Influence of Dose Rate on Mortality from Coronary Heart Disease in the Mayak Employee Cohort

Purpose: The study aimed to evaluate the impact of radiation dose rate on the mortality from ischemic heart disease (IHD) in a cohort of workers chronically exposed to ionizing radiation. Material and methods: The study considered the subcohort of the Mayak Production Association (PA) workers (WSC) who were hired between 1948 and 1982 and were living in the city of Ozyorsk (residents). The WSC included 13,156 individuals who were followed up until December 31, 2018 (13,156 individuals). To assess the impact of dose rate on the mortality from IHD, the dose window method was applied. In the first phase of the study, we analyzed the dose-response relationship using the excess relative risk (ERR) per unit dose of external radiation exposure (in Gy) based on the conventional linear model. Subsequently, we performed the analysis considering the radiation dose rate by utilizing annual doses recorded with individual film badge dosimeters. We defined the dose rate cut-off points from 5 to 50 mGy/year, with intervals of 5 mGy. To compare the conventional model with the dose-rate models, the maximum likelihood technique was used. All the calculations were carried out using the AMFIT module of the EPICURE software. Results: We found the significantly increased IHD mortality risk in workers exposed at dose rates >0.015 Gy/year, >0.020 Gy/year, >0.025 Gy/year, >0.030 Gy/year, >0.035 Gy/year, >0.040 Gy/year, >0.045 Gy/year, >0.050 Gy/year compared to dose rates below these cut-off points. The uninterrupted radiation exposure at dose rate above a cut-off point during 5 consecutive years considerably increased the IHD mortality risk. Exclusion of the adjustment for alpha dose from the model resulted in the decrease of the ERR/Gy at higher dose rate and to the loss of the statistical significance for certain cut-off points (0.045 and 0.050 Gy). On the contrary, the exclusion of this adjustment resulted in the increase in risk estimates at lower dose rates for all cut-off points without any changes in the statistical significance of the estimates. Conclusions: The study results indicate that the excess relative risks of the IHD mortality per unit dose of external radiation exposure in nuclear workers chronically exposed to ionizing radiation depended on the dose rate and the duration of the uninterrupted exposure at higher dose rates.