Nonparametric estimation of loss life expectancy of the Russian participants in clean-up operations following the Chernobyl accident

This article describes the study of probable effects of ionizing radiation on changes in life expectancy of the Russian participants in clean-up operations following the Chernobyl accident (liquidators). For the study the data on mortality among the liquidators registered at the National Radiation Epidemiological Registry were used. The follow-up study was started in 1992, at that time the study cohort consisted 66,615 males, their average age was 38.5 years, they resided in the entire territory of Russia. The liquidators were exposed to ionizing radiation during their clean-up work inside the Chernobyl exclusion zone in 1986 through 1987, the years of the largest radiation hazard and the most intensive clean-up operations, average radiation dose in the cohort was 132 mGy. The cohort was followed for 27 years. During this period 26 720 death cases with established cause of death were registered. Changes in the lifetime expectancy of the followed clean-up workers were estimated with the methods for non-parametric survival analysis. Average survival time in various dose groups was estimated with data on aggregated and specific causes of death. From analysis it became clear that to measure effects of radiation on changes in the lifetime expectancy it is necessary to assess the contribution of each of the main causes of death, even if a cause is not associated with radiation. The loss life expectancy caused by solid cancer was found in clean-up workers with doses ≥ 150 mGy. For 27-years of the follow-up study the life expectancy was reduced by 0.3 years per unit dose. If the follow-up study of effects of ionizing radiation on the loss life expectancy of the Chernobyl liquidators is continued, the loss life expectancy is probable to be pronounced.