Thyroid doses for the Chornobyl Tissue Bank: improved estimates based on revised methodology and individual residence and diet history

Increased thyroid cancer incidence has been one of the principal adverse health effects of the Chornobyl (Chernobyl) nuclear power plant accident. Accurate dose estimation is critical for assessing the radiation dose-response relationship. Current dosimetry estimates for individuals from the Chornobyl Tissue Bank (CTB) are based only on the limited information on their places of residence at the time of the accident and/or at the time of surgery for thyroid cancer. The present study aimed to assess whether additional residential and dietary history data collected during personal interviews would substantially impact dose estimates. This paper presents an assessment of thyroid doses from ¹³¹I intake for the 197 exposed individuals from the CTB with pathologically confirmed papillary thyroid cancer. Thyroid doses, which had been calculated for these individuals in 2010, were revised in this study using the recently substantially revised 'Thyroid Dosimetry 2020 system for Ukraine' (TDU20). In addition, residence and diet history data were collected during personal interviews with individuals for whom dosimetry-related data were scarce. The arithmetic mean of thyroid doses estimated in this study was 510 mGy (previously 700 mGy), while the median was 81 mGy (previously 120 mGy). A rather wide range of thyroid doses from zero to 11.9 Gy (previously up to 15.0 Gy) was observed among study participants. The uncertainties in doses were characterized by the geometric standard deviation of 1,000 individual stochastic doses. As a result, the geometric standard deviation varied from 1.3 to 5.3 with an overall arithmetic mean of 2.7 and a median of 2.9. This study clearly showed that the use of individual questionnaire data in dose assessment of individuals who completed personal dosimetry interviews had a noticeable impact on the thyroid dose values: the thyroid doses changed by more than 100 mGy in 31 out of 104 (29.8% of the total) individuals, while such changes due to the use of TDU20 were observed in 18 out of 104 (17.3%) individuals. Clearly, future focused studies using samples from the CTB would benefit from personal interviews to improve dose estimates. Another lesson learned from this study is that whenever a radiation accident occurs, it is important to ask affected people by health and radiation safety authorities to keep records of their own behavior and diet, and, if possible, those of their children.