Gd2SiO5:Ce (GSO:Ce) is a high-Z, nonhygroscopic fast emitting scintillator used in detectors of some positron tomography systems. The purpose of this study was to evaluate the luminescence of GSO:Ce scintillator at lower photon energies employed in other fields of medical imaging (e.g. x-ray computed tomography, general x-ray imaging, low energy gamma ray imaging). To this aim the absolute luminescence efficiency (emitted light flux over x-ray exposure), the matching factor (spectral compatibility to optical detectors) and the effective efficiency (combination of absolute efficiency with spectral compatibility) were experimentally determined. Various xray tube voltages ranging from 20 to 140 kV (employed in xray mammography, general radiography, and computed tomography) were used. In addition the behaviour of GSO: Ce under low energy gamma irradiation could be estimated from these data. Measurements were performed using an experimental set-up based on a photomultiplier coupled to an integration sphere. The GSO:Ce optical emission spectrum was measured under x-ray excitation using an optical grating monochromator. The efficiency of GSO:Ce was found to increase with increasing x-ray tube voltage, while the GSO:Ce spectrum, peaking at 440 and 490 nm, was found compatible with most optical detectors (photodiodes, photocathodes, charge coupled devices). However the spectral compatibility (0.77) and the effective efficiency were found highest for GSO coupled to photodiode.