Forecast of Radiation Risks of Thyroid Cancer among the Population of Areas of the Bryansk Region Contaminated as a Result of the Accident at the Chernobyl Nuclear Power Plant, allowing for Uncertainties in Risk Model Estimates

Purpose: Forecasting the lifetime attributable radiation risk of incidence with malignant neoplasm (MN) of the thyroid gland and identifying groups of increased radiation risk (HR) for the population of the Bryansk region currently (at the beginning of 2023) living in six areas most contaminated with radionuclides after the accident at Chernobyl NPP, based on a conservative approach, taking into account dose uncertainty factors and parameters of mathematical risk models. Material and methods: The mathematical model of the radiation risk of thyroid cancer is the model recommended by the International Commission on Radiological Protection (ICRP). The uncertainty assessment of radiation risks was carried out by simulation modeling, i.e. by multiple calculation of random realizations of the risk using the normal or log-normal distribution of all parameters involved in the calculation of this risk. Based on a set of random realizations, 95 % confidence limits of risks were estimated. The Unified Federal Database of the National Radiation and Epidemiological Register (NRER) containing reconstructed absorbed doses in the thyroid gland in the population was used as the initial data for the calculation. Results: At the beginning of 2023, the group of 37–40-year-old women is characterized by the maximum radiation risks of thyroid cancer. According to conservative estimates (according to the upper 95 % confidence limits of radiation risk assessments), up to 19.9 % of people from this group may experience the development of radiation-induced thyroid cancer in the future, and for 37-year-old women this proportion can be up to 30.0 %. The greatest risk is predicted for people living in the Krasnogorsk district of the Bryansk region. Radiation-induced thyroid cancer can develop in 40.1 % of individuals from this group. Radiation risks of thyroid cancer in men are up to 10 times lower than in women. For 74.5 % of the population of the entire studied cohort, it is predicted that the maximum individual risk of 5.0×10-5, established by NRB-99/2009 for the population under normal operation of ionizing radiation sources, will be exceeded. Conclusions: At present (since 2023 and for life), the population of the most polluted districts of the Bryansk region continues to be at a high risk of developing radiation-induced thyroid cancers. Women at the age of 0–3 years at the time of exposure (in 1986) should be allocated to the maximum risk group. The results of this work can be used in the preparation of recommendations by health authorities to improve medical monitoring of exposed citizens.