POLY2TET: a computer program for conversion of computational human phantoms from polygonal mesh to tetrahedral mesh

As a geometrical format for computational human phantoms, tetrahedral mesh (TM) is known to have significant advantages over polygonal mesh (PM), including higher compatibility with Monte Carlo radiation transport codes, higher computation speed, and the capability of modeling heterogeneous density variation in an organ of the phantom. In the present study, a computer program named POLY2TET was developed to convert the format of computational human phantoms from PM to TM and generate a sample source code or input file, as applicable, for the converted phantom to be used in some general-purpose Monte Carlo radiation transport codes (i.e. Geant4, PHITS, and MCNP6). The developed program was then tested using four existing high-fidelity PM phantoms. The computation speed, memory requirement, and initialisation time of the generated TM phantoms were also measured and compared with those of the original PM phantoms in Geant4. From the results of our test, it was concluded that the developed program successfully converts PM phantoms into the TM format. The organ doses calculated using the generated TM phantom for the three Monte Carlo codes all produced essentially identical dose values to those for the original PM phantoms in Geant4. The comparison of computation speed showed that compared to the original PM phantoms in Geant4, the TM phantoms in the three Monte Carlo codes were much faster in transporting the particles considered in the present study, i.e. by up to ∼2600 times for electron beams simulated in PHITS. The comparison of the memory requirement showed that the TM phantoms required more memory than the original PM phantoms, but, except for MCNP6, the memory required for the TM phantoms was still less than 12 GB, which typically is available in personal computers these days. For MCNP6, the required memory was much higher, i.e. 60-70 GB.