ESTRO 2024 - Abstract Book

S3420

Physics - Dose calculation algorithms

ESTRO 2024

left column), indicating poorer fit between simulations and measurements. For the homogeneous phantom (Fig1, left column), mean gamma values are overall equal between MC and CC (-5% to 6% difference between MC and CC mean gamma, averaged over all fields). These results indicate poor compatibility between the MC model and the heterogeneous ArcCHECK images. This may result from MC being highly sensitive to varying densities around the diodes in the heterogeneous image, leading to increased uncertainty in the fit between measurements and calculations. For homogeneous phantoms, MC and CC give comparable results; no performance benefits for either dose engine were found for these simple fields.

For the 13 clinical treatment plans in the preferred homogeneous configuration, MC resulted in a lower mean gamma as compared to CC for all 6MV FFF plans (Fig2, left column blue versus red, -58% to -10% difference) and a minority of the 6MV plans (-30% to +25% difference). The calculations on a heterogeneous phantom (Fig2, right column) resulted in more equal results between MC and CC. Interestingly, this is in contrast to the results for the rectangular fields, where the heterogeneous phantom resulted in consistently poorer gamma values for MC relative to CC. These results indicate that MC might offer performance benefits over CC for more complex treatment plans. Given that this overall advantage of MC is not observed for simple rectangular fields but only in the treatment plans, it is thought that this is because MC is better at simulating complex, small fields.