A collimator comprising a number of elements (leaves) that can be independently moved to produce radiation beams having complex shapes. For example, Varian's MLC has 52 motorized leaves, each 1 cm wide at isocenter, with 16 cm of overcenter travel. See al

Two banks of 60 leaves each, aligned along the X axis (with the lower jaws). Each leaf can move independently in the X direction, to crate a column that shape the beam from precise treatment. Each bank resides on a carriage that also can move in the X direction.