Year: 2026 | Month: January | Volume: 13 | Issue: 1 | Pages: 351-361
DOI: https://doi.org/10.52403/ijrr.20260133
Internal Dosimetry with Monte Carlo Code PHITS: Validation of Specific Absorbed Fraction Values for Voxel and Mesh-based Adult Male Phantoms
Asa Pratiwi1, Wahyu Setia Budi2, Pandji Triadyaksa2
1Master of Physics, Diponegoro University, Indonesia
2Department of Physics, Faculty of Sciences and Mathematics, Diponegoro University, Indonesia
Corresponding Author: Asa Pratiwi
ABSTRACT
In targeted radionuclide therapy (TRT), accurate internal dosimetry is crucial for maximizing therapeutic outcomes while minimizing side effects. The Particle and Ion Transport System (PHITS) is more accessible and user-friendly, although Monte Carlo (MC) simulations have become the gold standard in absorbed dose modeling and radiation transport. The purpose of this study is to evaluate the effectiveness of using PHITS version 3.35 (2025) for calculating internal dosimetry parameters and to quantitatively evaluate the differences in SAF values between the ICRP 110 reference voxel-based adult male phantom model and the ICRP 145 reference mesh-based phantom, validated against reference data. Review dosimetric parameters for at least nine source-target organ pairs, including absorbed fraction (AF) and specific absorbed fraction (SAF). This simulation includes monoenergetic photons and electron particles ranging in energy from low (≤0.1 MeV) to high (1 MeV). For most organs, the statistical uncertainty of the computation is kept below 5%. The results show that using a mesh phantom can make the estimation of internal dosimetric parameters such as SAF more anatomically representative. In general, electron SAFs are more sensitive than photon SAFs to differences in organ mass and geometric realism. This is especially true for large organs like the liver and kidneys, which have thin walls and are closely positioned across different organs. As a result, the internal dosimetry estimates produced by the mesh phantom are more anatomically representative than those produced by the voxel phantom.
Keywords: PHITS; Internal dosimetry; Nuclear medicine; Specific absorbed fraction; MRCP; voxelized phantoms
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