Monte Carlo simulation of photon specific absorbed fractions for internal self-dosimetry of the thyroid based on a Filipino model

Abstract

Specific absorbed fraction (SAF) is an important factor in self-dosimetry for internal organs. Differences between Filipino and Caucasian statistics may cause inaccurate dose estimation in internal dosimetry for Filipinos. In this study, the Oak Ridge National Laboratory (ORNL) adult phantom is rescaled using the height and weight of a Filipino reference man to become a model for Filipino males and females. Monte Carlo simulation using Monte Carlo N-Particle Transport code version 6.2 (MCNP6.2) is done to determine self-SAF values of the thyroid organ in each phantom. It was determined that the differences between the thyroid self-SAFs of a Filipino Male was higher than that of the ORNL adult phantom by 19.55% on average and that of the Filipino female was higher than that of the ORNL adult phantom by 21.61% on average. The scaling down of the thyroid phantom geometry resulted to an increase in self-SAF. The results show that the self-SAF computation using ORNL adult phantom is inaccurate for Filipinos and that rescaling the ORNL phantom or the use of a model suited for Filipino statistics is important before it can be used for accurate internal dosimetry.