Patent Number: 062663933
Section: claims

1. A multileaf collimator for use in a radiation system providing a radiation beam in a given beam direction, comprising: a first layer of a plurality of radiation blocking leaves, said leaves being arranged adjacent one another so as to form two opposed rows of adjacently positioned leaves and being movable in a longitudinal direction which is generally traverse to the beam direction so as to define a radiation beam shaping field between the opposed ends of the leaves;  a second layer of a plurality of radiation blocking leaves, said leaves of said second layer being arranged adjacent one another so as to form two opposed rows of adjacently positioned leaves and being movable in a cross-over direction which is generally traverse to the beam direction and angled with respect to said longitudinal direction so as to define a radiation beam shaping field between the opposed ends of the leaves of said second layer; and  actuator apparatus for moving said leaves of said first layer in the longitudinal direction and said leaves of said second layer in the cross-over direction, wherein said first and second layers are arranged one above another in an overlapping manner in the beam direction,  wherein said first layer has a first longitudinal axis and said second layer has a second longitudinal axis, and wherein said longitudinal axes at said leaves in said layers are mutually perpendicular, the layers lying in mutually parallel planes. 2. The multileaf collimator (12) according to claim 1 and wherein gaps (52) are formed generally traverse to the beam direction and generally in a plane of the X and Y directions (34, 44), each of said gaps (52) only allowing an amount of radiation to pass therethrough below a predetermined threshold. 3. The multileaf collimator (12) according to claim 1 and wherein said cross-over direction (44) is generally orthogonal to said longitudinal direction. 4. The multileaf collimator (12) according to claim 1 and wherein said leaves (32) of said first layer (30) and said leaves (42) of said second layer (40) are housed in a frame (50). 5. The multileaf collimator (12) according to claim 1 and comprising a source of radiation (19) for providing a radiation beam (20) in said given beam direction. 6. The multileaf collimator (12) according to claim 1 and comprising imaging apparatus (25) for imaging a target (37) irradiated by said radiation beam (20). 7. The multileaf collimator (12) according to claim 1 and comprising an optical control device (54) that monitors travel of any of the leaves (32, 42) and signals said actuator apparatus (38, 48) to stop moving said leaves (32, 42). 8. The multileaf collimator (12) according to claim 1 and comprising a plurality of said first layers (30) of radiation blocking leaves (32). 9. The multileaf collimator (12) according to claim 1 and comprising a plurality of said second layers (40) of radiation blocking leaves (42).