BACKGROUND: Accurate range verification is crucial in hadrontherapy to fully exploit the ballistic advantages of charged particles and prevent damage to healthy tissues. Among the proposed approaches, prompt gamma imaging (PGI) has emerged as an effective technique for real-time monitoring, but its performance is limited by the intense neutron background generated during irradiation, especially with carbon-ions. PURPOSE: This work presents a Monte Carlo study performed with the FLUKA code to investigate prompt gamma and neutron emission in proton and carbon-ion therapy. A prototype detection system based on a knife-edge collimator coupled to a pixelated LYSO scintillator was simulated to evaluate its capability for range verification. The aim is to quantify how neutron fields and neutron induced signals bias or degrade range related quantities, and how these effects differ between proton and carbon-ion beams. METHODS: The analysis includes the characterization of prompt gamma energy spectra and spatial profiles, the assessment of neutron fields within a treatment room, and the decomposition of the detector signal into primary gammas, secondary gammas, and neutrons. RESULTS: Results show that prompt gamma profiles correlate well with the Bragg peak position, particularly within the 3-7 MeV energy window, while carbon ions exhibit higher prompt gamma yields but also significantly stronger neutron backgrounds compared to protons. Detector simulations highlight the impact of neutron capture on lutetium, producing distinct peaks that must be accounted for in the detector signal analysis. The fall-off retrieval precision (FRP) analysis indicates that the distal fall-off of prompt gamma profiles can be used to estimate the Bragg peak position, while secondary radiation components introduce additional fluctuations that affect the achievable precision, particularly for carbon-ion beams. CONCLUSIONS: The study provides a detailed characterization of prompt gamma and neutron contributions in proton and carbon-ion therapy and highlights the main physical factors affecting PGI-based range monitoring, particularly in the presence of neutron-induced backgrounds. These results provide useful insights for the design and optimization of prompt gamma detection systems in clinical applications.
Bellotti et al. (Thu,) studied this question.