SITH: a SiPM Readout ASIC for Prompt Gamma-Ray Detection in Hadrontherapy Applications

We present the design and experimental characterization of SITH, a custom-designed 16-channel ASIC for the readout of arrays of silicon photomultipliers (SiPMs) coupled to pixelated scintillators. This integrated circuit measures both the energy and time-of-arrival of the detected gamma photons and it is tailored for the specific application of prompt gamma imaging (PGI) for particle range verification in hadrontherapy treatments. The SITH ASIC features a low input impedance (<10Ω), an input dynamic range close to 80 dB with a full scale range of 5 nC, multiple triggering logic (internal/external), a power dissipation of 14 mW/ch and the flexibility for being used with both pixelated as well as monolithic scintillation crystals. Moreover, the input stage of each channel can process high input currents (in the tens of mA range) and can be coupled to large-area photodetectors (up to tens of nF). The coincidence resolving time (CRT) of annihilation events measured with 3×3mm 2 SiPMs coupled with 3×3×5mm 3 LYSO scintillators is close to 200 ps FWHM. The reported experimental measurements were conducted with a 16-channel prototype of a prompt gamma-ray detection module, which provides a real-time measurement of the gamma-ray hit position, energy and time-of-arrival through 16 time-to-digital converters (TDCs) implemented in FPGA. The maximum count-rate per channel is approximately 3 Mcps.