A comparative investigation of Ce3+ doped single crystal scintillators covering radiotherapy and PET/CT imaging conditions

The aim of the present work is to study the performance of scintillators currently used in PET and animal PET systems, under conditions met in radiation therapy and PET/CT imaging. The results of this study will be useful in applications where both CT and PET photons as well as megavoltage cone beam CT (MV CBCT) photons could be detected using a common detector unit. To this aim crystal samples of GSO, LSO, LYSO, LuYAP and YAP scintillators, doped with cerium (Ce⁺³) were examined under a wide energy range (from 70keV to 4.5MeV). Evaluation was performed by determining the absolute luminescence efficiency (emitted light flux over incident x-ray exposure) in the energy range employed in X-ray CT, in Nuclear Medicine (70keV up to 662keV) and in radiotherapy (6MV or 2.5MeV-18MV or 4.5MeV). Measurements were performed using an experimental set-up based on a photomultiplier coupled to an integration sphere. The emission spectrum under x-ray excitation (130kVp) was measured using an optical grating monochromator to determine the spectral compatibility to optical photon detectors incorporated in medical imaging systems. Maximum absolute luminescence efficiency values were observed at 70 keV for YAP:Ce and LuYAP:Ce and at 140keV for LSO:Ce, LYSO:Ce and GSO:Ce. The highest absolute 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.