Abstract
Purpose: The paper deals with the occurrence of prostate cancer and mean survival time following a diagnosis of the disease among Chernobyl clean-up workers. Material and methods: Clinical and dosimetry data accumulated at the National Radiation and Epidemiological Registry (NRER) during the period from 1996 over 2018 were used for the study. The study cohort consisted of 69,698 men. During the follow-up 742 prostate cancer cases were detected, all patients had radiation dose records, the disease stage was established in 628 patients. To assess radiation risk maximum likelihood approach was used. Mean survival time was evaluated with the use of the relationship between a disease prevalence and newly detected disease cases intensity in a stationary population (diseases intensity is equal to intensity of mortality from all causes). Results: Excess relative risk of prostate cancer induction per 1 Gy was 0.74 (95 % CI: ‒0.31; 2.15) and it was statistically insignificant. Standardized incidence ratios between clean-up workers and male population of Russia within 95 % confidence limits do not differ from 1.0. Mean survival time after the disease diagnosis within the period from 1996 over 2018 was 3.5±1.3 years. The relationship between a survival time and a disease stage was estimated. Survival time for cases with 1–3 stages 3.3±2.9, 3.6±2.3, 4.3±2.7 years respectively. The less survival time for cases with stage 4 was 1.5±0.8 years. Mean mortality rate, i.e. the ratio of the number of clean-up workers died from prostate cancer to the total number of clean-up workers with diagnosed prostate cancer was 36.8 %, for stages 1–4 it was 20, 16, 37, 74 % respectively. Mean survival time in the groups with doses less than and higher than 150 mGy was 3.4±1.4 and 3.7±1.7, respectively. Presented data confirm the null hypothesis that there is no difference in survival times (p=0.20). Conclusion: Increase in prostate cancer incidence becomes the social problem not only in Russia but in other countries as well. The paper presents results of comprehensive radiation epidemiological analysis of prostate cancer incidence in cleanup workers, who constitute the representative sample of the Russian male population. The dose ‒ prostate cancer incidence relationship for the follow-up period from 1996 over 2018 is not statistically significant, although the value of excess relative risk per dose unit is positive. It is not unthinkable that the absence of statistical significance is caused due to limited length of the follow-up period. But at the same time, the fact that observed the standardized incidence ratio is 1.0 and characteristics of two groups with doses ≥150 mGy are similar, speaks of the lack of a significant radiation effect. The obtained results of the analysis confirm our view of the necessity to continue the study.
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