PNNL

Abstract

The objective of this study is to evaluate the uncertainties of the dosimetric modeling of active marrow exposure from bone-seeking 89,90Sr. The stochastic parametric skeletal dosimetry (SPSD) model was specifically developed to study the long-term effects of active marrow (AM) chronic exposure to 89,90Sr in the population of radioactively contaminated territories of the Ural region. The method allows evaluating the dose factors (DF(AM ? TBV) and DF(AM ? CBV)), which convert the radionuclide activity concentration in trabecular (TBV) and cortical (CBV) bone volumes into dose rate in the active marrow (AM), and their uncertainties. The sources of uncertainty can be subdivided into inherent uncertainties related to the individual variability of the simulated objects and introduced uncertainties related to model simplifications. Inherent uncertainty components are the individual variability of bone chemical composition, bone density, bone micro- and macro- architecture as well as AM distribution within the skeleton. The introduced uncertainties may result from the stylization of bone segment geometry, assumption of uniform cortical thickness, restriction of bone geometry and the selection of the applied voxel resolution. The inherent uncertainty depends on a number of factors of influence. First and foremost, it is the result of variability of AM distribution within the skeleton. Another important factor is the variability of bone micro- and macro- architecture. The inherent uncertainty of skeleton-average dose factors was found to be about 40-50%. The introduced uncertaintyassociated with the SPSD model approach does not exceed 16% and mainly depends on the error of bone-shape stylization. The overall inherent and introduced uncertainties of DF(AM ? TBV) and DF(AM ? CBV) are below 55% and 63%, respectively. The results obtained will be incorporated into the stochastic version of the Techa River Dosimetry System (TRDS-2016MC) that provides multiple realizations of the annual doses for each cohort member to obtain both a central estimate of the individual dose and information on the dose uncertainty.