A collimation assembly includes a multileaf collimator and motion assembly. The multileaf collimator includes a support body and a plurality of pairs of beam blocking leaves supported by the support body. The beam blocking leaves are longitudinally movable in a first direction. The motion assembly includes an actuator and a guide assembly operable to move the support body and thereby allowing the plurality of pairs of beam blocking leaves to move in a second direction generally transverse to the first direction.
