Requirements for a Compton camera for in-vivo range verification of proton therapy

To ensure the optimal outcome of proton therapy, in-vivo range verification is highly desired. Prompt gamma-ray imaging (PGI) is a possible approach for in-vivo range monitoring. For PGI dedicated detection systems, e.g. Compton cameras, are currently under investigation. The presented paper deals with substantial requirements regarding hardware and software that a Compton camera used in clinical routine has to meet. By means of GEANT4 simulations, we investigate the load on the detectors and the percentage of background expected in a realistic irradiation and we simulate gamma-ray detections, i.e. input data for the reconstruction. By reconstructing events from simulated sources of well-defined geometry, we show that large-area detectors are favourable. We determine the minimum number of valid events allowing for a statistically significant range assessment. Finally, an end-to-end test for a realistic patient scenario is presented: starting with a treatment plan, the gamma-ray emissions are calculated, the detector response is modelled, and the image reconstruction is performed. We conclude that, with respect to the achievable precision, the expected complexity, and high costs of an adequate detection system, in-vivo dosimetry with Compton cameras will hardly be realised.