Purpose: The Sphinx Compact (IBA dosimetry) is a relatively new daily QA phantom that offers the promise of efficient and fully automated proton QA that meets all of the recommendations of the AAPM TG224 report. Here, we summarize the data acquired using this phantom with the Mevion Hyperscan S250i system over a period of six months.
Methods: As part of daily QA protocol, the phantom was set up using room lasers and the positioning was verified using x-ray images of a fiducial marker within the phantom. Once the phantom was set up, a custom spot pattern wasdelivered that allows the verification spot position, spot shape, field homogeneity, beam energy and X-ray to proton beam coincidence. The image from the device was analyzed through the myQA software platform (IBA dosimetry) and the results were exported in CSV format. A separate database was created for further longitudinal analysis.
Results: The phantom has been in clinical use since April 2021. The spot position did not deviate from baseline by more than 1 mm (standard deviation of 0.2 mm), highest energy spot shape did show a trend that approached TG224 limits, requiring intervention to bring it back within specs. The beam flatness averaged 0.92% (0.12% standard deviation) and the depth of distal 80% dose did not change by more than 1 mm (standard deviation of 0.1 mm).
Conclusion: The data provided should allow future users to know what to expect from their daily measurements and properly set appropriate tolerance levels for warnings to be generated.