Purpose: To evaluate differences in secondary monitor unit (MU) calculations of RadCalc and PTW’s VERIQA. Following AAPM TG-219 recommendations, we are evaluating the impact of 3D secondary dose verification in our clinic.
Methods: Twenty thorax 6 and 10 MV VMAT patient plans were exported from the Pinnacle treatment planning system to the VERIQA software. MU values for each beam were recorded for each the Pinnacle plan, the RadCalc MU calculation, and the PTW VERIQA Monte Carlo calculation. The percent differences from the Pinnacle plan were calculated for RadCalc and VERIQA. The RadCalc dose calculation point was determined by the user while the PTW VERIQA MU calculation is based on the dose reference point from the DICOM RT plan file.
Results: The percent differences of the Pinnacle and RadCalc MU values ranged from 0.00% to 4.70%, and the percent differences of the Pinnacle and VERIQA MU values ranged from 0.04% to 7.97%. One source of discrepancy is attributed to the differences of the dose calculation algorithms. Another source stems from the fact that RadCalc uses beam data from the TPS with VERIQA utilizes independent data. Evaluation of the gamma index, isodose distributions, and DVHs showed good agreement between VERIQA and Pinnacle. Gamma indices were above 95% (3%/2mm) with small differences in the PTV DHVs.
Conclusion: The differences in MU calculations between the Pinnacle treatment planning system and RadCalc and VERIQA secondary verification software were comparable for dose reference. In addition to providing a quality secondary MU calculation verification, VERIQA is capable of producing other patient QA evaluation metrics, including 3D Monte Carlo dose calculation of organs at risk and targets as well as compute gamma indices for total volume and structures.
Funding Support, Disclosures, and Conflict of Interest: Funding was provided by PTW to complete this research.
Monitor Unit Calculations, Treatment Verification