Multi-leaf radiation attenuator for radiation therapy

In a radiation therapy machine having a radiation source for producing a radiation beam directed toward a patient at a gantry angle, the beam including a plurality of adjacent rays, a compensator comprising:

• a first plurality of radiation attenuating leaves;
• and
• a second plurality of radiation attenuating leaves;
• a first supporting structure for guiding the first plurality of leaves between a closed state, each leaf thus occluding every other ray of the beam, and an open state outside of the radiation beam;
• a second support structure for guiding the second plurality of leaves between a closed state, each leaf thus occluding those rays of the beam not occluded by the first plurality of leaves when the latter are in the closed state, and an open state outside of the radiation beam wherein the first plurality of leaves in the closed state are positioned closer to the radiation source than the second plurality of leaves in the closed state;
• motivation means for independently moving each leaf between the open and closed states;
• and
• timing means communicating with the motivation means for controlling the ratio of the period of time during which each leaf is in the closed state to the period during which each leaf is in the open state to control the average fluence of each ray of the beam.