Assessment and forecasting of the radiation risk of thyroid cancer and other radiation-induced diseases among the population of the territories contaminated as a result of the Chernobyl accident

As a result of the accident at the Chernobyl nuclear power plant on April 26, 1986, part of the territory of the Russian Federation was contaminated with radionuclides. In the first months after the accident, iodine radioisotopes generated doses of internal radiation to the thyroid of the population, which averaged about 0.1 Gy, but reached 4.5 Gy among children under 5 years of age. The total body radiation doses accumulated by residents of areas contaminated with cesium radioisotopes averaged 0.03 Sv, and for 98% of the population did not exceed 0.2 Sv. The assessment of radiation risks of the population of contaminated territories is of high scientific relevance due to the significant share of internal exposure in the formation of radiation doses and great practical importance due to the large number of this population. This work is an update of the radiation risk assessments of the population of the four most contaminated regions of Russia (Bryansk, Kaluga, Orel and Tula oblasts), conducted by the National Radiation Epidemiological Registry until 2019. Among the 311 thousand residents the average thyroid dose in children and adolescents was 0.171 Gy and 0.038 Gy in adults. During the followup period from 1991 to 2024, 1,790 cases of thyroid cancer were detected in the cohort: 542 cases among children and adolescents under the age of 18 at the date of the accident and 1,248 among adults. For the age of 20, the statistically significant coefficient of excess relative risk is ERR/Gr=4.49 and decreases with increasing age. As of the date of the accident, 43.4% of cases of thyroid cancer were radiationinduced among children and adolescents, and 59% of cases of thyroid cancer were radiationinduced for children under 5 years of age. The screening rate during the registration of thyroid cancer diseases was 5.8 for children and adolescents and 3.0 for adults. Statistically significant radiation risks for solid malignant neoplasms, including breast cancer in women, as well as for leukemia among the adult population of the most radionuclidecontaminated areas have not yet been identified. Further observations of a cohort of people living or who have lived in radionuclidecontaminated territories of the Russian Federation will increase the statistical power of radiation and epidemiological studies and clarify estimates of human radiation risks with prolonged exposure in low doses.