Solid cancer mortality risk in the cohort of Urals population exposed to radiation for up the age of 20

The objective of the current study is the direct assessment of the excess relative risk of solid cancer mortality in people affected by low dose-rate chronic exposure mainly in low-to medium dose range (up to 1 Gy) at the age of <20. The study cohort consists of the population exposed at the age of <20 as a result of two large radiation accidents at the “Mayak” Production Association. The size of the cohort is 32,762 persons, follow-up period – 71 years (from 1950 through 2020), the number of person-years at risk is – 1 218 855. For this cohort the mortality catchment area includes Chelyabinsk and Kurgan Oblasts. Over a 71-year follow-up period 1,788 solid cancer deaths were registered in the cohort. Mean dose accumulated in the stomach walls over the whole follow-up period was 0.04 Gy, maximum dose was 1.1 Gy. Statistical processing of data was performed using Amfit and Datab software packages (Epicure statistics software package). Solid cancer mortality risk was analyzed with the Poisson regression using simple parametric excess relative risk model. Statistical significance of the results was estimated using the maximum likelihood method with 95% probability. For the first time the direct assessments of the excess relative risk of solid cancer mortality have been obtained in the Urals Cohort of population exposed at age <20 for a 71-year period (Excess Relative Risk was 0.84/Gy, 95% confidence interval: 0.24-1.55 for 10-years minimal latency period and 0.83 (0.24-1.55) for 5-year minimal latency period). Statistically significant estimates of the excess relative risk have been obtained for specific groups within the cohort selected according to the sex, age at the onset of exposure, and Oblast of residence at the time of exposure.