Prototype Scintillating-Fiber SiPM-Based Beam Monitor for Conventional and FLASH Proton Therapy

The development of FLASH particle therapy, especially proton therapy, characterized by ultra-high dose rates (>40 Gy/s), presents significant challenges for dosimetry and beam monitoring. For example, ionization chambers (ICs) exhibit charge recombination effects leading to saturation, and other passive detectors cannot be used for real-time monitoring. This paper presents the idea, simulations and the preliminary prototype of a scintillating-fibers SiPM-based dosimeter for both high-flux and conventional dose-rate proton beam therapy. The prototype is based on 1 mm diameter plastic scintillating fibers, coupled to Silicon Photomultipliers (SiPMs). We estimated the interactions and the produced light signal within the fibers by the protons and towards the photodetectors using a semi-analytical model combining SRIM and analytical calculations. We estimated a light signal reaching the SiPMs in the range of 107–1011 photons (in a 50 ms beam pulse), for proton energies in the range 70–228 MeV, between the minimum and maximum beam current levels for conventional and FLASH conditions. Results highlight the very large dynamic range needed to be compatible with conventional and FLASH regimes. We also evaluated the linearity limits of the SiPMs and of the scintillating fibers. Finally, we preliminarily validated a reduced prototype version with a proton beam, demonstrating a good linearity of the system.