Room: Exhibit Hall | Forum 7
Purpose: Monte Carlo Dose Calculation (MCDC) is newly available in treatment planning systems (TPS) for Pencil Beam Scanning (PBS) proton therapy. Golden beam data (GBD) framework can potentially improve accuracy and reduce errors by validation of PBS-specific parameters and MCDC-specific heterogeneity modelling during TPS commissioning.
Methods: A GBD framework was developed to commission MCDC from RayStation 8A and Eclipse AcurosPT v13.7.20 for Varian ProBeam. Measurements included Bragg peaks and profiles of PBS single-spots and PBS field outputs. The phase parameters and numbers of protons/MU were obtained from in-air spot profile and PBS outputs of 100 cmÂ² square fields at 2 cm depth. Spot profiles and more PBS fields at depth were used to validate TPS in water. Five human tissues (lung, adipose, muscle, cartilage and bone) and two artificial materials (PMMA and PVC) are benchmarked between two TPS. Anthropomorphic and biological tissue phantoms are used to check the accuracy of CT stoichiometric calibration and proton transport in heterogeneous media.
Results: The maximum differences of phase parameters spot sigma and divergence between MCDC algorithms are below 4 Âµm and 0.26 mrad in air, respectively. Comparing TPS to measurement at depths in water, both MC algorithms predict spot sigma within 0.5 mm, the resolution of measurement device. AcurosPT underestimates number of protons per MU by ~2% and requires user adjustment in beam configuration, while RayStation is within 1% of measurement using Auto model. Spot sigma, proton range, and field dose in the studied materials mostly agree within 0.5 mm/1% between two TPS except some scenarios: PVC and cartilage with trace Cl element and lung near proton range. Proton range and dose distribution agree better with TPS in tissue than the anthropomorphic phantom.
Conclusion: The proposed GBD framework can be used to identify potential issues and improve PBS dosimetric accuracy during TPS commissioning.