Multiple layer multileaf collimator

A multileaf collimator (12) for use in a radiation system (10) providing a radiation beam (20) in a given beam direction, comprising:

• a first layer (30) of a plurality of radiation blocking leaves (32), said leaves (32) being arranged adjacent one another so as to form two opposed rows of adjacently positioned leaves (32) and being movable in a longitudinal direction (Y) (34) which is generally traverse to the beam direction so as to define a radiation beam shaping field (36) between the opposed ends of the leaves (32);
• a second layer (40) of a plurality of radiation blocking leaves (42), said leaves (42) of said second layer (40) being arranged adjacent one another so as to form two opposed rows of adjacently positioned leaves (42) and being movable in a cross-over direction (X) (44) which is generally traverse to the beam direction and angled with respect to said longitudinal direction (Y) (34) so as to define a radiation beam shaping field (46) between the opposed ends of the leaves (42) of said second layer (40);
• and
• actuator apparatus (38, 48) for moving said leaves of said first layer (30) in the longitudinal direction (Y) (34) and said leaves (42) of said second layer (40) in the cross-over direction (X) (44), wherein said first (30) and second (40) layers are arranged one above another in an overlapping manner in the beam direction.