Experimental stopping power estimation in a homogeneous phantom via prompt gamma timing towards proton therapy monitoring

The full potential of proton therapy is limited by uncertainties that prevent optimal dose distribution. Monitoring techniques can reduce these uncertainties and enable adaptive treatment planning. Spatiotemporal Emission Reconstruction from Prompt-Gamma Timing (SER-PGT) is a promising method that provides insights into both particle range and stopping power, the calculation of which normally requires knowledge about patient tissue properties that cannot be directly measured. We present the first experimental proof of principle obtained using a 226.9 MeV synchrotron-proton beam impinging on a homogeneous phantom at a subclinical intensity (2 - [Formula: see text] pps). SER-PGT uses data from a multidetector setup: a thin and segmented Low Gain Avalanche Diode for proton detection and Lanthanum Bromide-based crystals for photon detection. The estimated stopping power profile showed an 8%± 3% average error compared with the NIST PSTAR values, and a 2%± 2% deviation relative to water at 100 MeV. Range assessment in a phantom with a 4 cm air gap successfully identified the range shift with a 3 mm standard deviation. For this proof-of-principle irradiation scenario, the experimental results demonstrate the recovery of both range and stopping power information through SER-PGT, particle kinematics and PGT measurements in a homogeneous target.