Assessment of Radiation Risks of Mortality from Circulatory System Diseases in the Cohort of Liquidators of the Consequences of the Accident at the Chernobyl Nuclear Power Plant, Considering the Influence of Other Diseases Identified During the Obser

Purpose: To assess the radiation risk of mortality from circulatory system diseases (CSD) in the cohort of liquidators of the consequences of the Chernobyl accident, considering the impact of other diseases detected in them during the observation period. Material and methods: Radiation risks of mortality from CSD were studied in the cohort of liquidators of the consequences of the Chernobyl accident observed in the National Radiation and Epidemiological Register (NRER) system from 1986 to 2022. The studied deaths are included in the codes I00–I99 of the International Statistical Classification of Diseases of the 10th Revision (ICD-10). Among the 89,594 members of the studied cohort, 16,780 deaths from CSD were identified. Mean age at the beginning of exposure was 34 years, the average absorbed dose of external gamma exposure of the whole body was 0.133 Gy, the maximum dose was 1.5 Gy, the average duration of exposure was 2.6 months. To analyze the dependence of the radiation risk of mortality from CSD on the presence of other diseases in them, regression models of excess relative risk (ERR) and nonparametric relative risk (RR) estimates in dose groups were used. Results: The average estimate of the excess relative risk ratio ERR/Gy=0.53 for the entire cohort, which is quantitatively comparable to the previously obtained estimate of ERR/Gy=0.74 for mortality from solid malignancies in the same cohort. The assessment of the radiation risk of mortality from CSD in the cohort of liquidators of the consequences of the Chernobyl accident depends on the presence of diseases from other categories identified in them during the observation period. Diseases of respiratory (J00-J99) and digestive organs (K00–K93) are radiation-competing risk factors for death from CSD. The risk group for radiation-related mortality from CSD with an estimate of ERR/Gy=1.22 consists of relatively healthy liquidators without respiratory and digestive diseases. Nonparametric estimates of relative radiation risk (RR) confirm the correctness of the linear non-threshold model of radiation risk of mortality of liquidators from CSD, regardless of the degree of multimorbidity of their health status. Conclusions: The practical dose thresholds for mortality of liquidators from CSD depend on their health status and are in the range of 0.01–0.21 Gy, which is significantly less than the currently accepted ICRP level of 0.5 Gy. The determination of such thresholds does not mean that there is no effect of radiation at doses below the threshold doses. Further accumulation of radiation and epidemiological data in the NRER system will allow for the analysis of radiation risks considering multimorbidity, more detailed by diagnosis.