SU-E-T-499: Validation of the Varian Generic Phase Space Files for Monte Carlo Calculations of Dose Distributions for the TrueBeam Linac Head.

To validate the generic phase space files for Varian TrueBeam linac head simulations. The generic phase space files include the simulation results of 6MV, 10MV, 6MV FFF, and 10MV FFF (flattening-filter free) operating modes of TrueBeam for patient-independent linac head components. Using the generic phase space files as the radiation sources, the BEAMnrc Monte Carlo codes are used to simulate the patient-dependent parts of the TrueBeam linac and the resulting phase space files are generated at a plane just before entering a water phantom for 4 different field sizes (5×5, 10×10, 20×20, and 40×40 cm2 ). Dose distributions are calculated by DOSXYZnrc in the water phantom of size 50×50×40 cm3 . The percentage-depth-dose (PDD) curves and lateral dose profiles at three different depths (dmax, 10cm, 20cm) are obtained. Comprehensive comparisons have been made for a total of 64 dose profiles (including PDDs) between the Monte Carlo calculations and the measured data. The gamma index analysis is performed for all the comparisons. The matching of the calculated dose distributions to the measured ones is analyzed by the gamma index method with a criterion of 2% dose tolerance and 2 mm distance-to-agreement. Of the 64 comparisons, the minimum gamma index passing rate is at least 92%, after taking into account the statistical nature of the Monte Carlo calculated dose values. Despite the existence of latent variance of phase space files, the phantom dose calculation uncertainty can be less than 1% for field sizes as small as 5×5 cm2 . The computing time saved by using phase space files could be a factor of 5-10. The Varian generic phase space files are accurate and efficient radiation sources for Monte Carlo calculations of radiation dose distributions for TrueBeam linac head. This work was supported in part by Varian Medical Systems and the NIH (1R01 CA104205 and 1R21 CA153587).

Wang L ，Xing L ，Sawkey D ，Constantin M ，Svatos M ，Mok E ... -  《-》

A geometrical model for the Monte Carlo simulation of the TrueBeam linac.

Rodriguez M ，Sempau J ，Fogliata A ，Cozzi L ，Sauerwein W ，Brualla L ... -  《-》

Monte Carlo simulation of TrueBeam flattening-filter-free beams using varian phase-space files: comparison with experimental data.

Belosi MF ，Rodriguez M ，Fogliata A ，Cozzi L ，Sempau J ，Clivio A ，Nicolini G ，Vanetti E ，Krauss H ，Khamphan C ，Fenoglietto P ，Puxeu J ，Fedele D ，Mancosu P ，Brualla L ... -  《-》

A Monte Carlo approach to validation of FFF VMAT treatment plans for the TrueBeam linac.

Gete E ，Duzenli C ，Milette MP ，Mestrovic A ，Hyde D ，Bergman AM ，Teke T ... -  《-》

SU-E-T-496: Monte Carlo Simulation of a 6MV Varian Truebeam Without Flattening Filter Linac.

To simulate a 6 MV Varian Truebeam linac operating without flattening filter using an existing Phase space file(PhS) with the monte carlo packeage EGSnrc. An existing PhS file built after simulating the patient-independent part at the first step in traditional monte carlo simulation was employed. With this PhS being a source, the patient-dependent part was simulated and the dose distributions were calculated using EGSnrc. The 6 MV dose calculation were performed for field size of 10×10cm2 , 20×20cm2 , 30×30cm2 and 40×40cm2 in a 54×54×30 cm3 water phantom. The voxel size for the water phantom was 0.6×0.6×0.6cm3 . For the 10×10cm2 field, surface buildup calculations were performed using 0.6×0.6×0.3cm3 voxels within 1.8cm of the surface. Dose profiles and percent depth dose(PDD) curves were calculated following 1 billion histories for dose profiles and 500 million histories for PDD curves. Simulation results were compared with measured data for validation. Good agreement between simulations and measurements in water was observed. For the PDD curves, 95% of the calculated data points agree within 2% with the experimental measurements for depths between 1.8cm and 30 cm. In the buildup region, the agreement is within 2%, except several points with the deviation of 5% for the 10×10 cm2 open field. For the lateral dose profiles, the agreement is less than 3% at the depth of 1.3cm, 5cm, 10cm, 20cm and 30cm inside the 80% field size. It demonstrated that the existing phase space file is accurate and the simulation is reliable to be used for clinical patient dose calculations in future investigations. Project supported by the National Natural Science Foundation of China (30970866).

Song T ，Zhou L ，Jiang S 《-》