Very High Dose Rate Proton Dosimetry with Radioluminescent Silica-based Optical Fibers

We investigated the radiation-induced luminescence of Cerium and Nitrogen doped optical fibers at high dose-rates (> 40 Gy(H 2 O)/s) using high energy proton beams (19-73 MeV) at flux and fluences representative of FLASH radiotherapy treatments. For each fiber material, we evaluated the dosimetry performances of both pristine (not-irradiated) and pre-irradiated samples to study the effect of an X-ray pre-treatment, up to a dose of 260 kGy. The core sizes of 50 μm for the Ce-doped fiber and 62.5 μm for the N-doped one offer exploitability in terms of spatially-resolved dosimetry for proton therapy beams. We also improved the fiber dosimetry calibration running Geant4 and SRIM simulations to obtain the conversion factors between the dose rate values, usually given in water, and those for our silica-based samples. The two fibers exhibit promising features since with only one calibration, we can obtain information about the dose rate and the dose at the same time, due to the same fiber sensitivity to both quantities. Finally, we checked the sensors response for different proton energies, obtaining a less than 15% dispersion for the Ce-doped fiber sensitivity from 19 to 73 MeV. For very high dose rate applications, the pre-irradiated Ce-doped optical fiber shows the most promising characteristics.