Performance of the prompt gamma-ray timing system prototype under clinical-like conditions

Objective. Prompt gamma-ray timing (PGT) is a technique forin vivoproton range verification. This work presents the latest PGT system prototype and evaluates its operational performance in clinical-like settings.Approach. Irradiation fields with clinical characteristics were applied to an anthropomorphic head phantom using pencil beam scanning. A fully equipped PGT system, comprising eight detectors, measured emitted gamma rays. The study investigated: (1) the system's count rate capacity and statistical capabilities with clinical beams; (2) the impact of a proton range shifter on the PGT signal; (3) the influence of beam scanning on time distributions; (4) the temporal stability of the mean timing signal (PGT mean).Main results. The data acquisition system successfully handled count rates from a wide range of pencil beams (-protons/spot). Although the pile-up rejection mechanism reduced the maximum throughput by about half, the PGT system consistently recorded 100500 events for typical clinical spots (-protons/spot), enabling further signal enhancement through spot clustering and event aggregation across detectors. For low- and mid-energy layers (e.g. 104 MeV), most detected events (about 70%) originated from the range shifter, providing a target-independent reference that could be used to calibrate PGT distributions. Spot-wise time distributions showed shifts due to the scanning-beam dynamics; therefore, a dedicated correction method was developed. The stability of the PGT mean was limited mainly by long-term phase drift, introducing systematic uncertainties accumulating at 0.036-0.129 mm per second of irradiation, and statistical fluctuations, corresponding to random uncertainties of around 1.8-2.3 mm (1) for the eight-detector system prototype. Additionally, detector-specific responses to identical irradiation conditions were observed, outlining directions for further system optimization.Significance. The PGT system reliably operated under near-clinical conditions, with proposed solutions supporting its clinical translation. These results establish key methodological foundations for clinical application of PGT.