Monte Carlo Modeling and Verification of 6 MV Linear Accelerator

Abstract

Purpose: To model the ELEKTA COMPACT accelerator head by using EGSnrc/BEAMnrc/DOSXYZnrc and to validatethe simulation according to the depth-dose and lateral profiles of different radiation fields measured by the water phantom. Methods: IBA Blue Water Phantom2 and CC13 Ionization Chamber were used to measure the depth-dose curves at 10 cm × 10 cm field and profile curves at 10 cm depth underwater. In BEAMnrc, the main components of accelerator head and the initial electron beam are established based on the specifications file, and the phase space file containing the photon beam information is generated. In DOXYZnrc, phase space files were used to irradiate a homogeneous water phantom of the same size as the IBA water phantom, and the simulated percentage depth dose curves and lateral profiles were outputted. The accuracy of the model was evaluated by mean square error (MSE) compared with the measured data. PDD curves are used to determine the energy of the initial electron beam. Dose profile curves are used to adjust the flattening filter. The penumbra on lateral profiles is used to adjust the full-width half-maximum (FWHM) of the electron source. Result: The electron energy of 5.8 MeV was considered the best match after comparing the PDD curves of 5.6 - 6.2 MeV electron beams. The flattening filter can only be adjusted by trial. In the final result, the maximum fluctuation of profile curve within 80% of the maximum field size is less than 3%, which meets the requirements of field flatness. The optimum FWHM for different fields is not consistent due to the Transmission penumbra. But a match can be approached by adjusting the FWHM every 10 cm field size.