Simulation and Validation of a 6 MV Elekta Compact Accelerator Head

Abstract

The purpose of this study was to simulate the 6 MV Elekta Compact accelerator head installed in Iran- Mehr radiotherapy and oncology hospital (Birjand-Iran) using MCNPX2.6 Monte Carlo code. The simulation aimed to validate the accuracy of the model by comparing the simulated results with the measured percent depth dose (PDD) at 10 ×10 cm2 field and dose profile at 10 cm depth, which were obtained using a water phantom and Baldwin-farmer ionization chamber provided by PTW company. The main components of the linac's head, including the target, primary collimator, flattening filter, and secondary collimators, were simulated. A phase space file generation process involved the using of SSW (surface source write) and SSR (surface source read) cards to capture the particle source information. In this case, the horizontal plane was positioned 100 cm below the tungsten target. A significant number particle, specially 107 particles (photons and electrons), that traversed the surface were then recorded in a binary phase space file for use as an SSR card. The deposited energy of photons and electrons was recorded using a mesh tally (type 3) to calculate the PDD and beam dose profile. The model’s accuracy was evaluated by comparing the simulated results with the measured data, using relative error as the evaluation metric. The optimum energy of the initial electron beam was determined by analyzing the PDD curves. The full-width half-maximum (FWHM) of the electron source was adjusted based on the dose profile curves. After computing the PDD curves for electron beam energies ranging from 5.5 to 6.5 MeV with a step of 0.1 MeV, an electron energy of 5.8 MeV was determined to be the best match. To obtain the optimum FWHM, the profile dose curves were analyzed by varying the FWHM from 0.4 to 0.5 cm with a step of 0.01 cm. The optimum FWHM value of 0.44 cm was obtained. Different field sizes were simulated by adjusting the secondary collimators, and rotation matrices were obtained and used in the TRCL card. The simulated field sizes included 8×8, 10×10, 12×12, 15×15, 20×20, 25×25, 30×30, and 40×40 cm2 .