Commissioning the First Upright Proton Therapy System with Matched Beam Quality In a Synchrotron Based Two-Room Facility
Abstract
Purpose
We report the first clinical implementation integrating a 6D upright treatment chair and a vertical CT system for image-guided proton therapy on a synchrotron-based fixed-beamline. This design aims to improve patient workflow and reduce the facility footprint while preserving small-spot pencil-beam scanning(PBS) performance.
Methods
A 6D upright chair was integrated with a vertical CT system to provide diagnostic-quality imaging in the treatment position. Small-spot PBS performance was preserved by tuning to match our gantry-room with identical source-to-axis distances(SAD). A dedicated compact nozzle allows the snout to rotate toward the ceiling, providing sufficient clearance for patient CT simulation and alignment. An upright-specific coordinate and scan-direction convention was implemented, with scanning-magnet directions reversed relative to the gantry-room. Upright beam commissioning included MU/spot and output calibration, SAD verification, spot profile measurements, and integrated depth-dose(IDD) curves for energies 70.5-228.9MeV. Two range-shifter solutions were implemented to support variable air gaps and field sizes while maintaining spot quality.
Results
The system delivers 98 discrete energies with range spacing of <1mm at low energies and up to 6mm at high energies. Bragg peak widths(R80-R80) ranged from 1.2-8.4mm. Spot characteristics measured using the XRV2000 at isocenter showed spot sigma of 2-5.5mm for energies 228.9-70.5MeV. A fixed 4cm WET range shifter and 39cm snout position provided a maximum field size of 30×40cm². The snout-mounted range shifter uses 10 discrete positions enabled smaller, variable air gaps for a sharper penumbra. Output calibration was established using a SOBP beam, where 200MU corresponds to 200cGy with a SAD mid-plan setup.
Conclusion
Proton beam quality was maintained for high-quality treatment delivery, including the largest 30×40 cm² field size, in the upright configuration. This integrated synchrotron-based platform—vertical CT at the treatment position and a 6D upright chair—provides a practical foundation for broader future clinical deployment and continued development of upright proton therapy.