Assessment of radiation risks of malignant neoplasms among the population of Russian regions contaminated with radionuclides as a result of the Chernobyl accident

Some areas of the Russian Federation were contaminated with radionuclides released as a result of the Chernobyl accident. The current paper clarifies some items of the previously published study based on NRER (National Radiation-Epidemiological Registry, the Registry) data. The previous issue presented estimates of radiation risks of cancer incidence among the population of four the most contaminated regions of the Russian Federation: Bryansk, Kaluga, Oryol and Tula oblasts. Risks of thyroid cancer are estimated with account of screening effect. The cohort consisted of more than 327 thousand people resided in the contaminated areas. The average dose to the thyroid of children and adolescents was 0.174 Gy, the average dose to the thyroid of adults was 0.035 Gy. Thyroid cancer was diagnosed in 1549 members of the cohort during the follow-up period from 1991 over 2019, among them 423 cases were children and adolescents at the accident and 1126 cases were adults. Significant increase in thyroid cancer incidence was observed in adults exposed internally through the intake of iodine-131 at a young age. The statistically significant radiation risk of thyroid cancer persists over 30 years after exposure. The risk decreases with increasing the attained age. In people exposed to radiation before the age of 1 year and reaching the age of 20 years, the coefficient of excess relative risk of thyroid cancer (ERR/Gy) was 4.61. Radiation associated thyroid cancer is attributed to 20.6% of the cohort members exposed internally through the intake of radioiodine isotopes in their childhood and adolescence, and thyroid cancer from intake of radioiodine is attributed to 58% of cases exposed to radiation under 4 years of age. Marked screening effect (ES) was found during the disease diagnosing, screening coefficient was 5.6 for children and 2.1 for adults. There were not attributed to radiation statistically significant risks of solid cancers, including radiation induced breast cancer in females, in the cohort of people resided in the areas contaminated with radionuclides. Radiation risk of leukemia was also not identified, although the average value of excess relative risk in men exceeded zero. Further observations of the cohort of persons resided in areas contaminated with radionuclides will increase the statistical power of radiation-epidemiological studies and clarify the assessment of radiation risks of human for chronic exposure at low doses.