SU-E-T-507: Dose Calculation Quality of AcurosXB Involving a HD120 MLC Compared with Monte Carlo Methods

Advanced radiation therapy requires highly sophisticated dose calculation algorithms such as finite element based Boltzmann solvers or Monte Carlo (MC) methods. MC is commonly accepted as the golden standard method for dose calculation in high energy treatments and thus it is used for benchmarking other algorithms. In this work the quality of dose distribution calculated using the Boltzmann solver based AcurosXB algorithm within Eclipse (Varian Medical Systems) is investigated for volumetric modulated arc treatment (VMAT) plans involving the high definition MLC (HD120 MLC) by comparing doses with the validated Swiss Monte Carlo Plan (SMCP).

Within SMCP and Eclipse using AcurosXB, 10 VMAT H&N patient plans and corresponding verification plans were recalculated using fixed MUs. In SMCP, radiation transport and dose calculation were performed using VMC++ with a statistical uncertainty of 1%. The voxel size was 2.5 mm for SMCP and AcurosXB and the same material composition data was used for CT conversion. Dose volume histograms (DVH) were used in order to quantify the difference between the dose distributions of the patient plans. In addition, calculated verification plans were compared with measurements carried out with the Delta4 system (Scandidos) by using the gamma evaluation with 3%/3 mm criteria of points having a dose larger than 20% of isocenter dose.

DVHs for the patient plans showed good agreement between SMCP and AcurosXB calculations. Overall AcurosXB lead to an underestimation of the median dose values by about 1%. For measured total dose distributions of the verification plans on average 98.6% and 99.0% of the points fullfil the gamma criteria for the dose calculated using AcurosXB and SMCP, respectively.

Resulting AcurosXB dose distributions for VMAT H&N plans involving a HD120 MLC are in good agreement with calculated SMCP dose distributions.

This work was supported by Varian Medical Systems.