Model for the design of a prompt gamma detection system using large scintillators and digital silicon photomultipliers

Proton therapy is supposed to be advantageous compared to classical radiation therapy in oncology. But range uncertainties can arise easily and have to be corrected for, preferably immediately during irradiation. Prompt gammas are a good means of instantaneous localization of the dose deposition. Detection systems have to cope with high counting rates, an energy region of up to several MeV and increased background due to secondary emissions, while providing reliable information on energy, timing and location of the detected gamma ray. Various concepts utilize these prompt gammas for dose verification like collimated systems, Compton cameras or prompt gamma timing method. The digital silicon photomultiplier (dSiPM), being a favorable alternative to PMTs because of good timing performances and no requirement of further electronics, has been modelled in order to understand the complex behavior when working with monolithic scintillation crystals. Especially the selection of trigger- and validation-parameters may lead to different spectrum shapes. This model will be helpful for finding best parameter settings for the required task, because it determines the photons lost in various processes as well as the trigger timing information. Comparison of modelled spectra and measured spectra are presented.