Optimization of physics settings in GATE-RTion/Geant4 for independent dose calculation in carbon ion beam therapy

Abstract

At the MedAustron carbon ion beam therapy center the accuracy of every treatment plan obtained by the commercial treatment planning system is individually verified. These patient specific quality assurance measurements could be (partly) replaced by independent dose calculations to save valuable beam time and achieve a higher sensitivity in error detection.In this work, different physics models and settings in GATE-RTion(v1)/Geant4 (10.3) for independent Monte Carlo dose calculations in carbon ion beams were compared to each other. Their dose calculation accuracy was determined by investigating integrated radial profiles with depth, beam optics in terms of beam spot size and absorbed dose to water at reference conditions. These data were then compared to respective measurements performed during beam line commissioning. Following this, the setting QGSP_BIC_HP_EMZ was chosen to be the best option posing a good balance between dose simulation accuracy and calculation time. QGSP_BIC_HP_EMZ provided an average calculation time improvement by a factor 7.8 compared to the original settings without any evident reduction in simulation accuracy.Eventually, the irradiation of three dimensional targets of different shapes, sizes and at different measurement positions was simulated to validate the calculation accuracy of the final setting with spread out Bragg peaks. The comparison of these simulations to measurements resulted in a good agreement for clinically relevant cases with best agreement at shallow depths and increasing deviations with depth.