SU-E-T-498: A Preliminary Monte Carlo Simulation Study of the Varian TrueBeam Linear Accelerator.

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 4×4 cm and as large as 30×30 cm 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 0.8×0.8mm 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 20×20cm . 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.