Age- and sex- specific dose coefficients to convert the ingested 90 Sr activity into cumulative dose in active marrow
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Evaluation of active marrow (AM) dose and associated uncertainty from ingested bone-seeking 90 Sr isotopes, which may chronically irradiate the AM during the lifetime after intake, is of utmost importance. The aim of the study is to evaluate dose coefficients used to convert radionuclide intakes into dose to AM, which depend on sex, age at intake and time after intake. For this purpose, three tasks were solved. The first, dosimetric modeling was performed to obtain dose factors that convert 90 Sr activity concentration in cortical and trabecular bones into the respective dose rates in AM. The second task combined the dosimetric and biokinetic models to obtain age and sex specific dose coefficients. The third task evaluated dose coefficients uncertainties. Materials and Methods . The first task was solved using the stochastic parametric skeleton dosimetry approach for generation of computational phantoms as well as Monte Carlo simulation of radiation transport. The second task was done assuming a single intake at birth, 1-year, 5- year, 10- year, 13-year, 15 and 24 (adults) years old using the original biokinetic model. Uncertainties were evaluated using Monte Carlo modeling. Results . Skeleton-average dose factors for 90 Sr in trabecular bone vary in the range of 5.45×10 -11 – 3.93 ×10 -11 (Gy s -1 ) per (Bq g -1 ). Skeleton-average dose factors for 90 Sr in cortical bone vary in the range of 2.39×10 -11 – 1.03 ×10 -11 (Gy s -1 ) per (Bq g -1 ). The dose coefficients ( DCs ) may differ by up to 46 times depending on the age at the time of intake and sex (50 years of dose accumulation leads to 2×10 -7 Gy Bq -1 for an adult male to 92 ×10 -7 Gy Bq -1 for a newborn). The relative uncertainty for DC s are as follows: 50% for intake at age < 10 years old independent of sex; 45% for intake at age equal to 10 years independent of sex and 13 years old male; 40% for female of 13 years old as well as 15 years old and adults independent of sex. Conclusion. The obtained results are suitable for estimation of bone marrow dose accumulated more than 2 months after ingestions. The implication of age and sex specific DCs is significant to avoid underestimation of both AM dose reconstruction and prediction. In terms of dose reconstruction, the obtained results improved the accuracy of estimations of radiation risks in epidemiological studies of Urals population that resided on the contaminated territories.
