The purpose of this study is to perform a first characterization and proof of principle investigation of a Compton camera setup composed by a scatterer component consisting of a pixelated GAGG crystal read out by a SiPM multi-pixel photon counter (MPPC) and an absorber component consisting of a monolithic LaBr 3 (Ce) scintillator read out by a 256-fold multianode photomultiplier (PMT). The rationale of the study is to develop a Compton camera system as a future ion beam range verification device during particle therapy, via prompt gamma imaging. The properties to be investigated are the reconstruction efficiency and accuracy achievable with this system for detecting prompt-\gamma rays. The Compton camera system described has been tested with a laboratory radioactive Cesium137 source, in a certain geometrical configuration. The readout system is based on individual spectroscopy (NIM+VME) electronic modules, digitizing energy and time signals. The data have been analyzed to produce an input for the image reconstruction, performed using the MEGAlib toolkit software.