Evaluating the effects of statistical changes on internal dosimetry

Abstract

-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 131 I, 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 131 I. 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 131 I.

Studying the effects of the lung mass on the absorbed dose to the lung due to the administration of131I for therapeutic purposes

“…Considering that a specific organ mass differs from one person to another, one of the reasons for the deviation associated with phantoms is the variations in the organ mass. The coefficient of variation of the dose related to the lung mass has been calculated to be 18%, which can fully explain the aforementioned 13% discrepancy (Sajjadi et al, 2015 GEANT4 and DOSE3D) revealed that the variations among the results were relatively small. In the worst situation, the transport calculation method may result in up to 10% differences in organ absorbed doses (ICRP, 2010).…”

“…The dose (and S value) for photons is inversely proportional to the mass with the power, ranging from 1/2 to 1 at energies between 10 and 4000 keV (i.e., 1/2 for 4000 keV and 1 for 10 keV) (Eq. (2)) (Sajjadi et al, 2015) proportional to the mass −2/3 (Eq. (3)) (Snyder, 1970;Stabin et al 2005;Hansson, 2012):…”