Ultra fast prompt-gamma imaging for the online monitoring of the ion range in hadron therapy

International audience; Uncertainties in the ion range mean that the ideal ballistic properties of ions are not fully exploited in hadron therapy. Prompt γ imaging using a Compton camera has been proposed as a method of range verification for hadron therapy. Previous Monte Carlo studies of the CLaRyS Compton camera prototype demonstrated a 2 mm precision in the measured proton range for 108 particle histories using an iterative method of reconstruction of the γ emission profile. Using a hodoscope the reconstruction is simplified as for each detected event, the number of possible solutions is reduced to just two. Whilst the line cone reconstruction method is much faster than the iterative method, its precision was found to be worse due to the inability to discriminate between the two solutions. The aim of this study was to investigate the effect of temporal resolution on the precision of the range measured using the line cone reconstruction method and to propose a method of solution discrimination based on the time flight (TOF). To this end, GATE Monte Carlo simulations were performed. Protons of 160 MeV (109) were generated towards a cylindrical PMMA phantom. The GatePulseAdder was used to record coincidences between the scatterer and absorber stages of the CLaRyS camera. For each set of coincidences the line cone reconstruction was performed. For each solution, a TOF was estimated for the corresponding track (proton + γ) and compared to the TOF given by the simulation. The difference between the two, ΔTOF, was used to discriminate between the two solutions. The effect of the temporal resolution was investigated by placing an upper threshold on ΔTOF and the resulting emission profiles were compared to the real γ emission profile. It was found that a better temporal resolution resulted in a profile which more closely matches the real profile. It is envisaged to redesign the CLaRyS Compton camera with a fast scintillator such as CeBr3 to perform online range verification in hadron therapy.