Hybrid Compton-PET imaging for Ion-Range Monitoring in Hadron Therapy

Hadron therapy is a rapidly growing cancer treatment, offering high precision in targeting tumors while sparing healthy tissue. However, its full potential is limited by uncertainties in the range of therapeutic ions, largely due to current reliance on X-ray CT-based planning. Real-time, accurate range verification methods are needed to further improve treatment accuracy. Two main gamma-ray imaging techniques have been studied for in-beam range verification: Positron Emission Tomography and Prompt-Gamma Imaging. The first is sensitive to β + isotopes produced during irradiation but faces challenges like biological wash-out and low signal-to-background ratios. The latter uses prompt gamma-rays for real-time monitoring but is technically challenging due to high backgrounds and detection difficulties. Combining both into a hybrid PGI-PET approach leverages the strengths of both methods, offering high spatial and temporal resolution. In this study, the first experimental results using a hybrid imaging system in a cross configuration are presented. The experiment was carried out at the Western Proton Therapy Center in Germany with 100 and 125 MeV proton beams. Polyethylene phantoms were irradiated and imaged using both techniques during distinct beam on and beam off periods. Results demonstrate successful 2D reconstruction of both imaging techniques. The PGI images show the Bragg peak position as a maximum in the heat map, while the PET images offer high spatial resolution of β + byproducts, allowing indirect inference of the Bragg peak. These findings illustrate the potential of hybrid PGI-PET imaging for accurate, real-time verification of proton range in hadron therapy.