Patent ID: 7564951

Claim:
A multileaf collimator comprising: a first leaf block group including a plurality of leaf blocks arranged in a direction; a second leaf block group including a plurality of leaf blocks arranged in the same direction as the first leaf block group, the leaf blocks of the second leaf block group being opposed to the leaf blocks of the first leaf block group in a direction orthogonal to the direction in which the leaf blocks of the first leaf block group are arranged; a plurality of drive mechanisms provided on the respective leaf blocks of the first and second leaf block groups, the drive mechanisms moving the leaf blocks of the first or second leaf block group in an oncoming direction in which the leaf blocks of the first or second leaf block group come close to the leaf blocks of the second or first leaf block or in a departing direction in which the leaf blocks of the first or second leaf block group depart from the leaf blocks of the second or first leaf block group; a plurality of magnetic layers which are provided on the respective leaf blocks of the first and second leaf block groups so as to be positioned on faces of the leaf blocks along a moving direction of the leaf blocks, each of the magnetic layers having a first magnetized part which is magnetized in a north pole and a second magnetized part which is magnetized in a south pole; a plurality of magnetic sensors which are provided on the respective leaf blocks of the first and second leaf block groups, the magnetic sensors being stationary in a noncontact state with respect to the respective leaf blocks, the magnetic sensors varying output signals when the respective leaf blocks are moved in the oncoming direction or the departing direction; and a control device which controls the drive mechanisms according to the output signals delivered by the respective magnetic sensors so that a space defined between the leaf blocks of the first and second leaf blocks is adjusted into a target configuration.