The present invention relates a detector (11) for detecting megavoltage X-ray radiation (3), comprising a scintillator (2) including a plurality of heavy scintillating fibers (13) for emitting scintillation photons in response to incident megavoltage X-ray radiation (3), a support structure (15) for supporting said plurality of heavy scintillating fibers (13) and holding them in place； and a photodetector (17) for detecting the spatial intensity distribution of the emitted scintillation photons. The present invention further relates to an apparatus (35) for radiation therapy comprising a particle accelerator (37) and a detector (11) for detecting megavoltage radiation. Still further, the present invention relates to methods for detecting X-ray radiation and for radiation therapy.
