Tetrahedral mesh Visible Monkey phantom for radiation dosimetry research

Although the Visible Monkey (VM) phantom in both voxel and polygon-mesh (PM) models was constructed based on anatomical color-sliced images of a rhesus monkey, the PM model advanced over the voxel model is not watertight, having various defects (e.g., holes, self-interaction, and overlaps), and therefore cannot be implemented in Monte Carlo (MC) codes for dose calculations. In the present study, the original PM monkey phantom was refined with anatomical improvements applied to the skeletal system and the walled organs. The model was then converted into a high-quality/fidelity tetrahedral mesh (TM) model which can be implemented in MC radiation transport codes. By performing the PHITS MC dose calculations coupled with the TM phantom, organ doses for photon external exposures (0.03–10 MeV) and specific absorbed fractions for electron internal exposures (0.01–10 MeV) were calculated and compared with those calculated from the original VM voxel model. For external exposures, the two phantoms showed similar organ doses (differences <25 %). On the other hand, for internal exposures, significant differences (differences up to a factor of 42) were observed due to the geometrical (smooth organ surface) and anatomical (updated skeletal system and classification of wall and contents) improvements for the TM-type phantom.