Development of Proton Ultra-High-Dose-Rate Spatially Fractionated Radiotherapy Irradiations for Preclinical Experiments on a Compact Proton Synchrocyclotron
Abstract
Purpose
This study aims to investigate the develop ultra-high-dose-rate (UHDR) proton FLASH spatially-fractionated-radiation-therapy (FLASH-SFRT) irradiations on a compact proton synchrocyclotron for preclinical experiments.
Methods
A specialized FLASH-SFRT brass collimator measuring 11×11×8cm3 was designed with 71 circular apertures measuring 0.5cm diameter, 1.7cm center-to-center (c-t-c) distance. These apertures were designed to be divergently matched to a clinical proton synchrocyclotron (IBA Proteus®ONE) at a collimator-to-isocenter distance of 9cm. Dose calculations were performed with three different spot trajectories: 10×10cm2 uniformly-weighted map at 0.5cm spot spacing and targeted spot maps consisting of 0.5×0.5 and 1.0×1.0cm2 fields centered over each aperture at similar spot spacings. 2D profiles were measured at 2.0cm solid-water depth (2.066cm WET) with Lynx PT scintillator. Profile comparisons between different spot trajectories and between experiments and TPS were performed with 2D gamma analyses at 2%/2mm criteria. Absolute dose measurements were performed at the central peak and neighboring valley with Razor Nano and microDiamond detectors with cross-calibrations against an ADCL-calibrated PPC05 plane-parallel ion chamber.
Results
Lynx scintillator response at UHDRs were within ±1% with conventional dose-rate (CONV) response. Experimental 2D profiles across all spot trajectories were well-matched with gamma pass rates above 98.0%. Comparisons between experiments and TPS had gamma pass rates above 95.6%. Gamma analyses showed slight deviations at off-axis-distances beyond 4.5cm. Absolute UHDR doses measurements were within 1.32%±1.99% and -1.43%±3.15% across the peak and valley respectively. Proton PBS and voxel-wise maximum dose-rate calculations for targeted spot trajectories across the central nine apertures were above 60 and 300Gy/s respectively at a maximum nozzle current of 129.5 nA.
Conclusion
In this work, we demonstrated that FLASH-SFRT irradiations can be performed on a clinical proton synchrocyclotron with a brass collimator. Proton UHDRs can be achieved with targeted spot trajectories over each aperture.