Methodological approach to development of dosimetric models of the human skeleton for beta-emitting radionuclides

Abstract

Objective of the study : to develop a skeleton model for assessing red bone marrow dose from osteotropic beta-emitting radionuclides. This article describes the modeling methodology which takes into account the individual variability of the macro- and microstructure of bone tissue. Materials and methods: it is proposed to model bone sites with active hematopoiesis by dividing them into small segments described by simple geometric shapes. Spongiosa, which fills the segments, is modeled as an isotropic three-dimensional grid (carcass) of rod-like trabeculae that “run through” the bone marrow. In the process of randomization, multiple carcass deformations are simulated by changing the positions of the grid nodes and the thickness of the rods. Model grid parameters are selected in accordance with the parameters of spongiosa microstructures taken from the published papers. Stochastic modeling of radiation transport in heterogeneous environments simulating distribution of bone tissue and marrow in each of the segments is performed by Monte Carlo method. The model output for the lumbar vertebra is given as an example. The generated vertebral model allowed us to obtain the dosimetric characteristics of bone marrow irradiation, which are comparable to the results obtained with ICRP model developed based on the data of micro-images of bone structures. For the first time ever confidence intervals of dosimetric characteristics associated with individual variability of bone structure were evaluated. The developed methodology for the calculation of doses absorbed in the bone marrow from osteotropic radionuclides does not require additional studies of autopsy material. The obtained results will be used to calculate individual doses in a cohort of Techa riverside residents who were exposed due to Techa River contamination as a result of liquid radioactive waste discharges by the Mayak Production Association.