Validation of a FLASH-ready 25 MeV proton beamline for preclinical radiobiology experiments

Abstract Objective: Ultra-high dose rate irradiation (FLASH) is a promising way to reduce the adverse effects of radiotherapy treatment. However, the impact of dosimetric parameters on the FLASH effect is still not well understood and few devices can deliver irradiation in FLASH conditions. The aim of this study is to demonstrate the capability of a 25 MeV proton beamline to deliver the prescribed dose to a biological sample in conventional and FLASH conditions.Approach: We characterized the different parameters influencing dose delivery (beam energy, irradiation time, beam intensity) to confirm the accuracy of our irradiation protocol. In parallel, we developed a Monte-Carlo simulation of the beamline for irradiation planning. Then dose uniformity and reproducibility with respect to dose rate were then evaluated using radiochromic films.Main results: The uncertainty on dose delivery is around 1% for both conventional and FLASH dose rates. Dose monitoring shows that the prescribed dose is delivered within a margin of 3%, with a uniformity better than 5% for a dose rate up to 150 Gy/s.The results of the Monte-Carlo simulation of the beamline are in strong agreement with our experimental measurements, thus validating the model.Significance: This work demonstrates the validation of a passive irradiation beamline delivering uniform irradiation with dose rates up to 150 Gy/s for centimetric irradiation fields. By characterizing beam parameters independently, we propose a dose validation method for beam energies where standard dose-calibrated detectors cannot be used.