Thyroid Dose Estimates for a Cohort of Belarusian Persons Exposed in Utero and During Early Life to Chernobyl Fallout

Recall of residential history and dietary habits during pregnancy and lactation in the distant past: reliability of questionnaire-based radiation doses for persons exposed in utero and early life

This study evaluates the reliability of information obtained by standardized questionnaires used in by personal interviews for estimation of radiation thyroid doses of 1065 individuals in the Belarusian cohort of individuals who were exposed in utero and early life following the Chernobyl accident in April 1986. Data from two interviews conducted in 2012-2017 and in 2018-2022 with mothers, who were pregnant or gave birth shortly after the Chernobyl accident, were analysed. The most reliable answers dealt with various attributes related to residential history. In contrast, the reliability of answers regarding consumption rates of milk from privately owned cows or trade network was moderate, while the agreement in responses for consumption of milk products and leafy vegetables was fair. Information from the two interviews was used to calculate thyroid doses received by the cohort members. Specifically, 'model-based' thyroid doses due to 131I were estimated using input data on individual residential history and food consumption reported during the personal interviews and ecological data (131I ground deposition in the corresponding settlements). In addition, for a subset of cohort subjects (n = 205) whose mothers were measured for 131I thyroid activity, 'measurement-based' thyroid doses were calculated by adjusting the model-based dose using a scaling factor that is defined as the ratio of measured 131I thyroid activity to model-based 131I thyroid activity calculated for the date of measurement. A moderate agreement was observed for total (prenatal and postnatal) model-based thyroid doses due to 131I intake, the arithmetic mean ± standard deviation for the Jaccard similarity coefficient ([Formula: see text]) was 0.45 ± 0.34 (median = 0.39), while measurement-based doses showed a much better agreement with a [Formula: see text] of 0.78 ± 0.29 (median = 0.93). For model-based thyroid doses from external irradiation and from ingestion of 134Cs and 137Cs, [Formula: see text] was 0.82 ± 0.23 (median = 0.90) and 0.84 ± 0.24 (median = 0.96), respectively. Measurement-based doses due to ingestion of radiocaesium isotopes resulted in an almost perfect agreement, [Formula: see text] was 0.91 ± 0.19 (median = 1.0). The present findings suggest that long-term memory recall can be reliable, if a person is asked about unique or important life events, such as pregnancy and childbirth occurring around the time of a nuclear reactor accident. However, the substantial difference (more than 10 times) observed for model-bases doses calculated using the two questionnaires represents an important source of human factor uncertainties that needs to be considered in any dose response analyses. Other lessons learned from this study are that (i) individual measurements of radionuclides in the human body are the most valuable source of information for estimating radiation doses, and (ii) whenever a radiation accident occurs, a sample of affected people should be asked to keep a diary, if at all possible.

Assessment of internal exposure to 131I and short-lived radioiodine isotopes and associated uncertainties in the Ukrainian cohort of persons exposed in utero

This study revised the thyroid doses for 2582 Ukrainian in utero cohort members exposed to Chornobyl fallout (the Ukrainian in utero cohort) based on revision of: (i) 131I thyroid activity measured in the Ukrainian population, (ii) thyroid dosimetry system for entire Ukraine, and (iii) 131I ground deposition densities in Ukraine. Other major improvements included: (i) assessment of uncertainties in the thyroid doses considering shared and unshared error, and (ii) accounting for intake of short-lived radioisotopes of tellurium and iodine (132Te+132I and 133I). Intake of 131I was the major pathway for thyroid exposure, its median contribution to the thyroid dose was 97.4%. The mean prenatal and postnatal thyroid dose from 131I was 87 mGy (median = 17 mGy), higher than previous deterministic dose of 72 mGy (median = 12 mGy). For 39 individuals (1.5%) the dose exceeded 1.0 Gy, while the highest dose among the cohort members was 2.7 Gy. The geometric standard deviation (GSD) of 1000 individual stochastic doses varied from 1.9 to 5.2 with a mean of 3.1 and a median of 3.2. The lowest uncertainty (mean GSD = 2.3, median GSD = 2.2) was found for the subjects whose mothers were measured for 131I thyroid activity, while for individuals, whose mothers were not measured, the mean and median GSDs were 3.4. Uncertainties in thyroid doses were driven by shared errors associated with the parameters of the ecological model.

THYROID SCREENING AND RELIABILITY OF RADIATION THYROID DOSES FOR THE BELARUSIAN IN UTERO COHORT

OBJECTIVE

To describe the status and results of thyroid disease screening and assessment of reliability of radiationthyroid doses in the Belarusian in utero cohort of 2,965 individuals exposed to Chernobyl (Chornobyl) fallout.

MATERIALS AND METHODS

Thyroid screening examinations are currently underway including thyroid palpation by anendocrinologist, ultrasonographic examination by an ultrasonographer and analysis of blood samples for diagnosisof hypo- and hyperthyroidism, autoimmune thyroiditis, thyroid function tests (thyroid-stimulating hormone [TSH],thyroxine [T4], thyroid peroxidase antibody [anti-TPO], and thyroglobulin antibodies [anti-TG]). Reliability of (i)information from 780 pairs of questionnaires obtained during the first and second interviews of the mothers and (ii)thyroid doses, which were calculated for the cohort members using this information, is evaluated.

RESULTS

As of 15 August 2021, 1,267 in utero exposed study subjects had been screened. A single thyroid nodule wasdiagnosed in 167 persons (13.2 % of the total) and multiple thyroid nodules in 101 persons (8.0 %): 189 (14.9 %)persons had nodules detected for the first time at the screening while 79 (6.2 %) persons had nodules detected pre-viously (pre-screening nodules). Fifty-nine out of 268 subjects (22.0 %) with a suspicious thyroid nodule werereferred to fine needle aspiration biopsy, and among them 33 (55.9 %) were biopsied. Reasonable agreement wasobserved for modelqbased doses calculated for the Belarusian in utero cohort members using data from the two inter-views (Spearman's rank-correlation coefficient rs = 0.74, p < 0.001), while measurementqbased doses yielded almost per-fect agreement (rs = 0.99, p < 0.001).

CONCLUSIONS

During the thyroid screening, at least one thyroid nodule was identified in 268 of 1,267 (21.2 %) inutero exposed cohort members. Seven thyroid cancer cases were identified in the cohort, including 5 pre-screeningcases and 2 cases detected during the screening. Ongoing research on this unique cohort will provide importantinformation on adverse health effects following prenatal and postnatal exposure to radioiodine and radiocesium iso-topes, for which available epidemiological data are scant.

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.

Ground deposition of radionuclides in French Polynesia resulting from atmospheric nuclear weapons tests at Mururoa and Fangataufa atolls

This paper presents the results of the first comprehensive estimation of the ground deposition density of radionuclides in French Polynesia resulting from the 41 atmospheric nuclear weapons tests that were conducted between 1966 and 1974 at Mururoa and Fangataufa. For each test, the deposition density at the time of arrival of fallout was estimated for 33 radionuclides either from measurements of total ground deposition or from measurements of total beta-concentration in filtered air and exposure rate at different locations in French Polynesia. The results of the measurements were mainly taken from reports that were recently de-classified by the French Ministry of Defense. The highest total deposition densities in inhabited islands and atolls occurred in Gambier: 6.1 × 10⁷ Bq m^-2 after test Aldébaran conducted on 2 July 1966 and 9.2 × 10⁶ Bq m^-2 after test Phoebé conducted on 8 August 1971. Next was Tureia with deposition densities of 1.6 × 10⁷ Bq m^-2 after test Arcturus of 2 July 1967 and 1.2 × 10⁷ Bq m^-2 after test Encelade of 12 June 1971. In Tahiti, the most populated island in French Polynesia, major fallout occurred after tests Centaure of 17 July 1974 (3.4 × 10⁶ Bq m^-2), Sirius of 4 October 1966 (4.4 × 10⁵ Bq m^-2) and Arcturus of 2 July 1967 (1.1 × 10⁵ Bq m^-2); these three tests contributed about 94% to the total deposition density of radioactive fallout in Tahiti from all 41 tests and around 85% of the ¹³¹I deposition density. The results of this study are being used to reconstruct the radiation dose to the thyroid gland for the 950 subjects of a case-control study of thyroid cancer among French Polynesians exposed as children and adolescents to fallout from the atmospheric nuclear weapons tests conducted in 1966-1974.

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.

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.