Abstract:
A multileaf collimator includes leaves extending in a first direction; a frame supporting the leaves so that the leaves are advanceable and retractable in a state where the leaves are placed side by side in a second direction perpendicular to the first direction; shafts extending in the second direction and corresponding to the leaves; driving units respectively connected to base ends of the shafts for rotating the shafts around axial lines; and driving units provided at tips of the shafts and contacting portions of the leaves for advancing and retracting the leaves in the first direction by the rotation of the shafts around the axial lines. At least some of the shafts have the same shaft length. The driving units are arranged so that the positions thereof in the second direction are shifted from each other according to the positions of the tips of the shafts having the same length.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a multileaf collimator that controls the irradiation field of radiation radiated in order to perform radiation therapy, and a radiation therapy apparatus and a radiation therapy system using the same. 
       BACKGROUND ART 
       [0002]    As one of therapies for tumors, there is radiation therapy in which an affected part is irradiated. In the radiation therapy, it is desired to irradiate an affected part efficiently while suppressing the dose of radiation (radiation dose) to a patient to be as low as possible. 
         [0003]    Thus, multileaf collimators that control an irradiation field, that is, an irradiation area or irradiation shape of radiation, have been used. 
         [0004]    In the multileaf collimators, sheet-like multiple leaves are provided side by side at intervals in their respective thickness directions within a frame. The respective leaves are provided so as to be movable in directions along their respective surfaces. Since a portion of the irradiation area of radiation is shielded by such respective leaves, the irradiation field of the radiation is controlled. 
         [0005]    For example, PTL 1 discloses a configuration including a rack gear that is formed at an inner edge of an opening formed in each leaf, a pinion gear that meshes with the rack gear, and a motor that rotates the pinion gear rotate, as a driving mechanism that drives each leaf. 
         [0006]    Here, driving shafts of the motors are inserted into the openings of the multiple leaves that are provided side by side, in a direction (the thickness directions of the respective leaves) in which the leaves are provided side by side. The rack gear provided at the tip of the driving shaft meshes with the rack gear formed at the inner edge of the opening of each leaf. 
       CITATION LIST 
     Patent Literature 
       [0007]    [PTL 1] Japanese Patent No. 4436343 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0008]    Meanwhile, the motors as described above are fixed to an outer peripheral surface of the frame that houses the multiple leaves. Then, the intervals between the outer peripheral surface (the attachment surface for the motors) of the frame and the respective leaves vary in every leaf. Therefore, the lengths of the shafts of the motors that drive the respective leaves vary in every leaf. 
         [0009]    As a result, a number of types of shafts having different lengths should be prepared. For this reason, the types of parts that constitute the multileaf collimators are increased, which becomes a hindrance to suppression of part costs. Moreover, shafts having lengths according to the positions of the individual leaves should be prepared at the time of repair. That is, the number of parts to be stocked is increased, and this also becomes a hindrance to cost suppression. 
         [0010]    An object of the invention is to provide a multileaf collimator in which the number of types of parts of the multileaf collimator can be reduced and it is possible to suppress manufacture costs and maintenance costs, and a radiation therapy apparatus and a radiation therapy system using the same. 
       Solution to Problem 
       [0011]    According to a first aspect related to the invention, a multileaf collimator includes a plurality of leaves that extend in a first direction; a frame that supports the plurality of leaves so that the plurality of leaves are individually advanceable and retractable in a state where the plurality of leaves are placed side by side in a second direction perpendicular to the first direction. The multileaf collimator further includes a plurality of shafts that extend in the second direction and are provided to correspond to the plurality of leaves, respectively; and a plurality of driving units that are respectively connected to first ends of the plurality shafts in directions of axial lines and rotate the shafts around the axial lines. The multileaf collimator further includes advance and retraction driving sections that are provided at second ends of the shafts in the directions of the axial lines, contact portions of the leaves, and advance and retract the leaves in the first direction by the rotation of the shafts around the axial lines. Additionally, in the multileaf collimator, at least some of the plurality of shafts have the same shaft length as each other, and the plurality of driving units are arranged so that the positions thereof in the second direction are shifted from each other according to the positions of the second ends of the plurality of shafts having the same length. 
         [0012]    According to a second aspect related to the invention, in the multileaf collimator of the first aspect, at least some of the plurality of driving units may be supported via spacers with respect to the frame, and the thicknesses of the spacers in the second direction may be set in a plurality of steps according to the positions of the driving units in the second direction. 
         [0013]    According to a third aspect related to the invention, in the multileaf collimator of the first aspect, the frame may include pedestal parts that fix the driving units, and the heights of the pedestal parts of the second direction may be set in a plurality of steps according to the positions of the driving units in the second direction. 
         [0014]    According to a fourth aspect related to the invention, in the multileaf collimator of any one of the first aspect to the third aspect, the plurality of shafts may include shafts having at least two types of length. 
         [0015]    According to a fifth aspect related to the invention, in the multileaf collimator of any one of the first aspect to the fourth aspect, the driving units may be arranged so that the projection dimensions thereof from the frame in the second direction become gradually larger from the outside of an attachment surface of the frame to which the plurality of driving units are attached toward a central side of the attachment surface. 
         [0016]    According to a sixth aspect related to the invention, a radiation therapy apparatus includes the multileaf collimator of any one of the first to fifth aspects; and a radiation irradiation device that radiates radiation. 
         [0017]    According to a seventh aspect of the invention, a radiation therapy system includes the radiation therapy apparatus of the sixth aspect; and a control apparatus that controls the operation of the radiation therapy apparatus. 
       Advantageous Effects of Invention 
       [0018]    According to the above-described multileaf collimator, radiation therapy apparatus, and radiation therapy system, the number of types of parts of the multileaf collimator can be reduced, and it is possible to suppress manufacture costs and maintenance costs. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0019]      FIG. 1  is a view illustrating a functional configuration of a radiation therapy system in a first embodiment of the invention. 
           [0020]      FIG. 2  is a perspective view illustrating a schematic configuration of a radiation therapy apparatus that constitutes the radiation therapy system in the first embodiment of the invention. 
           [0021]      FIG. 3  is a sectional view illustrating a radiation irradiation device that constitutes the radiation therapy apparatus in the first embodiment of the invention. 
           [0022]      FIG. 4  is a perspective view illustrating the external appearance of a multileaf collimator that constitutes a portion of the radiation irradiation device in the first embodiment of the invention. 
           [0023]      FIG. 5  is a width-direction sectional view of the multileaf collimator in the first embodiment of the invention. 
           [0024]      FIG. 6  is a sectional view orthogonal to a thickness direction of each leaf of the multileaf collimator in the first embodiment of the invention. 
           [0025]      FIG. 7  is a perspective view illustrating leaves and a drive device that drives the leaves, in the first embodiment of the invention. 
           [0026]      FIG. 8  is a perspective view illustrating the configuration of a drive device in the first embodiment of the invention. 
           [0027]      FIG. 9  is a sectional view illustrating the arrangement structure of drive devices with respect to the leaves in the first embodiment of the invention. 
           [0028]      FIG. 10  is a sectional view illustrating the arrangement structure of the drive devices with respect to the leaves in a modification example of the first embodiment of the invention. 
           [0029]      FIG. 11  is a sectional view illustrating the arrangement structure of the drive devices with respect to the leaves of a multileaf collimator in a second embodiment. 
           [0030]      FIG. 12  is a sectional view illustrating the arrangement structure of the drive devices with respect to the leaves of a multileaf collimator in a third embodiment. 
           [0031]      FIG. 13  is a perspective view of main parts of the multileaf collimator in the third embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       [0032]      FIG. 1  is a view illustrating a functional configuration of a radiation therapy system  10  in a first embodiment of the invention. 
         [0033]    As illustrated in  FIG. 1 , the radiation therapy system  10  includes a therapy planning apparatus  11 , a control apparatus  12 , and a radiation therapy apparatus  20 . 
         [0034]    In the therapy planning apparatus  11 , properties (the strength, time, angle, position, radiation area, and the like of radiation to be radiated to a patient) of radiation to be radiated to preset and a patient, which are preset according to the contents of radiation therapy to be performed to a patient, are input from the outside. In the therapy planning apparatus  11 , various control parameter values for radiating radiation corresponding to the input properties of the radiation are output to the control apparatus  12 . 
         [0035]    The control apparatus  12  controls the operation of the radiation therapy apparatus  20  on the basis of the various parameter values produced by the therapy planning apparatus  11 . The control apparatus  12  is a computer apparatus, such as a personal computer, which executes processing on the basis of a predetermined program. The control apparatus  12  is connected to the radiation therapy apparatus  20  via a wireless or wired communication line so that information can be transmitted bidirectionally. 
         [0036]      FIG. 2  is a perspective view illustrating a schematic configuration of the radiation therapy apparatus  20  that constitutes the radiation therapy system  10 . 
         [0037]    As illustrated in  FIG. 2 , the radiation therapy apparatus  20  includes a ring frame  21 , a traveling gantry  22 , and a radiation irradiation device  24 . 
         [0038]    The ring frame  21  is formed in a tubular shape having a circular section. The ring frame  21  is disposed so that a central axis C 1  substantially faces a horizontal direction. The ring frame  21  has a downward extending rotating shaft  25  formed integrally with an outer peripheral surface of a lower end  21   a.  The rotating shaft  25  is supported by a base (not illustrated) so as to be rotatable around a central axis C 2  of the rotating shaft  25 . The rotating shaft  25  is rotated around the central axis C 2  of the rotating shaft  25  by a swiveling driving mechanism (not illustrated). Accordingly, the ring frame  21  is made rotatable around the central axis C 2  of the rotating shaft  25 , that is, around a vertical axis. 
         [0039]    The traveling gantry  22  is formed in a tubular shape having a circular section. The traveling gantry  22  is arranged on an inner peripheral side of the ring frame  21 . The traveling gantry  22  is supported so as to be rotatable along an inner peripheral surface of the ring frame  21 . Accordingly, the annular traveling gantry  22  is made rotatable around the central axis C 1  extending in the horizontal direction. The traveling gantry  22  is made swivable around the central axis C 1  by a gantry driving mechanism (not illustrated). 
         [0040]    The radiation irradiation device  24  is controlled by the control apparatus  12 , and radiates therapeutic radiation Sr. The radiation irradiation device  24  is supported by an inner peripheral surface  22   a  of the traveling gantry  22 . The radiation irradiation device  24  is provided so that the therapeutic radiation Sr to be radiated passes through an isocenter C 0  that is an intersection point between the central axis C 2  of the rotational operation of the ring frame  21  and the central axis C 1  of the rotational operation of the traveling gantry  22 . 
         [0041]    In this way, when the radiation irradiation device  24  is supported by the traveling gantry  22 , the radiation irradiation device  24  radiates the therapeutic radiation Sr so as to pass through the isocenter C 0  always irrespective of the rotational operation of the ring frame  21  around the central axis C 2  and the rotational operation of the traveling gantry  22  around the central axis C 1 . 
         [0042]    Additionally, the radiation therapy apparatus  20  includes diagnosing X-ray sources  26 A and  26 B, and sensor arrays  27 A and  27 B. 
         [0043]    The diagnosing X-ray sources  26 A and  26 B are arranged on an inner peripheral side of the traveling gantry  22 . The diagnosing X-ray sources  26 A and  26 B are arranged on both sides of the ring frame  21  in a circumferential direction with the center (the central axis C 2  of the rotational operation of the ring frame  21 ) of the radiation therapy apparatus  20  interposed therebetween. The diagnosing X-ray sources  26 A and  26 B are controlled by the control apparatus  12  and radiate diagnosing X-rays  101  toward the isocenter C 0 . The diagnosing X-rays  101  are conic cone beams that widen in the shape of a cone from the point of origin of the diagnosing X-ray sources  26 A and  26 B. 
         [0044]    The sensor arrays  27 A and  27 B are supported by the inner peripheral surface  22   a  of the traveling gantry  22 . The sensor arrays  27 A and  27 B are provided so as to face the diagnosing X-ray sources  26 A and  26 B with the isocenter C 0  interposed therebetween. The sensor arrays  27 A and  27 B receive the diagnosing X-rays  101  that are radiated from the diagnosing X-ray sources  26 A and  26 B and are transmitted through a photographic subject around the isocenter C 0 , and produce a transmission image of the photographic subject. The sensor arrays  27 A and  27 B include, for example, flat panel detectors (FPDs), X-ray image Intensifiers (II) or the like. 
         [0045]    The radiation therapy apparatus  20  further includes a table  28  and a table drive device  29 . A patient  200  to be treated by the radiation therapy system  10  lies on his/her side on an upper surface  28   a  of the table  28 . 
         [0046]    The table drive device  29  is controlled by the control apparatus  12  and moves the table  28 . The table drive device  29  is supported by a base (not illustrated). 
         [0047]      FIG. 3  is a sectional view illustrating the radiation irradiation device  24  that constitutes the radiation therapy apparatus  20 . 
         [0048]    As illustrated in  FIG. 3 , the radiation irradiation device  24  includes an electron beam accelerator  51 , an X-ray target  52 , a primary collimator  53 , a flattening filter  54 , a secondary collimator  55 , and a multileaf collimator  60 A. 
         [0049]    The electron beam accelerator  51  irradiates the X-ray target  52  with an electron beam S 0  produced by accelerates electrons. 
         [0050]    The X-ray target  52  is formed of tungsten, a tungsten alloy, or the like. The X-ray target  52  emits radiation S 1  if the target is irradiated with the electron beam S 0 . 
         [0051]    The primary collimator  53  is formed of lead, tungsten, or the like. A through-hole  53   h  is formed in the primary collimator  53 . The radiation S 1  radiated from the X-ray target  52  passes through the through-hole  53   h . The primary collimator  53  shields a portion of the radiation S 1  so that the radiation S 1  is not radiated by the through-hole  53   h  other than a desired portion. 
         [0052]    The flattening filter  54  is formed of aluminum or the like. The flattening filter  54  is arranged on an outlet side of the through-hole  53   h  of the primary collimator  53 . The flattening filter  54  has a substantially conical projection  54   a  on a side that faces the X-ray target  52 . In the flattening filter  54 , the shape of the projection  54   a  is designed so that a radiation dose in a plane perpendicular to a radial direction is substantially uniformly distributed after the radiation S 1  has passed through the flattening filter  54 . 
         [0053]    The secondary collimator  55  is formed of lead, tungsten, or the like. The secondary collimator  55  includes a through-hole  55   h  at a central part therein. The secondary collimator  55  radiates only radiation S 2  that has passed through the through-hole  55   h,  and shields a portion of the radiation S 1 . 
         [0054]    By passing through the above-described primary collimator  53 , the flattening filter  54 , and the secondary collimator  55 , a portion of the radiation S 2  having uniform intensity distribution is shielded by the multileaf collimator  60 A. The multileaf collimator  60 A undergoes the control of the control apparatus  12 , and produces the therapeutic radiation Sr that is set in the therapy planning apparatus  11  and is obtained according to the properties of radiation to be radiated to a patient. 
         [0055]      FIG. 4  is a perspective view illustrating the external appearance of the multileaf collimator  60 A that constitutes a portion of the radiation irradiation device  24 .  FIG. 5  is a width-direction sectional view of the multileaf collimator  60 A.  FIG. 6  is a sectional view of the multileaf collimator  60 A that is orthogonal to a second direction (hereinafter, referred to as a thickness direction T) that is a thickness direction of each leaf  70 . 
         [0056]    As illustrated in  FIGS. 4 to 6 , the multileaf collimator  60 A includes a frame  61 , a plurality of leaves  70 , and a drive device  90 . 
         [0057]    The frame  61  is formed in a substantially rectangular parallelepiped shape that is elongated in one direction. The frame  61  is arranged so that a first direction (hereinafter, referred to as a width direction W) that is a longitudinal direction of the frame is orthogonal to a radiation irradiation axis of the radiation irradiation device  24  extending along the central axis C 2 . A hollow leaf housing part  62  that is continuous in the width direction W is formed in the frame  61 . 
         [0058]    In the frame  61 , openings  63 , which pass through an outer peripheral side of the frame  61  and the leaf housing part  62 , are formed in an upper surface  61   a  on a side that faces the radiation irradiation device  24  and a lower surface  61   b  opposite to the upper surface (in  FIG. 4 , only the opening  63  of the upper surface  61   a  is illustrated). The openings  63  are formed at central parts of the upper surface  61   a  and the lower surface  61   b  in the width direction W. 
         [0059]    As illustrated in  FIGS. 4 and 5 , in the frame  61 , rectangular openings  64  and  64  are respectively formed in both side surfaces  61   c  and  61   d  orthogonal to the upper surface  61   a  and the lower surface  61   b.  The openings  64  and  64  are formed so as to be symmetrical to central parts of the side surface  61   c  or  61   d  in the width direction W. Rectangular base plates  65  are respectively mounted on the openings  64 . 
         [0060]    The leaves  70  are approximately formed in a substantially oblong shape. The leaves  70  are formed of, for example, tungsten, a tungsten alloy, or the like. 
         [0061]    As illustrated in  FIG. 5 , the plurality of leaves  70  are placed side by side at intervals in the thickness direction T. A leaf group  70 G is constituted of the plurality of leaves  70  that are placed side by side. In this embodiment, the leaf group  70 G is constituted by, for example, thirty leaves  70 . As illustrated in  FIG. 4 , two such leaf groups  70 G are arranged in a pair within the leaf housing part  62  within the frame  61  so as to face each other with the central part of the frame  61  in the width direction W interposed therebetween. 
         [0062]      FIG. 7  is a perspective view illustrating a leaf  70  and the drive device  90  that drives the leaf  70 . 
         [0063]    As illustrated in  FIGS. 6 and 7 , the leaf  70  is formed so that a linear upper edge  70   a  and a linear lower edge  70   b  are parallel to each other. As illustrated in  FIG. 6 , the upper edge  70   a  is arranged to face the upper surface  61   a  at a distance therefrom within the leaf housing part  62 . The lower edge  70   b  is arranged to face the lower surface  61   b  at a distance therefrom within the leaf housing part  62 . The leaf  70  is formed so that a front edge  70   c  that faces the central part of the frame  61  in the width direction W within the leaf housing part  62  swells in a circular-arc shape. Additionally, in the leaf  70 , a rear edge  70   d  that faces the outside of the frame  61  in the width direction W within the leaf housing part  62  is formed in the shape of a straight line orthogonal to the upper edge  70   a  and the lower edge  70   b.    
         [0064]    A pair of two leaf groups  70 G and  70 G arranged to face each other with the central part in the width direction W interposed therebetween within the leaf housing part  62  are arranged so that the front edge  70   c  of each leaf faces an area between the opening  63  of the upper surface  61   a  and the opening  63  of the lower surface  61   b  in the frame  61 . 
         [0065]    Slits  71  and  72  are formed in each leaf  70  so as to pass therethrough in the thickness direction T. The slits and  72  are respectively formed continuously in a direction in which the front edge  70   c  and the rear edge  70   d  of the leaf  70  are connected together. The slits  71  and  72  are formed side by side at an interval in the direction in which the upper edge  70   a  and the lower edge  70   b  of the leaf  70  are connected together. The slits  71  and  72  are formed at positions shifted further toward the rear edge  70   d  side than the front edge  70   c  so as not to be irradiated with the radiation S 2  that enters the leaf housing part  62  of the frame  61  from the opening  63  of the upper surface  61   a  of the frame  61 . 
         [0066]    In each leaf  70 , a rack gear  73  that is continuous along the width direction W is formed in at least one of the upper side  71   a  or  72   a  and the lower side  71   b  or  72   b  of the slit  71  or  72 . Here, in the leaf group  70 G, the rack gears  73  of the leaves  70  and  70  adjacent to each other in a direction in which the plurality of leaves  70  are placed side by side are formed at mutually different sides among the upper sides  71   a  and  72   a  and the lower sides  71   b  and  72   b  of the slits  71  and  72 . By adopting such a configuration, pinion gears  96  that mesh with the rack gear  73  can be prevented from interfering with each other between the leaves  70  and  70  adjacent to each other. 
         [0067]    Each of the plurality of leaves  70  that constitute each leaf group  70 G are supported by the frame  61  so as to be advanceable and retractable in a direction orthogonal to the thickness direction T and a direction in which the front edge  70   c  and the rear edge  70   d  are connected, that is, along the width direction W. For this reason, a plurality of sliding supporting members  66  are provided in the width direction W at intervals at an upper part and a lower part of each leaf group  70 G in the frame  61 . In this embodiment, two sliding supporting members on a central part side and on an outer peripheral side, respectively, of the frame  61  in the width direction W, that is, a total of four sliding supporting members  66  including are provided in each of the upper part and the lower part of each leaf group  70 G. 
         [0068]    As illustrated in  FIGS. 5 and 6 , in each of the sliding supporting members  66 , a plurality of supporting rollers  66   b  are rotatably mounted on a shaft  66   a  fixed to the frame  61 . The plurality of supporting rollers  66   b  are provided at positions corresponding to the respective leaves  70  that constitute the leaf group  70 G. 
         [0069]    As illustrated in  FIG. 6 , the supporting rollers  66   b  of at least two sliding supporting members  66  abut against the upper edge  70   a  and the lower edge  70   b  of each leaf  70 . Accordingly, each leaf  70  is individually supported by the frame  61  so as to be advanceable and retractable along the width direction W. 
         [0070]    Here, in the leaf group  70 G, the supporting rollers  66   b  of mutually different sliding supporting members  66  among the plurality of sliding supporting members  66  may abut against each other in the leaves  70  and  70  adjacent to each other in the thickness direction T in which the plurality of leaves  70  are placed side by side. By adopting such a configuration, the supporting rollers  66   b  can be prevented from interfering with each other between the leaves  70  and  70  adjacent to each other. 
         [0071]    The frame  61  includes a stopper  68  in order to restrict the amount of movement of each leaf  70  to the rear edge  70   d  side in the width direction W. 
         [0072]      FIG. 8  is a perspective view illustrating the configuration of the drive device  90 . 
         [0073]    As illustrated in  FIG. 7 , the drive device  90  is provided to correspond to each of the plurality of leaves  70 . As illustrated in  FIGS. 7 and 8 , the drive device  90  includes a motor (driving unit)  91 , a shaft  95 , and a pinion gear (advance and retraction driving section)  96 . 
         [0074]    The motor  91  is connected to a base end that is a first end of the shaft  95  in an axis direction. The motor  91  rotates the shaft  95  around its axis. As illustrated in  FIG. 5 , the motor  91  is supported by a base plate  65  serving as an attachment surface provided along the side surface  61   c  or  61   d  of the frame  61 . 
         [0075]    The motor  91  of the drive device  90  that drives half of the leaves  70  on a side near the side surface  61   c  among the plurality of leaves  70  that constitute the leaf group  70 G is supported by the base plate  65  provided on one side surface  61   c  of the frame  61 . The motor  91  of the drive device  90  that drives half of the leaves  70  on a side near the side surface  61   d  among the plurality of leaves  70  that constitute the leaf group  70 G is supported by the base plate  65  provided on the other side surface  61   d  of the frame  61 . 
         [0076]    As illustrated in  FIG. 7 , the shaft  95  is provided so as to extend in the thickness direction T of the leaves  70 . As illustrated in  FIGS. 6 and 7 , the shaft  95  is inserted into the slits  71  or  72  of the plurality of leaves  70  of the leaf group  70 G. As illustrated in  FIGS. 7 and 8 , the pinion gear  96  is provided at a tip that is a second end of the shaft  95  in the axis direction. The pinion gear  96  meshes with the rack gear  73  that is formed in any one of the upper sides  71   a  and  72   a  and the lower sides  71   b  and  72   b  of the slits  71  and  72 , which are portions of the leaf  70 . 
         [0077]    The drive device  90  is further provided with a rotary encoder  92  and a cover  94 . 
         [0078]    The rotary encoder  92  measures the rotational amount of the shaft  95 , and outputs the measurement result to the control apparatus  12 . 
         [0079]    The cover  94  is formed in a hollow tubular shape. The cover  94  is provided integrally with a housing  91   a  of the motor  91 . The end of the cover  94  opposite to the motor  91  is provided with a bearing  130 . The cover  94  has the shaft  95  inserted therethrough. The shaft  95  is rotatably supported by the bearing  130 . The cover  94  supports the shaft  95  with the bearing  130  at a position apart from the motor  91 . Accordingly, the shaft  95  is prevented from being deformed due to its own weight or the like, and even when the motor  91  and the leaf  70  are separated from each other, the pinion gear  96  reliably meshes with the rack gear  73 . 
         [0080]    A cutout  100  is formed in a portion of the cover  94  in the circumferential direction. The cutout  100  prevents all interference with other leaves  70  arranged closer to the motor  91  side than a leaf  70  having the rack gear  73  with which the pinion gear  96  of the shaft  95  inserted through this cover  94  meshes. 
         [0081]    In such a drive device  90 , the motor  91  is driven by the control of the control apparatus  12 , and rotates the shaft  95 . If the shaft  95  rotates, the pinion gear  96  rotates with the shaft  95 , and the rotary power thereof is transmitted to the rack gear  73 . Then, the leaf  70  provided with the rack gear  73  advances and retracts along the width direction W. 
         [0082]    In this way, the respective leaves  70  that constitute the leaf group  70 G are advanced and retracted along the width direction W in each of the pair of two leaf groups  70 G. A portion of the radiation S 2  that has been incident from the opening  63  of the upper surface  61   a  of the frame  61  is shielded by the leaves  70  of the leaf groups  70 G on both sides. Accordingly, the therapeutic radiation Sr having the shape of a predetermined irradiation field is produced by the multileaf collimator  60 A. 
         [0083]      FIG. 9  is a sectional view illustrating the arrangement structure of the drive devices  90  with respect to the leaves  70 . 
         [0084]    As illustrated in  FIG. 9 , the plurality of drive devices  90  are respectively provided to correspond to the plurality of leaves  70  that constitute the leaf group  70 G. Therefore, the positions of the pinion gears  96  provided at the tips of the shafts  95  are different from each other in the thickness direction T of the leaves  70 , in the respective drive devices  90  that drive the plurality of leaves  70 . The lengths of the plurality of shafts  95  are made the same as each other in the respective drive devices  90  that drive the plurality of leaves  70 . For this reason, the plurality of motors  91  are arranged so that the positions thereof in the thickness direction T are shifted from each other according to the respective tips of the plurality of shafts  95 , that is, the positions of the pinion gears  96 . 
         [0085]    In this embodiment, the motor  91  of each drive device  90  is provided in a base plate  65  of the side surface  61   c  or  61   d  of the frame  61  via a spacer  97 . The spacer  97  is tubular, and has the shaft  95  and the cover inserted therethrough. In addition, in  FIG. 9 , illustration of the cover  94  is omitted for the sake of convenience of illustration (in the following, the same also applies to  FIGS. 10 to 12 ). 
         [0086]    The thicknesses of the spacers  97  in the thickness direction T are set in a plurality of steps. Accordingly, the frame  61  is made to support the drive devices  90  while the positions of the plurality of motors  91  in the thickness direction T are shifted from each other, using the shafts  95  of the same length. 
         [0087]    In the radiation therapy system  10  as described above, therapy is performed as follows. 
         [0088]    First, a user fixes the patient  200  to the table  28  of the radiation therapy apparatus  20  in a posture indicated by therapeutic planning input to the therapy planning apparatus  11 . 
         [0089]    The control apparatus  12  actuates the swiveling driving mechanism (not illustrated) and a gantry drive device (not illustrated), and swivels the ring frame  21  and the traveling gantry  22  around the central axes C 1  and C 2 . The radiation irradiation device  24  is moved so that the therapeutic radiation Sr is radiated the position of an affected part of the patient  200  at an irradiation angle indicated by the therapeutic planning. Additionally, the control apparatus  12  makes each leaf  70  advanced and retracted by the drive device  90  so that the shape of the irradiation field of the therapeutic radiation Sr is changed to a shape indicated by the therapeutic planning input to the therapy planning apparatus  11  in the multileaf collimator  60 A. 
         [0090]    Thereafter, the therapeutic radiation Sr of a dose indicated by the therapeutic planning input to the therapy planning apparatus  11  is radiated to the affected part of the patient  200 , using the radiation irradiation device  24 . 
         [0091]    According to the multileaf collimator  60 A of the above-described embodiment, the lengths of the plurality of shafts  95  are made the same as each other between the drive devices  90  that respectively drive the plurality of leaves  70  constituting the leaf group  70 G. Moreover, the plurality of motors  91  are arranged so that the positions thereof in the thickness direction T are shifted from each other according to the positions of the pinion gears  96  of the respective tips of the plurality of shafts  95 . 
         [0092]    By adopting such a configuration, the lengths of the shafts  95  corresponding to the plurality of leaves  70 , respectively, can be unified. As a result, the type of parts that constitute the multileaf collimator  60 A can be reduced. Additionally, since it is not necessary to prepare the shafts  95  having lengths according to the positions of the respective leafs  70  at the time of repair, the number of parts to be stocked can be reduced. 
         [0093]    Additionally, according to the multileaf collimator  60 A of the above-described embodiment, the motors  91  are provided on the side surface  61   c  or  61   d  that is an outer peripheral surface of the frame  61  via the spacers  97 , and the thicknesses of the spacers  97  in the thickness direction T are set in a plurality of steps. 
         [0094]    By adopting such a configuration, the plurality of motors  91  are arranged so that the positions thereof in the thickness direction T are shifted from each other according to the positions of the respective tips of the plurality of shafts  95  of which the lengths are united. 
         [0095]    As a result, the number of types of parts of the multileaf collimator  60 A can be reduced, and it is possible to suppress manufacture costs and maintenance costs. 
         [0096]    Moreover, the manufacture costs and maintenance costs of the entire radiation therapy apparatus  20  and the entire radiation therapy system  10  can be suppressed by adopting the multileaf collimator  60 A to form the radiation therapy apparatus  20  and the radiation therapy system  10 . 
       Modification Example of First Embodiment 
       [0097]    In the first embodiment, the motors  91  are provided on the side surface  61   c  or  61   d  of the frame  61  via the spacers  97 . However, the invention is not limited to this. If the plurality of motors  91  are arranged so that the positions thereof in the thickness direction T are shifted from each other according to the positions of the respective tips of the plurality of shafts  95  of which the lengths are united, it is possible to adopt, for example, another configuration as illustrated below. 
         [0098]      FIG. 10  is a sectional view illustrating a modification example of the arrangement structure of the drive devices  90  with respect to the leaves  70 . 
         [0099]    As illustrated in this  FIG. 10 , pedestal parts  98  to which the motors  91  are fixed are formed integrally with the base plate  65  provided on the side surface  61   c  and  61   d  that is the outer peripheral surfaces of the frame  61 . The pedestal parts  98  are each formed in the shape of a step, and the heights thereof in the thickness direction T may be set in a plurality of steps corresponding to the positions of the respective motors  91  in the thickness direction T. 
         [0100]    By adopting such a configuration, the plurality of motors  91  are arranged so that the positions thereof in the thickness direction T are shifted from each other according to the positions of the pinion gears  96  of the respective tips of the plurality of shafts  95  of which the lengths are united. Accordingly, similar to a case where the spacers  97  are used, the number of types of parts of the multileaf collimator  60 A can be reduced, and it is possible to suppress manufacture costs and maintenance costs. In this case, since it is not necessary to use the spacers  97 , the number of parts that constitute the multileaf collimator  60 A can be reduced. 
       Second Embodiment 
       [0101]    Next, a second embodiment of the multileaf collimator related to the invention will be described. A multileaf collimator  60 B illustrated in the second embodiment is different from the multileaf collimator  60 A of the first embodiment in terms of the setting of the lengths of the shafts  95 . Therefore, in the description of the second embodiment, description will be made with the same reference numerals given to the same parts as those of the first embodiment, and duplication description will be omitted. That is, the description about the overall configuration of the multileaf collimator  60 B and the configurations of the radiation therapy apparatus  20  and the radiation therapy system  10  that are the same as the configuration described in the first embodiment will be omitted. 
         [0102]      FIG. 11  is a sectional view illustrating the arrangement structure of the drive devices with respect to the leaves of the multileaf collimator  60 B in the second embodiment. 
         [0103]    As illustrated in  FIG. 11 , in the multileaf collimator  60 B, the drive devices  90  are respectively provided to correspond to the plurality of leaves  70  that constitute the leaf group  70 G. 
         [0104]    The lengths of the plurality of shafts  95  are made into two long and short types between the respective drive devices  90  that drive the plurality of leaves  70 . 
         [0105]    The leaves  70  near the center in the direction (thickness direction T) in which the leaves  70  are placed side by side among the plurality of leaves  70  that constitute the leaf group  70 G are driven by the drive devices  90  using shafts  95 L with a longer length. The leaves  70  near the outer periphery in the direction (thickness direction T) in which the leaves  70  are placed side by side among the plurality of leaves  70  that constitute the leaf group  70 G are driven by the drive devices  90  using shafts  95 S with a shorter length than the shafts  95 L. 
         [0106]    In this case, although the plurality of motors  91  are arranged so that the positions thereof in the thickness direction T are shifted from each other, the spacers  97  may be used as illustrated in  FIG. 11 , or the pedestal parts  98  may be used as illustrated in  FIG. 10 . 
         [0107]    In the multileaf collimator  60 B of this embodiment, the shafts  95  of the plurality of drive devices  90  that drive the plurality of leaves  70 , respectively, are set to two types of shafts including the shafts  95 L with a longer length and the shafts  95 S with a shorter length. Therefore, the lengths of the shafts  95  can be made the same as each other in the plurality of drive devices  90  using the longer shafts  95 L and the plurality of drive devices  90  using the shorter shafts  95 S, respectively. Accordingly, the number of the types of parts that constitute the multileaf collimator  60 B can be reduced. Additionally, by setting the shafts  95  to the two types, the types of the spacers  97  or the pedestal parts  98  for shifting the plurality of motors  91  so that the positions thereof in the thickness direction T from each other can also be reduced. 
         [0108]    Moreover, since the shorter shafts  95 S are used for the leaves  70  near the outer periphery in the direction (thickness direction T) in which the leaves  70  are placed side by side among the plurality of leaves  70  that constitute the leaf group  70 G, the projection dimensions of the motors  91  from the side surface  61   c  or  61   d  of the frame  61  can be suppressed to be small. Accordingly, the size of the multileaf collimator  60 B can be reduced. As a result, the degree of freedom of operation of the radiation irradiation device  24  within the ring frame  21  and the traveling gantry  22  can be improved. 
         [0109]    In the second embodiment, the shafts  95  of the plurality of drive devices  90  are set to two types of shafts including the shafts  95 L with a longer length and the shafts  95 S with a shorter length. However, the shafts can be set to three or more types of shafts. In this case, in at least the plurality of shafts  95 , the lengths of the shafts  95  are made the same as each other. 
       Third Embodiment 
       [0110]    Next, a third embodiment of the multileaf collimator related to the invention will be described. A multileaf collimator  60 C illustrated in the third embodiment is different from the multileaf collimator  60 B of the second embodiment in terms of the setting of the lengths of the shafts  95 . Therefore, in the description of the third embodiment, the same reference numerals will be given to the same parts, and duplication description will be omitted. That is, differences from the second embodiment will mainly be described, and the description of the overall configuration of the multileaf collimator  60 C and the configurations of the radiation therapy apparatus  20  and the radiation therapy system  10  that are the same as the configurations described in the first and second embodiments will be omitted. 
         [0111]      FIG. 12  is a sectional view illustrating the arrangement structure of the drive devices with respect to the leaves of the multileaf collimator in the third embodiment.  FIG. 13  is a perspective view of main parts of the multileaf collimator. 
         [0112]    As illustrated in  FIGS. 12 and 13 , in the multileaf collimator  60 C, the drive devices  90  are respectively provided to correspond to the plurality of leaves  70  that constitute the leaf group  70 G. 
         [0113]    The plurality of drive devices  90  provided to correspond to the plurality of leaves  70 , respectively, are arranged so that the projection dimensions thereof in the thickness direction T from the side surface  61   c  or  61   d  become larger gradually toward the central side. More specifically, in the side surface  61   c  or  61   d  of the frame  61 , the projection dimensions of the motors  91  in the thickness direction T are increased gradually toward an outer side in the direction of the central axis C 2  and from an outer side in the width direction W toward central sides in the respective directions. That is, the plurality of motors  91  supported by the base plate  65  are arranged so that the projection dimensions thereof become larger toward the outside of the base plate  65  and the projection dimensions become larger toward the center sides. 
         [0114]    Here, the shafts  95  of the respective drive devices may be unified into the same length as in the configuration illustrated in the first embodiment, or may be unified into the plurality of types of lengths as in the configuration illustrated in the second embodiment. In the example of  FIG. 12 , similar to the configuration illustrated in the second embodiment, the plurality of drive devices  90  may be configured using the shafts  95 L and  95 S having two types of lengths. 
         [0115]    Additionally, in order to arrange the plurality of motors  91  so that the positions thereof in the thickness direction T are shifted from each other, the spacers  97  may be used as illustrated in  FIG. 12 , or the pedestal parts  98  may be used as illustrated in  FIG. 10 . 
         [0116]    According to the multileaf collimator  60 C of this embodiment, in the side surface  61   c  or  61   d  of the frame  61 , the projection dimensions of the motors  91  become smaller toward the outer peripheral side of the plurality of drive devices  90 . Therefore, the size of the multileaf collimator  60 B can be reduced. As a result, the degree of freedom of operation of the radiation irradiation device  24  within the ring frame  21  and the traveling gantry  22  can be improved. 
         [0117]    Additionally, in the side surface  61   c  or  61   d  of the frame  61 , the projection dimensions of the motors  91  become gradually larger from the outside of the plurality of drive devices  90  toward the central side thereof. Therefore, for example, in the case of maintenance, the motors  91  on the outside do not easily cause an obstruction, even in the motors  91  on the central side. As a result, workability in which a worker&#39;s hand easily reaches the motors  91  can be improved. 
         [0118]    Moreover, when the plurality of drive devices  90  are covered with a cover member  99  (refer to  FIG. 12 ) from the outside, a central part of the cover member  99  can be formed in a smooth curved surface so as to protrude gradually. Therefore, degradation of design by the projection of the motors  91  can be prevented. 
       Other Embodiments 
       [0119]    In addition, the invention is not limited to the above-described embodiments, and design changes can be made without departing from the concept of the invention. 
         [0120]    For example, the configurations of the respective parts of the multileaf collimators  60 A,  60 B, and  60 C can be appropriately changed to configurations other than those described above. For example, instead of the pinion gears  96 , the leaves  70  may be advanced and retracted by pressing rollers against the upper sides  71   a  and  72   a  and the lower sides  71   b  and  72   b  of the slits  71  and  72  and rotationally driving the rollers with the motors  91 . 
         [0121]    Moreover, other arbitrary configurations may be adopted regarding the configurations of the respective parts the radiation therapy apparatus  20  and the radiation therapy system  10  other than the multileaf collimators  60 A and  60 B and  60 C. 
       INDUSTRIAL APPLICABILITY 
       [0122]    By making the lengths of the shafts the same as each other in at least some of the plurality of shafts, the number of types of parts of the multileaf collimator can be reduced, and it is possible to suppress manufacture costs and maintenance costs. 
       REFERENCE SIGNS LIST 
       [0123]      10 : Radiation Therapy System 
         [0124]      11 : Therapy Planning Apparatus 
         [0125]      12 : Control Apparatus 
         [0126]      20 : Radiation Therapy Apparatus 
         [0127]      21 : Ring Frame 
         [0128]      21   a : Lower End 
         [0129]      22 : Traveling Gantry 
         [0130]      22   a : Inner Peripheral Surface 
         [0131]      24 : Radiation Irradiation Device 
         [0132]      25 : Rotating Shaft 
         [0133]      26 A: Radiation Source 
         [0134]      27 A,  27 B: Sensor Array 
         [0135]      28 : Table 
         [0136]      28   a : Upper Surface 
         [0137]      29 : Table Drive Device 
         [0138]      51 : Electron Beam Accelerator 
         [0139]      52 : X-Ray Target 
         [0140]      53 : Primary Collimator 
         [0141]      53   h : Through-Hole 
         [0142]      54 : Field Flattening Filter 
         [0143]      54   a : Projection 
         [0144]      55 : Secondary Collimator 
         [0145]      55   h : Through-Hole 
         [0146]      60 A,  60 B,  60 C: Multileaf Collimator 
         [0147]      61 : Frame 
         [0148]      61   a : Upper Surface 
         [0149]      61   b : Lower Surface 
         [0150]      61   c,    61   d : Side Surface 
         [0151]      62 : Leaf Housing Part 
         [0152]      63 : Opening 
         [0153]      65 : Base Plate 
         [0154]      66 : Sliding Supporting Member 
         [0155]      66   a : Shaft 
         [0156]      66   b : Supporting Roller 
         [0157]      68 : Stopper 
         [0158]      70 : Leaf 
         [0159]      70 G: Leaf Group 
         [0160]      70   a : Upper Edge 
         [0161]      70   b : Lower Edge 
         [0162]      70   c : Front Edge 
         [0163]      70   d : Rear Edge 
         [0164]      71 ,  72 : Slit 
         [0165]      71   a,    72   a : Upper Side 
         [0166]      71   b,    72   b : Lower Side 
         [0167]      73 : Rack Gear 
         [0168]      90 : Drive Device 
         [0169]      91 : Motor (Driving Unit) 
         [0170]      91   a : Housing 
         [0171]      92 : Rotary Encoder 
         [0172]      94 : Cover 
         [0173]      95 ,  95 L,  95 S: Shaft 
         [0174]      96 : Pinion Gear (Advance And Retraction Driving Section) 
         [0175]      97 : Spacer 
         [0176]      98 : Pedestal Part 
         [0177]      99 : Cover Member 
         [0178]      101 : Diagonizing X-Ray 
         [0179]      130 : Bearing 
         [0180]      200 : Patient 
         [0181]    C 0 : Isocenter 
         [0182]    C 1 : Central Axis 
         [0183]    C 2 : Central Axis 
         [0184]    S 0 : Electron Beam 
         [0185]    S 1 , S 2 : Radiation 
         [0186]    Sr: Therapeutic Radiation