Development of a SiPM-based detection module for prompt gamma imaging in proton therapy

We describe here a new SiPM-based prototype of detection module for prompt gamma imaging (PGI) in proton therapy, illustrating the preliminary experimental results in terms of energy resolution. Treatments delivered by proton therapy are affected by uncertainties on the range of the beam within the patient. To reduce these margins and deliver safer treatments, different projects are currently investigating real-time range control by imaging prompt gammas emitted along the proton tracks in the patient. The potential of this concept for real-time range monitoring has recently been confirmed, also with Silicon PhotoMultiplier (SiPM-based) gamma cameras. The prototype here presented is based on a 2-dimensional projection of the beam on a pixelated detection module to improve count rate capability thanks to the detector segmentation. The photodetector is produced with a new High-Density (HD) SiPMs technology available at Fondazione Bruno Kessler (FBK, Italy) and designed to improve the detection of high-energy gamma rays. The detector is composed by an array of 8 × 8 SiPMs: a single SiPM has an active area of 4 mm × 4 mm, 15 μm × 15 μm microcells, for a total of 70000 microcells. Each SiPM is coupled to a 4 mm × 4 mm × 22 mm LYSO crystal. Signals are processed by two ASICs, improving the compactness of the system, and acquired by an external Data Acquisition System (DAQ). The module also implements an automatic temperature control strategy based on a SiPMs gain stabilization loop. The module was characterized in term of energy resolution up to 1.33 MeV. Preliminay results showed an estimated energy resolution of about 13%, 11% and 9% at 662 keV, 1.17 MeV and 1.33 MeV respectively.