Establishmet of Reproducible Ultra-High-Dose Rate Proton Beams Based on a Clinical Cyclotron System

Abstract

Purpose: Stable delivery of ultra-high-dose rates (UHDRs) proton beams for FLASH research remains technically challenging. This study aimed to develop a UHDR proton beam on a clinical cyclotron with minimal beamline modifications and a time-gated control approach for experimental and preclinical FLASH research. Methods: UHDR proton beams were generated using a cyclotron-driven passive-scattering system without the range modulator and scatterer. Field broadening was achieved with thin lead foil, while a Raspberry Pi-based time-gated system was implemented to control beam-on duration independent of the monitor chamber. Beam profiles were evaluated using EBT-XD films. Results: Millisecond-scale beam delivery with high temporal reproducibility was attained for beam-on durations. A stable reference UHDR beam was established at 228 MeV and 200 nA, producing a Gaussian-like lateral profile with a 28.8 mm full width at half maximum at 2 g/cm2. Film dosimetry confirmed a central-axis dosage rate of approximately 70 Gy/s. Conclusions: This study demonstrates that clinically available clinical cyclotron systems can be adapted to generate UHDR proton beams suitable for FLASH research through time-gated control and minimal beamline modifications. The established reference beam configuration has potential for experimental and preclinical FLASH proton studies.