In Japan with introduction of BSS exemption levels the Radiation Safety

Table 1. Normal, Positive Science versus Post-Normal Science (by D. Haag and Kaupenjohann, 2001)

Normal science •

Epistemology

• •

Rationality Methods

• • •

Peer Community Problems/issues Uncertainty

•

Risk

Essentialist Abstraction Scientific truth Instrumental Established Universal Closed Experts Disciplinary Technical Low

Scientific

Post-normal science Constructivist Context Plurality of perspectives Communicative Problem-driven Specific Extended peer community Real World Epistemic High Social Construction

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Committee issued recently a report on the exemption levels of NORMs (naturally occurring radioactive materials) containing Uranium, Thorium, and Samarium in industries and commodities. There are still needs to define regulatory levels for varieties of nuclides.

3.3. Problems in corporate governance of Japanese community The criticality accident at JCO nuclear fuel facility in 1999 frightened the all Japanese as the event happened in a neighborhood of the daily life. Systematic violations against detailed regulations in the criticality control were grown within the company year by year aiming at more effective production. It happened as a result of a corporate ill-decision which is a typical pattern of the group decision. The government amended the law on the Regulation of Nuclear Source Material, Fuel and Reactors by introducing a whistle-blowing system and other policies to strengthen nuclear disaster prevention in 2000.

3.4. Difficulty to acquire public understanding of radiation safety Nowadays people become more risk-conscious. It is difficult to persuade people by talking about principles or concepts of radiation protection for them to feel secure. The use of the word such as LNT-hypothesis, ALARA principle, or stochastic effect etc. deteriorates the understanding of people about the effect of low dose of radiation in reality. Indeed, the principles of ALARA and the LNT-hypothesis are very significant in the frame work of radiation protection. However, these have double-edged significance for the people. It is desirable to regulate strictly a toxic substance in society7, at the same time the influence of the substance is more severely perceived by an individual. Mass-media like exaggerated news of radiation hazards. For low-dose issues, I think it is still necessary to re-examine the biological meanings of LNT-hypothesis from more realistic view points, although LNTissues have been discussed quite long at established international bodies.

4. DISCUSSIONS ON THE LNT-HYPOTHESIS It is justifiable to apply the linear no-threshold (LNT) hypothesis for the purpose of radiation protection to assure a conservative estimation of the effects. Nevertheless, we should discriminate the reality of what is actually happening at very low doses of radiation in the whole body of man from the hypothesis, even though we do not have a firm evidence to reject the LNT-hypothesis. Not only in case of a nuclear emergency but also for a decision making for nuclear policy, the public wants to know the real aspects of the effects of radiation even at very low doses, those considered as gray region. However, there are still many experts who do not discriminate the hypothesis from the reality. A paper written by ICRP [6], states that "in Publication 60 (1990 recommendation) the definition of a dose limit was changed to mean the boundary above which the consequential risk would be deemed unacceptable". Here one can not discriminate the meaning of the risk as level of protection and a realistic level of a risk from radiation. Although UNSCEAR tried to review comprehensively the biological and epidemiological data relating to the health effects of radiation (cf. Figure 4 revised by the author), this seems yet insufficient because there are ignored evidences from whole body studies demonstrating the systematic defense mechanism against radiation in organisms, and they even suggest challenging possibilities for new concepts and approaches. There are findings to establish a new paradigm of carcinogenesis with several distinct processes of interacting genes with micro-environmental components in tissues. [7,8].

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Figure 4. The pathways that link initial radiation damage to somatic cell, the cellular responses/consequences and later expressing health effects (from J. Matsubara, on the basis of UNSCEAR 2000 Report)

4.1. Why discussions are needed It remains indeed problematic to use low-dose extrapolation by LNT hypothesis to arrive at actual features of the effects of very low doses of radiation for the following reasons. 1. Epidemiological evidences demonstrating a significant excess of hazards such as cancer or genetic effects due to radiation at doses less than 100 mSv are scarce and problematic. They depend mainly on the data of acute radiation exposure at Hiroshima and Nagasaki. 2. There is variation of individual sensitivity against toxic substances. If data are compiled to the population as a whole, a linear dose-response curve is obtained even if there is a threshold at the individual level [9]. 3. Statistical significance depends on variance of the data and size of the population surveyed. If we increase the sample-size we can reach statistical significance even at very small absolute differences from the control. Actually the degree of the difference is important than a statistical significance of yes or no. Due to the presence of multiple agents for carcinogenesis, it is difficult to separate the effect of radiation from effects of other confounding agents. 4. In order to demonstrate a clear harmful effect of radiation it is necessary to obtain the data from pure and sensitive cells or from animals under strictly controlled experimental condition which is unusual in daily situation. The scientific community welcomes molecular studies on cellular systems, but tends to reject the results from whole-body studies because the data tend to vary with experimental conditions even if such data suggest a certain biological meaning. There are few experts of radiation protection specializing in the whole-body studies or having interests in biological protection mechanisms.

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5. The LNT-hypothesis is based on physical events without cooperative effects, and is simple and easy to understand, while actual phenomena existing in the whole-body are complex and sometimes sophisticated. A dogmatic application of the LNT-hypothesis discourages various experimental challenges and inhibits the establishment of original scientific protocols or active discussions. Recently a report from whole body studies on the dose response of mice appeared in Radiat. Res. [10]. The study was performed using 4000 SPF-mice at strictly controlled environment during the whole life span of the mice under varied radiation exposure levels supported by local governmental grants. The purpose of the study is to evaluate the biological effects of radiation at low-dose rates using life span and neoplasm incidence as parameters. The primary object of this study must have been to observe the whole body reaction of mice against radiation of different exposures of dose-rates and total amounts of radiation as an index of life-span or death. With these chronic experiments one can analyze quantitative differences of the reaction(index) of mice between the exposed and the control(not irradiated) groups. The important thing is to clarify the quantitative degree of the difference of survivals from the control. The very degree in comparison to the control reflects the individual defense power against radiation of each exposed group. With their results as shown in Figure 5 one can see dynamic patterns of death of each group as a whole and can notice remarkable difference of life-shortening in the highest dose group. While, differences are small in other two groups of less dose rates. Trends are similarly seen in both results from males and females. If the difference is smaller one naturally understand or speculate the stronger possibility of the presence of protection against radiation in lower dose-rate groups. In this paper authors did not clarify the quantitative degree of the differences from the control. They concluded that there is no evidence of radio-adaptive response or of threshold. It is a pity that their discussions are too simple, because such refined data based on laborious long-term observations would provide various hints for more intensive biological discussions.

4.2. What to observe ? We must make sure that the LNT hypothesis is based on the denial of the presence of a threshold and that the presence of a threshold means that individuals have a protective power till a certain level of total dose or dose-rate of radiation or a toxic substance in the body. Let me summarize what to consider about real features of the effects of low dose of radiation from biological view points.

1) Evidences obtained from epidemiological studies from Hiroshima-Nagasaki, and Chernobyl demonstrate clear biological realities that there exist radiosensitive cancers as leukemia, breast cancer, and childhoodthyroid cancer, but it remains difficult to prove the excess of other cancer-risks or genetic effects at doses less than 50 mSv. 2) The LNT hypothesis predicts that risk is influenced only by dose. However, R. Mitchel observed in mice that low doses modify various host reactions as apoptosis and DNA repair competence . He found that low doses of radiation increase the latency of spontaneous lymphomas in radio-sensitive mice [11]. 3) T. Nomura observed the difference of radio-sensitivity of tumors with different tissues and with doserates based on his repeated whole body studies with mice [12]. H. Tanooka [13] tried to review clinical epidemiological reports in order to classify the reported varieties of tumors with levels of threshold and with dose rates. If we investigate biological reasons of the difference of the tumor-characters and of threshold values, we shall get more information to control carcinogenesis in future.

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Figure 5. Survival Curves for B6C3F1 Mice (Cited from S. Tanaka et al. 2003)

4) Most cancers have acquired the same set of several functional capabilities. There, apoptosis play a key role in the development of cancer [8]. The perturbation of cancer genes occurs with micro-stimuli as free radicals, chemicals, or hormones and it is affected by inter-cell-communications in the surrounding extracellular matrix. It is said that the basement membrane of the cell is a key player both in the maintenance of normal tissue architecture and in tumor development [7]. 5) It is important to investigate what is really happening in the body from both aspects of damages and protective responses, because radiation hazard at a low dose, e.g. delayed cancer appears as a result of the overall balance between competing stress-related biochemical functions in the whole body (see Figure 6). 6) An individual has specific and nonspecific immune functions. The author could prove that animals(mice) demonstrate increased stress-response against higher dose of radiation as similarly as chemicals, by inducing increased metallothinein which is anti-oxidative [14]. Metallothionein is a controller of organic radicals in the membranes [15]. If radiation energy is transferred to organic radicals of which half lives are 10 to 20 hours, it opens new possibilities to control radiation damages by various chemicals. 16. It provides a reason why the induction of metallothionein in the body produces radio-resistance in mice [14].

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• Free radical formation • DMA Damage • Membrane Damages

• • • • •

Free radical scavenge Anti-oxidative response DMA repair Immune response Apoptosis

Figure 6. Reality is a Balance between Harm and Defense

Figure 7. The relationship between effective doses and dose rates. Cited from J. Magae, Y Hoshi, C. Fumkawa, Y. Kawakami and H. Ogata: Quantitative analysis of biological responses to ionizing radiation, including doses, irradiation time, and dose rate [from Radiat. Res. 160, 543-548 (2003), all rights reserved].

7) M. Yonezawa found radio-adaptive response at the whole body level, i.e. a spot irradiation to mice produce radio-resistance with specific doses and timings (e.g. 2 month after 10 cGy or 2 weeks after 50 cGY) [17]. The authors observed an increase of immune reactions at the same specific radiation doses and timings [18], [19]. This is an example that animals react against different stressors in a generalized manner as Hans Selye proposed in 1934. 8) Recently Ogata et al [20] clarified the degree of radio-tolerance as a function of dose-rate based on the experimental data of micro-nuclei formation of Magae et al. [21] as shown in Figure 7. The ED50 quickly enhances when dose rates approach to zero. It means that the radio-tolerance is higher with smaller dose rates. With discussions on the degrees of radio-resistance in the body, choosing proper quantitative measures of

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body response, dose-rates, total doses and timings, one can get dose-response curves to arrive at valuable information in order to promote discussions more quantitatively about the balance between the harm and protective power in the body. 9) The following epidemiological studies using effective indicators as stable/unstable chromosomal aberrations [22] in addition to those in Chernobyl or Mayak. It will supply valuable information to bridge knowledge between cellular events and physiological events in men. * Comparative studies on populations with different life styles. [23] * Studies on populations in areas with high radiation background [24]. * Studies on workers at different industries.

REFERENCES [1]

T. R. Mckeown, The Role of Medicine ( Princeton Univ. Press, 1979)

[2] U. S. Bureau of the Census, Historical Statistics of the United States: Colonial Times to 1979 Part 1 (Government Printing Office,!975),pp58 [3]

WHO, World Health Statistics Annual, U. N. Demographic yearbook 1993

[4]

S.O. Funtowic2, J.R. Revetz, Environmental Toxicol. Chem. 13, 1881 (1994)

[5]

D. Haag M. Kaupenjohann, 144, 45(2001)

[6]

ICRP, J. Radiol. Prot. 23,129(2003)

[7]

D. Hanahan, R. A. Weinberg, Cell, 100, 57(2000)

[8]

T. Jacks, R.A.Weinberg, Cell, 111, 923(2002)

[9]

Hattis Air polution Studies (2000)

[10]

S.Tanaka, I. B. Tanaka,III, S.Sasagawa, K. Ichinohe, T. Takabatake, M. Matsushita, H. Otsu , F. Sato, Radiat. Res. 160, 376 (2003)

[11]

R. E. J. Mitchell, J. S. Jackson, R. A. McCann, D. R. Boreham, Radiat. Res. 152, 273 (1999)

[12]

T. Nomura, Radiation and Homeostasis, (Elsevier Science, Amaterdam,2002), pp!05

[13]

H.Tanooka

[14]

J. Matsubara, Y. Tajima, M. Karasawa, Radiat. Res. Ill,

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Current Trends in Radiation Protection H. Metivier, L. A.rranz E. Gallego and A. Sugier (eds.)

Living in Contaminated Territories: A Lesson in Stakeholder Involvement Jacques Lochard1 Centre d'etude surl'Evaluationde la Protection dans le domaine Nucleaire (CEPN), Route du Panorama, BP 48, 92263 Fontenay-aux-Roses Cedex, France

Abstract. Experience of long term radioactive contamination of the environment, especially in the territories the most affected by the Chernobyl accident, have shown that the omnipresence of radioactivity in the daily life was deeply altering the relationships of the individuals towards their environment, perceived as globally deteriorated, and to the others. Inhabitants of contaminated territories experience a general loss of control on their daily life and on the means to improve their protection and the one of their children. The need to develop comprehensive and inclusive approaches for the long term management and rehabilitation of potentially contaminated areas is now broadly recognised, notably in the post September llth context. The experience of the ETHOS project in the republic of Belarus directly affected by the Chernobyl accident, illustrates a successful participatory approach involving the population and the local authorities and professionals in the day-to-day management of the radiological situation. This experience has shown that the direct involvement of the population in the management of the radiological situation was a necessary approach to complete the rehabilitation programme implemented by public authorities in contaminated territories, especially in the long term. This paper highlights, through the major outcomes of the ETHOS experience, some key features of the stakeholder involvement process and the role it can play in the management of long term contaminated sites and territories.

1. INTRODUCTION International experience, particularly in those countries most affected by the Chernobyl accident, has demonstrated that the long term management and rehabilitation of contaminated territories is not a narrow radiological issue that can be dealt with solely by technical means. The presence of contamination is affecting the whole society and the quality of life in all aspects: health, environmental, economic, social, cultural, ethical and political. The living conditions are deeply affected and even a return to a so-called radiological

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E-mail: [email protected]

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normality is far from ensuring normal living conditions. Implementation of countermeasures proved to generate negative societal impacts such as stress among the general public as well as distrust towards experts and public authorities. Moreover, the implementation of corrective strategies such as risk communication and psychological care tend to reinforce the perceived ambiguities of protective strategies and consequently generate social distrust. The need to develop comprehensive and inclusive approaches for the long term management and rehabilitation of potentially contaminated areas is now broadly recognised, notably in the post September 11th context. A key feature of such approaches is the importance of involving the population and the local authorities and professionals in the day to day management of the affected territories. This was identified as critical for success in a recent UNDP report on "The Human Consequences of the Chernobyl Nuclear Accident — A Strategy for Recovery" drawing the lessons of 17 years of experience with the management of contaminated territories in the CIS countries [1]. It is to note that the role of stakeholder involvement in the management of prolonged exposure situations has been also acknowledged by ICRP in its Publication 82 as a means to improve the decision-making process related to the implementation of radiological protection actions [2]. The paper presents the lessons of the ETHOS Project, a stakeholder involvement experience that took place in the late nineties in the contaminated territories of Belarus affected by the Chernobyl accident. The objective of this project, partly sponsored by the European Commission, was to help the population in 5 villages in the South East of the country to regain control on their living conditions severely affected by the intrusion of the contamination. The first part describes some key characteristics of living in a contaminated territory, particularly the loss of control of the population on daily life. The second part presents the stakeholder involvement process that took place during the implementation of the ETHOS project. The third part draws some general lessons on the role of stakeholder involvement can play in the management of long term contaminated sites and territories.

2. LIVING IN CONTAMINATED TERRITORIES The expression "living in contaminated territories" calls for some clarification as it may imply that such a situation could be seen as normal or at least acceptable under certain conditions as far as the risk is concerned. As a matter of fact, the decision for inhabitants to stay in a contaminated territory whether on a voluntary basis or because they have no possibility to move out as they would wish cannot be resolved solely on scientific and technical considerations. This is an ethical and political issue which calls for a democratic involvement of the persons directly affected in the evaluation of the situation to decide to leave or to stay and, in the latter case, in the development of concrete strategies to improve their living conditions respecting at the same time their health and their dignity. In this perspective, the position adopted in this paper is to explore how it is possible for those who reside in a contaminated environment to become more vigilant and responsible with regards to the radiological situation and more broadly to improve the quality of their own lives and the life of their children. It is beyond the scope of this section to describe in details all the characteristics of living in contaminated territories. Several past studies have provided such analyses [3,4]. The objective here is just to highlight the exclusion process which is at stake for those living in a contaminated environment. This process leads progressively to a loss of control of the population on daily life which undermine the effectiveness of classical "top-down" rehabilitation strategies.

2.1. The exclusion process The sudden intrusion of radioactivity in the daily life of a population is generating deep disruptions at the health, psychological, social and economic levels. This is a new reality entering the human condition and

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each affected individual is suddenly confronted which a situation which is profoundly altering all aspects of his or her private and social life. The contamination is an invisible and non palpable presence which can only be detected by sophisticated equipments used by experts. Moreover, in the absence of past experience and words in the common language, it remains unspeakable for non specialists. As such it is straight off a worrying and hostile presence which is reinforced by the scientific and technical nature of the social response and the uncertainties related to the long term potential health effects. This presence is affecting the relationships of each individual with himself, the others and the territory he or her is living in. First, it is questioning everyone with regard his relation to risk and consequently to his own death. It actualises this last one which is normally pushed aside as an eventuality concerning only the others; those who are ill or are taking risk voluntarily. In this confrontation each individual remains without words to express his or her fear. The contamination is also altering the relationship to the others. How to behave with those who are not contaminated? How these last ones perceive those living in a contaminated territories? It is well known that relocated children coming from the contaminated zones around Chernobyl were often put aside in the classrooms in the non affected regions. It was also reported that young people living in non contaminated areas were refusing to envisage to marry someone coming from the affected zone. As far as the relationship to the territory is concerned, beyond the fact that the familiar neighbourhood is perceived as hostile, it is also profoundly destabilised by the general loss of value. Not only the economic value of the land and the products is downgraded but also the intangible value of the common natural heritage like the fauna or the flora as well as the aesthetic value of the landscapes. It is to note that this devaluation is reinforced by the zoning process of the affected territories which acts as an official endorsement of the loss of value. As a result of these various changes, the quality of life as a whole, as well as the environment, are perceived as being irreversibly depreciated. Each individual is thus immersed in a new reality of which he is at the same time put aside because of his lack of experience to behave and act adequately in such a type of situation. This leads to a general feeling within everyone's mind of being excluded from his own familiar world and to loose progressively the control on his day to day life. Finally, this exclusion process which is also generating a loss of self-confidence among the population is strongly reinforced by the technical management of the contamination driven by the authorities with the support of experts.

2.2. The side-effects of the technical response It is obvious that many aspects of the post-Chernobyl management have re-enforced the exclusion process described above. First because the management was strongly centralised and prescriptive, and did not allow any kind of public involvement. This is not surprising for the very emergency situation, where time is missing to envisage any kind of "inclusive response". The weak point is that this prescriptive management have lasted for years after the accident, more and more excluding the population from the problems associated with the radioactivity. A key factor of exclusion for example, was certainly the "zoning" of the territories, that were classified according to the soil contamination. This zoning explicitly put a separation line between "those who were contaminated" and "those who were not", leading to a real social exclusion of those people which were relocated. Another important factor that increased the distance to radioactivity was the technical management of the situation: countermeasures and policies have been derived for many years based on scientific expertise, performed by specialists without neither involving the inhabitants in the evaluation nor giving them any feedback results from this evaluation. This strongly re-enforced the conviction that radioactivity was too technical and was not a matter to be either understood or appropriated by the population. Beyond this obvious aspects it is interesting to mention some more insidious processes related to the risk assessment and management process which play an important role independently from the importance

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of the contamination. Such processes are clearly operating in the management of slightly contaminated sites from past activities for example. The first one is the measurement of the contamination. This is an action which, independently of its more or less sophisticated technical aspect, is radically reducing the complexity of the situation, characterised by a set of relationships between the people and the environment, into a physical phenomenon: the quantity of energy delivered by the radioactive atoms present on the soil, in the products or in the body. As a result, each particular situation involving distinct individuals with their own concerns, is apprehended by a set of universal quantitative indicators which finally put aside this intimate reality. This effect is generally neglected by the experts who quite often mix up the results of their measurements with the reality of the situations. Measurements are necessary to drive emergency actions but clearly insufficient when dealing with the long-term rehabilitation of affected territories for which it is necessary to consider the complexity of the relations between the inhabitants and their common environment, which in no doubt cannot be reduced to a physical quantity of radiation. The introduction of concentration or dose limits is another process which is reinforcing the exclusion of the population. For this last one, limits are splitting their familiar world into two category of situations: those which are good and those which are bad. They are thus creating an artificial separation between situations which by nature are forming a continuum. There is a great difference between a milk with a level of contamination just a few percent above the commercialisation limit and a milk with a level of contamination which is twice or threefold higher than this limit. In practice the limit erases the notion of quality which allows to better differentiate the situations. Furthermore, the role of limits in a long lasting contamination situation is very different from the one for normal situations i.e. controlled practices. For these situations, limits delineate the domain within which the risk is considered as socially acceptable and allow to identify deviations which in principle remain exceptional. In contaminated territories, limits qualify the situations as "good" or "bad" and at the same time those who are living there or producing foodstuff on one side or the other. When a farmer is discovering that his milk is above the limit, this is the entire production process including the pasture and the caws which is devaluated. Most often this is experienced as a defeat sometime even a loss of self-respect. The setting of limits for contaminated territories is thus a delicate issue because it qualifies the environment, the places, the products and the persons. They also qualify actions and dictate behaviours as for example not eating certain foodstuffs or not spending too much time in certain places. Limits appears thus an instrument restricting individual freedom and separating the inhabitants from their environment and the others. A last point worth to mention is the side-effect of countermeasures. In most cases they are decided by experts and authorities on cost-benefit considerations and are applied at the collective level on a planning mode. Concretely, there objective is to maintain individuals at a certain distance from the contamination or to reduce as low as reasonably achievable (ALARA) the levels of contamination in the environment and the foodstuffs when the presence of population is tolerated. In a general context where the only presence of radioactive residues is an exclusion factor for the inhabitants, the introduction of countermeasures is just reenforcing the process. Individual becomes dependant of mechanisms on which they have no control at all. For many inhabitants of contaminated territories, the implementation of countermeasures, particularly those which are affecting ancestral relationships with the environment and the traditional modes of production are perceived first as intrusive and generating interdictions before to be considered as a means of protection. Altogether, the management of the situation, focussed on its radiological dimension, is progressively raising the concern among the population and re-enforcing the hostile character of the environment. Neither the limits nor the countermeasures are able to generate social confidence. The previous developments allows to better understand the various attitudes or strategies adopted by a population living in a contaminated territory to face the radiological situation day after day. The most frequent attitude is the withdrawal into oneself which generally leads to a denial of the risk. Many people, for example in the contaminated territories of Belarus express the view that after several years of exposure

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to the contamination they became immunised against radiation like Colorado beetles against pesticides. This is a way to support further the situation. Other inhabitants just give up. They adopt a fatalist attitude, feel abandoned and victims of a great injustice. Both attitudes generally lead to an increase of the risk. More seldom, some individuals maintain a position of responsibility and face the situation. The price to pay to stand this position is rather high because they accept to live in a permanent worry and vigilance. This is only possible with a good knowledge of the situation and the possibility to act in a prudent way which means to be personally involved in the rehabilitation process. Finally, the inhabitants of a contaminated territory are permanently confronted to the dilemma to leave the place or to stay and to organise the daily life for them and the future generations.

3. THE STAKEHOLDER INVOLVEMENT PROCESS IN THE ETHOS PROJECT A complete description of the implementation and achievements of the ETHOS Project can be found in the final report prepared for the European Commission [5] and several articles which present in more details some aspects of the project [6-8]. This section is highlighting the stakeholder involvement dimension.

3.1. A pragmatic approach for improving living conditions in contaminated areas The ETHOS Project emerged from different investigations which had been conducted in the Ukraine, Russia and Belarus in 1992 — 1994 aiming to better understand the living conditions of the populations in the contaminated territories and to shed light on the wide-ranging social consequences of the accident remaining unresolved [3,4]. The objective of the ETHOS approach was to develop sustainable rehabilitation approaches in villages affected by the Chernobyl accident, in order to improve the living conditions, by actively mobilising the inhabitants, and the local authorities and professionals. This approach was complementary to the public actions and practical. The aim was not to produce new scientific knowledge but to apply the existing ones in the development of practical know-how for the populations. The ETHOS approach was addressing both technical and social aspects of the problems posed by the contamination. It involved an interdisciplinary team of European experts, with specific skills in radiation protection, agronomy, social risk-management, communication and co-operation in complex situations. The ETHOS approach placed the inhabitants of the villages at the centre of strategies to improve the situation. All the actions conducted in the context of the project were deeply rooted in the local problems that the population was facing, and were systematically implemented with the involvement of all actors concerned by the problems at stake. Practical radiation protection became progressively one of the multiple components of the "global" quality of the living environment. Each individual actively participated in the actions for rehabilitation, which were not considered anymore to be under the unique responsibility of experts and authorities. According to this approach, no pre-existing solution were given a priori to the problems raised by the local actors. If a problem was pointed out, an evaluation was carried out first by the local actors (voluntary inhabitants, authorities and specialists in various fields at the local, regional and national levels) without preconceived ideas about the way to solve it. As well, the ETHOS approach was not based on any pre-determined methodology laying down all the conditions for action. Instead, the ETHOS participants primarily established an ethical framework as guiding principles in the process to re-establish the trust of involved actors. One major position adopted consisted in refusing to make any prior assessment of the situation which did not involve the local actors, which did not shed any light on the situation, or which did not suggest any possible action, systematically rejecting any solution which did not contribute directly to improving the quality of life.

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In this process, the ETHOS participants also refused to use average dose estimates, bearing in mind the high disparity of individual situations as far as food products contamination and individual habits were concerned. An attempt was then made to find protection actions, making maximum use of room of manoeuvre, which — more often than not — already existed but were badly exploited. These actions sometimes required the population to make difficult choices between conflicting interests and wishes. For example, a typical dilemma for the villagers was to abandon the secular tradition of consuming products of the forest.

3.2. The two phases of the Project In a first phase of the project (1996 — 1998), the ETHOS approach was implemented in the village of Olmany located in district of Stolyn in the Southern part of Belarus. During this first phase a few tens of villagers have been involved in a step-by-step to progressively regain control on their day-to-day life. The main steps of this process were the following: — First step. Listening and learning from the villagers about their concerns, difficulties, wishes, both at the level of their individual life and as citizens living in a contaminated zone. This allowed to built a co-operation framework between the local population, the Belarusian local, regional and national authorities and the ETHOS European experts. - Second step. Common evaluation of the local radiological situation, performed jointly by the involved villagers, the local professionals and the ETHOS experts. - Third step. Identification of possible protection actions to be implemented locally with a minimum of additional resources. — Fourth step. Establishment (or reestablishment) of links between the villagers and the local authorities and professionals. Having reached this stage, it was then possible to develop a real cooperation between all involved stakeholders with the common objective of improving the quality of life in the village taking into account the constraints and difficulties associated with the local radiological situation. An important feature of the stakeholder involvement process in the ETHOS approach was the identification of success criteria for the Project. Based on the extensive discussions with the villagers, and the local professionals and authorities a set of 80 project success criteria were identified during the first phase of the Project. They were classified into five main topics: — Development of a practical radiation protection culture, - Autonomy of local stakeholders, — Development of quality for the Project participants, — Demonstration of concrete changes in the place of intervention, — Sustainability, partnership and trust. These criteria were maintained as a guide throughout the project, but were more formally used in an end-of-project evaluation in 1999. In the second phase of the project (1999 — 2001), the ETHOS approach has been extended to 4 localities inside the district of Stolyn (Belaoucha, Gorodnaya, Retchitsa, Terebejov) with the objective of studying the possibility and the conditions for its future diffusion by Belarus local authorities and professionals in the whole contaminated territories of the country. This phase was characterised by:

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The empowerment, by the ETHOS European experts, of local professional from the health care, education and agriculture systems, as well as those in charge of radiation monitoring (food products and whole body) to allow them to take in charge the further implementation of the ETHOS approach. The involvement of the different levels of authorities (local, regional, national) as well as national Belarusian scientific institutes to accompany this process, The development of a practical radiation protection culture among the villagers including the conditions for its transmission to future generation through the school system.

In concrete terms, the ETHOS approach has meant that several groups of volunteers from the inhabitants of the villages, the existing administrative and professional networks involved at the local and national levels have been created in the various villages. These groups have worked on local practical projects focused the following concerns:

— The improvement of the radiological protection of the children in connection with the monitoring of their health; - The development of a practical radiological risk culture among the children at school; — The production, processing and marketing of private agricultural products of good radiological quality (mainly potatoes); — The development of an operational monitoring system of the radiological situation (foodstuffs and whole body).

All these practical projects were structured with the objective to promote radiological quality as a contributor to the global quality of life and not only as a factor of constraints and contradictions.

4. LESSONS OF THE ETHOS PROJECT FOR STAKEHOLDER INVOLVEMENT The ETHOS experience has shown that the direct involvement of the population in the day-to-day management of the radiological situation was a necessary approach to complete the rehabilitation programme implemented by public authorities in contaminated territories, especially in the long term. The ETHOS experience has also demonstrated that to be effective and sustainable, the involvement of the local population must rely on the dissemination of a "practical radiological protection culture" within all segments of the population, and especially within professionals in charge of public health and education. The experience from the ETHOS project has shown that the development of such a culture was based on 3 key pillars:

— An inclusive radiation monitoring system. This system call for a basic comprehensive practical knowledge about the mechanisms through which man is exposed and a direct access to monitoring equipment, by which the radiological quality7 of the environment can be evaluated and the levels of internal and external exposure of individuals and the whole population can be controlled.

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— The transmission of practical knowledge about the control of the radiological situation to future generations through the education system. Basically, the establishment of such a shared culture implies the setting up within the contaminated territories of a specific infrastructure related to the health care and education system. This infrastructure must bring together public and non-governmental organisations to implement the necessary management procedures. The involvement of non-governmental organisations and representatives of the public in the practical implementation of rehabilitation strategies has proved to be a key factor in the enhancement of public trust and confidence. An important feature is that the rehabilitation issue as it was tackled in the ETHOS experience was not reduced to only technical aspects, driven solely by radiation protection considerations. Nevertheless, radiological measurements constitute a key point of the whole system of radiation monitoring and protection. They provide information on the situation and its evolution with time. The measurement can reveal to concerned stakeholders practical information that opens possibilities for action and improvement. Several criteria are essential to meet requirements for the provision of reliable measurements including: — The proximity of food measuring points close to households and easy access to whole body monitoring equipment, including mobile systems; - The existence of several independent sources of measurement (e.g. pluralism); — The coherence of the used measurement units. The measurement should not only be used to prove compliance with statutory regulations (e.g. 'maximum permitted levels' in foodstuffs or 'dose limits') but also to supply quantitative information to stakeholders and affected individuals on where, when and how they are exposed to radiation, even when levels of contamination are relatively low. The ETHOS experience also revealed the importance for the stakeholders involved, to continuously be able to evaluate the "success" of the process which is going on, from its beginning to the changes in their daily life which can result from it. As Beierle puts it [6], an important aspect of participatory approaches is for the public participants to see the process through to its completion, and so to encourage them to cope with adversity and to keep them motivated and confident in making the process work. In this process the identification by all involved parties at the very beginning of the success criteria for their involvement is a key element.

5. CONCLUSION The post-Chernobyl experience has clearly shown that top-down, centralised, prescriptive and normative approaches focused on the control of the radiological risk which are necessary in the emergency phase become rapidly inefficient for the long term management of contaminated territories. They do not "adequately"

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take into account the complexity of the situation and as a consequence, in the absence of public involvement, they generate a phasing out of the personal initiative among the population and a general feeling of abandonment and fatalism. They also generate a dependency culture within the affected population, social distrust and loss of confidence in authorities and experts. The ETHOS Project has demonstrated among other that, because exposures are mainly driven by individual behaviour and family modes of living, and because collective countermeasures fail to take into account the individual situations, the active involvement of the population and the local authorities and professionals in the assessment and management process of the radiological situation, is feasible and necessary to break the vicious circle of exclusion, loss of control and fatalism. From the methodological point of view, the ETHOS project, like other types of public participation approaches reveals the recurrent following features in the stakeholder involvement process which are also the keys for success [5]: - Participation of a wide panel of stakeholders. This is especially important to avoid possible exclusion of persons or groups which can reveal to be in fact key actors in the process. The structure developed to involve the stakeholders must clearly allow their possible and easy withdrawal in order to favour their voluntary commitment; — Empowerment of local people. This is a means to encourage the appropriation by stakeholders of the local situation and to favour their autonomy in the involvement process; — Flexibility. It is a necessary feature to avoid crushing the initiative of local people, which could be prejudicial to their commitment first, and to the success of a project further on. It is also important to accept to change the strategies when identifying deadlocks and paying attention to "turning points" and "opportune moments" all along the intervention; — Individual relationships between involved stakeholders. This must also concern the experts involved in the process. It is an important aspect to enable all those involved in a project to increase their self-confidence and to confront situations and personal interests; — Working with all levels of authority and functions linked to the problem. In order to develop solutions to complex problems with multiple dimensions (health, environment, social, economic, etc) and authorities, experts and professionals at the local, regional, national and international levels must be involved and bridges must be build between these different levels. Finally, the stakeholder involvement experience in the ETHOS Project has illustrated new forms of governance for the rehabilitation of contaminated territories based on actions developed in a common good perspective by all concerned parties. The classic form of scientific rationality, and particularly the basic concepts and principles of radiological protection, have been mobilised and appropriated by the involved actors to conduct an inclusive democratic process aiming at the construction of individual and collective choices adapted to the concerns of the population. The ETHOS experience has also demonstrated that to be sustainable the management of the situation by the stakeholders must rely on the dynamic of economic development grounded primarily on the individual initiatives of the local actors. Following this perspective, the Belarus government initiated in October 2003 an international programme (Cooperation for Rehabilitation — CORE) to develop these new rehabilitation approaches during 5 years in 4 contaminated districts of the country based on a partnership between local, national and international stakeholders [11]. This programme includes the development of an inclusive and pluralist radiological monitoring at the local level to support the various initiatives of the population and the local authorities and professionals and to improve the health status as well as the social and economic situation in the territories. It also comprises an educational dimension to ensure the transmission to the future generations of the necessary know-how to live in a contaminated territory as well as the memory of the Chernobyl accident.

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ACKNOWLEDGMENTS The author wishes to particularly thank Samuel Lepicard from CEPN for his invaluable help in the preparation and drafting of this paper.

REFERENCES [1] UNDP-UNICEF, The Human Consequences of the Chernobyl Nuclear Accident: a Strategy for Recovery, January 2002. [2] ICRP, Protection of the Public in Situations of Prolonged Radiation Exposure, Publication 82, Annals of the ICRP, Vol.29, NO i-2 1999.. [3] Girard P., Heriard Dubreuil G., Consequences sociales et psychiques de 1'accident de Tchernobyl, Rapport Mutadis 93/JSP2/PG/GHD/003, (1994). [4]

Girard P., Heriard Dubreuil G, Conditions de vie dans les territoires contamines 8 ans apres 1'accident de Tchernobyl, Rapport Mutadis 95/JSP2/PG/GHD/003, (1995).

[5] The ETHOS project in Belarus, Final report, ETHOS(99- RP(1), (1999). (http://www.cepn.asso.fr/fr/ethos.html) [6] Heriard Dubreuil G. et al., Chernobyl Post-Accident Management: The ETHOS Project, Health Physics, Vol. 77, pp. 361-372, (1999). [7] Lochard J., Stakeholder Involvement in the Rehabilitation of Living Conditions in Contaminated Territories Affected by the Chernobyl Accident, In: Proceedings of the International Symposium on 'Restoration of Environments with Radioactive Residues', IAEA International Symposium, Arlington, VA, USA, 29 November-3 December 1999, IAEA-SM-359/5.2, 2000, pp. 495-506 (1999). [8] Lepicard S., Heriard Dubreuil G, Practical improvement of the radiological quality of milk produced by peasant farmers in the territories of Belarus contaminated by the Chernobyl accident — The ETHOS project, Journal of Environmental Radioactivity, Vol.56, pp 241 —253, (2001). [9] Rigby J., Principes et processus a l'oeuvre dans un projet d'amelioration des conditions de vie dans les territories contamines par la catastrophe de Tchernobyl — ETHOS I (1996 — 1998), These de Doctorat, Universite de Technologic de Compiegne, (2003). [10]

Beierle T, Cayford J., Democracy in Practice — Public Participation in Environmental Decisions, Resources for the Future, Washington, DC, 2002.

[11]

CORE, Cooperation for Rehabilitation of Living Conditions in Chernobyl Affected Areas of Belarus — Declaration of Principles of the CORE Programme, Minsk, October 2003. (http://www.un.org/ha/Chernobyl/)

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