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Improving Spot Scanning Proton Therapy Patient-Specific Quality Assurance Through Early Application of Second-Check Dose Calculation Software


D Mackin

D Mackin*, X Zhang, Y Li, M Taylor, M Kerr, C Holmes, N Sahoo, F Poenisch, H Li, M Lii, R Amos, R Wu, K Suzuki, M Gillin, X Zhu, M.D. Anderson Cancer Center, Houston, TX

SU-E-T-157 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

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 αβγ 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.

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