A Preliminary Monte Carlo Simulation Study of the Varian TrueBeam Linear Accelerator
D Johnson*, Y Chen, E Schnell, S Ahmad, University of Oklahoma Health Sciences Center, Oklahoma City, OKSU-E-T-498 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall
Purpose: To benchmark the quality of Monte Carlo simulation results with the commissioning data for a Varian TrueBeam accelerator.
Methods: IAEA phase space files of a 6MV TrueBeam accelerator provided by Varian were implemented using GEANT4 Monte Carlo code. The present application consisted of upper and lower jaws and a cubic water phantom of 0.125 cubic meters in volume. Both radial and transverse dose profiles (in 5 different depths) and a central axis percentage depth dose (PDD) curve were recorded in the phantom. Field sizes of as small as 4x4 cm² and as large as 30x30 cm² were simulated with 2.0E9 incident particles each. The results were then compared with our commissioning data performed in a Wellhoffer Blue Phantom with a 0.13cc ion-chamber and a 0.8x0.8mm diode.
Results: The GEANT4 simulated PDD curve compared favorably within ~2% against the measured ion-chamber PDD for all field sizes and against the measured diode PDD for all fields less then 20x20cm². The simulated in-plane and cross-plane profiles compared well within 2 mm at the 50% level against the measured profiles for all field sizes.
Conclusions: These results demonstrate the feasibility of utilizing Monte-Carlo simulated beam data in the commissioning of a linear accelerator. The increasing speed and capability of the desktop computer will result in the adoption of Monte-Carlo techniques for dosimetric calculations.