A multi-element-amorphous-silicon detector-array real-time imager and dosimeter for diagnostic or megavoltage X rays having megavoltage photons having a plurality of photodiodes (30) made of hydrogenated amorphous silicon arrayed in columns and rows upon a glass substrate (12). Each photodiode (30) is connected to a thin film field effect transistor (52) also located up- on the glass substrate (12). Upper and lower metal contacts (22, 38) are located below and above the photodiodes (30) to provide the photodiodes (30) with a reverse bias. The capacitance of each photodiode (30) when multiplied by the resistance of the field effect transistor (52) to which it is connected yields an RC time constant sufficiently small to allow real time imaging.