Design study of a Compton camera for prompt γ imaging during ion beam therapy

In hadron therapy in order to fully take advantage of the assets of the ion irradiation, the position of the Bragg peak has to be monitored accurately. Here, we propose a monitoring method relying on the detection in real time of the prompt γ emitted quasi instantaneously during the nuclear fragmentation processes. Our detection system combines a beam hodoscope and a double scattering Compton camera. The prompt γ emission points are reconstructed by intersecting the ion trajectories given by the hodoscope and the Compton cones reconstructed with the camera. We studied the influence of various parameters such as the photon energy and the inter-detector distances on the Compton camera response to a photon point source. This study was carried out by means of Geant4 simulations. In the current configuration, for a photon source with a typical prompt γ spectrum, the spatial resolution of the Compton camera is about 5.6 mm and the detection efficiency 10^-5.