Room: Exhibit Hall | Forum 7
Purpose: To report commissioning experience for a Mevion S250i with Hyperscan pencil-beam scanning (PBS) proton therapy system.
Methods: Mevion S250i is equipped with adaptive aperture for beam sharpening and capable of delivering fast volumetric PBS with a 190-degree rotating, gantry-mounted proton accelerator and a robotic couch system. The commissioning included testing and verification of mechanical and imaging system, beam data collection, and commissioning of a RaySearch RayStation treatment planning system (TPS). First, mechanical integrity of gantry and couch, safety interlocks, and performance of imaging system were tested. Second, beam data (integrated depth doses (IDDs), spot profiles, output variations, and an IROC TLD audit) were collected through effective sampling of 152 Bragg peak energies. Third, the TPS was commissioned through four sets of data collections (an in-water Bragg peak IDD scan of the highest energy (227.15 MeV), in-air spot profile scans of the highest energy at six different distances from the source, an absolute output of the highest energy at 5 cm depth, and an HU-to-mass density conversion curve) and tested with plans for simple and AAPM TG119 targets through dose measurements with a parallel plate chamber, film, and a 2D array detector. Finally, an anthropomorphic phantom was scanned and heterogeneity effects were tested by the 2D array detector in conjunction with end-to-end testing.
Results: Beam characteristics (ranges, output variations, and spot positions) agreed well with the vendor specifications. The TPS calculations for the simple-target and phantom plans were in good agreement with measured ones (<3% error and gamma passing rate â‰¥95% with 3%/3 mm criteria) except for small targets (target dimension â‰¤ ~3 cm). Dose difference of the IROC TLD measurement was within 2%. The end-to-end test showed the TPS reasonably predicted dose in heterogeneous medium.
Conclusion: The commissioning of the proton system was successfully completed for clinical use.