A comparative study of clinically used fast Monte Carlo dose engines for proton therapy

Several fast Monte Carlo (MC) codes have been implemented and used to simulate proton transport and calculate patient doses in proton therapy. The resulting dose is typically compared to full MC codes, rather than other fast MC codes.

The primary goal of this study was to compare the gamma pass rates (GPRs) of dose calculation from different fast MC codes to evaluate the accuracy of the computation and modeling among these codes.

Two GPU codes and one CPU MC code were commissioned to model our clinical proton beamline at University of Texas MD Anderson Cancer Center. The GPU models use single 2D Gaussian models, whereas the CPU model uses a double 2D Gaussian model. For comparative evaluation, 70 cancer patients were randomly selected from our clinical practice, 10 from each of the following treatment sites: head and neck, brain, esophagus, lung, mediastinum, spine, and prostate. The calculated dose was compared with the dose from the verification plan created in the clinical treatment planning system (TPS) using 3D gamma analysis.

The accuracy of dose calculation for all fast MC codes compared very well with the calculation from the TPS for the examined patient plans. GPR for all treatment sites ranged from 96.29% to 99.99%. In general, the double Gaussian model pass rate surpassed the single Gaussian model rate despite a slight accuracy reduction for prostate cases. GPRs for the single Gaussian codes ranged from 96.29% to 99.34%, whereas the double Gaussian model achieved a range of 98.68% to 99.99%.

All commissioned codes we examined demonstrated acceptable 3D GPR across all patients and treatment sites tested. Although the CPU MC code was commissioned using a double 2D Gaussian model, the single 2D Gaussian model used in the GPU codes proved to be sufficiently effective, yielding a high GPR.