Shielding for patient-scattered radiation from elekta precise linear accelerator by Monte Carlo simulation

Abstract

In shielding design of a radiotherapy treatment room, the requirements of dose limits outside the room must be fulfilled. The primary beam from the linear accelerator, the leakage radiation from the gantry and the scattered radiation from the patient and other objects contribute to the radiation exposure outside the room. In this dissertation, we focused on the scattered radiation from the patient irradiated by the primary radiation beam including 6, 10 and 25 MV from an Elekta Precise linear accelerator. By using Monte Carlo simulations, we analysed the characteristics of the scattered radiation, so that we have better understanding of the scattered radiation when designing the shielding of a treatment room. The angular distributions and energy spectrum of the scattered radiation are presented. It was found that both the number of scatter particles and energy of the scatter particles increase with increasing primary beam energy and decreasing scatter angle. We also performed Monte Carlo simulations to collect the transmission data of scattered particles passing through the shielding wall made of the concrete commonly used in Hong Kong. The simulated results are tabulated and could be used for radiation protection purposes for the estimation of the radiation exposure behind the shielding concrete wall due to the patient scattered radiation.