SU‐E‐T‐257: A Monte Carlo Simulation Study of Photon Beam with Energies 6X, 10X, 6FFF, 10FFF From a TrueBeam Linear Accelerator

Abstract

Purpose: To compare the quality of Monte Carlo simulation results of photon beams with multiple energies with the corresponding measured beam commissioning data from a Varian TrueBeam accelerator. Methods: IAEA phase space files for photon beam energies 6X, 10X, 6FFF, 10FFF from TrueBeam linear accelerator provided by Varian were implemented as source files in the GEANT4 Monte Carlo code. The simulation geometry consisted of upper and lower tungsten alloy jaws and a cubic water phantom (50 × 50 × 50 cm3). Central axis depth dose curves (PDD) for multiple field sizes (1×1, 2×2, 4×4, 6×6, 10×10, 20×20, 30×30 cm2) and radial and transverse dose profiles for identical field sizes at 5 different depths (Dmax, 5, 10, 20, 30 cm) for all four energies were recorded in the phantom. Each simulation was performed with 2.0E9 incident particles. The results of PDD and profiles from simulations were then compared with the corresponding beam commissioning data collected with a Wellhoffer Blue Phantom using a 0.13cc ion‐chamber and a 0.8 × 0.8 mm2 diode. Results: The GEANT4 simulated PDD curve for photon beam compared favorably well, within ∼2%, against the corresponding measured ion‐chamber PDD for all energies and field sizes. The simulated in‐plane and cross‐plane profiles also compared well, within 2 mm, at the 50% level against the measured profiles for all energies, field sizes and depths. Conclusion: For the commissioning of a linear accelerator, the feasibility of utilizing Monte‐Carlo simulated beam data has been demonstrated in this study. The increase of computer speed and capabilities may Result in the adoption of Monte‐Carlo techniques for future machine commissioning and dose calculations.