Monte Carlo Simulations of Photon Absorbed Fractions in a Frog Voxel Phantom

For radiation protection of the environment, a voxel-based frog phantom was developed using cryosection data, which have been available on a Web site of the Lawrence Berkeley National Laboratory. The voxel-based frog phantom includes 16 segmented organs/tissues: brain, blood vessel, duodenum, eye, heart, ileum, kidneys, intestine, liver, lung, nerve, skeleton, soft tissue, spleen, stomach, and stomach contents. The voxel-based frog phantom has a mass of 3.37 times 10^-2 kg. The dimensions are 7.1 (length) times 3.3 (width) times 2.4 (height) cm³. The voxel size is 0.0175 times 0.0175 times 0.0175 cm³. In this paper, the voxel-based frog phantom is applied to evaluating photon absorbed fractions (AFs) in the segmented organs/tissues. The sources were assumed to be monoenergetic in the photon energy range from 10 keV to 4 MeV. The radiation transport was simulated using the Monte Carlo method. Consequently, it was confirmed that the photon AFs for organ self-absorption are dependent on the masses of the source/target organs. It would appear that the photon AFs for organ self-absorption are expressed by a continuous function of photon energy emitted by the source. The photon AFs for organ crossfire might be subject to the geometry effect, such as size and shape of source/target and distance between the source and target.