Prompt gamma timing for range verification with carbon ion irradiation: first experimental measurements and...

Prompt gamma timing (PGT) is a promising technique forin vivorange verification in particle therapy, exploiting the time-of-flight between primary particles and prompt gamma rays emitted by nuclear interactions. PGT distribution is highly sensitive to beam energy and target density, which, under controlled detector positioning, makes it particularly valuable in real-time monitoring of particle range, detection of morphological changes, and implementation of adaptive treatment strategies to further optimize dose delivery.Objective.In this study, we investigate for the first time the application of the PGT approach in carbon ion therapy.Approach.Measurements were performed using a dedicated high-performance detection system composed of a silicon strip sensor for primary ion timing and a secondary radiation detector consisting of a LaBr3(Ce) scintillator read out by a SiPM matrix. Carbon ion beams with kinetic energies of 166.41, 268.86, and 398.84 MeV u-1irradiated a homogeneous 30.0 cm thick polymethyl methacrylate target at the National Centre of Oncological Hadrontherapy (Pavia, Italy). The secondary radiation detector was positioned in four different off-beam positions to assess the robustness of the PGT technique. Monte Carlo simulations based on the Geant4 toolkit were carried out for all experimental scenarios to evaluate agreement with measurements and assess the predictive capability of the simulation framework.Main results.A quantitative bin-by-bin comparison of experimental and simulated PGT intensities demonstrated strong agreement within the 95% confidence interval, with no incompatible bins at 166.41 MeV u-1, at most 1% at 268.86 MeV u-1, and up to 8% at 398.84 MeV u-1, depending on detector position. Prompt gammas were identified as the dominant contribution to the detected signals, particularly for detector positions upstream with respect to the primary particle beam, minimizing signal contamination from neutrons and charged fragments.Significance.The validated experimental-simulation framework confirms the capability of the proposed PGT system to resolve energy-dependent differences and highlights its potential for detecting clinically relevant changes in the particle beam range, supporting further development toward real-time monitoring in carbon ion therapy.