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Chernobyl is located in Ukraine, 20 km south of Belarus and near the Russian border. It will be linked indelibly in people's minds as the site of the world's worst nuclear accident in April 1986. Thirty firemen who quelled the smouldering fires of the burning reactor died shortly after excessive exposure to lethal radiation, over 100 000 citizens living in the surrounding area were evacuated, vast areas in the Ukraine, Russia and Belarus were contaminated with radioactive debris spewing from the blazing nuclear core, and hundreds of thousands of workers from all over the former Soviet Union were sent to clean up the contaminated environment and to entomb the extinguished nuclear reactor in a `sarcophagus' (UNSCEAR 1988, NEA 1996, Karaoglou et al 1996, IAEA 1996). The only late health affect ascribed to the reactor accident is a remarkable increase in the incidence (but not mortality) of childhood thyroid cancer among surrounding populations heavily exposed to radioactive iodines, most notably I-131 (half-life a bit over 8 days). The radioactive iodines concentrate to relatively high levels in the thyroid gland after consumption of foodstuffs, but primarily after drinking milk. Childhood leukaemia, however, has not occurred in excess in the most heavily contaminated areas in Belarus (Ivanov et al 1993), Europe (Parkin et al 1996), or Scandinavia (Auvinen et al 1994, Hjalmars et al 1994). The whole body doses from caesium-137 and other radionuclides were apparently much too low to result in a detectable increase over that expected from natural causes (Linet and Boice 1993, Boice and Linet 1994).

Until recently, little information has been published on the possible health effects among the clean-up workers, who have also been called liquidators, emergency workers, accident recovery workers. Those sent in 1986 - 87 to within the 30 km zone around the damaged reactor received the highest exposures and number about 300 000. The workers were mainly male, 20 - 39 years of age, and received on average 100 mGy. Few, perhaps only 4%, received over 250 mGy. Biological dosimetry studies of large numbers of Chernobyl clean-up workers from the Baltic countries generally support the physical dose estimates on a population basis (Bigbee et al 1996, 1997, Inskip et al 1997a). Based on extrapolation from high dose atomic bomb survivor data, the relative risk (observed/expected) of cancer mortality from a 100 mGy brief whole body dose would be of the order of 1.05 (UNSCEAR 1994, Pierce et al 1996). The ability for epidemiological studies to detect a risk of cancer following such low exposures is accordingly low and extremely problematic because it would require very large numbers followed carefully for perhaps 50 years (Boice 1997).

For leukaemia, however, the situation is different because the risk coefficient is much higher than for solid tumours and any radiation-related excess would be anticipated to occur much earlier and primarily within 10 years of exposure. The relative risk of leukaemia following 100 mGy might be about 1.2 - 1.4 (Preston et al 1994, UNSCEAR 1994). However, because most of the excess, perhaps 80%, would be anticipated within 10 years, the relative risk during the first 10 years of follow up might be of the order of 3 - 4 (Cardis et al 1996), and certainly within the capability of epidemiology to observe. In fact, the predicted excess of leukaemia (excluding chronic lymphocytic leukaemia (CLL) which has never been linked to radiation in any population) occurring within 10 years among 200 000 clean-up workers exposed to 100 mGy might be of the order of 100 - 150 for 100 mGy, compared with a background of about 40 occurring `naturally' (Cardis et al 1996). To date, however, an `epidemic' of leukaemia of this magnitude has not been reported in any series of Chernobyl clean-up workers (Rahu et al 1997, Karaoglou et al 1996, IAEA 1996).

The new report by Ivanov and colleagues (this issue) on the 155 000 Russian liquidators adds new understanding to the study of radiogenic leukaemia in the former Soviet Union and new caution in interpreting such studies. While the data are the same as in an earlier publication by the same group (Ivanov et al 1997), the interpretation is diametrically different. In the previous cohort analysis, a significant risk of leukaemia was associated with the mean radiation dose received (excess relative risk, ERR/Gy of 4.3; 95% CI 0.8 - 7.8) which was surprisingly close to that estimated among atomic bomb survivors (Preston et al 1994, UNSCEAR 1994). However, general population rates of cancer incidence in Russia were used as the comparison and it was not possible to separate out CLL. This estimate of risk is now seen to have been terribly biased and very misleading. The new case-control analysis within the same cohort of liquidators takes estimated dose into account, assumes a two-year minimum latency for radiogenic leukaemia, and excludes CLL. There was no significant correlation made between leukaemia and any measure of exposure. The erroneous risk estimate in the earlier investigation was because of ascertainment bias, using an inappropriate comparison population, and including a leukaemia subtype that has never been linked to radiation in any human population. Chernobyl clean-up workers receive annual examinations and thus leukaemias are readily detected and recorded. Perhaps even too much, in that 50% of the initial diagnoses of leukaemia were not confirmed (Cardis et al 1996). On the other hand, registration of malignancy in Russia is not complete, and for some unknown reason the proportion of CLL among liquidators is much higher than in the general population of persons of similar age (Parkin et al 1992). Thus the biased radiation risk coefficient was due to increased surveillance among the workers that resulted in relatively complete (or more complete) registration of leukaemias; underreporting of leukaemias in the general population that resulted in an underestimate of leukaemia; and the peculiar excess of CLL among workers which may be due to chance, surveillance, misdiagnoses, or non-radiation factors unique to workers sent to Chernobyl from Russia. Interpretation of these early epidemiological studies of Chernobyl workers must be made with care. Despite the relatively straightforward design and defensible assumptions and analyses, results may nonetheless be in error due to bias and confounding associated with differences in surveillance, completeness of follow up, choice of a comparison group, and choice of leukaemia subtypes to include in the analysis.

The new analysis improves greatly on the previous one by making internal comparisons based on the nested case-control design. To eliminate the bias associated with noncomparable comparison with the general population, Ivanov et al (this issue) matched each leukaemia case with a liquidator control with similar characteristics and then evaluated whether the exposures differed and whether risk varied by categories of dose. It did not. At first glance, the 48 leukaemias appear excessive based upon a probable background rate of 3 - 4 non-CLL/100 000 per year anticipated from non-Chernobyl factors for men of these ages. But 14 leukaemias occurred within 2 years and are unlikely to be due to radiation and 10 were CLL which is not radiation related. Thus only 24 leukaemias were available for analysis in years 2 - 8 following the Chernobyl accident. In the absence of any radiation effect, the background number expected would be of the order of 18 - 27 (155 000 workers × 6 yr × (3 - 4)/100 000/yr). However, the data cannot exclude the possibility that radiation has not contributed to a slight increase in risk. The analysis of these 24 leukaemia cases and matched controls did suggest a slight trend with dose, although the trend was not statistically significant and the range of possible risks was broad (ERR/Gy = 1.67; 95% CI 5.9 - 9.2). While there are uncertainties in predicting what the radiation excess might be during these 8 years, the best estimates, without including a dose and dose rate effectiveness factor (DRREF), are of the order of a 3-fold excess or 60 - 80 cases (Cardis et al 1996). Clearly, the observed total number of 24 non-CLL is not consistent with such an excess over background predicted based on models from high dose and dose rate exposures and not applying a DRREF (Cardis et al 1996).

The Russian data are also consistent with a small but comprehensive study of Estonia clean-up workers recently published (Tekkel et al 1997, Rahu et al 1997). A nearly complete roster of 4800 workers was compiled from a variety of sources, including military lists. Over 80% had recorded doses and the mean dose was essentially the same as that seen in Russia, 100 mGy. Comprehensive biodosimetry using flow cytometry and the glycophorin A mutational assay of red blood cells, and chromosome aberration analyses using fluorescent in situ hybridisation techniques, confirmed that high exposures were infrequent and unlikely, and that the mean population dose might adequately characterise the exposure, although an even lower mean dose than 100 mGy is possible (Bigbee et al 1996, 1997, Inskip et al 1997a). A thyroid screening study of 2500 workers with ultrasound and fine needle aspiration revealed no increase in thyroid nodular disease or cancer that could be related to dose (Inskip et al 1997a). Cause specific mortality was determined through linkage with national death registry data and cause specific cancer incidence was determined through linkage with national cancer registry data. No leukaemias were reported against only 1 expected based on population rates, and relative risks higher than about 3 could be excluded with 95% confidence. The only significant finding was a 50% increase in death due to suicide. Future analyses are planned with the 12 000 workers from the other two Baltic countries, Latvia and Lithuania (Inskip et al 1997b).

What then can be concluded about the risk of cancer among Chernobyl clean-up workers some 10 years after the accident?

(1) No excess of leukaemia has been demonstrated to date. No excess of thyroid cancer or other solid cancers has been linked to Chernobyl radiation among clean-up workers.

(2) It is likely that few workers received high doses (over 250 - 500 mGy). Thus large populations will need to be studied epidemiologically to discern convincingly any radiation effect for leukaemia. The likelihood of detecting a risk of solid cancers, which would not be anticipated to start until 10 years after exposure, is exceedingly small if it holds true that leukaemia is not measurably increased among liquidators. This excludes, however, the possibility that ingestion or inhalation of significant amounts of fission fragments occurred.

(3) There is the need, then, for additional study of the leukaemia experience to date, including combined series from Russia, Ukraine, Belarus and the Baltics if at all possible. Care will have to be taken with regard to dose estimation, cancer surveillance among the liquidators, underreporting among the general population, excluding the first 2 years of observation, and excluding CLL from the analyses.

(4) The risk of leukaemia predicted from models based on studies of high dose and high dose rate exposures (atomic bomb survivors and medical series) are not consistent, it appears, with the observed numbers of leukaemias seen among liquidators. Why might this be so?

(a) The Chernobyl doses may be lower than estimated. (b) Leukaemia cases among liquidators might have been missed. (c) The risk model may be incorrect (a DRREF of 2 may be appropriate and the time response may differ following low dose and low dose rate exposures). (d) Risk from low doses delivered at low rates may be much less than predicted from higher doses at higher dose rates, possibly because of the opportunity for cellular damage to be repaired. [It may be interesting to debate whether sending 300 000 persons to Chernobyl (mean, 100 mGy) will eventually result in fewer leukaemias and cancers than if 30 000 persons had been sent (with 1000 mGy, mean)]. (e) The time for radiation-induced leukaemias to develop after exposures in 1986 - 87 might be much longer than suggested from studies of populations exposed to high doses delivered at high dose rates.

Observations to date have several implications if borne out. A low excess of leukaemia implies that the possible excess of solid tumours later in life will be very low and outside the realm of epidemiological detection. Thus future studies should aim to combine series to have any hope of detecting a leukaemia effect, and focus should be on the groups likely to have received the highest doses, such as the 4% estimated to have received > 250 mGy, the 5000 soldiers who were on the roof shortly after the accident, and the 1200 helicopter pilots dumping material on the reactor to contain the fire. Further, other accident-related, rather than radiation-related, problems may deserve more attention, in particular psychological effects. For example, the only significant finding among Estonian clean-up workers was a 50% increase in suicides (Rahu et al 1997), indicating, perhaps, the severe stress associated with the accident experience. Finally, with the publication of sound epidemiologic studies on the range of risks, it appears that the health consequences may be much less than perceived by most of the world's population. Other than thyroid cancer in children, where the numbers of incident cases are large but the number of deaths is apparently small, not all and perhaps only a few cancers and leukaemias might eventually be attributed to the radiation received during the clean-up activities among the many hundreds of thousands workers involved in civilisation's most remarkable environmental decontamination undertaking.

Acknowledgment

The author wishes to acknowledge helpful discussions with Drs Dale Preston and Kiyo Mabuchi of the Radiation Effects Research Foundation, Hiroshima, Japan.

References

Auvinen A, Hakama M, Arvela H, Hakulinen T, Rahola T, Suomela M, Soderman B and Rytömaa T 1994 Fallout from Chernobyl and incidence of childhood leukaemia in Finland 1976 - 92 Br. Med. J. 309 151 - 7

Bigbee W L, Jensen R H, Veidebaum T, Tekkel M, Rahu M, Stengrevics A, Auvinen A, Hakulinen T, Servomaa K, Rytömaa T, Obrams G I and Boice J D Jr 1997 Biodosimetry of Chernobyl clean-up workers from Estonia and Latvia using the glycophorin A in vivo somatic cell mutation assay Radiat. Res. 147 215 - 24

Bigbee W L, Jensen R H, Rahu M, Tekkel M, Veidebaum T, Stengrevics A, Auvinen A, Hakulinen T, Obrams I and Boice J D Jr 1996 Glycophorin A biodosimetry in Chernobyl clean-up workers from the Baltic countries Br. Med. J. 312 1078 - 9

Boice J D Jr (ed) 1997 Radiation epidemiology: past and present Implications of New Data on Radiation Cancer Risk vol 18 (Bethesda, MD: NCRP) pp 7 - 28

Boice J D Jr and Linet M 1994 Chernobyl, childhood cancer and chromosome 21 (Editorial) Br. Med. J. 309 139 - 40

Cardis E, Anspaugh L, Ivanov V K, Likhtarev I A, Mabuchi K, Okeanov A E and Prisyazhniuk A E 1996 Estimated long term health effects of the Chernobyl accident Proc. Int. Conf. on One Decade After Chernobyl: Summing Up the Consequences of the Accident STI/PUB/1001 (Vienna: IAEA) pp 241 - 79

Hjalmars U, Kulldorff M and Gustafsson G, for the Swedish Child Leukaemia Group 1994 Fallout from the Chernobyl accident and risk of acute childhood leukaemia in Sweden Br. Med. J. 309 154 - 7

Inskip P D, Hartshorne M F, Tekkel M, Rahu M, Veidebaum T, Auvinen A, Crooks L A, Littlefield L G, McFee A F, Salomaa S et al 1997a Thyroid nodularity and cancer among Chernobyl clean-up workers from Estonia Radiat. Res. 147 225 - 35

Inskip P D, Tekkel M, Rahu M, Veidebaum T, Hakulinen T, Auvinen A, Rytömaa T, Servomaa K, Obrams G I, Stengrevics A et al 1997b Studies of leukaemia and thyroid disease among Chernobyl clean-up workers from the Baltics NCRP Proc. 18 123 - 41

International Atomic Energy Agency, European Commission and World Health Organization 1996 Proc. Int. Conf. on One Decade After Chernobyl: Summing Up the Consequences of the Accident STI/PUB/1001 (Vienna: IAEA)

Ivanov E P, Tolochko G, Lazarev V S and Shuvaeva L 1993 Childhood leukaemia after Chernobyl Nature 365 702

Ivanov V K, Tsyb A F, Gorsky A L, Maksyutov M A, Rastopehin E M, Konogorov A P, Korelo A M, Biryukov A P and Matyash V A 1997 Leukaemia and thyroid cancer in emergency workers of the Chernobyl accident: estimation of radiation risks (1986 - 1995) Radiat. Environ. Biophys. 36 9 - 16

Ivanov V K, Tsyb A F, Konogorov A P, Rastopchin E M and Khait S E 1997 Case-control analysis of leukaemia among Chernobyl accident emergency workers residing in the Russian Federation 1986 - 1993 J. Radiol. Prot. 17 137

Karaoglou A et al (eds) 1996 The Radiological Consequences of the Chernobyl Accident EUR 16544EN (Brussels: European Commission)

Linet M and Boice J D Jr 1993 Radiation from Chernobyl and risk of childhood leukaemia (Commentary) Eur. J. Cancer 29 1 - 3

NEA 1996 Committee on Radiation Protection and Public Health Chernobyl - Ten Years On: Radiological and Health Impact (Paris: OECD)

Parkin D M, Clayton D, Black R J, Masuyer E, Friedl H P, Ivanov E, Sinnaeve J, Tzvetansky C G, Geryk E, Storm H H et al 1996 Childhood leukaemia in Europe after Chernobyl 5-year follow-up Br. J. Cancer 73 1006 - 12

Parkin D M et al 1992 Cancer Incidence in Five Continents vol VI IARC Publ No 120 (Lyon: IARC)

Pierce D A, Shimizu Y, Preston D L, Vaeth M and Mabuchi K 1996 Studies of the mortality of A-bomb survivors. Report 12, Part 1. Cancer 1950 - 1990 Radiat. Res. 146 1 - 27

Preston D L, Kusumi S, Tomonaga M, Izumi S, Ron E, Kuramoto A, Kamada N, Dohy H, Matsuo T et al 1994 Cancer incidence in atomic bomb survivors. Part III: leukaemia, lymphoma, and multiple myeloma 1950 - 87 Radiat. Res. 137 S68 - S97

Rahu M, Tekkel M, Veidebaum T, Pukkala E, Hakulinen T, Auvinen A, Rytömaa T, Inskip P D and Boice J D Jr 1997 The Estonian study of Chernobyl clean-up workers: III. Incidence of cancer and mortality Radiat. Res. 147 653 - 7

Tekkel M, Rahu M, Veidebaum T, Hakulinen T, Auvinen A, Rytömaa T, Inskip P D and Boice J D Jr 1997 Estonian study of Chernobyl clean-up workers: design and questionnaire data. Radiat. Res. 147 641 - 52

United Nations Scientific Committee on the Effects of Atomic Radiation 1988 Sources, Effects and Risks of Ionizing Radiation 1988 Report to the General Assembly, with annexes. Publ E.88.IX.7 (New York: United Nations)

United Nations Scientific Committee on the Effects of Atomic Radiation 1994 Sources and Effects of Ionizing Radiation 1994 Report to the General Assembly, with scientific annexes. Publ E.94.IX.11 (New York: United Nations)

The Chernobyl Record is a collection of documents relevant for practically all aspects of the Chernobyl accident. Eyewitness reports, photographs and excerpts of technical and scientific publications are all compiled to give a multi-faceted picture.

The introduction contains an informative description of early health effects due to acute radiation exposures. Concerning dose quantities related to low level or protracted exposures, the reader might prefer to read the original reports of the ICRP.

In the Chernobyl Record basic aspects of nuclear power reactors of type RBMK-1000 are presented together with maps and several pictures of the plant at Chernobyl - before and after the accident. The detailed reconstruction of the accident is enriched by several eyewitness reports. Many photographs and drawings illustrate the construction of the sarcophagus that was build to shield the environment from the radionuclides inside the demolished reactor. The environmental release of radionuclides during the accident and resulting radiation exposures are compared to the other major population exposures that occurred in the past sixty years. The use of nuclear power in the world is summarised and accidents that have happened in nuclear power plants are listed.

An overview of the early medical response to the Chernobyl accident provides reports of members of the medical staff involved. Methods of dose reconstruction are reviewed and dose estimates for the emergency worker are given. Histories of patients with acute radiation syndrome are followed-up. Psychological illnesses are frequently observed among the emergency workers. The evacuation and the resettlement of the population in the contaminated territories are again illustrated with many photographs.

Extensive information is given on the contamination of the environment and of foodstuffs, doses to the population, and on decontamination work. The discussion includes an overview of the development of radiation safety standards in the former USSR and compares it with internationally adopted standards.

For the population that continued to live in the contaminated territories, psychological and social problems have been reported in various surveys. An overview is given on studies of late health effects that are known to be related to exposures to ionising radiation, including brain damage in utero, mental retardation, reproductive health patterns, and haematological, thyroid and ocular diseases.

General aspects of radiation-induced cancer and risk specification are summarised. Subsequently, the increased thyroid cancer incidence rate among those who were exposed due to the Chernobyl accident during childhood or adolescence is described.

Finally, the book gives an informative insider view, the Legaslov testament, together with the comments of his widow. Valery Legaslov, the first deputy director of the Kurchatov Institute of Atomic Energy, Moscow, died two years after the Chernobyl accident, and his personal experiences during the accident, together with a description of the problems in the USSR which contributed to the catastrophe, were published in 1988 in Pravda, and now translated for publication in theChernobyl Record.

In summary, the Chernobyl Record is worthwhile reading for the interested layman as well as for the expert who will find information in the book that is not easily accessible otherwise. Unfortunately, the author sometimes gets lost in an overwhelming number of details, and it is difficult for the reader to derive a clear general message. Smaller parts of the book are not fully adequate, e.g. the ICRP recommended dose limit of 1 mSv for the population is given and it is not made clear that this limit does not apply to an accidental situation. However, in total, theChernobyl Record is recommended as an historical overview with a unique collection of documents, and an extensive and useful list of relevant references.

Twenty years ago on 26 April 1986, the Chernobyl nuclear reactor accident occurred (or, more precisely, the explosion that marked the start of the accident occurred - the resultant fire lasted several days). This is by far the largest unintentional release of radioactive material into the environment and caused widespread contamination in Europe, which was sufficiently great in the vicinity of Chernobyl to require evacuation of the population. Much attention has been paid to the possible effects on health of the resulting exposure to radiation, but the rapidity of the appearance and the magnitude of the excess cases of childhood thyroid cancer in the heavily contaminated areas of Belarus, Ukraine and Russia took most people by surprise. The striking excess of thyroid cancer among those exposed as children is undoubtedly attributable to the high thyroid doses received from radioiodine released during the accident; but many of these cases might have been prevented by the swift administration of stable iodine to block the uptake of the short-lived radioisotopes of iodine (as occurred in the town of Pripyat, close to Chernobyl) and especially by the prevention of the consumption of contaminated foodstuffs, in particular milk. It was a milk ban in the most affected parts of West Cumbria in the immediate aftermath of the Windscale reactor accident in October 1957 that significantly reduced thyroid doses and the risk of thyroid cancer (and the dose and risk calculations upon which this milk ban was based were largely conducted by John Dunster, whose death has recently been announced). However, the Chernobyl accident and the consequent contamination was on a much larger scale than occurred after the Windscale fire, and the logistics of determining the areas upon which the greatest attention should have been focused should not be underestimated. Nonetheless, the authorities in the former USSR did obtain, with some rapidity, information on the extent of the contamination from experts that were dispatched to Chernobyl immediately after the accident, and at least some action could have been taken to alleviate the risk of thyroid cancer due to radioiodine intake. The high radiation levels that were found in some locations close to Chernobyl show how fortunate it was that population centres were not worse affected, or the consequences of the accident could have been much more serious, and with the relatively swift evacuation of people from the area surrounding the reactor, doses that would have posed a risk of acute health effects were avoided.

Apart from thyroid cancer, what health effects attributable to the Chernobyl accident have been found so far? In the general population, there are indications of excess cases of childhood leukaemia and breast cancer among those living in the heavily contaminated regions of Belarus, Ukraine and Russia, although the evidence is still equivocal. Such excesses would be predicted given the magnitude of the doses and number of people involved. The significant psychological impact of the accident should not be forgotten. This impact is understandable when people are uprooted from their villages and sent to towns where their presence may not be entirely welcome, and the worry of the possible effect on health of the exposure to radiation must also take is toll. Then there are those sent to deal with the accident and its aftermath. Of course, the most heavily exposed emergency workers received doses that were sufficiently high to kill them in the weeks and months after the accident, but the doses received by the many recovery workers used to clean up Chernobyl once the release of radioactivity had ceased were sufficient for an excess risk of leukaemia to be detected. It should be remembered that all these studies have been carried out during a period when the consequences of the break-up of the USSR have had a profound effect upon the health of the population. Not only has this produced dramatic changes in the background of risk factors against which the influence of the Chernobyl accident must be assessed, but the record-keeping that is necessary for proper epidemiological studies has inevitably suffered. Clearly, this does not assist the reliable evaluation of any radiation-related effects.

It is unfortunate, although entirely predictable, that the issue of the effects on health of the Chernobyl accident has become part of the political debate over the future role of nuclear energy in the generation of electricity, which has inevitably led to dispute over the level of effects either observed or anticipated. It is difficult to avoid the inference that some of the more extreme claims are driven by a political agenda rather than a desire to arrive, in an objective a manner as possible, at the best estimates of the excess risks due to Chernobyl radioactivity. This is why the review of Cardis et al that appears in this issue of the journal (pages 127-140) is to be especially welcomed. These experienced and reputable scientists have endeavoured to derive a balanced and impartial picture of the health effects of the Chernobyl accident on the basis of the presently available evidence. It is only through such efforts that a proper perspective of the impact of the accident can be gained - otherwise we are lost in a sea of campaigning rhetoric and partisan posturing. Reviews like that produced by Cardis et al are not easy to write because they will certainly come in for noisy criticism from the extreme wings; but their value in allowing a broader audience to gain a reasonable impression of what is (and is not) understood about the health impact of events like the Chernobyl accident is great and the authors are to be applauded.

2001 marks the 15th anniversary of the Chernobyl accident. The Academy of Medical Sciences thought it appropriate to present some of the findings from studies of the people who were exposed to fallout from the accident, and to discuss these in the light of recent advances in the understanding of the way in which radiation can interact with the genome. The meeting was organised by Dillwyn Williams, Cambridge, and Alec Jeffreys, Leicester, who each chaired a session. In the first presentation, Roger Cox (NRPB) pointed out that although risk was usually presented on a population basis following radiation exposure, it was important to remember that inter-individual variation could be relevant when considering cancer risk to individuals. He described current understanding on the genetic basis of variation in radiosensitivity by first reviewing the distinct clinical syndromes, e.g. basal cell naevus syndrome, Li Fraumeni syndrome, which exhibit around a 10-fold increase in sensitivity and have a distinct genetic basis. These syndromes are extremely rare, affecting less than 1% of the population. Much more common but less expressive is the polymorphic variation seen in a wide range of genes and this is more likely to distort the population risk. Data to support this view includes studies of early onset breast cancer in the Japanese atomic bomb survivors and the observation by David Scott of increased chromosomal radiosensitivity in groups of unselected patients with certain cancers. Cox described how advances in mouse genetics are providing evidence for proof of principle for the genetic mechanisms associated with radiosensitivity. He concluded that natural polymorphic variation can be a major factor in determining the risk from radiation exposure, that the gene loci involved are probably mainly tissue specific, will also influence spontaneous risk and that there is likely to be locus interaction.

Eric Wright (Dundee) described clonal experiments using haemopoietic stem cells which illustrated that de novo genetic changes could arise in the progeny of surviving irradiated target cells. This induction of persistent transmissible genomic instability has been observed in vitro and in vivo and for a range of mutational endpoints. He noted that genomic instability resulted in an increase in abnormalities with characteristics of spontaneous mutations rather than those induced directly by radiation in the target cell. Oxidative stress is a likely mechanism with a bystander effect also being involved. Genomic instability is induced at a high frequency and is a genome wide process. The induction of genomic instability appears to be influenced by genotype and Wright concluded that it is related to the efficiency with which cells recognise damage.

Two presentations were given by Yuri Dubrova (Leicester). In the first he described mouse studies which indicated that paternal irradiation could induce instability in hypervariable tandem repeat minisatellite loci in the germ line. Not only was this seen as an increase in paternally derived alleles in the F1, but the instability seemed to persist in the F1 germ line resulting in increased mutation frequencies in the F2 and subsequently in the F3 generation. In his second presentation Dubrova reviewed his earlier work on minisatellite mutations in families in Belarus exposed to radiation as a result of the Chernobyl accident in which he had found an increase in germline mutation rate in three independent sets of minisatellite loci. In this study of 127 families the comparison group had been 120 UK families. He also presented some unpublished work on a new study of Ukrainian families in which 82 children conceived before the Chernobyl accident and 230 children conceived after the accident were compared. An 80% increase in paternal mutation rate was observed but there was no increase in maternal mutation rate. Time of conception after the accident did not influence the results. The spontaneous rates seen in this study were similar to those previously reported for the UK controls and for a control population in Khazakstan, leading Dubrova to suggest that he has now provided proof that the Chernobyl accident has affected the mutation rate. However, he observed that extrapolation of such a genetic effect to the whole genome is unlikely to be manifest in a study of adverse reproductive outcomes since only 5% are attributable to de novo mutations, and hence rates of clinical endpoints will not be affected. Dubrova was asked about the incompatibility of the doubling dose derived from the mouse studies compared with the much lower doubling dose he had inferred for the human exposure due to the Chernobyl accident. It was suggested that there was a difference of two orders of magnitude and from knowledge of other endpoints, e.g. chromosome aberrations, this difference was not easily reconciled.

Dillwyn Williams described the initial scepticism which greeted reports of increases in childhood thyroid cancer following the Chernobyl accident and how these only became accepted following confirmation of diagnoses by a number of western groups. It is now recognised that between 1990 and 1997 there was an approximate 30-fold increase in childhood thyroid cancer in the most heavily contaminated areas, although the number of cases has now started to decline. Examination of the pathology of the childhood thyroid cancers in Ukraine and Belarus has indicated a greater proportion of papillary cancers in comparison with childhood thyroid cancers in UK. Papillary cancers tend to be associated with ret/trk gene rearrangements whereas follicular cancers are characterised by point mutations. Whereas this may give some indication of the mechanisms of radiation-induced effects, the different subtypes, as well as being different genetically, also have different latency periods. It is, therefore, still not possible to say which types are radiation induced and an increase in follicular adenomas and carcinomas may yet be seen in the future. Questions also still remain with respect to cancers in other organs, e.g. breast and salivary glands, which are known to concentrate iodine.

The final presentation was given by Gerry Thomas, Cambridge, who outlined the international collaboration after Chernobyl which had led to the development of the tissue and nucleic acid bank of tumour and normal material from thyroid cancer patients. She outlined the ethical issues such as informed consent and the importance of the resource being established in the country supplying the material. Minsk, Obninsk and Kiev maintain their own tissue/nucleic acid banks and databases, with copies of all data being sent to the co-ordinating centre in Cambridge. The aim of the collaboration is to collect a resource of DNA and RNA for research from patients under 19 years of age at the time of the Chernobyl accident who have a confirmed diagnosis and the necessary documentation relating to sex, age and exposure. The project was launched in 2000 and applications are now invited for access to this material.

The Academy of Medical Sciences was established to promote medical science across traditional disciplinary boundaries. This meeting provided a valuable forum for radiobiologists and epidemiologists to interact in the examination of current thinking on radiobiological mechanisms that might impact on radiation risk, and how this relates to observations of clinical outcomes. It is, therefore, unfortunate that the meeting appeared to have received little prior publicity and was not well attended.

Current ICRP policy in radiological protection (ICRP Publication 60) is based on the independent restriction of exposure and sources for practice and intervention. Such subdivision of exposure and sources leads to a number of problems and contradictions in different applications. In a recent memorandum of the ICRP, published in the Journal of Radiological Protection in 2001, and ICRP Publications 81 and 82, the directions for settling some of these problems are indicated. This paper shows that in Ukraine, after the Chernobyl accident, a number of problems and contradictions occurred as the result of strictly separated limitation of the sources and exposure. These are demonstrated through four `radiological paradoxes': (1) resettlement of inhabitants from territories radioactively contaminated after the Chernobyl accident to `clean' ones, but with anomalous high levels of radon exposure in houses; (2) necessity of summation of the Chernobyl accidental doses and doses caused by normally operating nuclear power plant (NPP) to meet the requirements of Ukrainian law, which is based on the principle of `social equity' of different sources of exposure; (3) the necessity to answer the question of primary importance: when will the Chernobyl accident finally end and when can exposure from contaminated territories be considered as exposure from old contamination? (4) the start of decommissioning of the Chernobyl NPP and transformation of the `Object Shelter' (located inside the exclusion zone) are now slowed down because of the absence of a definite ideology for dose limitation of workers involved, who are exposed to several types of source simultaneously. The authors believe that the concept of controllable dose as presented by Professor Roger H Clarke on behalf of the ICRP can resolve such paradoxes. The changes to ICRP policy need to be made carefully in order to provide an orderly transition.

The Estonian study of Chernobyl cleanup workers was one of the first investigations to evaluate the possible health consequences of working in the Chernobyl area (the 30 km exclusion zone and/or adjacent territories) after the 1986 reactor accident. The cohort consists of 4831 men who were dispatched in 1986–1991 for tasks involving decontamination, construction of buildings, transport, radiation measurement, guard duty or other activities. By 31 December 2012, the follow-up of the cohort yielded 102 158 person-years of observation. Exposure and health data were collected by postal questionnaires, biodosimetry evaluations, thyroid screenings, and record-linkages with cancer, causes of death and health insurance reimbursement registers and databases. These data cover socio-demographic factors, employment history, aspects of health behaviour, medical history, work and living conditions in the Chernobyl area, biomarkers of exposure, cancer and non-cancer disease occurrence and causes of death. Cancer incidence data were obtained for 1986–2008, mortality data for 1986–2011 and non-cancer morbidity data for 2004–2012. Although the cohort is relatively small, it has been extensively examined and benefited from comprehensive nationwide population and health registers. The major finding was an increased risk of suicide. Thyroid examinations did not reveal an association with thyroid nodular disease and radiation dose, but did indicate the importance of accounting for screening when making comparisons with unscreened populations. No risk of leukaemia was observed and risks higher than 2.5-fold could be excluded with 95% confidence. Biodosimetry included GPA analyses and chromosomal translocation analyses and indicated that the Estonian cleanup workers experienced a relatively low mean exposure of the order of 0.1 Gy. One value of the Estonian study is in the methodologic processes brought to bear in addressing possible health effects from the Chernobyl accident. Twenty-five years of research are summarised and opportunities for the future listed.

On 26 April 2016, thirty years will have elapsed since the occurrence of the Chernobyl accident, which has so far been the most severe in the history of the nuclear reactor industry. Numerous epidemiological studies were conducted to evaluate the possible health consequences of the accident. Since the credibility of the association between the radiation exposure and health outcome is highly dependent on the adequacy of the dosimetric quantities used in these studies, this paper makes an effort to overview the methods used to estimate individual doses and the associated uncertainties in the main analytical epidemiological studies (i.e. cohort or case-control) related to the Chernobyl accident. Based on the thorough analysis and comparison with other radiation studies, the authors conclude that individual doses for the Chernobyl analytical epidemiological studies have been calculated with a relatively high degree of reliability and well-characterized uncertainties, and that they compare favorably with many other non-Chernobyl studies. The major strengths of the Chernobyl studies are: (1) they are grounded on a large number of measurements, either performed on humans or made in the environment; and (2) extensive effort has been invested to evaluate the uncertainties associated with the dose estimates. Nevertheless, gaps in the methodology are identified and suggestions for the possible improvement of the current dose estimates are made.

The author discusses the handling of the Chernobyl accident and its implications for emergency planning in general. His comments are divided between three areas: information, co-ordination and procedures.

Presents a radiocaesium deposition pattern over Ireland resulting from the Chernobyl accident. Contaminated grassland soils from over 110 sites were analysed using gamma ray spectrometry. ¹³⁴Cs, ¹³⁷Cs and ⁴⁰K were measured in all samples. The Chernobyl ¹³⁷Cs was identified using an initial Chernobyl fallout ¹³⁷Cs to ¹³⁴Cs ratio of 1.90. The results show a mean deposition level of 3.2 kBq m^-2 of ¹³⁷Cs due to Chernobyl. The range of deposition was from 0.3 to 14.2 kBq m^-2. The distribution pattern is presented both on a National Grid sub-zone basis and a higher resolution shaded map. A similarly shaded map shows the rainfall levels responsible for most of the washout. It is pointed out that some areas on both east and west coasts with maximum rainfall did not have maximum caesium deposition. In other areas a better correlation between rainfall and caesium deposition exists. A mean figure for the pre-Chernobyl ¹³⁷Cs in surface soil is provided.