First Experimental Measurement of Prompt Gamma Imaging With Real-Time Neutron Rejection via Pulse Shape Discrimination

Abstract

Prompt gamma imaging (PGI) holds strong potential for range verification in hadrontherapy; yet, its performance is challenged by neutron-induced background, especially in carbon ion treatments. To mitigate this issue, a dedicated imaging system integrating pulse shape discrimination (PSD) capabilities for real-time neutron discrimination was designed and experimentally validated. The detector employs a Cs₂LiYCl₆:Ce (CLYC) scintillator coupled to SiPM arrays and compact acquisition electronics, allowing real-time computation of digital PSD coefficients. Interaction point reconstruction within the crystal is achieved through an artificial neural network (ANN), whose inputs are the SiPM signal amplitudes processed by four custom 16-channel GAMMA application-specified integrated circuits (ASICs). In this work, the system is operated as a prompt gamma (PG) camera using a knife-edge (KE) collimator to retrieve PG emission profiles from the irradiated target, enabling range verification while efficiently reducing uncorrelated neutron contributions. We present the outcomes of the first experimental PGI campaign at the Centro Nazionale di Adroterapia Oncologica (CNAO), Pavia, Italy, during carbon ion irradiation, demonstrating, according to our knowledge, the first improvement in Bragg peak (BP) localization precision enabled by PSD-based neutron background rejection.