Dosimetric characterization of an encapsulated waterproof silicon carbide detector with UHDR electron and proton beams for FLASH radiotherapy

Abstract Silicon Carbide (SiC) detectors have been widely demonstrated to be suitable alternative detectors for dosimetry in FLASH radiotherapy, showing radiation hardness and dose-rate independence at the FLASH radiotherapy instantaneous dose rates. However, the practical use of such devices in the preclinical/clinical environment still requires the development of special handy housing enabling the quality assurance (QA) measurements under the reference dosimetric conditions. A 10 μm thick, 4.5 mm2 area SiC detector produced by the STLab company was recently embedded at the INFN-Catania Division inside a plastic waterproof 15 mm diameter cylindrical housing. This encapsulated version of SiC (eSiC) allows the measurement of the dose in reference conditions and of the dose profiles in liquid/solid water phantoms for assuring high accuracy dosimetry QA procedures.Dosimetric characterizations were performed with both electron and proton beams at conventional and ultra-high dose rates (UHDR). A first experiment was carried out at the Centro Pisano for Flash Radiotherapy (CPFR) using UHDR 9 MeV electron beams to confirm the linearity of the charge response as a function of the dose per pulse (DPP) after the encapsulation procedure. A linearity from 1.8 Gy/pulse up to about 12 Gy/pulse, corresponding to an instantaneous dose rate of 3 MGy/s, was found.The percentage depth dose (PDD) distribution in water of 9 MeV electron beams was also measured and compared with the PDD measured with a PTW flashDiamond detector, used as reference dosimeter. The eSiC detector was also tested with proton beams accelerated by the IBA Proteus 235 cyclotron at the Trento Proton Therapy facility. A response independence on the total delivered dose (1-30 Gy) and average dose rate (50-530 Gy/s) was found using the UHDR 228 MeV proton beam available along the experimental beamline. The depth dose distribution measured with the eSiC within a liquid water phantom was successfully compared with the one simultaneously measured by the IBA PPC05 reference chamber, using 180 MeV clinical proton beams. The excellent results demonstrated that this first realized eSiC prototype can be used to accurately perform reference and relative dosimetry with UHDR electron and proton beams, contributing to support the clinical translation of FLASH radiotherapy.