Full in-beam PET measurements of 62 MeV protons onto a PMMA target

Positron emission tomography (PET) is a valuable technique to monitor in situ and non-invasively the particle range in ion beam therapy exploiting the beta+ activity produced in nuclear interactions along the beam path within the target volume. Due to the high random rates and dead-time losses induced by the particle spills, as of to date data are usually acquired during beam pauses or after the irradiation. We have developed a new PET prototype with a faster photon discrimination component that reduces the front-end dead time, and a modularized acquisition system that parallelizes the sensitive detector area, so as to enable data acquisition also during therapeutic irradiation (full in-beam measurement). The PET system has been able to sustain the single photon count rates and acquire coincidences during the beam, in conditions of sub-clinical beam currents. A study on the paralyzation conditions and dead time losses under different beam currents is presented and the feasibility of a full in-beam PET scanner is discussed.