A . Bouzouita et al .: Radioprotection 2024 , 59 ( 4 ), 296 – 305 299 Fig . 2 . Dose to organ conversion factors as function of primary gamma-ray energy for different organs of the female ICRP110 voxel phantom and for sources uniformly distributed in the ground .
ICRP110 voxel phantom and uniformly distributed soil sources are presented in Figure 2 . The DCF increases with emission energy and is of a similar magnitude across different organs due to comparable shielding effects . The absorbed dose rate in various organs for the natural radioactive series of 238 U , 232 Th and the 40 K radionuclide as well as for the
anthropogenic 137 Cs radionuclide are shown in Tables 1 and 2 for a female and male phantoms . Gamma ray emission energies and yields for the different series are issued from ( Askri , 2015 ). The advantage of voxel-based Monte Carlo simulations over mathematical phantoms is evident in the detailed dose distribution information . Tables 1 and 2 indicate higher organ DCFs for the 232 Th series compared to the 238 U series , attributed to the higher gamma emission yield of 232 Th . The 137 Cs and 40 K radionuclides exhibit lower DCFs
due to lower emission energies and decay probabilities , respectively . Skin DCFs are higher due to its large surface area and the energy loss of secondary electrons in the skin layers ( Xu et al ., 2023 ; Krstic and Nikezic , 2009 ). Organs such as testes and breasts also show higher doses due to their protruding structure , while other organs receive comparable doses due to structural shielding .
Table 3 shows a comparison between the results of the present work and those of Sanusi et al . ( 2021 ), who used a single-stage Monte Carlo simulation on MCNP code with a mathematical MIRD phantom . The comparison is also done with the organ DCFs , which are obtained indirectly by multiplying the organ conversion coefficients ( Sv / Gy ) normalising the absorbed doses in organs to kerma free in air that were calculated by Zankl et al . ( 1997 ) and the absorbed dose in air conversion factors from Saito and Jacob ( 1995 ). Their calculation was performed in towstage Monte Carlo simulation using an early version of a MIRD mathematical phantom and the Monte Carlo YURI code ( Saito and Moriuchi , 1985 ). Our results show higher DCFs for most organs , likely due to the more accurate voxel-based geometry , the optimised geometry of the soil-air medium and the different physical models used here . The discrepancy in red bone marrow DCFs can be attributed to the more detailed skeleton constituents considered in our voxel phantom compared to the MIRD phantom . It is worth to note that in the MIRD phantom , eight skeleton constituents are taken into account instead of 19 taken into account in the ICRP110 voxel-based phantom used in the present work ( Sanusi et al ., 2021 ). A large discrepancy can also be seen for the muscle and the skin tissues . As stated by Sanusi et al . ( 2021 ), there is no way to mathematically represent a clear and precise muscle tissue distribution in the phantom . Therefore , for the MIRD phantom , the body volume of head , neck , trunk , and legs approximates the muscles ( Sanusi et al ., 2021 ). For