Evaluating the effects of statistical changes on internal dosimetry

Currently, internal dosimetry evaluations are performed using reference computational phantoms. There are significant discrepancies in the organ absorbed doses regarding the variations in organ mass. In this study, to investigate the effects of changes in the lung mass on the results of internal dosimetry, 98 similar mathematical phantoms were developed, so that the masses of their lungs changed with a Gaussian distribution. The lung was selected as the source. Doses delivered to the organs/tissues for photons with different energy levels, and also per decay of ¹³¹I, were calculated using MCNPX. The results showed that changing the mass of the lung has effects on the dose of the lung, especially for low-energy photons and electrons resulting from the decay of ¹³¹I. According to the statistical distribution in terms of the SAF as a function of the lung mass, the average value of organ SAFs and the coefficient of variations were estimated. The uncertainties of the lung SAF due to the lung mass variation can be described by the coefficient of variation (CV), which changed from 9% to 19%. This occurs for photon energy in the range of 10 to 4000 keV. This figure stands at 18% per decay of ¹³¹I. (authors)