Purpose: To evaluate the efficacy of the IBA-dosimetry myQA iON program for replacing traditional patient specific quality assurance (PSQA) methods for proton therapy.
Methods: The myQA iON software (IBA-dosimetry) includes Monte Carlo (MC) dose computation to verify the dose generated by treatment planning systems (TPS) via gamma analysis for proton plans. It also compares and verifies a plan’s dose with dose calculated using machine LOG files. In this study, we have evaluated the MC calculated dose distribution with dose generated by our TPS, Varian Eclipse V16.1 using PCS V16.1. We also compared the dose calculated for each field of each plan on a virtual QA phantom with MC calculations and with our historic PSQA measurements for each patient. We evaluated 10 prostate plans which used a single field uniform dose technique, and 9 brain plans which used an intensity modulated proton therapy technique. All plans used pencil beam scanning. We used a 2%/2 mm and 3%/3 mm criteria for global gamma analysis. PSQA measurements used a MatriXX (IBA-dosimetry) device and 3%/3mm gamma analysis.
Results: Monte Carlo results showed good agreement with the TPS, both for brain and prostate cases, using the 2%/2 mm and 3%/3 mm criteria with a mean 98% passing rate. For cases showing disagreement (>5%) between Monte Carlo results and our historic PSQA measurements, PSQA was re-measured which resulted in close agreement with Monte Carlo results.
Conclusion: MC, PSQA and TPS dose comparison all showed very good agreement, validating the use of the PSQA software as a viable resource. The MC calculations have already revealed examples of cases where historic PSQA was measured incorrectly and prompted re-measurement. Furthermore, the log file analysis of this software will be validated for our clinical cases using measurements with the aim of this software ultimately replacing our traditional measurement-based PSQA.