proton therapy, ultra‐high dose rate FLASH, robotic motion technique, Medical physics. Medical radiology. Nuclear medicine, R895-920, Neoplasms. Tumors. Oncology. Including cancer and carcinogens, RC254-282

Abstract Previously, a synchrotron‐based horizontal proton beamline (87.2 MeV) was successfully commissioned to deliver radiation doses in FLASH and conventional dose rate modes to small fields and volumes. In this study, we developed a strategy to increase the effective radiation field size using a custom robotic motion platform to automatically shift the positions of biological samples. The beam was first broadened with a thin tungsten scatterer and shaped by customized brass collimators for irradiating cell/organoid cultures in 96‐well plates (a 7‐mm‐diameter circle) or for irradiating mice (1‐cm2 square). Motion patterns of the robotic platform were written in G‐code, with 9‐mm spot spacing used for the 96‐well plates and 10.6‐mm spacing for the mice. The accuracy of target positioning was verified with a self‐leveling laser system. The dose delivered in the experimental conditions was validated with EBT‐XD film attached to the 96‐well plate or the back of the mouse. Our film‐measured dose profiles matched Monte Carlo calculations well (1D gamma pass rate >95% with the criteria of 2%/1 mm/2% dose threshold). The FLASH dose rates were 113.7 Gy/s for cell/organoid irradiation and 191.3 Gy/s for mouse irradiation. These promising results indicate that this robotic platform can be used to effectively increase the field size for preclinical experiments with proton FLASH.