SU‐E‐T‐157: Improving Spot Scanning Proton Therapy Patient‐Specific Quality Assurance Through Early Application of Second‐Check Dose Calculation Software

Purpose: We discuss the spot scanning proton therapy (SSPT) patient‐specific quality assurance (QA) procedure at MD Anderson Proton Therapy Center‐Houston, with emphasis on how we verify the dose calculation of the Eclipse treatment planning system. We present our second‐check dose calculation software, HPlusQA, and then present a case study to show how a slightly unorthodox application of the second‐check software can greatly improve the efficiency of SSPT QA. Methods: In our study, we validated HPlusQA and determined its performance with respect to Eclipse by comparing the calculations of point doses to measured values. To validate the use of HPlusQA as a dose calculation second check, we determined how well gamma index scores comparing HPlusQA to Eclipse predict the gamma index scores comparing dose measurement to Eclipse. To present a more informative distribution of the gamma index score comparison, we introduced the αβ? transformation. Results: In our study, both HPlusQA and Eclipse agreed with the measured dose to within 2% on average. The agreement was worse at the end of the proton beam range. HPlusQA had a 79% success rate at predicting when the Eclipse dose calculations would be outside the QA tolerance levels.More importantly, we show how we plan to apply HPlusQA to patient‐specific QA. We use a patient case study to demonstrate how HPlusQA can lead to great improvement in the efficiency of SSPT patient‐specific QA. Conclusion: A dose calculation second check such as HPlusQA allows for early detection of many treatment planning system dose calculation errors. Early detection of errors means less time spent on measurements and a more efficient SSPT patient‐specific QA process.