Оценка риска и дозовых порогов при плутониевом пневмосклерозе

Abstract

Purpose: To assess risks curves, dose thresholds, and their uncertainties for plutonium-induced pneumosclerosis (PPS) among Mayak PA workers based on developed methods of mathematical modeling. Material and methods: PPS risk modeling with further calculation of dose thresholds and their uncertainties was performed using a comparative analysis of estimates of individual absorbed lung doses from incorporated plutonium-239 provided by two Mayak Worker Dosimetry Systems: MWDS-2008 and MWDS-2013. To carry out the calculations, four groups of workers were formed: workers with PPS induced only by plutonium (pure PPS; n = 107); workers with PPS induced by both plutonium and other factors (mixed PPS; n = 46); workers with undefined PPS (n = 153); control workers (comparison group; n = 188). Weibull’s dose distribution model was applied to assess risk curves. Dose distribution parameters were calculated using the least square technique. Dose thresholds were estimated using two basic methods: quantile threshold method and estimation based on dose distribution functions for each group with PPs and the comparison group. Common uncertainties were calculated using two methods: Monte-Carlo method and error propagation. Results: Risk curves were plotted based on Weibull’s models for three groups of workers diagnosed with PPS. Modeling results were statistically significant (R2 = 0.96 – 0.99) with both dosimetry systems used (MWDS-2008 and MWDS-2013). Median absorbed lung alpha-dose (D50) estimated using Weibull’s model varied significantly with the dosimetry system. E.g., in the group with pure PPS D50= 0.79 Gy when MWDS-2008 was used while the corresponding estimate was D50= 2.05 Gy when MWDS-2013 was used, demonstrating more than a two-fold difference between the estimates. Dose thresholds for PPS occurrence and their standard uncertainties were estimated. With MWDS-2013 used, the dose thresholds were D0= 0,63 Gy for the lung and D0= 1.0 Gy for alveolar-interstitial lung tissues, respectively. The mean relative uncertainty of these thresholds was U = 23 %. Quantile dose thresholds were an order of magnitude lower than those above and their standard uncertainty, on the contrary, was 23 % higher: the mean uncertainty of 5 % quantile was U = 60 % while the corresponding value for 1 % quantile was U = 95 %. Conclusions: For the first time dose thresholds and their uncertainties for the formation of PPS with internal alpha irradiation were estimated. The reported results are of considerable interest both for scientific and practical application in radiation safety and medicine.