Design of a 64-channel modular platform for high-speed readout of scintillator-based detectors for range monitoring in hadrontherapy

The development of an electronic readout platform specifically designed for real-time range verification systems to be used in hadrontherapy is presented. Such modular systems are composed of multiple 64-channel gamma camera modules based on pixelated LYSO scintillator coupled with 15 μm cell SiPM arrays. Both the detector and the associated electronics are specifically designed to support range verification through Prompt Gamma Imaging (PGI). Such an application requires a specific electronics readout able to operate in a wide energy range (up to 10 MeV) and at high counting rates (up to 1 Mcps/ch). The system's modular structure allows it to accommodate various treatment plans and overcomes limitations related to patient anatomy and beam positioning. The detector is composed of 64-channel modules, each covering an area of 52.6 × 52.6 mm2, with each module consisting of two 32-channel front-end electronics readout and data acquisition systems (DAQ). The SiPMs outputs are processed by two 16-channel SITH ASICs. These integrated circuits are optimized for reading SiPM arrays and can handle high input currents (on the order of tens of milliamps), which makes them suitable for large-area photodetectors and high energy gamma rays. The DAQ architecture is based on a 32-channel sub-module and consists of two multi-channel Analog to Digital Converters (ADC) and an FPGA. The energy signals from the ASICs are digitized by an octal-channel, 12-bit, 65 Msps ADC. This ADC is multiplexed 2:1 to read all 16 channels of each ASIC. For precise timing measurements, 32 Time-to-Digital Converters (TDCs) are integrated within the FPGA, achieving a temporal resolution better than 300 ps (FWHM). In FPGA firmware a time-coincidence strategy has been implemented in order to reconstruct interactions resulting from Compton scattering and pair production.