Post-Chornobyl Thyroid Cancers in Ukraine. Report 1: Estimation of Thyroid Doses

A Historical Survey of Key Epidemiological Studies of Ionizing Radiation Exposure

In this article we review the history of key epidemiological studies of populations exposed to ionizing radiation. We highlight historical and recent findings regarding radiation-associated risks for incidence and mortality of cancer and non-cancer outcomes with emphasis on study design and methods of exposure assessment and dose estimation along with brief consideration of sources of bias for a few of the more important studies. We examine the findings from the epidemiological studies of the Japanese atomic bomb survivors, persons exposed to radiation for diagnostic or therapeutic purposes, those exposed to environmental sources including Chornobyl and other reactor accidents, and occupationally exposed cohorts. We also summarize results of pooled studies. These summaries are necessarily brief, but we provide references to more detailed information. We discuss possible future directions of study, to include assessment of susceptible populations, and possible new populations, data sources, study designs and methods of analysis.

Risk of thyroid cancer in Ukrainian cleanup workers following the Chornobyl accident

Although much is known about the radiation-related risk of thyroid cancer in those exposed at young ages, less is known about the risk due to adult exposure, particularly in men. We aimed to examine the association between thyroid radiation dose received during adulthood and thyroid cancer risk in men. We conducted a nested case-control study (149 cases; 458 controls) of male, Ukrainian cleanup workers who first worked in the Chornobyl zone between ages 18 and 59 years, with cases identified through linkage with the National Cancer Registry of Ukraine from 1988 to 2012. Individual thyroid doses due to external and internal exposure during the cleanup mission and during residence in contaminated settlements were estimated (total dose mean 199 mGy; range 0.15 mGy to 9.0 Gy). The excess odds ratio per gray (EOR/Gy) for overall thyroid cancer was 0.40 (95% CI: - 0.05, 1.48; p-value = 0.118). Time since exposure was borderline significant (p-value = 0.061) in modifying this association so that less time since exposure was associated with a stronger EOR/Gy. An elevated, but nonsignificant association was observed for follicular thyroid cancer (EOR/Gy = 1.72; 95% CI: - 0.25, 13.69; p-value = 0.155) based on a small number of cases (n = 24). Our findings for radiation-related overall thyroid cancer risk are consistent with evidence of increased risks observed in most of the other studies of adult exposure, though the magnitude of the effect in this study is lower than in the previous case-control study of Chornobyl cleanup workers.

Thyroid doses in Ukraine due to 131I intake after the Chornobyl accident. Report II: dose estimates for the Ukrainian population

This paper describes the revision of the thyroid dosimetry system in Ukraine using new, recently available data on (i) revised 131I thyroid activities derived from direct thyroid measurements done in May and June 1986 in 146,425 individuals; (ii) revised estimates of 131I ground deposition density in each Ukrainian settlement; and (iii) estimates of age- and gender-specific thyroid masses for the Ukrainian population. The revised dosimetry system estimates the thyroid doses for the residents of the settlements divided into three levels depending on the availability of measurements of 131I thyroid activity among their residents. Thyroid doses due to 131I intake were estimated in this study for different age and gender groups of residents of 30,353 settlements in 24 oblasts of Ukraine, Autonomous Republic Krym, and cities of Kyiv and Sevastopol. Among them, dose estimates for 835 settlements were based on 131I thyroid activities measured in more than ten residents (the first level), for 690 settlements based on such measurements done in neighboring settlements (the second level), and for 28,828 settlements based on a purely empirical relationship between the thyroid doses due to 131I intake and the cumulative 131I ground deposition densities in settlements (the third level). The arithmetic mean of the thyroid doses due to 131I intake among 146,425 measured individuals was 0.23 Gy (median of 0.094 Gy); about 99.8% of them received doses less than 5 Gy. The highest oblast-average population-weighted thyroid doses were estimated for residents of Chernihiv (0.15 Gy for arithmetic mean and 0.060 Gy for geometric mean), Kyiv (0.13 and 0.051 Gy) and Zhytomyr (0.12 and 0.049 Gy) Oblasts followed by Rivne (0.10 and 0.039 Gy) and Cherkasy (0.088 and 0.032 Gy) Oblasts, and Kyiv City (0.076 and 0.031 Gy). The geometric mean of thyroid doses estimated in this study for the entire Ukraine essentially did not change in comparison with a previous estimate, 0.020 vs. 0.021 Gy, respectively. The ratio of geometric mean of oblast-specific thyroid doses estimated in the present study to previously calculated doses varied from 0.51 to 3.9. The highest increase in thyroid doses was found in areas remote from the Chornobyl nuclear power plant with a low level of radioactive contamination: by 3.9 times for Zakarpatska Oblast, 3.5 times for Luhansk Oblasts and 2.9 times for Ivano-Frankivsk Oblast. The developed thyroid dosimetry system is being used to revise the thyroid doses due to 131I intake for the individuals of post-Chornobyl radiation epidemiological studies: the Ukrainian-American cohort of individuals exposed during childhood and adolescence, the Ukrainian in utero cohort, and the Chornobyl Tissue Bank.

Thyroid doses in Ukraine due to 131I intake after the Chornobyl accident. Report I: revision of direct thyroid measurements

The increased risk of thyroid cancer among individuals exposed during childhood and adolescence to Iodine-131 (131I) is the main statistically significant long-term effect of the Chornobyl accident. Several radiation epidemiological studies have been carried out or are currently in progress in Ukraine, to assess the risk of radiation-related health effects in exposed populations. About 150,000 measurements of 131I thyroid activity, so-called 'direct thyroid measurements', performed in May-June 1986 in the Ukrainian population served as the main sources of data used to estimate thyroid doses to the individuals of these studies. However, limitations in the direct thyroid measurements have been recently recognized including improper measurement geometry and unknown true values of calibration coefficients for unchecked thyroid detectors. In the present study, a comparative analysis of 131I thyroid activity measured by calibrated and unchecked devices in residents of the same neighboring settlements was conducted to evaluate the correct measurement geometry and calibration coefficients for measuring devices. As a result, revised values of 131I thyroid activity were obtained. On average, in Vinnytsia, Kyiv, Lviv and Chernihiv Oblasts and in the city of Kyiv, the revised values of the 131I thyroid activities were found to be 10-25% higher than previously reported, while in Zhytomyr Oblast, the values of the revised activities were found to be lower by about 50%. New sources of shared and unshared errors associated with estimates of 131I thyroid activity were identified. The revised estimates of thyroid activity are recommended to be used to develop an updated Thyroid Dosimetry system (TD20) for the entire population of Ukraine as well as to revise the thyroid doses for the individuals included in post-Chornobyl radiation epidemiological studies: the Ukrainian-American cohort of individuals exposed during childhood and adolescence, the Ukrainian in utero cohort and the Chornobyl Tissue Bank.

Ceramide mediates radiation-induced germ cell apoptosis via regulating mitochondria function and MAPK factors in Caenorhabditis elegans

Studies about radiation damage in vivo are very significant for healthy risk assessment as well as cancer radiotherapy. Ceramide as a second messenger has been found to be related to radiation-induced apoptosis. However, the detailed mechanisms in living systems are still not fully understood. In the present study, the effects of ceramide in gamma radiation-induced response were investigated using Caenorhabditis elegans. Our results indicated that ceramide was required for gamma radiation-induced whole-body germ cell apoptosis by the production of radical oxygen species and decrease of mitochondrial transmembrane potential. Using genetic ceramide synthase-related mutated strains and exogenous C₁₆-ceramide, we illustrated that ceramide could regulate DNA damage response (DDR) pathway to mediate radiation-induced germ cell apoptosis. Moreover, ceramide was found to function epistatic to pmk-1 and mpk-1 in MAPK pathway to promote radiation-induced apoptosis in Caenorhabditis elegans. These results demonstrated ceramide could potentially mediated gamma radiation-induced apoptosis through regulating mitochondrial function, DDR pathway and MAPK pathway.

Total Diet Study to Assess Radioactive Cs and 40K Levels in the Japanese Population before and after the Fukushima Daiichi Nuclear Power Plant Accident

We conducted a total diet study (TDS) of ¹³⁷Cs, ¹³⁴Cs, and ⁴⁰K to assess their average dietary exposure levels in a Japanese adult population before and after the Fukushima Daiichi nuclear power plant (FDNPP) accident. Nineteen market baskets were evaluated in 2006–2011. In each basket, a TDS sample comprising tap water and 160–170 food items, which were combined into 13 groups, were collected for analysis by gamma-ray spectrometry. From 2006 to 2010, the ¹³⁷Cs activity concentration in the “fish and shellfish” group was 0.099 Bq/kg, representing the highest value obtained, whereas the total committed effective dose (CED) of radiocesium isotopes (¹³⁷Cs + ¹³⁴Cs) was 0.69 μSv. In 2011, “milk and dairy products” from Sendai City had a Cs activity concentration of 12 Bq/kg, representing the highest values among all food groups studied. However, the annual CED of radioactive Cs in Fukushima City was 17 μSv after the FDNPP accident, which is 60-fold lower than the maximum permissible dose of 1 mSv/year. The mean CED obtained for ⁴⁰K was 180 μSv, which is comparable to the global average. Our results reveal the average dietary exposure of ¹³⁷Cs, ¹³⁴Cs, and ⁴⁰K, which can aid in estimating the radiological safety of foods.

NEUROENDOCRINE EFFECTS OF PRENATAL IRRADIATION FROM RADIOACTIVE IODINE (review)

BACKGROUND

Neuroendocrine effects of the prenatal radiation exposure from radioactive iodine in an event of nuclear power reactor accidents are a key issue in the field of radiation medicine and radiation safety because of a dramatic radiosensitivity of the developing organism.

OBJECTIVE

Review of contemporary epidemiological, clinical and experimental data on neuroendocrine effects of prenatal exposure to 131I.

OBJECT AND METHODS

Search in the PubMed/MEDLINE and Google Scholar abstract databases, along with a manual search for the relevant data sources.

RESULTS

Estimated absorbed doses of intrauterine thyroid irradiation from radioactive iodine were obtained based on ICRP Publication 88, both with estimates of effective radiation doses on embryo and fetus, and estimates of the brain equivalent doses upon exposure in utero. The latter ones are subject to updating. The evidence-based data has been presented regarding a radiation-associated reduction of head and chest circumference at birth, as well as a radiation-associated excess of goiter with large thyroid nodules, and possibly of thyroid cancer after a prenatal exposure to 131I radionuclides. Data on intrauterine brain damage are controversial, but most researchers share the view that there are cognitive and emotional-behavioral disorders due to prenatal and postnatal irradiation and psy- chosocial impacts. Incidence increase of non-cancerous endocrine disorders and degenerative vascular disease of retina was noted. An experimental model of intrauterine irradiation from 131I on Wistar rats was for the first time ever created, extrapolating the radioneuroembryological effects in rats to individuals prenatally exposed after the Chornobyl disaster. Late neuropsychiatric and endocrine effects may be resulted from the relatively short-term impact of ionizing radiation at a level previously been considered safe. The necessity of neuropsychiatric and endocrinological monitoring of individuals exposed prenatally to ionizing radiation after the Chornobyl catastrophe throughout their life is substantiated. Experimental animal studies are a key direction in the further research of radiation effects, especially associated with low radiation doses. Further experimental and clinical neuroradiobio- logical studies aimed at exploration of the effect of ionizing radiation on hippocampal neurogenesis are most rele- vant nowadays.

Estimation of Radiation Doses for a Case-control Study of Thyroid Cancer Among Ukrainian Chernobyl Cleanup Workers

Thyroid doses were estimated for 607 subjects of a case-control study of thyroid cancer nested in the cohort of 150,813 male Ukrainian cleanup workers who were exposed to radiation as a result of the 1986 Chernobyl nuclear power plant accident. Individual thyroid doses due to external irradiation, inhalation of I and short-lived radioiodine and radiotellurium isotopes (I, I, I, Te, and Te) during the cleanup mission, and intake of I during residence in contaminated settlements were calculated for all study subjects, along with associated uncertainty distributions. The average thyroid dose due to all exposure pathways combined was estimated to be 199 mGy (median: 47 mGy; range: 0.15 mGy to 9.0 Gy), with averages of 140 mGy (median: 20 mGy; range: 0.015 mGy to 3.6 Gy) from external irradiation during the cleanup mission, 44 mGy (median: 12 mGy; range: ~0 mGy to 1.7 Gy) due to I inhalation, 42 mGy (median: 7.3 mGy; range: 0.001 mGy to 3.4 Gy) due to I intake during residence, and 11 mGy (median: 1.6 mGy; range: ~0 mGy to 0.38 Gy) due to inhalation of short-lived radionuclides. Internal exposure of the thyroid gland to I contributed more than 50% of the total thyroid dose in 45% of the study subjects. The uncertainties in the individual stochastic doses were characterized by a mean geometric standard deviation of 2.0, 1.8, 2.0, and 2.6 for external irradiation, inhalation of I, inhalation of short-lived radionuclides, and residential exposure, respectively. The models used for dose calculations were validated against instrument measurements done shortly after the accident. Results of the validation showed that thyroid doses could be estimated retrospectively for Chernobyl cleanup workers two to three decades after the accident with a reasonable degree of reliability.

Radiation Exposure to the Thyroid After the Chernobyl Accident

INTRODUCTION

The Chernobyl accident resulted in a considerable release of radioactivity to the atmosphere, particularly of Iodine-131 (¹³¹I), with the greatest contamination occurring in Belarus, Ukraine, and western part of Russia.

MATERIAL AND METHODS

Increase in thyroid cancer and other thyroid diseases incidence in population exposed to Chernobyl fallout in these counties was the major health effect of the accident. Therefore, a lot of attention was paid to the thyroid doses, mainly, the ¹³¹I intake during two months after the accident. This paper reviews thyroid doses, both the individual for the subjects of radiation epidemiological studies and population-average doses. Exposure to ¹³¹I intake and other exposure pathways to population of affected regions and the Chernobyl cleanup workers (liquidators) are considered.

RESULTS

Individual thyroid doses due to ¹³¹I intake varied up to 42 Gy and depended on the age of the person, the region where a person was exposed, and their cow's milk consumption habits. Population-average thyroid doses among children of youngest age reached up to 0.75 Gy in the most contaminated area, the Gomel Oblast, in Belarus. Intake of ¹³¹I was the main pathway of exposure to the thyroid gland; its mean contribution to the thyroid dose in affected regions was more than 90%. The mean thyroid dose from inhalation of ¹³¹I for early Chernobyl cleanup workers was estimated to be 0.18 Gy. Individual thyroid doses due to different exposure pathways varied among 1,137 cleanup workers included in the epidemiological studies up to 9 Gy. Uncertainties associated with dose estimates, in terms of mean geometric standard deviation of individual stochastic doses, varied in range from 1.6 for doses based on individual-radiation measurements to 2.6 for "modelled" doses.

CONCLUSION

The ¹³¹I was the most radiologically important radionuclide that resulted in radiation exposure to the thyroid gland and cause an increase in the of rate of thyroid cancer and other thyroid diseases in population exposed after the Chernobyl accident.

American Thyroid Association Scientific Statement on the Use of Potassium Iodide Ingestion in a Nuclear Emergency

This document serves to summarize the issues and the American Thyroid Association (ATA) position regarding the use of potassium iodide as a thyroid blocking agent in the event of a nuclear accident. The purpose is to provide a review and updated position statement regarding the advanced distribution, stockpiling, and availability of potassium iodide in the event of nuclear radiation emergencies in the United States.

Integration of a radiation biomarker into modeling of thyroid carcinogenesis and post-Chernobyl risk assessment

Strong evidence for the statistical association between radiation exposure and disease has been produced for thyroid cancer by epidemiological studies after the Chernobyl accident. However, limitations of the epidemiological approach in order to explore health risks especially at low doses of radiation appear obvious. Statistical fluctuations due to small case numbers dominate the uncertainty of risk estimates. Molecular radiation markers have been searched extensively to separate radiation-induced cancer cases from sporadic cases. The overexpression of the CLIP2 gene is the most promising of these markers. It was found in the majority of papillary thyroid cancers (PTCs) from young patients included in the Chernobyl tissue bank. Motivated by the CLIP2 findings we propose a mechanistic model which describes PTC development as a sequence of rate-limiting events in two distinct paths of CLIP2-associated and multistage carcinogenesis. It integrates molecular measurements of the dichotomous CLIP2 marker from 141 patients into the epidemiological risk analysis for about 13 000 subjects from the Ukrainian-American cohort which were exposed below age 19 years and were put under enhanced medical surveillance since 1998. For the first time, a radiation risk has been estimated solely from marker measurements. Cross checking with epidemiological estimates and model validation suggests that CLIP2 is a marker of high precision. CLIP2 leaves an imprint in the epidemiological incidence data which is typical for a driver gene. With the mechanistic model, we explore the impact of radiation on the molecular landscape of PTC. The model constitutes a unique interface between molecular biology and radiation epidemiology.

Doses for post-Chernobyl epidemiological studies: are they reliable?

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.

Estimation of radiation risk in presence of classical additive and Berkson multiplicative errors in exposure doses

In this paper, the influence of measurement errors in exposure doses in a regression model with binary response is studied. Recently, it has been recognized that uncertainty in exposure dose is characterized by errors of two types: classical additive errors and Berkson multiplicative errors. The combination of classical additive and Berkson multiplicative errors has not been considered in the literature previously. In a simulation study based on data from radio-epidemiological research of thyroid cancer in Ukraine caused by the Chornobyl accident, it is shown that ignoring measurement errors in doses leads to overestimation of background prevalence and underestimation of excess relative risk. In the work, several methods to reduce these biases are proposed. They are new regression calibration, an additive version of efficient SIMEX, and novel corrected score methods.

Genomic copy number analysis of Chernobyl papillary thyroid carcinoma in the Ukrainian-American Cohort

One of the major consequences of the 1986 Chernobyl reactor accident was a dramatic increase in papillary thyroid carcinoma (PTC) incidence, predominantly in patients exposed to the radioiodine fallout at young age. The present study is the first on genomic copy number alterations (CNAs) of PTCs of the Ukrainian-American cohort (UkrAm) generated by array comparative genomic hybridization (aCGH). Unsupervised hierarchical clustering of CNA profiles revealed a significant enrichment of a subgroup of patients with female gender, long latency (>17 years) and negative lymph node status. Further, we identified single CNAs that were significantly associated with latency, gender, radiation dose and BRAF V600E mutation status. Multivariate analysis revealed no interactions but additive effects of parameters gender, latency and dose on CNAs. The previously identified radiation-associated gain of the chromosomal bands 7q11.22-11.23 was present in 29% of cases. Moreover, comparison of our radiation-associated PTC data set with the TCGA data set on sporadic PTCs revealed altered copy numbers of the tumor driver genes NF2 and CHEK2. Further, we integrated the CNA data with transcriptomic data that were available on a subset of the herein analyzed cohort and did not find statistically significant associations between the two molecular layers. However, applying hierarchical clustering on a 'BRAF-like/RAS-like' transcriptome signature split the cases into four groups, one of which containing all BRAF-positive cases validating the signature in an independent data set.

Dose-dependent expression of CLIP2 in post-Chernobyl papillary thyroid carcinomas

This study showed a clear dose-response relationship for the CLIP2 radiation marker in post-Chernobyl papillary thyroid carcinoma cohorts for young patients and hints to different molecular mechanisms in tumors induced at low doses compared to moderate/high doses.

A previous study on papillary thyroid carcinomas (PTC) in young patients who were exposed to ¹³¹iodine from the Chernobyl fallout revealed an exclusive gain of chromosomal band 7q11.23 in exposed cases compared to an age-matched control cohort. CLIP2, a gene located within band 7q11.23 was shown to be differentially expressed between exposed and non-exposed cases at messenger RNA and protein level. Therefore, a standardized procedure for CLIP2 typing of PTCs has been developed in a follow-up study. Here we used CLIP2 typing data on 117 post-Chernobyl PTCs from two cohorts of exposed patients with individual dose estimates and 24 non-exposed controls to investigate a possible quantitative dose-response relationship of the CLIP2 marker. The ‘Genrisk-T’ cohort consisted of 45 PTCs and the ‘UkrAm’ cohort of 72 PTCs. Both cohorts differed in mean dose (0.59 Gy Genrisk-T, 1.2 Gy UkrAm) and mean age at exposure (AaE) (2 years Genrisk-T, 8 years UkrAm), whilst the median latency (16 years Genrisk-T, 18 years UkrAm) was comparable. We analyzed the association between the binary CLIP2 typing and continuous thyroid dose with logistic regression. A clear positive dose-response relationship was found for young PTC cases [age at operation (AaO) < 20 years, AaE < 5 years]. In the elder age group a higher proportion of sporadic tumors is assumed due to a negligible dose response, suggesting different molecular mechanisms in sporadic and radiation-induced cases. This is further supported by the association of elder patients (AaO > 20 years) with positivity for BRAF V600E mutation.

Thyroid cancer study among Ukrainian children exposed to radiation after the Chornobyl accident: improved estimates of the thyroid doses to the cohort members

In collaboration with the Ukrainian Research Center for Radiation Medicine, the U.S. National Cancer Institute initiated a cohort study of children and adolescents exposed to Chornobyl fallout in Ukraine to better understand the long-term health effects of exposure to radioactive iodines. All 13,204 cohort members were subjected to at least one direct thyroid measurement between 30 April and 30 June 1986 and resided at the time of the accident in the northern parts of Kyiv, Zhytomyr, or Chernihiv Oblasts, which were the most contaminated territories of Ukraine as a result of radioactive fallout from the Chornobyl accident. Thyroid doses for the cohort members, which had been estimated following the first round of interviews, were re-evaluated following the second round of interviews. The revised thyroid doses range from 0.35 mGy to 42 Gy, with 95% of the doses between 1 mGy and 4.2 Gy, an arithmetic mean of 0.65 Gy, and a geometric mean of 0.19 Gy. These means are 70% of the previous estimates, mainly because of the use of country-specific thyroid masses. Many of the individual thyroid dose estimates show substantial differences because of the use of an improved questionnaire for the second round of interviews. Limitations of the current set of thyroid dose estimates are discussed. For the epidemiologic study, the most notable improvement is a revised assessment of the uncertainties, as shared and unshared uncertainties in the parameter values were considered in the calculation of the 1,000 stochastic estimates of thyroid dose for each cohort member. This procedure makes it possible to perform a more realistic risk analysis.

Comparison of transcriptomic signature of post-Chernobyl and postradiotherapy thyroid tumors

BACKGROUND

We previously identified two highly discriminating and predictive radiation-induced transcriptomic signatures by comparing series of sporadic and postradiotherapy thyroid tumors (322-gene signature), and by reanalyzing a previously published data set of sporadic and post-Chernobyl thyroid tumors (106-gene signature). The aim of the present work was (i) to compare the two signatures in terms of gene expression deregulations and molecular features/pathways, and (ii) to test the capacity of the postradiotherapy signature in classifying the post-Chernobyl series of tumors and reciprocally of the post-Chernobyl signature in classifying the postradiotherapy-induced tumors.

METHODS

We now explored if postradiotherapy and post-Chernobyl papillary thyroid carcinomas (PTC) display common molecular features by comparing molecular pathways deregulated in the two tumor series, and tested the potential of gene subsets of the postradiotherapy signature to classify the post-Chernobyl series (14 sporadic and 12 post-Chernobyl PTC), and reciprocally of gene subsets of the post-Chernobyl signature to classify the postradiotherapy series (15 sporadic and 12 postradiotherapy PTC), by using conventional principal component analysis.

RESULTS

We found that the five genes common to the two signatures classified the learning/training tumors (used to search these signatures) of both the postradiotherapy (seven PTC) and the post-Chernobyl (six PTC) thyroid tumor series as compared with the sporadic tumors (seven sporadic PTC in each series). Importantly, these five genes were also effective for classifying independent series of postradiotherapy (five PTC) and post-Chernobyl (six PTC) tumors compared to independent series of sporadic tumors (eight PTC and six PTC respectively; testing tumors). Moreover, part of each postradiotherapy (32 genes) and post-Chernobyl signature (16 genes) cross-classified the respective series of thyroid tumors. Finally, several molecular pathways deregulated in post-Chernobyl tumors matched those found to be deregulated in postradiotherapy tumors.

CONCLUSIONS

Overall, our data suggest that thyroid tumors that developed following either external exposure or internal (131)I contamination shared common molecular features, related to DNA repair, oxidative and endoplasmic reticulum stresses, allowing their classification as radiation-induced tumors in comparison with sporadic counterparts, independently of doses and dose rates, which suggests there may be a "general" radiation-induced signature of thyroid tumors.

Reconstruction of individual thyroid doses to the Ukrainian subjects enrolled in the Chernobyl Tissue Bank

The Chernobyl Tissue Bank (CTB) is an organisation that collects and stores samples of tumoral thyroid tissue obtained from Ukrainian and Russian subjects who were treated surgically for a thyroid cancer and had been exposed to (131)I from the Chernobyl accident. By 2012, the CTB had collected specimens of thyroid tissue from 2267 residents of Ukraine for the purpose of radiation research. Arithmetic mean thyroid doses and uncertainties have been estimated for all but 24 subjects for whom residence at the time of exposure was not found. The subjects have been classified into six groups or sub-groups according to the type of dosimetry-related information that is available for each of them. Excluding the 325 subjects with negligible radiation exposure, the arithmetic mean of the thyroid dose over all subjects is estimated as 0.4 Gy, with individual values ranging from <1 mGy to 13 Gy. The uncertainties in the individual thyroid dose estimates, characterised by the geometric standard deviations of their probability distributions, range from 1.3 to 8.7, with an arithmetic mean of 3.2.

Iodine-131 dose-dependent gene expression: alterations in both normal and tumour thyroid tissues of post-Chernobyl thyroid cancers

BACKGROUND

A strong, consistent association between childhood irradiation and subsequent thyroid cancer provides an excellent model for studying radiation carcinogenesis.

METHODS

We evaluated gene expression in 63 paired RNA specimens from frozen normal and tumour thyroid tissues with individual iodine-131 (I-131) doses (0.008-8.6 Gy, no unirradiated controls) received from Chernobyl fallout during childhood (Ukrainian-American cohort). Approximately half of these randomly selected samples (32 tumour/normal tissue RNA specimens) were hybridised on 64 whole-genome microarrays (Agilent, 4 × 44 K). Associations between I-131 dose and gene expression were assessed separately in normal and tumour tissues using Kruskal-Wallis and linear trend tests. Of 155 genes significantly associated with I-131 after Bonferroni correction and with ≥2-fold increase per dose category, we selected 95 genes. On the remaining 31 RNA samples these genes were used for validation purposes using qRT-PCR.

RESULTS

Expression of eight genes (ABCC3, C1orf9, C6orf62, FGFR1OP2, HEY2, NDOR1, STAT3, and UCP3) in normal tissue and six genes (ANKRD46, CD47, HNRNPH1, NDOR1, SCEL, and SERPINA1) in tumour tissue was significantly associated with I-131. PANTHER/DAVID pathway analyses demonstrated significant over-representation of genes coding for nucleic acid binding in normal and tumour tissues, and for p53, EGF, and FGF signalling pathways in tumour tissue.

CONCLUSION

The multistep process of radiation carcinogenesis begins in histologically normal thyroid tissue and may involve dose-dependent gene expression changes.

Iodine-131 dose dependent gene expression in thyroid cancers and corresponding normal tissues following the Chernobyl accident

The strong and consistent relationship between irradiation at a young age and subsequent thyroid cancer provides an excellent model for studying radiation carcinogenesis in humans. We thus evaluated differential gene expression in thyroid tissue in relation to iodine-131 (I-131) doses received from the Chernobyl accident. Sixty three of 104 papillary thyroid cancers diagnosed between 1998 and 2008 in the Ukrainian-American cohort with individual I-131 thyroid dose estimates had paired RNA specimens from fresh frozen tumor (T) and normal (N) tissue provided by the Chernobyl Tissue Bank and satisfied quality control criteria. We first hybridized 32 randomly allocated RNA specimen pairs (T/N) on 64 whole genome microarrays (Agilent, 4×44 K). Associations of differential gene expression (log₂(T/N)) with dose were assessed using Kruskall-Wallis and trend tests in linear mixed regression models. While none of the genes withstood correction for the false discovery rate, we selected 75 genes with a priori evidence or P kruskall/P trend <0.0005 for validation by qRT-PCR on the remaining 31 RNA specimen pairs (T/N). The qRT-PCR data were analyzed using linear mixed regression models that included radiation dose as a categorical or ordinal variable. Eleven of 75 qRT-PCR assayed genes (ACVR2A, AJAP1, CA12, CDK12, FAM38A, GALNT7, LMO3, MTA1, SLC19A1, SLC43A3, ZNF493) were confirmed to have a statistically significant differential dose-expression relationship. Our study is among the first to provide direct human data on long term differential gene expression in relation to individual I-131 doses and to identify a set of genes potentially important in radiation carcinogenesis.

I-131 dose response for incident thyroid cancers in Ukraine related to the Chornobyl accident

BACKGROUND

Current knowledge about Chornobyl-related thyroid cancer risks comes from ecological studies based on grouped doses, case-control studies, and studies of prevalent cancers.

OBJECTIVE

To address this limitation, we evaluated the dose-response relationship for incident thyroid cancers using measurement-based individual iodine-131 (I-131) thyroid dose estimates in a prospective analytic cohort study.

METHODS

The cohort consists of individuals < 18 years of age on 26 April 1986 who resided in three contaminated oblasts (states) of Ukraine and underwent up to four thyroid screening examinations between 1998 and 2007 (n = 12,514). Thyroid doses of I-131 were estimated based on individual radioactivity measurements taken within 2 months after the accident, environmental transport models, and interview data. Excess radiation risks were estimated using Poisson regression models.

RESULTS

Sixty-five incident thyroid cancers were diagnosed during the second through fourth screenings and 73,004 person-years (PY) of observation. The dose-response relationship was consistent with linearity on relative and absolute scales, although the excess relative risk (ERR) model described data better than did the excess absolute risk (EAR) model. The ERR per gray was 1.91 [95% confidence interval (CI), 0.43-6.34], and the EAR per 10⁴ PY/Gy was 2.21 (95% CI, 0.04-5.78). The ERR per gray varied significantly by oblast of residence but not by time since exposure, use of iodine prophylaxis, iodine status, sex, age, or tumor size.

CONCLUSIONS

I-131-related thyroid cancer risks persisted for two decades after exposure, with no evidence of decrease during the observation period. The radiation risks, although smaller, are compatible with those of retrospective and ecological post-Chornobyl studies.

Estimation of the thyroid doses for ukrainian children exposed in utero after the chernobyl accident

This paper describes methods for estimating thyroid doses to Ukrainian children who were subjects of an epidemiological study of prenatal exposure and presents the calculated doses. Participants were 2,582 mother-child pairs in which the mother had been pregnant at the time of the Chernobyl accident on 26 April 1986 or in the 2-3 mo following when (131)I in fallout was still present. Among these, 1,494 were categorized as "exposed;" a comparison group of 1,088 was considered "relatively unexposed." Individual in utero thyroid dose estimates were found to range from less than 1 mGy to 3,200 mGy, with an arithmetic mean of 72 mGy. Thyroid doses varied primarily according to stage of pregnancy at the time of exposure and level of radioactive contamination at the location of residence. There was a marked difference between the dose distributions of the exposed and comparison groups, although nine children in the latter group had calculated doses in the range 100-200 mGy. For those children who were born after the accident and prior to the end of June 1986, postnatal thyroid doses were also estimated. About 7.7% (200) of the subjects received thyroid doses after birth that were at least 10% of their cumulative doses.

Thyroid cancer incidence in Ukraine: trends with reference to the Chernobyl accident

For the first time, a comparative analysis of thyroid cancer incidence in Ukraine after the Chernobyl accident was done in a cohort that is almost as large as the general population. On the basis of thyroid doses from radioactive iodine in individuals aged 1-18 years at the time of accident, geographic regions of Ukraine with low and high average accumulated thyroid doses were established and designated "low-exposure" and "high-exposure" territories, respectively. A significant difference of thyroid cancer incidence rates as a function of time between the two territories was found. That is, the increase in the incidence was higher in high-exposure regions than in low-exposure regions. The incidence rates varied substantially among the different attained age-groups, especially in the youngest one (up to 19 years old). The analysis that was adjusted for screening and technological effects also indicated that in the high-exposure regions, thyroid cancer incidence rates at the age of diagnosis of 5-9, 10-14 and 15-19 years were significantly higher in those born in 1982-1986 compared to those born in 1987-1991, while in the low-exposure regions, no significant difference was observed. The observed probable excess of radiation-induced thyroid cancer cases in adults exposed to radioactive iodine from the Chernobyl accident, especially in females, may be due to the high power of the present study. However, it should be noted that our investigation was not essentially free from ecological biases.

Methods for estimation of radiation risk in epidemiological studies accounting for classical and Berkson errors in doses

With a binary response Y, the dose-response model under consideration is logistic in flavor with pr(Y=1 | D) = R (1+R)(-1), R = λ(0) + EAR D, where λ(0) is the baseline incidence rate and EAR is the excess absolute risk per gray. The calculated thyroid dose of a person i is expressed as Dimes=fiQi(mes)/Mi(mes). Here, Qi(mes) is the measured content of radioiodine in the thyroid gland of person i at time t(mes), Mi(mes) is the estimate of the thyroid mass, and f(i) is the normalizing multiplier. The Q(i) and M(i) are measured with multiplicative errors Vi(Q) and ViM, so that Qi(mes)=Qi(tr)Vi(Q) (this is classical measurement error model) and Mi(tr)=Mi(mes)Vi(M) (this is Berkson measurement error model). Here, Qi(tr) is the true content of radioactivity in the thyroid gland, and Mi(tr) is the true value of the thyroid mass. The error in f(i) is much smaller than the errors in ( Qi(mes), Mi(mes)) and ignored in the analysis. By means of Parametric Full Maximum Likelihood and Regression Calibration (under the assumption that the data set of true doses has lognormal distribution), Nonparametric Full Maximum Likelihood, Nonparametric Regression Calibration, and by properly tuned SIMEX method we study the influence of measurement errors in thyroid dose on the estimates of λ(0) and EAR. The simulation study is presented based on a real sample from the epidemiological studies. The doses were reconstructed in the framework of the Ukrainian-American project on the investigation of Post-Chernobyl thyroid cancers in Ukraine, and the underlying subpolulation was artificially enlarged in order to increase the statistical power. The true risk parameters were given by the values to earlier epidemiological studies, and then the binary response was simulated according to the dose-response model.

Subclinical hypothyroidism after radioiodine exposure: Ukrainian-American cohort study of thyroid cancer and other thyroid diseases after the Chornobyl accident (1998-2000)

BACKGROUND

Hypothyroidism is the most common thyroid abnormality in patients treated with high doses of iodine-131 (131I). Data on risk of hypothyroidism from low to moderate 131I thyroid doses are limited and inconsistent.

OBJECTIVE

This study was conducted to quantify the risk of hypothyroidism prevalence in relation to 131I doses received because of the Chornobyl accident.

METHODS

This is a cross-sectional (1998-2000) screening study of thyroid diseases in a cohort of 11,853 individuals < 18 years of age at the time of the accident, with individual thyroid radioactivity measurements taken within 2 months of the accident. We measured thyroid-stimulating hormone (TSH), free thyroxine, and antibodies to thyroid peroxidase (ATPO) in serum.

RESULTS

Mean age at examination of the analysis cohort was 21.6 years (range, 12.2-32.5 years), with 49% females. Mean 131I thyroid dose was 0.79 Gy (range, 0-40.7 Gy). There were 719 cases with hypothyroidism (TSH > 4 mIU/L), including 14 with overt hypothyroidism. We found a significant, small association between (131)I thyroid doses and prevalent hypothyroidism, with the excess odds ratio (EOR) per gray of 0.10 (95% confidence interval, 0.03-0.21). EOR per gray was higher in individuals with ATPO < or = 60 U/mL compared with individuals with ATPO > 60 U/mL (p < 0.001).

CONCLUSIONS

This is the first study to find a significant relationship between prevalence of hypothyroidism and individual (131)I thyroid doses due to environmental exposure. The radiation increase in hypothyroidism was small (10% per Gy) and limited largely to subclinical hypothyroidism. Prospective data are needed to evaluate the dynamics of radiation-related hypothyroidism and clarify the role of antithyroid antibodies.

Screening effects in risk studies of thyroid cancer after the Chernobyl accident

In this article scenarios have been developed, which simulate screening effects in ecological and cohort studies of thyroid cancer incidence among Ukrainians, whose thyroids have been exposed to (131)I in the aftermath of the Chernobyl accident. If possible, the scenarios were based on directly observed data, such as the population size, dose distributions and thyroid cancer cases. Two scenarios were considered where the screening effect on baseline cases is either equal to or larger than that of radiation-related thyroid cancer cases. For ecological studies in settlements with more than ten measurements of the (131)I activity in the human thyroid in May-June 1986, the screening bias appeared small (<19%) for all risk quantities. In the cohort studies, the excess absolute risk per dose was larger by a factor of 4 than in the general population. For an equal screening effect on baseline and radiation-related cancer (Scenario 1) the excess relative risk was about the same as in the general population. However, a differential screening effect (Scenario 2) produced a risk smaller by a factor of 2.5. A comparison with first results of the Ukrainian-US-American cohort study did not give any indication that a differential screening effect has a marked influence on the risk estimates. The differences in the risk estimates from ecological studies and cohort studies were explained by the different screening patterns in the general population and in the much smaller cohort. The present investigations are characterized by dose estimates for many settlements which are very weakly correlated with screening, the confounding variable. The results show that under these conditions ecological studies may provide risk estimates with an acceptable bias.

A screening study of thyroid cancer and other thyroid diseases among individuals exposed in utero to iodine-131 from Chernobyl fallout

BACKGROUND

Like stable iodine, radioiodines concentrate in the thyroid gland, increasing thyroid cancer risk in exposed children. Data on exposure to the embryonic/fetal thyroid are rare, raising questions about use of iodine 131 (I-131) in pregnant women. We present here estimated risks of thyroid disease from exposure in utero to I-131 fallout from the Chernobyl nuclear accident.

METHODS

We conducted a cross-sectional thyroid screening study (palpation, ultrasound, thyroid hormones, and, if indicated, fine needle aspiration) from 2003 to 2006. Participants were 2582 mother-child pairs from Ukraine in which the mother had been pregnant at the time of the accident on April 26, 1986, or 2 months after the time during which I-131 fallout was still present (1494 from contaminated areas, 1088 in the comparison group). Individual cumulative in utero thyroid dose estimates were derived from estimated I-131 activity in the mother's thyroid (mean 72 mGy; range 0-3230 mGy).

RESULTS

There were seven cases of thyroid carcinoma and one case of Hurthle cell neoplasm identified as a result of the screening. Whereas the estimated excess odds ratio per gray for thyroid carcinoma was elevated (excess odds ratio per gray 11.66), it was not statistically significant (P = 0.12). No radiation risks were identified for other thyroid diseases.

CONCLUSION

Our results suggest that in utero exposure to radioiodines may have increased the risk of thyroid carcinoma approximately 20 yr after the Chernobyl accident, supporting a conservative approach to medical uses of I-131 during pregnancy.

Thyroid cancer incidence among people living in areas contaminated by radiation from the Chernobyl accident

As a result of the Chernobyl nuclear power plant accident, massive amounts of radioactive materials were released into the environment and large numbers of individuals living in Belarus, Russia, and Ukraine were exposed to radioactive iodines, primarily 131I. Iodine-131 concentrated in the thyroid gland of residents of the contaminated areas, with children and adolescents being particularly affected. In the decade after the accident, a substantial increase in thyroid cancer incidence was observed among exposed children in the three affected countries, and compelling evidence of an association between pediatric thyroid cancer incidence and radiation exposure to the thyroid gland accumulated. The data currently available suggest that both the magnitude and patterns of thyroid cancer risk are generally consistent with those reported following external exposure. Based on data from case-control studies, iodine deficiency appeared to enhance the risk of developing thyroid cancer following exposure from Chernobyl. Results from a recent large cohort study, however, did not support these findings. Data on adult exposure are limited and not entirely consistent. Similarly, information on thyroid cancer risks associated with in utero exposure is insufficient to draw conclusions. The lack of information on these two population groups indicates an important gap that needs to be filled. Twenty years after the accident, excess thyroid cancers are still occurring among persons exposed as children or adolescents, and, if external radiation can be used as a guide, we can expect an excess of radiation-associated thyroid cancers for several more decades. Since considerable uncertainties about the long-term health effects from Chernobyl remain, continued follow-up of the exposed populations should provide valuable information.

Third annual Warren K. Sinclair keynote address: retrospective analysis of impacts of the Chernobyl accident

The accident at the Chernobyl Nuclear Power Plant in 1986 was the most severe in the history of the nuclear industry, causing a huge release of radionuclides over large areas of Europe. The recently completed Chernobyl Forum concluded that after a number of years, along with reduction of radiation levels and accumulation of humanitarian consequences, severe social and economic depression of the affected regions and associated psychological problems of the general public and the workers had become the most significant problem to be addressed by the authorities. The majority of the >600,000 emergency and recovery operation workers and five million residents of the contaminated areas in Belarus, Russia, and Ukraine received relatively minor radiation doses which are comparable with the natural background levels. An exception is a cohort of several hundred emergency workers who received high radiation doses and of whom 28 persons died in 1986 due to acute radiation sickness. Apart from the dramatic increase in thyroid cancer incidence among those exposed to radioiodine at a young age and some increase of leukemia in the most exposed workers, there is no clearly demonstrated increase in the somatic diseases due to radiation. There was, however, an increase in psychological problems among the affected population, compounded by the social disruption that followed the break-up of the Soviet Union. Despite the unprecedented scale of the Chernobyl accident, its consequences on the health of people are far less severe than those of the atomic bombings of the cities of Hiroshima and Nagasaki. Studying the consequences of the Chernobyl accident has made an invaluable scientific contribution to the development of nuclear safety, radioecology, radiation medicine and protection, and also the social sciences. The Chernobyl accident initiated the global nuclear and radiation safety regime.

Radiation dosimetry for highly contaminated Belarusian, Russian and Ukrainian populations, and for less contaminated populations in Europe

The explosions at the Chernobyl Nuclear Power Plant (CNPP) in Ukraine early in the morning of 26 April 1986 led to a considerable release of radioactive materials during 10 d. The cloud from the reactor spread many different radionuclides, particularly those of iodine (131I) and cesium (134Cs and 137Cs), over the majority of European countries, but the greatest contamination occurred over vast areas of Belarus, the Russian Federation and Ukraine. As the major health effect of Chernobyl is an elevated thyroid cancer incidence in children and adolescents, much attention has been paid to the thyroid doses resulting from intakes of 131I, which were delivered within 2 mo following the accident. The thyroid doses received by the inhabitants of the contaminated areas of Belarus, Russia, and Ukraine varied in a wide range, mainly according to age, level of ground contamination, milk consumption rate, and origin of the milk that was consumed. Reported individual thyroid doses varied up to approximately 40,000 mGy, with average doses of a few to 1,000 mGy, depending on the area where people were exposed. In addition, the presence in the environment of long-lived 134Cs and 137Cs has led to a relatively homogeneous exposure of all organs and tissues of the body via external and internal irradiation, albeit at low rates. Excluding the thyroid doses, the whole-body (or effective) dose estimates for the general population accumulated during 20 y after the accident (1986-2005) range from a few millisieverts (mSv) to some hundred mSv with an average dose of approximately 10 mSv in the contaminated areas of Belarus, Russia, and Ukraine. In other European countries, both the thyroid and the effective doses are, on average, much smaller.

Chronic contamination with 137cesium in rat: effect on liver cholesterol metabolism

After the Chernobyl nuclear accident, epidemiological studies on human populations living in 137Cs-contaminated areas revealed the increase frequencies of thyroid cancer and evoked the apparition of cardiovascular diseases, hormonal effect, liver alteration, and lipid disorder. Actually, it raises a problem of public safety for the populations living on these territories that are exposed to low levels of 137Cs during a long period through food. Then it is necessary to study potential effect of this chronic contamination. To mimic this situation, the authors investigate the potential biological effects of chronic exposure to 137Cs at a postaccidental dose (150 Bq/rat/day) on hepatic metabolism of cholesterol in rat. Plasma lipid level, gene expression and activity were analyzed. It was observed that in 137Cs-exposed rats, gene expression of low-density lipoprotein receptor (LDLr), apolipoprotein B (apoB), and liver X receptor alpha (LXRalpha) are increased (95%, p < .05; 34%, p < .05; 20%, p < 0.05, respectively), whereas transporter adenosine triphosphate-binding cassette transporter G5 (ABCG5) is decreased (42%, p < .05). In addition, cytochrome P450 27A1 (CYP27A1) activity is increased (34%, p < .05) in contaminated rat liver. In conclusion, the results suggest that 137Cs contamination at low-level induces molecular modifications of the liver cholesterol metabolism without leading to a dysregulation of its homeostasis. These results suggest that chronic long term exposure at low-level of 137Cs may evolve to lipid disorder.

Radiation exposure to the population of Europe following the Chernobyl accident

On the occasion of the 20th anniversary of the Chernobyl accident an attempt has been made to evaluate the impact of the Chernobyl accident on the global burden of human cancer in Europe. This required the estimation of radiation doses in each of the 40 European countries. Dose estimation was based on the analysis and compilation of data either published in the scientific literature or provided by local experts. Considerable variability has been observed in exposure levels among the European populations. The average individual doses to the thyroid from the intake of (131)I for children aged 1 y were found to vary from approximately 0.01 mGy in Portugal up to 750 mGy in Gomel Oblast (Belarus). Thyroid doses to adults were consistently lower than the doses received by young children. The average individual effective doses from external exposure and ingestion of long-lived radiocaesium accrued in the period 1986-2005 varied from approximately 0 in Portugal to approximately 10 mSv in Gomel Oblast (Belarus) and Bryansk Oblast (Russia). The uncertainties in the dose estimates were subjectively estimated on the basis of the availability and reliability of the radiation data that were used for dose reconstruction in each country.

Questionnaire- and measurement-based individual thyroid doses in Ukraine resulting from the Chornobyl nuclear reactor accident

The U.S. National Cancer Institute (NCI), in cooperation with the Ministries of Health of Belarus and of Ukraine, is involved in epidemiological studies of thyroid diseases presumably related to the Chornobyl accident, which occurred in Ukraine on 26 April 1986. Within the framework of these studies, individual thyroid absorbed doses, as well as uncertainties, have been estimated for all members of the cohorts (13,215 Ukrainians and 11,918 Belarusians), who were selected from the large group of children aged 0 to 18 whose thyroids were monitored for gamma radiation within a few weeks after the accident. Information on the residence history and dietary habits of each cohort member was obtained during personal interviews. The methodology used to estimate the thyroid absorbed doses resulting from intakes of (131)I by the Ukrainian cohort subjects is described. The model of thyroid dose estimation is run in two modes: deterministic and stochastic. In the stochastic mode, the model is run 1,000 times for each subject using a Monte Carlo procedure. The geometric means of the individual thyroid absorbed doses obtained in the stochastic mode range from 0.0006 to 42 Gy. The arithmetic and geometric means of these individual thyroid absorbed doses over the entire cohort are 0.68 and 0.23 Gy, respectively. On average, the individual thyroid dose estimates obtained in the deterministic mode are about the same as the geometric mean doses obtained in the stochastic mode, while the arithmetic mean thyroid absorbed doses obtained in the stochastic mode are about 20% higher than those obtained in the deterministic mode. The distributions of the 1000 values of the individual thyroid absorbed dose estimates are found to be approximately lognormal, with geometric standard deviations ranging from 1.6 to 5.0 for most cohort subjects. For the time being, only the thyroid doses resulting from intakes of (131)I have been estimated for all subjects. Future work will include the estimation of the contributions to the thyroid doses resulting from external irradiation and from intakes of short-lived ((133)I and (132)Te) and long-lived ((134)Cs and (137)Cs) radionuclides, as well as efforts to reduce the uncertainties.

Chronic contamination with 137Cesium affects Vitamin D3 metabolism in rats

Twenty years after Chernobyl disaster, many people are still chronically exposed to low dose of (137)Cs, mainly through the food consumption. A large variety of diseases have been described in highly exposed people with (137)Cs, which include bone disorders. The aim of this work was to investigate the biological effects of a chronic exposure to (137)Cs on Vitamin D(3) metabolism, a hormone essential in bone homeostasis. Rats were exposed to (137)Cs in their drinking water for 3 months at a dose of 6500 Bq/l (approximately 150 Bq/rat/day), a similar concentration ingested by the population living in contaminated territories in the former USSR countries. Cytochromes P450 enzymes involved in Vitamin D(3) metabolism, related nuclear receptors and Vitamin D(3) target genes were assessed by real time PCR in liver, kidney and brain. Vitamin D, PTH, calcium and phosphate levels were measured in plasma. An increase in the expression level of cyp2r1 (40%, p<0.05) was observed in the liver of (137)Cs-exposed rats. However a significant decrease of Vitamin D (1,25(OH)D(3)) plasma level (53%, p=0.02) was observed. In brain, cyp2r1 mRNA level was decreased by 20% (p<0.05), while the expression level of cyp27b1 is increased (35%, p<0.05) after (137)Cs contamination. In conclusion, this study showed for the first time that chronic exposure with post-accidental doses of (137)Cs affects Vitamin D(3) active form level and induces molecular modifications of CYPs enzymes involved its metabolism in liver and brain, without leading to mineral homeostasis disorders.

Post-Chornobyl Thyroid Cancers in Ukraine. Report 2: Risk Analysis

On April 26, 1986, the worst nuclear reactor accident to date occurred at the Chornobyl (Chernobyl) power plant in Ukraine. Millions of people in Ukraine, Belarus and Russia were exposed to radioactive nuclides, especially (131)I. Since then, research has been conducted on various subgroups of the exposed population, and it has been demonstrated that the large increase in thyroid cancer is related to the (131)I exposure. However, because of study limitations, quantified risk estimates are limited, and there remains a need for additional information. We conducted an ecological study to investigate the relationship between (131)I thyroid dose and the diagnosis of thyroid cancer in three highly contaminated oblasts in Northern Ukraine. The study population is comprised of 301,907 persons who were between the ages of 1 and 18 at the time of the Chornobyl accident and were living in 1,293 rural settlements in the three study oblasts. Twenty-four percent of the study population had individual thyroid dose estimates and the other 76% had "individualized" estimates of thyroid dose based on direct thyroid measurements taken from a person of the same age and gender living in the same or nearby settlement. Cases include 232 thyroid cancers diagnosed from January 1990 through December 2001, and all were confirmed histologically. Dose-response analyses took into account differences in the rate of ultrasound examinations conducted in the three study oblasts. The estimated excess relative risk per gray was 8.0 (95% CI = 4.6-15) and the excess absolute risk per 10,000 person-year gray was estimated to be 1.5 (95% CI = 1.2-1.9). In broad terms, these estimates are compatible with results of other studies from the contaminated areas, as well as studies of external radiation exposure.

A Cohort Study of Thyroid Cancer and Other Thyroid Diseases After the Chornobyl Accident: Thyroid Cancer in Ukraine Detected During First Screening

BACKGROUND

The Chornobyl accident in 1986 exposed thousands of people to radioactive iodine isotopes, particularly (131)I; this exposure was followed by a large increase in thyroid cancer among those exposed as children and adolescents, particularly in Belarus, the Russian Federation, and Ukraine. Here we report the results of the first cohort study of thyroid cancer among those exposed as children and adolescents following the Chornobyl accident.

METHODS

A cohort of 32 385 individuals younger than 18 years of age and resident in the most heavily contaminated areas in Ukraine at the time of the accident was invited to be screened for any thyroid pathology by ultrasound and palpation between 1998 and 2000; 13 127 individuals (44%) were actually screened. Individual estimates of radiation dose to the thyroid were available for all screenees based on radioactivity measurements made shortly after the accident and on interview data. The excess relative risk per gray (Gy) was estimated using individual doses and a linear excess relative risk model.

RESULTS

Forty-five pathologically confirmed cases of thyroid cancer were found during the 1998-2000 screening. Thyroid cancer showed a strong, monotonic, and approximately linear relationship with individual thyroid dose estimate (P<.001), yielding an estimated excess relative risk of 5.25 per Gy (95% confidence interval [CI] = 1.70 to 27.5). Greater age at exposure was associated with decreased risk of radiation-related thyroid cancer, although this interaction effect was not statistically significant.

CONCLUSION

Exposure to radioactive iodine was strongly associated with increased risk of thyroid cancer among those exposed as children and adolescents. In the absence of Chornobyl radiation, 11.2 thyroid cancer cases would have been expected compared with the 45 observed, i.e., a reduction of 75% (95% CI = 50% to 93%). The study also provides quantitative risk estimates minimally confounded by any screening effects. Caution should be exercised in generalizing these results to any future similar accidents because of the potential differences in the nature of the radioactive iodines involved, the duration and temporal patterns of exposures, and the susceptibility of the exposed population.

Cancer consequences of the Chernobyl accident: 20 years on

26 April 2006 marks the 20th anniversary of the Chernobyl accident. On this occasion, the World Health Organization (WHO), within the UN Chernobyl Forum initiative, convened an Expert Group to evaluate the health impacts of Chernobyl. This paper summarises the findings relating to cancer. A dramatic increase in the incidence of thyroid cancer has been observed among those exposed to radioactive iodines in childhood and adolescence in the most contaminated territories. Iodine deficiency may have increased the risk of developing thyroid cancer following exposure to radioactive iodines, while prolonged stable iodine supplementation in the years after exposure may reduce this risk. Although increases in rates of other cancers have been reported, much of these increases appear to be due to other factors, including improvements in registration, reporting and diagnosis. Studies are few, however, and have methodological limitations. Further, because most radiation-related solid cancers continue to occur decades after exposure and because only 20 years have passed since the accident, it is too early to evaluate the full radiological impact of the accident. Apart from the large increase in thyroid cancer incidence in young people, there are at present no clearly demonstrated radiation-related increases in cancer risk. This should not, however, be interpreted to mean that no increase has in fact occurred: based on the experience of other populations exposed to ionising radiation, a small increase in the relative risk of cancer is expected, even at the low to moderate doses received. Although it is expected that epidemiological studies will have difficulty identifying such a risk, it may nevertheless translate into a substantial number of radiation-related cancer cases in the future, given the very large number of individuals exposed.

Cancer mortality among populations residing in counties near the Hanford site, 1950-2000

A descriptive epidemiologic study of cancer mortality among residents of counties near the Hanford nuclear facility site in Richland, Washington, was conducted. Between 1944 and 1957, radioactive 131I was released into the environment from the Hanford site. Cancer mortality from 1950 through 2000 was evaluated in four counties with the highest estimated exposure to 131I and compared with the cancer mortality experience in five demographically similar counties in Washington State with minimal 131I exposure. Overall, cancer rates in the study counties were slightly below those in the comparison counties [relative risk (RR) 0.95; 95% confidence interval (CI) 0.93-0.97], due mainly to a low risk for lung cancer (RR 0.89; 95% CI 0.85-0.93). Thyroid cancer (n=33; RR 0.84; 95% CI 0.56-1.26), female breast cancer (n=1,233; RR 0.99; 95% CI 0.92-1.06), leukemia other than chronic lymphocytic leukemia (n=492; RR 0.95; 95% CI 0.85-1.06), and childhood leukemia (n=71; RR=1.06; 95% CI 0.78-1.43) were not significantly increased in the exposed counties. Furthermore, there was no evidence that the cancer death rates over time differed between study and comparison counties. Patterns over time of thyroid cancer in particular were similar for exposure and comparison counties. Although based on a geographic correlation design, these data suggest that living near the Hanford site has not increased cancer rates.

Thyroid cancer among Ukrainians and Belarusians who were children or adolescents at the time of the Chernobyl accident

Our objective is to assess the regional and temporal dependences of the baseline cases contributing to thyroid cancer incidence among those exposed in childhood or during adolescence in Belarus and Ukraine after the Chernobyl accident. Data are analysed for Kyiv and Sevastopol City and the 25 oblasts (regions) in Ukraine, and for Minsk and Gomel City and the 6 oblasts in Belarus. Average thyroid doses due to the Chernobyl accident were assessed for every birth year in the period from 1968 to 1985. Case data pertain to people who underwent surgical removal of thyroid cancers during the period 1986 to 2001 and who were allocated to their place of residence at the time of the accident. The 35 oblasts/cities were subdivided into an upper, middle and lower group of baseline thyroid cancer incidence. Poisson regressions were performed to estimate age, time and gender dependences of the baseline incidence rates in the three groups. The majority of oblasts/cities with high average doses and the majority of Belarusian oblasts/cities belong to the upper group of baseline thyroid cancer incidence. The baseline in the upper group is estimated to be larger than in the middle group by a factor of 2.3, and by a factor of 4.0 when compared to the lower group. The baseline incidence increases with age and with time since exposure. Estimated baseline incidence rates were found to increase from 1988 to 1999 by factors of three and two for the upper and the two lower groups respectively. The estimated thyroid cancer incidence rates in Belarus and Ukraine, and their dependences on gender and age, are consistent with observed rates found in the larger cancer registries of other countries. In conclusion, the baseline cases are found to contribute about 70% to the thyroid cancer incidence in Ukraine, and about 40% to the incidence in Belarus.

Thyroid Cancer Risk in Areas of Ukraine and Belarus Affected by the Chernobyl Accident

The purpose of the present study was to analyze the thyroid cancer incidence risk after the Chernobyl accident and its degree of dependence on time and age. Data were analyzed for 1034 settlements in Ukraine and Belarus, in which more than 10 measurements of the (131)I content in human thyroids had been performed in May/June 1986. Thyroid doses due to the Chernobyl accident were assessed for the birth years 1968-1985 and related to thyroid cancers that were surgically removed during the period 1990-2001. The central estimate for the linear coefficient of the EAR dose response was 2.66 (95% CI: 2.19; 3.13) cases per 10(4) PY-Gy; for the quadratic coefficient, it was -0.145 (95% CI: -0.171; -0.119) cases per 10(4) PY-Gy(2). The EAR was found to be higher for females than for males by a factor of 1.4. It decreased with age at exposure and increased with age attained. The central estimate for the linear coefficient of the ERR dose response was 18.9 (95% CI: 11.1; 26.7) Gy(-1); for the quadratic coefficient, it was -1.03 (95% CI: -1.46; -0.60) Gy(-2). The ERR was found to be smaller for females than for males by a factor of 3.8 and decreased strongly with age at exposure. Both EAR and ERR were higher in the Belarusian settlements than in the Ukrainian settlements. In contrast to ERR, EAR increases with time after exposure. At the end of the observation period, excess risk estimates were found to be close to those observed in a major pooled analysis of seven studies of childhood thyroid cancer after external exposures.