A system for radiotherapy is described. The system includes an accelerator of an electron beam, an imaging apparatus, a control unit and a radiation dose sensor connected to the control unit equipped with a program configured to execute the steps: (i) setting a first intensity of the electron beam, according to a predefined image of a target zone, the intensity to be emitted in a first radiation (ii) operating said accelerator to emit the first radiation being a fraction of the first intensity (iii) detecting a real intensity during the first radiation by the radiation dose sensor (iv) acquiring an image of the zone (v) calculating an intermediate intensity according to the image acquired in the step (iv) and according to the real intensity and (vi) comparing the first intensity with the intermediate intensity to calculate a final beam intensity for a subsequent second radiation
