Comparison of measured and calculated dose distribution of ⁹⁰Y Beta-ray source in a small phantom simulated mice

Abstract

Medical Internal Radiation Dosimetry Methods assume that the beta particle energy is absorbed completely in the source organ. However, the organs of mice used in fundamental experiments for internal radiotherapy are relatively small compared to the range of high-energy ⁹⁰Y beta particles. Therefore, it is well known that the high-energy beta particle can escape the source organ, resulting in large cross-organ doses. The more realistic geometric model such as a voxel-phantom based on Computed Tomography scans for the mouse has been needed for accurately estimating internal doses from administered beta particle emitters. Then it becomes important to simulate the beta particle transport precisely using the Monte Carlo code. The purpose of this study is to validate a user code to simulate the beta particle transport in the Monte Carlo code system (EGS5) by comparing with the absorbed dose measured with a number of small Fluorescent Glass Dosimeters and two capsules (9.6MBq, 1.1MBq) of ⁹⁰YCl₃ solution implanted in a small phantom (Tough-Water; 30mm x 30mm x 70mm) simulated mice. It was found that the absorbed dose distribution in this phantom simulated with this user code gives rather good agreement with the measured results.