easyPET.3D Measurement of Positron Emitter Maps in Proton-Irradiated PMMA Phantoms

Accurate range verification is a critical component of proton therapy, ensuring that the high dose gradients characteristic of Bragg peaks are delivered precisely to the target volume. This work presents the first experimental evaluation of the easyPET.3D, a compact and cost-effective preclinical PET scanner, as a potential tool for quality control assessement. Homogeneous PMMA phantoms were irradiated at the Paul Scherrer Institute Gantry 1 facility using proton beam energies ranging from 138 MeV to 195 MeV. The resulting 3D β+ activity distributions were reconstructed and analyzed to assess the system's spatial accuracy, stability, and sensitivity. For the intermediate energy of 160 MeV, the measured activity profile showed a high degree of agreement with Monte Carlo (GATE) simulations, with a difference of 0.24 mm in the R_50%position. The system exhibited robust performance under varying irradiation conditions. Doubling the number of delivered protons relative to a clinically relevant value resulted in a deviation of only 0.4 mm in the calculated range, confirming the method's reproducibility. Furthermore, the system successfully resolved distinct beam paths in a dual-energy irradiation mode, distinguishing tracks separated vertically by 10 mm and quantifying longitudinal range differences.Sensitivity tests indicated that the system is capable of detecting longitudinal phantom displacements as small as 1mm. The relationship between expected and measured displacements followed a linear trend with a slope of 1.13, indicating a systematic overestimation of 13%, and an offset of 0.45mm, reflecting a small baseline bias. While further optimization of detector sensitivity and reconstruction algorithms is required to reduce acquisition times for routine clinical workflows, these findings validate the potential of easyPET.3D as a promising, accessible solution for proton range verification.