38 Plastic Scintillator Dosimetry of Ultrahigh Dose-Rate 200 MEV Electrons at Clear

Very high energy electron (VHEE) beams with energies greater than 100 MeV may be promising candidates for FLASH radiotherapy due to their favourable dose distributions and accessibility of ultrahigh dose-rates (UHDR). Combining VHEE with the normal tissue-sparing FLASH effect of UHDR radiotherapy could improve patient outcomes. The standard dosimeters used for conventional radiotherapy, including ionization chambers and film, have limited application to UHDR radiotherapy due to deficits in dose rate independence and temporal resolution. Plastic scintillator detectors (PSDs) are a potential alternative. PSDs connected to a Medscint Hyperscint RP-100 were used to measure the response to 200 MeV electrons produced by the CERN Linear Electron Accelerator for Research (CLEAR). The dose-response linearity and radiation hardness of PSDs under UHDR VHEE conditions was investigated, using dose rates up to 1.21 × 10 ⁹ Gy/s. Two scintillators were investigated: a polystyrene-based BCF-12 and a proprietary polyvinyltoluene (PVT)-based material. The BCF-12 probe exhibited linear light output with dose per train from 4.9 to 125.2 Gy, and dose rates up to 1.16 × 10 ⁹ Gy/s within a single pulse. The output of the PVT-based probe was linear from 3.9 to 59.5 Gy per train, and dose rates up to 9.92 × 10 ⁸ Gy/s. While output linearity was retained (R ² > 0.998) after delivering 26.2 and 13.8 kGy to the BCF-12 and PVT-based probe, respectively, the light output was reduced by < 1.5%/kGy. The performance of PSDs in this work suggest they may be useful real-time dosimeters for applications in UHDR VHEE radiotherapy.