Thyroid neoplasia risk is increased nearly 30 years after the Chernobyl accident

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.

Genomic characterization of cervical lymph node metastases in papillary thyroid carcinoma following the Chornobyl accident

Childhood radioactive iodine exposure from the Chornobyl accident increased papillary thyroid carcinoma (PTC) risk. While cervical lymph node metastases (cLNM) are well-recognized in pediatric PTC, the PTC metastatic process and potential radiation association are poorly understood. Here, we analyze cLNM occurrence among 428 PTC with genomic landscape analyses and known drivers (131I-exposed = 349, unexposed = 79; mean age = 27.9 years). We show that cLNM are more frequent in PTC with fusion (55%) versus mutation (30%) drivers, although the proportion varies by specific driver gene (RET-fusion = 71%, BRAF-mutation = 38%, RAS-mutation = 5%). cLNM frequency is not associated with other characteristics, including radiation dose. cLNM molecular profiling (N = 47) demonstrates 100% driver concordance with matched primary PTCs and highly concordant mutational spectra. Transcriptome analysis reveals 17 differentially expressed genes, particularly in the HOXC cluster and BRINP3; the strongest differentially expressed microRNA also is near HOXC10. Our findings underscore the critical role of driver alterations and provide promising candidates for elucidating the biological underpinnings of PTC cLNM.

Dose-response analysis of protracted absorbed organ dose and site-specific cancer incidence in Sweden after the Chernobyl nuclear power plant accident

Background

Adult males in Sweden exhibit an increased risk of cancer associated with an increased absorbed dose to the colon from the Chernobyl accident.

Methods

A closed cohort, with information on hunter status, included all individuals living in northern Sweden in 1986. Complete annual information on exposure to 137Cs at the dwelling coordinate was available for a total of 2,104,101 individuals. A nested case-control method with four controls matched for year of cancer diagnosis and year of birth, was used. Individual absorbed organ doses were calculated between 1986 and 2020 including external and internal exposure. Hazard ratios (HR) per mGy with 95% confidence intervals (95% CI) were calculated using conditional logistic regression adjusted for rural/nonrural habitat, education level and pre-Chernobyl cancer incidence 1980 to 1985. A total of 161,325 cancer cases in males and 144,439 in females were included.

Results

The adjusted HR per mGy for all cancer sites combined was 1.027 (95% CI = 1.022, 1.031) in males and 1.011 (95% CI = 1.006, 1.017) in females. In a post hoc analysis accounting for both remaining confounding from hunter lifestyle and the pre-Chernobyl cancer incidence by county, the adjusted HR per mGy for all cancer sites combined was 1.014 (95% CI = 1.009, 1.019) in males and 1.000 (95% CI = 0.994, 1.006) in females. The post hoc analysis suggested an increased risk of cancer in the colon, pancreas, and stomach, respectively, in males, and lymphoma in females.

Conclusions

Increased cancer risk estimates were found for some specific cancer sites but remaining uncontrolled confounding due to hunter lifestyle could not be ruled out.

Exposure to the Thyroid from Intake of Radioiodine Isotopes after the Chornobyl Accident. Report I: Revised Doses and Associated Uncertainties for the Ukrainian-American Cohort

Thyroid doses from intake of radioiodine isotopes (131I, 132Te+132I, and 133I) and associated uncertainties were revised for the 13,204 Ukrainian-American cohort members exposed in childhood and adolescence to fallout from the Chornobyl nuclear power plant accident. The main changes related to the revision of the 131I thyroid activity measured in cohort members, the use of thyroid-mass values specific to the Ukrainian population, and the revision of the 131I ground deposition densities in Ukraine. Uncertainties in doses were assessed considering shared and unshared errors in the parameters of the dosimetry model. Using a Monte-Carlo simulation procedure, 1,000 individual stochastic thyroid doses were calculated for each cohort member. The arithmetic mean of thyroid doses from intake of 131I, 132Te+132I, and 133I for the entire cohort was 0.60 Gy (median = 0.22 Gy). For 9,474 subjects (71.6% of the total), the thyroid doses were less than 0.5 Gy. Thyroid doses for 42 cohort members (0.3% of the total) exceeded 10 Gy while the highest dose was 35 Gy. Intake of 131I contributed around 95% to internal thyroid exposure from radioiodine isotopes. The geometric standard deviation of individual stochastic thyroid doses varied among cohort members from 1.4 to 4.3 with an arithmetic mean of 1.6 and a median of 1.4. It was shown that the contribution of shared errors to the dose uncertainty was small. The revised thyroid doses resulted, in average, in around 40% decrease for cohort members from Zhytomyr Oblast and an increase of around 24% and 35% for the cohort members from Kyiv and Chernihiv Oblast, respectively. Arithmetic mean of TD20 doses for the cohort was around 8% less than that estimated in TD10, 0.60 Gy vs. 0.65 Gy, respectively; however, global median of TD20 doses somewhat increased compared to TD10: 0.22 Gy vs. 0.19 Gy, respectively. The difference between TD10 and TD20 was mainly due to a revision of the individual 131I thyroid activity measured in the cohort members.

Clinicopathological Implications of the BRAF V600E Mutation in Papillary Thyroid Carcinoma of Ukrainian Patients Exposed to the Chernobyl Radiation in Childhood: A Study for 30 Years After the Accident

With time after the Chernobyl accident, the number of papillary thyroid carcinomas (PTCs) driven by the BRAF^V600E oncoprotein is growing in patients exposed to radiation at a young age. Clinicopathological associations of BRAF^V600E in PTCs from patients with internal radiation history have not been sufficiently studied so far. This work analyzes the structural characteristics, proliferative activity, invasive features, clinical information, and dosimetric data in the BRAF^V600E-positive and BRAF^V600E-negative PTCs from the Ukrainian patients exposed to Chernobyl radiation and treated over 30 years after the accident. The study included 428 PTCs from patients aged 4-49 years at surgery who lived in the six northern regions of Ukraine most contaminated by ¹³¹I, were ≤18 years of age at the time of exposure, and were operated on from 1990 to 2017. Immunohistochemical staining for BRAF^V600E was performed with the VE1 antibody. The probability of causation (POC) of a tumor due to radiation was determined using an interactive online NIH/NCI software. BRAF^V600E was detected in 136/428 (31.8%) PTCs. In comparison with the BRAF^V600E-negative PTCs, the BRAF^V600E-positivity was associated with older patient age at the accident and at surgery, a longer period of latency, and lower POC. The BRAF^V600E-positive PTCs were characterized by smaller tumor size, higher Ki67 labeling index, more frequent oncocytic changes, multifocality, and dominant papillary growth pattern. Tumor invasive features were less frequent in the BRAF^V600E-positive PTCs and did not change with POC level. Despite a less aggressive tumor phenotype, BRAF^V600E was a risk factor for recurrence, namely radioiodine-refractory (RAI-R) recurrent metastases. Multivariate models of RAI-R included BRAF^V600E and/or histopathological parameters closely correlating with BRAF^V600E such as tumor size, multifocality, dominant papillary growth pattern, or oncocytic changes. Thus, the BRAF^V600E-positive PTCs from patients from a high-risk group for radiogenic thyroid cancer diagnosed in the 30 years after the Chernobyl accident did not display higher invasiveness regardless of POC level, but in view of the prognostic impact of this genetic alteration, knowledge of the BRAF status may be beneficial for middle-aged patients with radiogenic PTC considered for RAI therapy, and suggests more careful follow-up of patients with the BRAF^V600E-positive tumors.

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.

Cancer risk following low doses of ionising radiation - Current epidemiological evidence and implications for radiological protection

Recent studies suggest that every year worldwide about a million patients might be exposed to doses of the order of 100 mGy of low-LET radiation, due to recurrent application of radioimaging procedures. This paper presents a synthesis of recent epidemiological evidence on radiation-related cancer risks from low-LET radiation doses of this magnitude. Evidence from pooled analyses and meta-analyses also involving epidemiological studies that, individually, do not find statistically significant radiation-related cancer risks is reviewed, and evidence from additional and more recent epidemiological studies of radiation exposures indicating excess cancer risks is also summarized. Cohorts discussed in the present paper include Japanese atomic bomb survivors, nuclear workers, patients exposed for medical purposes, and populations exposed environmentally to natural background radiation or radioactive contamination. Taken together, the overall evidence summarized here is based on studies including several million individuals, many of them followed-up for more than half a century. In summary, substantial evidence was found from epidemiological studies of exposed groups of humans that ionizing radiation causes cancer at acute and protracted doses above 100 mGy, and growing evidence for doses below 100 mGy. The significant radiation-related solid cancer risks observed at doses of several 100 mGy of protracted exposures (observed, for example, among nuclear workers) demonstrate that doses accumulated over many years at low dose rates do cause stochastic health effects. On this basis, it can be concluded that doses of the order of 100 mGy from recurrent application of medical imaging procedures involving ionizing radiation are of concern, from the viewpoint of radiological protection.

Revisiting the Geographical Distribution of Thyroid Cancer Incidence in Fukushima Prefecture: Analysis of Data From the Second- and Third-round Thyroid Ultrasound Examination

BACKGROUND

After the first-round (Preliminary Baseline Survey) ultrasound-based examination for thyroid cancer in response to the accident at the Fukushima Daiichi Nuclear Power Plant in 2011, two rounds of surveys (Full-scale Survey) have been carried out in Fukushima Prefecture. Using the data from these surveys, the geographical distribution of thyroid cancer incidence over 6 or 7 years after the disaster was examined.

METHODS

Children and adolescents who underwent the ultrasound-based examinations in the second- and/or third-round (Full-scale) survey in addition to the first-round survey were included. With a discrete survival model, we computed age, sex, and body mass index standardized incidence ratios (SIRs) for municipalities. Then, we employed spatial statistics to assess geographic clustering tendency in SIRs and Poisson regression to assess the association of SIRs with the municipal average absorbed dose to the thyroid gland at the 59-municipality level.

RESULTS

Throughout the second- and third-round surveys, 99 thyroid cancer cases were diagnosed in the study population of 252,502 individuals. Both flexibly shaped spatial scan statistics and maximized excess events test did not detect statistically significant spatial clustering (P = 0.17 and 0.54, respectively). Poisson regression showed no significant dose-response relationship: the estimated relative risks of lowest, middle-low, middle-high, and highest areas were 1.16 (95% confidence interval [CI], 0.52-2.59), 0.55 (95% CI, 0.31-0.97), 1.05 (95% CI, 0.79-1.40), and 1.24 (95% CI, 0.89-1.74).

CONCLUSION

There was no statistical support for geographic clustering or regional association with radiation dose measures of the thyroid cancer incidence in the cohort followed up to the third-round survey (fiscal years 2016-2017) in Fukushima Prefecture.

Thyroid dose estimates for the genome-wide association study of thyroid cancer in persons exposed in Belarus to 131I after the Chernobyl accident

The Chernobyl accident on 26 April 1986 led to a sharp increase in thyroid cancer (TC) incidence in the individuals exposed to radiation in childhood. The major risk factor for TC was exposure to Iodine-131 (131I). Here, we estimated the thyroid doses due to 131I intake for 2041 participants of the genome-wide association study of TC in Belarusian people exposed to radioactive fallout from the Chernobyl accident. The following parameter-values specially developed in this study were used to estimate individual thyroid doses: (i) scaling factors for adjustment of the model-based doses, (ii) age and gender diet to characterize 131I intake, and (iii) area-, age- and gender-specific S-values for the thyroid gland per 131I decay in the thyroid. The most reliable doses were calculated for 103 people with measured 131I thyroid activity (the arithmetic mean of 1.2 Gy, median 0.52 Gy), and 275 individuals with detailed residential history and dietary data (the arithmetic mean of 0.41 Gy, median 0.24 Gy). The arithmetic mean of thyroid doses among all study participants was 0.23 Gy (median 0.082 Gy); the highest individual dose was 9.0 Gy. Special attention was paid to the reliability and validity of the obtained estimates, in particular for the individuals without 131I thyroid activity measurements and individual data on residential history and diet, by comparing those with the doses from other post-Chernobyl epidemiological studies. Overall, the doses estimated in the current study were in reasonable agreement with previously reported thyroid doses. These doses will be used in the genome-wide association study of TC in people exposed in Belarus to 131I after the Chernobyl accident.

Prognostic analysis of recurrence in children and adolescents with differentiated thyroid cancer

Background:

The standard treatment for pediatric differentiated thyroid carcinoma (DTC) still requires consideration because of a lack of clinical evidence. The purpose of this study was to summarize the clinical experiences and explore the risk factors for post-operative recurrence through a retrospective analysis to develop better clinical strategies for pediatric DTC.

Methods:

This study retrospectively analyzed children and adolescents with DTC who were treated between January 1999 and December 2014 at the Cancer Hospital, Chinese Academy of Medical Sciences. Clinicopathological results and outcomes were collected. A log-rank test of Kaplan-Meier curves and the Cox regression model were used to determine the factors associated with recurrence.

Results:

Data of 150 patients were collected in this study. During the follow-up, there was only one disease-related death. The recurrence rates at 3, 5, and 10 years were 13.6%, 18.7%, and 28.6%, respectively. There was a significant difference in the rate of recurrence according to age (P < 0.001), extrathyroidal extension (P < 0.001), lymph node metastasis (P = 0.023), and invasion of the trachea and esophageal wall (P = 0.004). Cox regression analysis demonstrated that age (P = 0.006) and extrathyroidal extension (P = 0.013) were significant dependent factors of post-operative recurrence.

Conclusions:

The prognosis of DTC in children and adolescents is favorable. A close follow-up is recommended because of the high recurrence rate. A comparatively higher recurrence rate was observed in the younger age group, and new age-based divisions may be needed to conveniently evaluate the possibility of recurrence.

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.

Radiation-related genomic profile of papillary thyroid carcinoma after the Chernobyl accident

The 1986 Chernobyl nuclear power plant accident increased papillary thyroid carcinoma (PTC) incidence in surrounding regions, particularly for radioactive iodine (¹³¹I)-exposed children. We analyzed genomic, transcriptomic, and epigenomic characteristics of 440 PTCs from Ukraine (from 359 individuals with estimated childhood ¹³¹I exposure and 81 unexposed children born after 1986). PTCs displayed radiation dose-dependent enrichment of fusion drivers, nearly all in the mitogen-activated protein kinase pathway, and increases in small deletions and simple/balanced structural variants that were clonal and bore hallmarks of nonhomologous end-joining repair. Radiation-related genomic alterations were more pronounced for individuals who were younger at exposure. Transcriptomic and epigenomic features were strongly associated with driver events but not radiation dose. Our results point to DNA double-strand breaks as early carcinogenic events that subsequently enable PTC growth after environmental radiation exposure.

Increased cancer risk in male hunters compared to the general male population in Northern Sweden after the Chernobyl Nuclear Power Plant accident?

Male hunters in Swedish counties with high fallout of ¹³⁷Cs after the Chernobyl Nuclear Power Plant (NPP) accident have higher radiation exposure due to higher consumption of game compared with the general population.

Methods

Cancer incidence in Sweden was studied in 9 counties with different ¹³⁷Cs fallout after the Chernobyl NPP accident in 1986. In total, 9,267 cancer cases occurred in hunters and 138,909 cancer cases in non-hunters to 31 December 2015. Incidence rate ratios (IRR) with 95% confidence intervals (CI) were calculated using unexposed hunters, or non-hunters, as reference to study internal radiation exposure or hunter life style, respectively.

Results

Directly age standardized total cancer incidence showed an increasing trend in non-hunters. For hunters, the total cancer incidence was significantly lower up to 2001 when the total cancer incidence crossed over the weaker non-hunter trend and remained higher for the following 15 years. IRRs for total cancer in hunters versus non-hunters for each county did not show any clear exposure response pattern. IRRs for hunters versus non-hunters were higher regardless of rural/non-rural status with slightly higher risk estimates for the rural settings. The IRR for hunters was 1.06 (95% CI 1.04-1.08) 1986-2015, representing an excess of 531 cancer cases in hunters.

Conclusion

An increased total incidence of cancer was identified for male hunters compared with male non-hunters. No obvious association between cancer and ¹³⁷Cs from the Chernobyl NPP accident could be identified, although the exposure classification was too crude to exclude such an association.

Reliability of thyroid doses due to 131I intake exceeding 5 Gy in a cohort of Belarusian children exposed to Chernobyl fallout

High thyroid doses due to Iodine-131 (¹³¹I) intake among individuals exposed in childhood and adolescence to Chernobyl fallout raise questions about their reliability and their impact on the analysis of the radiation-related risk of thyroid cancer and other thyroid diseases in the exposed population. In the present study, an in-depth examination was conducted of thyroid doses from ¹³¹I intake over 5 Gy calculated for 131 subjects of the Belarusian-American cohort of individuals exposed after the Chernobyl accident. Thyroid doses in this cohort study were estimated based on individual radiation measurements of ¹³¹I thyroidal activity and detailed questionnaire data on individual behavior and consumptions of locally produced foodstuffs. Therefore, these doses provide the best basis for assessing reliability. The analysis showed that the result of direct thyroid measurement was mistakenly assigned to three out of 131 study subjects (2.3% of the total), and, therefore, the instrumental thyroid dose for these individuals cannot be correctly estimated. This study confirmed with a high degree of confidence the reliability of thyroid doses due to ¹³¹I intake exceeding 5 Gy that were calculated for the Belarusian-American cohort members.

Lessons learned from Chernobyl and Fukushima on thyroid cancer screening and recommendations in case of a future nuclear accident

Exposure of the thyroid gland to ionizing radiation at a young age is the main recognized risk factor for differentiated thyroid cancer. After the Chernobyl and Fukushima nuclear accidents, thyroid cancer screening was implemented mainly for children, leading to case over-diagnosis as seen in South Korea after the implementation of opportunistic screening (where subjects are recruited at healthcare sites). The aim of cancer screening is to reduce morbidity and mortality, but screening can also cause negative effects on health (with unnecessary treatment if over-diagnosis) and on quality of life. This paper from the SHAMISEN special issue (Nuclear Emergency Situations - Improvement of Medical And Health Surveillance) presents the principles of cancer screening, the lessons learned from thyroid cancer screening, as well as the knowledge on thyroid cancer incidence after exposure to iodine-131. The SHAMISEN Consortium recommends to envisage systematic health screening after a nuclear accident, only when appropriately justified, i.e. ensuring that screening will do more good than harm. Based on the experience of the Fukushima screening, the consortium does not recommend mass or population-based thyroid cancer screening, as the negative psychological and physical effects are likely to outweigh any possible benefit in affected populations; thyroid health monitoring should however be made available to persons who request it (regardless of whether they are at increased risk or not), accompanied with appropriate information and support.

Activity concentrations of 131I and other radionuclides in cow's milk in Belarus during the first month following the Chernobyl accident

The accident at the Chernobyl nuclear power plant (NPP) in Ukraine on April 26, 1986 led to a considerable release of radioactive material resulting in environmental contamination over vast areas of Belarus, Ukraine and western Russian Federation. The major health effect of the Chernobyl accident was an increase in thyroid cancer incidence in people exposed as children and adolescents, so much attention was paid to the thyroid doses resulting from intakes of ¹³¹I. Because cow's milk consumption was the main source of ¹³¹I intake by people, it was important to measure the ¹³¹I activity concentrations in cow's milk to calculate, or to validate, the thyroid doses to the exposed population. Almost 11,000 measurements of total beta-activity in cow's milk were performed using a DP-100 device during the first month after the Chernobyl accident in the most contaminated regions of Belarus. Using an ecological model and calibration coefficients for the DP-100 device the activity concentration of ¹³¹I in cow's milk was derived as well as the activity concentrations of the other radiologically important radionuclides, namely ¹³⁴Cs, ¹³⁷Cs, ⁸⁹Sr and ⁹⁰Sr. The activity concentrations of other radionuclides, such as ⁹⁰Y, ¹³²Te, ¹³²I, ¹³³I, ¹³⁶Cs, ¹⁴⁰Ba, ¹⁴⁰La, ¹⁴¹Ce and ¹⁴⁴Ce, in cow's milk were also estimated and were shown to be of minor importance. The concentrations of ⁹⁵Zr, ⁹⁵Nb, ¹⁰³Ru and ¹⁰⁶Ru in cow's milk were negligible. The data obtained in this study were validated by comparing derived ¹³¹I and ¹³⁷Cs concentrations in cow's milk with gamma-spectrometry measurements performed in milk produced in the same location close to the same date. The results of this study were essential to assess and validate the radiation doses received by the subjects of epidemiological studies related to the health consequences of the Chernobyl accident.

Biologically-based modeling of radiation risk and biomarker prevalence for papillary thyroid cancer in Japanese a-bomb survivors 1958-2005

PURPOSE

Thyroid cancer of papillary histology (PTC) is the dominant type in radio-epidemiological cohorts established after nuclear accidents or warfare. Studies on post-Chernobyl PTC and on thyroid cancer in the life span study (LSS) of Japanese a-bomb survivors consistently revealed high radiation risk after exposure during childhood and adolescence. For post-Chernobyl risk assessment overexpression of the CLIP2 gene was proposed as molecular biomarker to separate radiogenic from sporadic PTC. Based on such binary marker a biologically-based risk model of PTC carcinogenesis has been developed for observational Chernobyl data. The model featured two independent molecular pathways of disease development, of which one was associated with radiation exposure. To gain credibility the concept for a mechanistic risk model must be based on general biological features which transcend findings in a single cohort. The purpose of the present study is therefore to demonstrate portability of the model concept by application to PTC incidence data in the LSS. By exploiting the molecular two-path concept we improve the determination of the probability of radiation causing cancer (POC).

MATERIALS AND METHODS

The current analysis uses thyroid cancer incidence data of the LSS with thyroid cancer diagnoses and papillary histology (n = 292) from the follow-up period between 1958 and 2005. Risk analysis was performed with both descriptive and biologically-based models.

RESULTS

Judged by goodness-of-fit all applied models described the data almost equally well. They yielded similar risk estimates in cohorts post-Chernobyl and LSS. The preferred mechanistic model was selected by biological plausibility. It reflected important features of an imperfect radiation marker which are not easily addressed by descriptive models. Precise model predictions of marker prevalence in strata of epidemiological covariables can be tested by molecular measurements. Application of the radiation-related molecular pathway from our preferred model in retrospective risk assessment decreases the threshold dose for 50% POC from 0.33 (95% confidence interval (CI) 0.18; 0.64) Gy to 0.04 (95% CI 0.01; 0.19) Gy for females and from 0.43 (95% CI 0.17; 1.84) Gy to 0.19 (95% CI 0.05; 1.00) Gy for males. These improvements are still not sufficient to separate radiation-induced from sporadic PTC cases at very low doses <0.015 Gy typical for the Fukushima accident.

CONCLUSIONS

Successful application of our preferred mechanistic model to LSS incidence data confirms and improves the biological two-path concept of radiation-induced PTC. Model predictions suggest further molecular validation studies to consolidate the basis of biologically-based risk estimation.

Belarusian in utero cohort: A new opportunity to evaluate the health effects of prenatal and early-life exposure to ionising radiation

In April 1986, the Chernobyl nuclear accident resulted in wide-scale contamination of Belarus with significantly elevated levels of radioiodine isotopes, mainly iodine-131 (131I), and long-lived radiocaesium isotopes, mainly caesium-137 (137Cs). Various groups of the population were affected by exposure to ionising radiation, including pregnant women and their foetuses. This paper describes the methods and results related to the establishment of a cohort of 2965 Belarusian people exposed in utero due to Chernobyl fallout. The cohort consists of individuals whose mothers resided in the most radioactively contaminated areas in Belarus at the time of the accident. Prenatal and postnatal doses to the thyroid due to intake of 131I, external irradiation and ingestion of radiocaesium isotopes were estimated for all cohort members. Ongoing research on this unique cohort will provide important information on adverse health effects following prenatal and postnatal exposure to radioiodine and radiocaesium isotopes, for which available epidemiological data are scant.

The Effect of Inflammation on the Formation of Thyroid Nodules

BACKGROUND

Some studies have demonstrated that inflammation is highly associated with the prevalence of thyroid nodules (TNs). However, more confounders, such as metabolic diseases, should be adjusted.

METHODS

A clinical study collecting 2722 subjects was conducted to confirm the association between inflammation and TNs. The underlying mechanism was investigated in combination with bioinformatics analysis.

RESULTS

In the clinical study, propensity score matching was used to match metabolic parameters and other confounders, and it is observed that subjects with high inflammation had a higher prevalence of TNs and thyroid-stimulating hormone (TSH) than those with low inflammation. After further matching TNs, it is found that inflammation was positively associated with TSH, which was also demonstrated in a population without TNs. In bioinformatics study, inflammation did not promote TNs formation directly. Instead, it inhibited the synthesis of thyroid hormone, which might be the cause of the elevated TSH coexisting with inflammation.

CONCLUSION

Inflammation promotes the development of TNs disease, probably due to its indirect effect through inhibiting the synthesis of thyroid hormone, which results in the elevation of TSH.

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.

Association of radiation risk in the second and third generations with polymorphisms in the genes CYP1A1, CYP2E1, GSTP1 and changes in the thyroid

Background

To study the association of radiation risk in the 2nd –3rd generations with polymorphisms in the genes CYP1A1, CYP2E1, GSTP1 and changes in the thyroid.

Methods

5 polymorphic gene variants (rs1048943, rs4646421, rs2070676, rs3813867, rs1695) were studied in 399 people living in the East Kazakhstan region in this research. 248 people of the 2nd - 3rd generation lived in the territory with radiation exposure in Abai, Borodulikha areas, and 151 people the comparison group lived in Kurchum district without radiation exposure comparable in sex and age with control group.

Results

The results show that there is a significant association of rs1048943 in exposed and unexposed groups (p < 0.003), and the absence of association of rs4646421, rs2070676, rs3813867, rs1695 in the studied groups. The mean value of thyroxine in carriers of the AG + GG genotype of rs4646421 is significantly lower than in AA genotype carriers (p = 0.04); no significant changes were found in genotypes’ distribution with thyroid-stimulating hormone and anti-thyroid peroxidase indicators. Significant changes were in levels of anti-thyroid peroxidase between exposed and unexposed groups (p = 0.007). The thyroxine - thyroid-stimulating hormone levels were not significantly different in exposed and unexposed groups (p > 0.3).

Conclusions

This study demonstrated the association of rs1048943 polymorphism with living in the radiation zone in the 2nd and 3rd generations for the first time. Thyroxine levels decrease was identified in the 2nd and 3rd generation residents of the exposed area, as well as a significant increase of anti-thyroid peroxidase occurs in individuals of the 2nd and 3rd generation living in areas with radiation exposure.

Thyroid Cancer after Exposure to Radioiodine in Childhood and Adolescence: 131I-Related Risk and the Role of Selected Host and Environmental Factors

In this study, we expanded on a previously published population-based case-control study on subjects exposed to iodine-131 (131I) from Chernobyl fallout at age ≤18 years using improved individual 131I absorbed thyroid doses. We further studied the impact of iodine deficiency and other selected host risk factors on 131I-related thyroid cancer risk after childhood exposure. We included 298 thyroid cancer cases and 1934 matched controls from the most contaminated regions of Belarus and the Russian Federation. We performed statistical analysis using conditional logistic regression models. We found a statistically significant linear quadratic dose-effect association between thyroid cancer and 131I thyroid dose in the range up to 5 grays (Gy). Self-reported personal history of benign nodules, any thyroid disease except thyroid cancer, family history of thyroid cancer, increased body mass index, and deficient stable iodine status at the time of the accident were statistically significant risk factors (p < 0.05 for each factor) for thyroid cancer after adjustment for thyroid 131I dose effect. Subjects who received stable iodine supplementation in the years after the accident had a significantly lower 131I-related risk of thyroid cancer. Our findings are important for thyroid cancer prevention, and for further improvement of medical surveillance in the affected populations.

Radiation-Induced Thyroid Cancers: Overview of Molecular Signatures

Enormous amounts of childhood thyroid cancers, mostly childhood papillary thyroid carcinomas (PTCs), after the Chernobyl nuclear power plant accident have revealed a mutual relationship between the radiation exposure and thyroid cancer development. While the internal exposure to radioactive ¹³¹I is involved in the childhood thyroid cancers after the Chernobyl accident, people exposed to the external radiation, such as atomic-bomb (A-bomb) survivors, and the patients who received radiation therapy, have also been epidemiologically demonstrated to develop thyroid cancers. In order to elucidate the mechanisms of radiation-induced carcinogenesis, studies have aimed at defining the molecular changes associated with the thyroid cancer development. Here, we overview the literatures towards the identification of oncogenic alterations, particularly gene rearrangements, and discuss the existence of radiation signatures associated with radiation-induced thyroid cancers.

A model for estimating the total absorbed dose to the thyroid in Swedish inhabitants following the Chernobyl Nuclear Power Plant accident: implications for existing international estimates and future model applications

The time-integrated absorbed dose to the thyroid gland in the years after a fallout event can indicate the potential excess number of thyroid cancers among young individuals after a radionuclide release. Typical mean values of the absorbed dose to the thyroid have been calculated previously using reported data on radioiodine obtained from air sampling and dairy milk surveys in Sweden after the Chernobyl fallout, not including the contribution from ¹³⁴Cs and ¹³⁷Cs. We have developed a model for Swedish conditions taking these additional dose contributions into account. Our estimate of the average time-integrated absorbed dose to the thyroid, D _th,tot, during the first 5 years after fallout ranged from 0.5-4.1 mGy for infants and from 0.3-3.3 mGy for adults. The contribution to D _th,tot from ¹³¹I through inhalation and milk consumption varied considerably among different regions of Sweden, ranging from 9%-79% in infants, and from 4%-58% in adults. The external irradiation and exposure from the ingestion of ^134,137Cs in foodstuffs accounted for the remaining contributions to D _th,tot (i.e. up to 96% for adults). These large variations can be explained by the highly diverse conditions in the regions studied, such as different degrees of fractionation between wet and dry deposition, different grazing restrictions on dairy cattle, and differences in ^134,137Cs transfers through food resulting from differences in the local fallout. It is our conclusion that the main contribution to D _th,tot from nuclear power plant fallout in areas subjected to predominantly wet deposition will be from external exposure from ground deposition, followed by internal exposure from contaminated food containing the long-lived fission product ¹³⁷Cs and the neutron-activated fission product ¹³⁴Cs. The contribution from ^134,137Cs to the thyroid absorbed dose should thus be taken into account in future epidemiological studies.

Demographic and onco-epidemiological situation in radioactive contaminated territory of Zhytomyr Oblast

We performed an assessment of demographic parameters of occurrence of malignant tumours and mortality of the population which lives in the radioactive contaminated territory of Zhytomyr Oblast (Yemilchynskyi, Luhynskyi, Narodytskyi, Korostenskyi, Olevskyi, and Ovrutskyi districts) over a 32-year period (1985–2017). The source material for the study of the demographic situation and malignant tumours in the population of the radioactive contaminated administrative districts of Zhytomyr Oblast during 1985–2017 was the statistical data of the Management of Healthcare of Zhytomyr Oblast State Administration, Central Department of Statistics in Zhytomyr Oblasts, reports on occurrences of malignant tumours of the state institution Center of Medical Statistics of the Ministry of Healthcare of Ukraine, data of the Radiological Control Service in Zhytomyr Oblast. It was determined that over 1985–2017 in the radioactive contaminated territory of Zhytomyr Oblast, a natural decline of population was observed, maximum values of which occurred in 2005 (except Narodnytsky district – 2000). The highest levels of occurrence of tumours and mortality caused by them among the adult population were observed 14 years after the Chornobyl nuclear power plant disaster. The peak of the occurrence of malignant tumours among children in the radioactive contaminated territory of Zhytomyr Oblast was observed 9 years after the explosion. A relationship was determined between doses of irradiation of the population and the risk of occurrence of malignant tumours in the radioactive contaminated regions of Zhytomyr Oblast. Taking into account that the method of calculation of passport dose (average annual effective dose of irradiation) was developed 23 years ago, nowadays it can lead to errors. This is related to change in amounts of consumption of different products by the population, which needs to be considered when determining radiological risks. The obtained data indicate that analysis of demographic and onco-epidemiological consequences of the Chornobyl catastrophe remains a relevant issue nowadays and will remain so in the near future.

Histopathological analysis of papillary thyroid carcinoma detected during ultrasound screening examinations in Fukushima

Thyroid ultrasound screening of young residents in Fukushima Prefecture, Japan, showed a high detection rate of papillary thyroid carcinoma (PTC). Detailed morphological analysis of these tumors was not presented to date. This study sets out to evaluate changes in histopathological and invasive characteristics of Fukushima PTC with time after the nuclear accident of March 2011 in all available cases and in different age subgroups. Histological specimens of 115 PTCs from patients aged 18 years or younger at the time of the Fukushima Dai‐ichi Nuclear Power Plant accident, who underwent surgical resection at Fukushima Medical University during 2012‐2016, were reviewed. Patients were divided into those treated during the first 4 years after the accident (n = 78, shorter‐onset) or later (n = 37, longer‐onset). The whole group and 3 age subgroups: children (aged less than 15 years), adolescents (aged from 15 to less than 19 years), and young adults (aged from 19 years) at surgery were analyzed. No statistically significant time‐related changes in tumor structure or invasiveness were found in the whole group or in age‐matched subgroups. Statistically significant age‐related downtrend was observed for intrathyroid spread in the whole group of patients. The absence of temporal changes in tumor morphological characteristics and tumor invasiveness strongly suggests common etiology of the shorter‐ and longer‐onset Fukushima PTCs, which are unlikely related to the effect of exposure to very low doses of radiation.

Thyroid Cancer and Benign Nodules After Exposure In Utero to Fallout From Chernobyl

Background

Children and adolescents exposed to radioactive iodine-131 (I-131) in fallout from the 1986 Chernobyl nuclear accident appear to be at increased risk of thyroid cancer and benign thyroid nodules. The prenatal period is also considered radiosensitive, and the fetal thyroid can absorb I-131 from the maternal circulation.

Objectives

We aimed to estimate the risk of malignant and benign thyroid nodules in individuals exposed prenatally.

Methods

We studied a cohort of 2582 subjects in Ukraine with estimates of I-131 prenatal thyroid dose (mean = 72.6 mGy), who underwent two standardized thyroid screening examinations. To evaluate the dose-response relationship, we estimated the excess OR (EOR) using logistic regression.

Results

Based on a combined total of eight cases diagnosed at screenings from 2003 to 2006 and 2012 to 2015, we found a markedly elevated, albeit not statistically significant, dose-related risk of thyroid cancer (EOR/Gy = 3.91, 95% CI: -1.49, 65.66). At cycle 2 (n = 1,786), there was a strong and significant association between I-131 thyroid dose and screen-detected large benign nodules (≥10 mm) (EOR/Gy = 4.19, 95% CI: 0.68, 11.62; P = 0.009), but no significant increase in risk for small nodules (<10 mm) (EOR/Gy = 0.34, 95% CI: -0.67, 2.24; P = 0.604).

Conclusions

The dose effect by nodule size, with I-131 risk for large but not small nodules, is similar to that among exposed children and adolescents in Belarus. Based on a small number of cases, there is also a suggestive effect of I-131 dose on thyroid cancer risk.

THYROID DISEASES AMONG ATOMIC BOMB SURVIVORS

Systematic epidemiological studies of Hiroshima and Nagasaki atomic bomb survivors have made substantial contributions to the understanding of radiation effects on human health. A recent study of atomic bomb survivors reported that an increased risk of thyroid cancer associated with childhood exposure might have persisted for more than 50 years after exposure. In analyses of non-cancer thyroid diseases, several cross-sectional studies, including the latest study focusing on survivors exposed in childhood, suggested that the risk of thyroid nodules increased, while risks of thyroid dysfunction and autoimmunity were not apparent several decades after radiation exposure. However, careful interpretations are needed because only limited data from cross-sectional studies are available. Further longitudinal studies are necessary to improve our understanding of the effect of radiation on the thyroid and its function.

A nested case-control study of polychlorinated biphenyls, organochlorine pesticides, and thyroid cancer in the Janus Serum Bank cohort

BACKGROUND

Polychlorinated biphenyls (PCBs) and organochlorine pesticides have been associated with altered thyroid hormone levels in humans, but their relationship with thyroid cancer is unknown.

METHODS

We conducted a nested case-control study of thyroid cancer in the Norwegian Janus Serum Bank cohort using pre-diagnostic blood samples from 1972 to 1985. Incident thyroid cancer (n = 108) was ascertained through 2008. Controls were matched 2:1 by age, date of blood draw, gender, and county. We used gas chromatography/mass spectrometry to quantify 36 PCB congeners and metabolites of pesticides DDT, chlordane, hexachlorocyclohexane, and hexachlorobenzene. PCBs and pesticide metabolites were evaluated individually and summed by degree of chlorination and parent compound, respectively. Odds ratios (OR) and 95% confidence intervals (CI) were computed using conditional logistic regression per specified increase in lipid-adjusted concentration. We additionally stratified analyses by birth cohort (1923-1932, 1933-1942, 1943-1957).

RESULTS

Increasing concentration of DDT metabolites (OR_{per 1000 ng/g} = 0.80, 95%CI = 0.66-0.98) was inversely associated with thyroid cancer. Associations for PCBs were null or in inverse direction. We observed interactions for total PCBs, moderately-chlorinated PCBs, and chlordane metabolites with birth cohort (p ≤ 0.04). Among participants born 1943-1957, total PCBs (OR_{per 100 ng/g} = 1.25, 95%CI = 1.00-1.56), moderately-chlorinated PCBs (OR_{per 100 ng/g} = 1.31, 95%CI = 1.01-1.70), and chlordane metabolites (OR_{per 10 ng/g} = 1.78, 95%CI = 1.09-2.93) were positively associated with thyroid cancer. For individuals born before 1943, associations were generally null or in the inverse direction.

CONCLUSIONS

Emissions of PCBs and OC pesticides varied over time. Different risk patterns by birth cohort suggest the potential importance of timing of exposure in thyroid cancer risk. Further evaluation of these associations is warranted.

Epidemiology of Late Health Effects in Ukrainian Chornobyl Cleanup Workers

This article summarizes the results of 30 y of follow-up of cancer and noncancer effects in Ukrainian cleanup workers after the Chornobyl accident. The number of power plant employees and first responders with acute radiation syndrome under follow-up by the National Research Center for Radiation Medicine decreased from 179 in 1986-1991 to 105 in 2011-2015. Cancers and leukemia (19) and cardiovascular diseases (21) were the main causes of deaths among acute radiation syndrome survivors (54) during the postaccident period. Increased radiation risks of leukemia in the Ukrainian cohort of 110,645 cleanup workers exposed to low doses are comparable to those among survivors of the atomic bomb explosions in Japan in 1945. Additionally, an excess of chronic lymphocytic leukemia was demonstrated in the cleanup workers cohort for 26 y after the exposure. A significant excess of multiple myeloma incidence [standardized incidence rate (SIR) 1.61 %, 95% confidence interval (CI) 1.01-2.21], thyroid cancer (SIR 4.18, 95% CI 3.76-4.59), female breast cancer (SIR 1.57 CI 1.40-1.73), and all cancers combined (SIR 1.07; 95% CI 1.05-1.09) was registered. High prevalence was demonstrated for cardio- and cerebrovascular diseases and mental health changes. However, the reasons for the increases require further investigation. To monitor other possible late effects of radiation exposure in Chornobyl cleanup workers, analytical cohort and case-control studies need to include cardiovascular pathology, specifically types of potentially radiogenic cancers using a molecular epidemiology approach. Possible effects for further study include increased rates of thyroid, breast, and lung cancers and multiple myeloma; reduction of radiation risks of leukemia to population levels; and increased morbidity and mortality of cleanup workers from cardio- and cerebrovascular pathology.