Patent Number: 
Section: claims

1. 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; anda 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. 2. The multileaf collimator according to claim 1, wherein the first and second magnetized parts magnetized in the north and south poles respectively are disposed alternately in a direction of movement of the leaf blocks. 3. The multileaf collimator according to claim 1, wherein each leaf block of the first and second leaf block groups has a face extending in a direction of movement of the leaf blocks, the face having concave and convex portions formed alternately, and each magnetic layer is disposed on the face of each leaf block so as to cover the concave and convex portions. 4. A control device for a multileaf collimator which includes 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 a 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, the control device comprising:a movement starting unit which carries out a movement starting process in which movement of the leaf blocks in the departing direction is processed with a predetermined origin position serving as a starting point when an operation of the drive mechanism is started, the movement starting unit carrying out the movement starting process for everyone of the leaf blocks of the first and second leaf block groups;a movement amount detection unit which carries out a movement amount detection process in which an amount of movement of each leaf block in the departing direction is detected on the basis of the origin position based on a variation in an output signal delivered by the magnetic sensor, the movement amount detection unit carrying out the movement amount detecting process for every one of the leaf blocks of the first and second leaf block groups;a determination unit which carries out a determining process which determines whether a result of detection by the movement amount detection unit has reached a target movement amount, the determination unit carrying out the determining process for every one of the leaf blocks of the first and second leaf block groups; anda movement stopping unit which carries out a movement stopping process in which the movement stopping unit stops an operation of the drive mechanism when the determination unit has determined that a result of detection by the movement amount detection unit has reached the target movement amount, the movement stopping unit carrying out the movement stopping process for every one of the leaf blocks of the first and second leaf block groups. 5. A method of controlling a multileaf collimator which includes 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, the method comprising:starting movement of the leaf blocks in the departing direction with a predetermined origin position serving as a starting point when an operation of the drive mechanism is started, the movement starting step being carried out for every one of the leaf blocks of the first and second leaf block groups;detecting an amount of movement of each leaf block in the departing direction on the basis of the origin position based on a variation in an output signal delivered by the magnetic sensor, the movement amount detecting step being carried out for every one of the leaf blocks of the first and second leaf block groups;determining whether a result of detection by the movement amount detection unit has reached a target movement amount, the determining step being carried out for every one of the leaf blocks of the first and second leaf block groups; andstopping an operation of the drive mechanism when the determination unit has determined that a result of detection by the movement amount detection unit has reached the target movement amount, the movement stopping step being carried out for every one of the leaf blocks of the first and second leaf block groups. 6. A radiation treatment machine comprising:a treatment table on which a patient is put;a radiation generator which applies medical treatment radiation to an affected part of the patient on the treatment table; anda multileaf collimator which adjusts the radiation applied to the patient according to a shape of the affected part, the 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; anda 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. 7. The radiation treatment machine according to claim 6, wherein the first and second magnetized parts magnetized in the north and south poles respectively are disposed alternately in a direction of movement of the leaf blocks. 8. The radiation treatment machine according to claim 6, wherein each leaf block of the first and second leaf block groups has a face extending in a direction of movement of the leaf blocks, the face having concave and convex portions formed alternately, and each magnetic layer is disposed on the face of each leaf block so as to cover the concave and convex portions.