Patent Number: 
Section: claims

1. A multi-leaf collimator device for radiotherapy, comprising:a frame that has a box shape and through-holes formed in top and bottom surfaces thereof;a plurality of collimators that are received in the frame, wherein each of the collimators comprises a rack gear formed on a top surface of the collimator, and the collimators are symmetrically arranged in a left-right direction about a central portion of to the frame and are slidably provided on the frame; anda motion driving unit that comprises a pinion gear that is formed to be detachable from the rack gear formed on the top surface of the collimator, and is provided on the frame to move the pinion gear in a front-back direction of the frame and a up-down direction of the frame. 2. The multi-leaf collimator device of claim 1, wherein two motion driving units are symmetrically arranged in the left-right direction of the frame. 3. The multi-leaf collimator device of claim 1, wherein the motion driving unit comprises:a ball screw that extends in a direction perpendicular to a direction in which the collimator slides;a first motor that is coupled to an end portion of the ball screw;a ball nut that is coupled to the ball screw;a moving member that is fixed to the ball nut;an elevation member that is elevatably coupled to the moving member;the pinion gear that is provided on a lower end portion of the elevation member to be rotatable relative to the elevation member;a pulley that is integrally coupled to a rotational shaft of the pinion gear;a second motor that is fixed to an upper end portion of the elevation member; anda timing belt that connects a rotational shaft of the second motor and the pulley. 4. The multi-leaf collimator device of claim 3, further comprising a linear motion guide that is disposed parallel to the ball screw such that the moving member is slidable. 5. The multi-leaf collimator device of claim 3, wherein the elevation member is elevatable by using air pressure. 6. The multi-leaf collimator device of claim 5, wherein the motion driving unit is controlled by a computer.