The influence of dose uncertainty on the assessment of radiation risks of non-cancer mortality among Russian participants in the liquidation of the consequences of the accident at the Chernobyl Nuclear Power Plant

Currently, the system of standards and rules of radiation protection considers the need to constraint the absorbed radiation doses in order to prevent the development of deterministic effects of ionizing radiation on humans. Deterministic effects in terms of mortality include bone marrow syndrome with a dose threshold of 1 Gy, gastrointestinal syndrome and pneumonitis with dose thresholds of 6 Gy. For inclusion in international radiation safety standards, a threshold of 0.5 Gy for cardiovascular and cerebrovascular diseases is being discussed. The wide experience of radiation-epidemiological studies shows that the deterministic effects of mortality are not limited to those effects that are currently considered in the system of standards and rules of radiation protection. This paper presents estimates of radiation risks of mortality from diseases of the circulatory system (CSD) and the digestive system, as well as dose thresholds corresponding to these effects, in the Russian cohort of liquidators of the Chernobyl accident registered in the National Radiation and Epidemiological Register (NRER), who have registered doses from external whole-body exposure to gamma radiation within 1 Gy. The risks were estimated over the follow-up period 1986-2020. The stability of estimated radiation risks of mortality from CSD and from the digestive system diseases in relation to the uncertainty of personal doses received by liquidators has been studied. The absorbed doses received by 11% of the liquidators were estimated from the data of personal dosimeters, the maximum error was about 50%. For the remaining 89% of liquidators, group and route doses were registered, and the maximum uncertainty of individual doses was about 500%. For CSD mortality, the excess relative rates per 1 Gy (ERR/Gy) were 0.361 and 0.349, excluding and considering dose uncertainties, respectively. For mortality from diseases of the digestive system, ERR/Gy=0,791 excluding dose uncertainty and ERR/Gy=0,726 with considering dose uncertainty. Uncertainties in individual dose estimates result in 5% and 8% reductions in ERR/Gy estimates (for CSD mortality and digestive disease, respectively). This reduction in risk estimates is not related to a bias in the dose estimates. It is caused by the statistical properties of radiation risk models in conventional radiation epidemiology. If the excessive mortality from the studied causes is attributed to deterministic effects, then the estimates of the corresponding dose thresholds, considering the uncertainty of individual doses, also increase quite slightly: for CSD - from 0,028 Gy to 0,029 Gy, and for diseases of the digestive system - from 0,013 Gy to 0,014 Gy. The obtained results confirm the high stability and validity of radiation risk assessments of non-oncological diseases obtained earlier from the doses of Russian participants in the liquidation of the consequences of the Chernobyl accident registered in the unified federal database of the NRER.