SU‐E‐T‐122: Routine Quality Assurance for the MEVION S250 Proton System

Purpose: We have established a robust and efficient daily routine to ensure our proton radiotherapy imaging and delivery systems operate as expected. Our goal was to prioritize tests according to impact, and have them completed by our therapists in 30 minutes. Methods: Morning warm‐up includes recording of machine startup parameter and noting faults, and connectivity to MOSAIQ. Safety checks include warning lights; Beam On, X‐ray On, and Magnet On, audio/video, door interlocks, neutron detector, beam pause recovery, and pendant functions. Patient alignment checks include lasers vs. scribed phantom. Imaging checks include; panel distance, image and centering vs. lasers, isocentricity (scribed phantom), 2D/2D match (offset fiducials) using Daily (dosimetry) QA device, 6D table translations/angulations, and coincidence of proton and x‐ray beam with film. Daily dosimetric checks focus on any one of 24 options available, using the Daily QA3 device and a range compensator (RC) idealized for the particular option. All options are checked over 5 weeks. With a single exposure the designated; range, modulation, output peak/plateau ratio, SOBP flatness, and lateral profile symmetry/flatness are measured and reviewed. The custom RC has 4 quadrants of different thickness that shadow detectors strategically, corresponding to one location in the plateau, two in the SOBP, and one just beyond the range. Results: Daily QA takes <30 minutes. The single exposure for dosimetric checks is sensitive enough to detect; a change in output of 1%, change in range and modulation of 1mm, and changes in SOBP flatness and profile attributes of 2%. Using the daily dosimetry device for imaging saves considerable time. Conclusion: We have daily tests for an efficient yet robust to ensure patient and employee safety. These tests fall in line with the forthcoming TG224 report.