Room: AAPM ePoster Library
Purpose: To develop a Matlab-based systematic tool for analyzing the machine log files for the Mevion S250i Hyperscan pencil beam scanning proton therapy system. We analyzed the log files from the daily QA plans, which consisted of three beams: a warmup with uniform spot dose and spacing, a spot position check to drive the system to cover the field, and a dose check for daily output measurements.
Methods: The daily QA plans were run 253 times between Jan 14, 2019 and February 6, 2020. For each log file, our code computed the distance between the planned and measured positions of each pulse, as well as the differences between each pulse’s planned and measured MUs. The spot position errors, MU errors, the log file’s date and beam number were all recorded for analysis.
Results: Over 1.01×10^6 spots were cumulatively delivered in these plans. Overall, the mean spot position error was 0.85 mm and the mean MU delivery error was -2.1%. The mean spot position error and standard deviation (s) when plotted as a function of time correlates with the periodic maintenance of the machine and fine-tuning for optimal performance. After our latest software update in September 2019, the mean spot position error for the spot check beam was 0.61 mm (s = 0.46 mm) and 97.9% of spots were within 2 mm of target. After the update, the mean MU error for the dose check beam was -1.1%, (s = 2.4%) and 81.7% of MUs were with ±3% of target.
Conclusion: We have developed a systematic tool for analyzing multiple machine log files for the Mevion S250i Hyperscan system. In forthcoming publications we will be applying this analysis tool for the quality assurance of treatment log files.