Mouse Brain Dosimetry in Small Animal CT with GATE Monte Carlo Simulations

Abstract

As small animal studies using radiation exposure increase, it becomes more important to estimate accurate dose for the animals in order to explain and control the potential radiation toxicity or treatment efficacy. The purpose of this study was to determine the radiation dose in a realistic mouse brain tissue for dosimetric estimates using geant4 application for tomographic emission simulations (GATE), and to extend its techniques to various small animal CT applications. The realistic mouse phantom (MOBY phantom) is based on high resolution 3D magnetic resonance microscopy data, and the geometry was developed using a segmented C57BL/6 mouse that weighed 33 g. Recently, 37 segmented tissues have been added to voxel-based MOBY brain developed by Johns Hopkins University. A small animal CT system (micro-CT) with Gd2O2S scintillator was performed using 50 kVp, 0.15 mAs (0.5 second), 360° of rotation, and 400 projections. For validating simulation studies with respect to physical measurements for micro-CT, the measured and simulated airkerma values were compared, and the measured and simulated values measured in the validation CT ion chamber study were 3.32 and 3.69 μC/kg air, respectively. The total absorbed dose over all measurements to the brain (37 tissues) is 60.2 mGy. Among tissues of brain, the absorbed dose of cerebral_cortex (20.55 mGy) was highest while the one of pineal_gland (0.02 mGy) was lowest. This result can be used in control of brain tissue doses and preclinical targeted radiotherapy experiments as dosimetric database. In addition, in order to calculate accurate absorbed dose of brain tissues, accurate modeling is needed for X-ray spectrum, detector alignment, and uncertainty in elemental composition of simulated materials.Keywordsmouse brain dosimetryMOBY phantommicro- CTGATE Monte Carlo simulationabsorbed radiation dose