CHEMONO: A Cherenkov-Only Monolithic Detector for PGI in Proton Range Verification

Proton range verification (PRV) in proton therapy is an unmet clinical need. Prompt-gamma imaging (PGI) using thick collimators is a PRV modality that has obtained the most success to-date. The gamma detectors in such approach consist of scintillation crystals coupled to photodetectors. In this work, we report the development and use of detectors made of monolithic pure Cherenkov emitter crystals for the same purpose. We demonstrate for the first time the ability of such detector configuration to provide spatial resolution information in one direction using measurements from a collimated slit. The detector consisted of a PbF2 crystal with dimensions 25 ×25 × 10 mm coupled to a S13361-3050AE-08 array of 8x8 SiPMs from Hamamatsu. The SiPM array was connected to a row-column readout, with 8+8 channels, and triggered on the sum of the columns. Three different event reconstruction algorithms were tested: center of gravity (CoG), rise to the power (RTP), and neural-network (NN). The NN yielded the best spatial resolution, with 3.7±0.9 mm full width half maximum (FWHM) in average for all positions. CoG and RTP also showed a consistent shift with the change of position of the slit, although with more modest results, between 4 mm and 7 mm in average for all positions. This is the first characterization of monolithic pure Cherenkov emitters for Multi-MeV gamma imaging. Results are promising for this detector concept, showing that it can offer an alternative for collimated PGI in PRV with potential of sustaining high count rates, with effective background rejection, and low production costs based on the cost of primary components of the crystals.