Investigation of the performance of Ce3+ doped single crystal scintillators covering radiotherapy and PET/CT imaging conditions

The presented work is an investigation of the performance of currently used scintillators in PET and animal PET systems, under conditions met in radiation therapy and PET/CT imaging. The results of this study could be useful in designing a common detector system where both the CT and PET photons and/or megavoltage cone beam CT (MV CBCT) photons could be detected. The short decay time of the Ce³⁺ doped single crystal scintillators favors their use in combined PET/CT detectors. To this aim cerium (Ce⁺³) doped crystal samples of GSO, LSO, LYSO, LuYAP and YAP scintillators were examined under a wide energy range (from 70 keV to 4.5 MeV). Evaluation was performed by determining i) the luminescence efficiency (emitted light energy flux over incident x-ray or gamma -ray energy flux) in the energy range employed in X-ray CT, in Nuclear Medicine (70 keV up to 662 keV) and in radiotherapy (6 MV and 18 MV), ii) the spectral matching factor (expressing the spectral compatibility to optical photon detectors) and (iii) The effective efficiency (combination of luminescence efficiency with spectral compatibility). Maximum luminescence efficiency values were observed at about 70 keV for YAP:Ce and LuYAP:Ce and at 140 keV for LSO:Ce, LYSO:Ce and GSO:Ce. The highest luminescence efficiency of all the scintillators examined was observed for LSO:Ce. Finally the light emission performance of LSO:Ce and LYSO:Ce scintillation materials was found adequate for use in a single detector multimodality scanner.