Abstract: The invention concerns a method, a sensor and a radiographic imaging system in real time for discriminating the low energy ionizing radiation, corresponding at least partially to dispersion radiation, thereby eliminating their contribution in the sensed image, so as to increase the contrast, for relatively reduced amounts of incident radiation. In the figure is presented a radiographic system more particularly designed for radiotherapy, basically consisting of an accelerator (1) emitting a collimated beam (3) of photons and in particular of X-rays towards a patient lying down (2). The patient is positioned so as to enable the best possible localization not only of the collimated gamma or X-ray beam impact but its depth as well and the localization of the portion where the major part of the dose is to be delivered.