Assessment of absorbed dose in digital and MIRD phantoms by MCNP in thorax area
This paper describes the development of mathematical models, called phantoms, for the assessment of absorbed doses caused by internal radionuclides. In more developed phantoms, anatomical models based upon 3D imaging methods are used. Cross-sectional anatomical models consist of numerous arrays of voxels, each of which individually corresponds to an organ. The digital phantom presented in this paper was simulated based on a 38-year-old reference man, with height and weight similar to the reference man reported in the International Committee of Radiation Protection (ICRP). A total of 222 345 voxels with regard to weight and density information were implemented in 45 cross-sections in the Monte-Carlo N-particle (MCNP) environment. Tissue inhomogeneity and organ geometry were also taken into account. The Dose Point Kernel (DPK) method was used to calculate the absorbed dose in target and source organs. In order to compare the results with ICRP reports, specific absorbed doses in kidney, liver and lung were calculated. Assessment results of self-absorbed dose were done, considering an organ as both source and target, at different energies. We found good correlation between our results and those of Stabin and Yoriyaz (2002). The results showed that self-absorbed doses are greater at lower energies for kidney, liver and lung, while they decrease at high energy. The self-absorbed dose of the liver is the same as in the Medical Internal Radiation Dose (MIRD), MCNP and Stabin's method; furthermore similar patterns in kidney, lung and liver graphs imply that the phantom is well behaved. Fluctuations in digital phantom voxel size affect the results of absorbed dose in different organs.
Keywords: digital phantoms, simulation, voxel phantoms, dose point kernel, DPK, medical internal radiation dose, MIRD, Monte-Carlo N-particle, MCNP, internal dose, mathematical modelling, low radiation, absorbed doses, kidney, liver, lung