A radiation delivery system includes a chair on which the patient may be seated during treatment and a modulating assembly (10) for use in radiotherapy comprises a modulator wheel (15), said modulator wheel being shaped as a rim defining the circumference of a circle or an elliptic shape, and having varying thickness around the circumference, said modulator wheel (15) being arranged in such a way that a beam traveling from a radiation source (13) to a patient will intersect the rim of the modulator wheel, said wheel being arranged to rotate in such a way that the beam will intersect the rim in varying positions around the circumference. The wheel will modulate the energy of the beams passing through material having varying thickness as the modulator wheel rotates.