Abstract:
A radiation irradiation method includes the steps (a) and (b). The step (a) is the step of irradiating a first part of a subject with first radiation radiated in a radial pattern from a first point. The step (b) is the step of irradiating a second part different from said first part of said subject with second radiation radiated in a radial pattern from a second point. A first position of said first point relative to said subject correspond to a second position of said second point relative to said subject.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a radiation irradiation method and a radiotherapy apparatus controller, and especially relates to a radiation irradiation method and a radiotherapy apparatus controller that are used for irradiating an affected area with radiation for radiotherapy. 
         [0003]    2. Description of the Related Art 
         [0004]    The radiotherapy is known which is treatment of disease by irradiating an affected area (a tumor) with therapeutic radiation. Radiation produced by the bremsstrahlung is exemplified as the therapeutic radiation. It is desired for the radiotherapy that effectiveness of treatment is high and that a radiation dose with which normal cells are irradiated is smaller than a radiation dose with which cells in the affected area are irradiated. That is to say, it is desired for the radiotherapy to control an area irradiated with the therapeutic radiation with higher precision than ever and to control the radiation dose of the therapeutic radiation with which the affected area is irradiated with higher precision than ever. 
         [0005]    In Japanese Laid-Open Patent Application JP-Heisei 8-511452T (corresponding to WO9428971, EP0810006, EP0810005, EP0703805), a radiotherapy apparatus is disclosed which has a degree of freedom of regulated angle for radiating beams only in a plane of a gantry. It is not necessarily for a radiation shield to be fixed, to be attached to the gantry, or to rotate with consistently shielding against a main beam. A regulated movement reduces a danger of a collision between a patient and the gantry, and provides an extremely accurate radiotherapy planning. The radiotherapy apparatus composed as described above can include an X-ray tomography image-formation system into one gantry. Two systems cooperate, and design and execute a treatment activity in which a treatment area with non-uniform figure is accurately irradiated and a tissue surrounding the area is irradiated at minimum by using many of configuration parts of the same hardware. The radiotherapy apparatus can include a collimator for minimizing an irradiation to benign tumor neighboring malignant tumor by changing a width of a radiation fan beam when the treatment area of the patient intersects an area exposed to the beam. The width of the fan beam can be controlled so that multiple contiguity resemblance slices can be treated for a certain period in a treatment period. 
         [0006]    In Japanese Patent JP3746744, a radiotherapy apparatus is disclosed which has superior treatment performance. The radiotherapy apparatus includes: an irradiation head including a therapeutic radiation generation part which has an electron gun, a linear accelerator and a target and a gimbals mechanism which oscillates the therapeutic radiation generation part; a supporting and moving mechanism supporting and moving the irradiation head on a predetermined spherical coordinates; a microwave generation part allocated on a static position for generating microwave to be supplied to above mentioned irradiation head; and a waveguide part whose one end is electromagnetically connected to the microwave generation part and whose other end is electromagnetically connected to the linear accelerator. The radiotherapy apparatus is characterized by connecting a waveguide of the waveguide part mounted on above mentioned gimbal mechanism with a waveguide of the waveguide part from the micro wave generation part by using a flexible waveguide. 
         [0007]    In Japanese Patent JP3746747 (Japanese Laid-Open Patent Application JP2004-097646), a radiotherapy apparatus is disclosed which can monitor a condition of a treatment field in real time even during a radiation irradiation treatment. The radiotherapy apparatus includes: a radiation irradiation head for irradiating a treatment field of a subject with therapeutic radiation; a X-ray source for irradiating the treatment field of the subject with diagnostic X-ray; and a sensor array for detecting transmission X-ray of the diagnostic X-ray that penetrated the subject under the treatment and outputting it as diagnostic image data. The sensor array moves in conjunction with movement of the radiation irradiation head. 
         [0008]    In Japanese Laid-Open Patent Application JP2002-065876, a radiotherapy method is disclosed which prevents parts that are excessively irradiated with overlapping radiation dose on a border area of irradiation sections and parts that are irradiated with no radiation dose, even in a case that fractionated irradiation is carried out by dividing the irradiation section into a plurality of sections in direction of predetermined width of an irradiation field because the whole tumor cannot be irradiated with one time radiation. The radiotherapy method is a treatment method including steps of: dividing the irradiation section into several parts in direction parallel to the width of the irradiation field in predetermined direction by collimating means; and irradiating a treated area in an affected area with radiation in units of respective irradiation sections. When the border area on which the divided irradiation sections face each other, the collimating means is moved in direction parallel to the width of the irradiation field in order to reduce radiation dose towards the side of the facing irradiation section. 
         [0009]    In Japanese Laid-Open Patent Application JP2004-321408 (corresponding to U.S. Pat. No. 6,984,835), a radiation irradiation apparatus is disclosed which has a large irradiation field and secures a flatness of a distribution of radiation dose in the irradiation field without strengthening a performance of an accelerator and an irradiation field enlargement device. The radiation irradiation apparatus irradiates an irradiated area set on an irradiation table with radiation beam transferred from an accelerator. The radiation irradiation apparatus is characterized by including: a beam blocking means for blocking the radiation beam; a position control means for controlling the position of the irradiation table so that the whole irradiated area is irradiated in a plurality of irradiation areas including superposition areas specified by a plurality of irradiation using the radiation beam; and a multi-leaf collimator control means for leveling a distribution of radiation dose to the whole irradiated area including the superposition area by making a distribution of the radiation dose in the superposition area of the respective irradiation areas have a gradient and irradiating with the plurality of radiation beam. 
         [0010]    International publication WO03018131 (corresponding to U.S. Pat. No. 7,085,347, U.S. Pat. No. 6,977,987) discloses a radiological treatment apparatus. The radiological treatment apparatus includes a radiation head having a linear accelerator and a head waveguide part having one end part electromagnetically connected to the linear accelerator; a supportedly moving mechanism movably supporting the radiation head on a predetermined first spherical coordinate; a microwave oscillator generating microwave supplied to the radiation head and disposed at a stationary position; a fixed waveguide part having one end part electromagnetically connected to the microwave oscillator and the other end part positioned on the supportedly moving mechanism; and a movable waveguide electromagnetically connected to the other end part of the fixed waveguide part having one end part positioned on the supportedly moving mechanism. 
         [0011]    U.S. Pat. No. 5,442,675 discloses a dynamic collimator for radiation therapy. The radiation therapy machine having a radiation source for directing a beam of radiation along a beam plane toward a patient with a treatment volume, the therapy machine including a collimator disposed between the radiation source and the patient, to control the beam width normal to the beam plane, the machine including a means for supporting and moving the patient with respect to the beam plane along a translation axis wherein the treatment volume includes a plurality of adjacent slices, each slice associated with a sinogram, indicating desired fluence profiles to be directed toward one associated slice, the machine includes: a comparison means for comparing sinograms of adjacent slices to generate a difference value; a control signal means receiving the difference value from the comparison means for indicating whether the difference value is within a predetermined limit by means of a correlation signal; and a collimator control means receiving the correlation signal from the control signal means for controlling the collimator to adjust the beam width to simultaneously irradiate adjacent slices of the treatment volume when the correlation signal indicates that the difference value is within the predetermined limit. 
         [0012]    U.S. Pat. No. 5,548,627 discloses a radiation therapy machine for treating a patient having a treatment volume. The machine includes: a gantry for rotation with a gantry plane; a radiation source disposed on the gantry for rotation with the gantry about an axis of rotation, the radiation source directing a radiation beam of a predetermined intensity appropriate to treat tumorous tissue toward the axis of rotation form a plurality of first gantry angles along the gantry plane; an x-ray source disposed on the gantry for rotation with the gantry about the axis of rotation, the x-ray source for producing an x-ray beam directed toward the axis of rotation from a plurality of second gantry angles in a plane parallel to the gantry plane, the radiation source and the x-ray source positioned in separate parallel planes so that the radiation beam and x-ray beam do not intersect; an x-ray detector disposed on the gantry and diametrically opposed to the x-ray source for receiving the x-ray beams therefrom and producing x-ray data; and a computer means for receiving the x-ray data and generating a tomographic image therefrom. 
         [0013]    U.S. Pat. No. 5,724,400 discloses a radiation therapy machine for treating a patient with high energy radiation. The radiation therapy machine includes: a gantry for rotation within a gantry plane; a table disposed along an axis of translation for supporting a patient and for moving the patient along the axis of translation, the axis of translation positioned within the rotation of the gantry; a radiation source disposed on the gantry for producing a radiation beam within a fan beam plane substantially parallel to the gantry plane, the beam including a plurality of rays diverging in the beam plane about one central ray, the central ray directed at the patient from a variety of gantry angles along the gantry plane; and an attenuation means disposed between the radiation source and the patient for independently controlling the intensity of each ray as a function of gantry angle. The attenuation means includes: a plurality of radiation attenuating leaves; a supporting member positioned generally between the radiation source and the patient for guiding the leaves between a closed state within the radiation beam, each leaf thus occluding one ray of the beam, and an open state outside of the radiation beam to allow unobstructed passage of the ray; motivation means for independently moving each leaf between the open and closed states; and timing means communicating with the motivation means for controlling the ratio of the period of time during which each leaf is in the closed state to the period during which each leaf is in the open state to control the average energy fluence of each ray of the beam. 
       SUMMARY OF THE INVENTION 
       [0014]    Therefore, an object of the present invention is to provide a radiation irradiation method and a radiotherapy apparatus controller for controlling a position of an area which is irradiated with the therapeutic radiation in a subject with higher precision than ever and controlling the radiation dose with which the area is irradiated with higher precision than ever. 
         [0015]    Another object of the present invention is to provide a radiation irradiation method and a radiotherapy apparatus controller for controlling a radiation dose with which the area of the subject is irradiated with higher precision than ever and for miniaturizing a radiation irradiation device that emits the radiation. 
         [0016]    Still another object of the present invention is to provide a radiation irradiation method and a radiotherapy apparatus controller for controlling a radiation dose with which the area of the subject is irradiated with higher precision than ever and for miniaturizing an irradiation field shape controller that changes a shape of an irradiation field which is irradiated with the radiation. 
         [0017]    This and other objects, features and advantages of the present invention will be readily ascertained by referring to the following description and drawings. 
         [0018]    In order to achieve an aspect of the present invention, the present invention provides a radiation irradiation method including: (a) irradiating a first part of a subject with first radiation radiated in a radial pattern from a first point; and (b) irradiating a second part different from the first part of the subject with second radiation radiated in a radial pattern from a second point. A first position of the first point relative to the subject correspond to a second position of the second point relative to the subject. 
         [0019]    In the radiation irradiation method, the step (a) may include (a 1 ) irradiating the first part with the first radiation radiated by a radiation irradiation apparatus which radiates radiation in a radial pattern from a point. The step (b) may include (b 1 ) moving the radiation irradiation apparatus after the step (a 1 ) such that the radiation irradiation apparatus radiates the second radiation. 
         [0020]    The radiation irradiation method may further includes (c) changing a shape of irradiation field irradiated with the radiation in the subject by an irradiation field shape controlling device which shields against a part of the radiation. 
         [0021]    In the radiation irradiation method, the step (a) may include (a 1 ) irradiating the first part with the first radiation radiated by a radiation irradiation apparatus which radiates radiation in a radial pattern from a point. The step (b) may include (b 1 ) moving the radiation irradiation apparatus after the step (a 1 ) such that the radiation irradiation apparatus radiates the second radiation and the point does not move relatively to the subject, and (b 2 ) irradiating a third part of the subject with third radiation radiated by the radiation irradiation apparatus while the radiation irradiation apparatus is moving. 
         [0022]    The radiation irradiation method may further include (c) changing a shape of irradiation field irradiated with the radiation in the subject by an irradiation field shape controlling device which shields against a part of the radiation. 
         [0023]    The radiation irradiation method may further include: (d) detecting a motion of the subject; and (e) moving a radiation irradiation apparatus which radiates radiation in a radial pattern from a point based on the motion such that the radiation irradiation apparatus radiates the first radiation to the first part and the second radiation to the second part even though the first part and the second part move. 
         [0024]    In order to achieve another aspect of the present invention, the present invention provides computer program product with program code means for carrying out all steps according to any of the above-mentioned radiation irradiation methods if the program runs on a computer. 
         [0025]    The present invention provides computer program product with program code means according to the above-mentioned computer program product which are stored on a storage means which can be read by the computer. 
         [0026]    In order to achieve another aspect of the present invention, the present invention provides a radiotherapy apparatus controller including: an irradiation portion configured to irradiate a part of a subject with radiation by a radiation irradiation apparatus which radiates the radiation in a radial pattern from a point; and a head swing portion configured to move the radiation irradiation apparatus by a driving apparatus which moves the radiation irradiation apparatus relatively to the subject such that the point does not move relatively to the subject. 
         [0027]    The radiotherapy apparatus controller may further include: a motion collecting portion configured to collect a motion of the subject by a motion detecting apparatus which detects the motion; and a moving body tracking portion configured to move the radiation irradiation apparatus based on the motion by the driving apparatus such that the radiation irradiation apparatus radiates the radiation to the part even though the part moves. 
         [0028]    The radiotherapy apparatus controller may further include: a irradiation field shape controller configured to change a shape of irradiation field irradiated with the radiation in the subject by an irradiation field shape controlling device which shields against a part of the radiation. 
         [0029]    The radiotherapy apparatus controller may further include: a motion collecting portion configured to collect a motion of the subject by a motion detecting apparatus which detects the motion; and a moving body tracking portion configured to move the radiation irradiation apparatus based on the motion by the driving apparatus such that the radiation irradiation apparatus radiates the radiation to the part even though the part moves. 
         [0030]    In order to achieve another aspect of the present invention, the present invention provides a radiotherapy apparatus including a support member configured to be movable to a subject; a radiation irradiation apparatus configured to radiate radiation from a point; and a head swing mechanism configured to support the radiation irradiation apparatus movable to the support member such that the point is fixed to the support member. 
         [0031]    In the radiotherapy apparatus, the head swing mechanism may support the radiation irradiation apparatus to the support member such that the radiation irradiation apparatus is rotatable to rotational axes. 
         [0032]    In the radiotherapy apparatus, the head swing mechanism may include: an intermediate member which is supported by the support member such that the intermediate member is rotatable centering around a first axis. The radiation irradiation apparatus is supported by the intermediate member such that the radiation irradiation apparatus is rotatable centering around a second axis. The first axis intersects with the second axis. 
         [0033]    In order to achieve another aspect of the present invention, the present invention provides a radiotherapy system including: a radiation irradiation apparatus configured to radiate radiation in a radial pattern from a point; a driving apparatus configured to move the radiation irradiation apparatus relatively to a subject; and a radiotherapy apparatus controller according to any of the above-mentioned radiotherapy apparatus controllers, configured to control the radiation irradiation apparatus and the driving apparatus. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]      FIG. 1  is a block diagram showing an embodiment of a radiotherapy system according to the present invention; 
           [0035]      FIG. 2  is a perspective view showing a radiotherapy apparatus; 
           [0036]      FIG. 3  is a sectional view showing a therapeutic radiation irradiation device; 
           [0037]      FIG. 4  is a perspective view showing an head swing mechanism; 
           [0038]      FIG. 5  is a block diagram showing an embodiment of a radiotherapy apparatus controller according to the present invention; 
           [0039]      FIG. 6  is a plain view showing an affected area of a patient seen from a hypothetical point source; 
           [0040]      FIG. 7  is a sectional view showing therapeutic radiation emitted to a plurality of parts in the affected area; 
           [0041]      FIG. 8  is a graph showing an intensity distribution of the therapeutic radiation in width direction; 
           [0042]      FIG. 9  is a graph showing a dose distribution of the therapeutic radiation emitted to the affected area; and 
           [0043]      FIG. 10  is a sectional view showing a comparative example of the therapeutic radiation emitted to the plurality of parts in the affected area. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0044]    The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purposed. 
         [0045]    An embodiment of a radiotherapy system according to the present invention will be described referring to drawings. The radiotherapy system  1  includes a radiotherapy apparatus controller  2  and a radiotherapy apparatus  3  as shown in  FIG. 1 . The radiotherapy apparatus controller  2  is a computer such as a personal computer. The radiotherapy apparatus controller  2  is connected to the radiotherapy apparatus  3  so that information can be interactively transmitted between the radiotherapy apparatus controller  2  and the radiotherapy apparatus  3 . 
         [0046]      FIG. 2  shows the radiotherapy apparatus  3 . The radiotherapy apparatus  3  includes a rotation drive device  11 , an O-ring  12 , a traveling gantry  14 , a head swing mechanism  15 , and a therapeutic radiation irradiation device  16 . The rotation drive device  11  rotatably supports the O-ring  12  on a base centering around a rotational axis  17 , rotates the O-ring  12  centering around the rotational axis  17  under the control of the radiotherapy apparatus controller  2 , and outputs a rotational angle of the O-ring  12  against the base. The rotational axis  17  is parallel to the vertical direction. The O-ring  12  is formed in a ring shape centering around a rotational axis  18 , and rotatably supports the traveling gantry  14  centering around the rotational axis  18 . The rotational axis  18  is perpendicular to the vertical direction, and runs through an isocenter  19  included in the rotational axis  17 . The rotational axis  18  is further secured to the O-ring  12 , and, for this reason, rotates with the O-ring  12  centering around the rotational axis  17 . The traveling gantry  14  is formed in ring shape centering around the rotational axis  18 , and is arranged so as to be a concentric circle with the ring of the O-ring  12 . The radiotherapy apparatus  3  further includes a traveling driving device not shown in  FIG. 2 . The traveling driving device rotates the traveling gantry  14  centering around the rotational axis  18  under control of the radiotherapy apparatus controller  2 , and outputs a traveling angle of the traveling gantry  14  against the O-ring  12 . 
         [0047]    The head swing mechanism  15  is secured inside the ring of the traveling gantry  14 , and supports the therapeutic radiation irradiation device  16  on the traveling gantry  14  so that the therapeutic radiation irradiation device  16  can be arranged inside the traveling gantry  14 . The head swing mechanism  15  has a pan axis  21  and a tilt axis  22 . The tilt axis  22  is secured to the traveling gantry  14 , and is parallel to the rotational axis  18  without intersecting with the rotational axis  18 . The pan axis  21  is orthogonal to the tilt axis  22 . The head swing mechanism  15  rotates the therapeutic radiation irradiation device  16  centering around the pan axis  21  under the control by the radiotherapy apparatus controller  2 , and rotates the therapeutic radiation irradiation device  16  centering around the tilt axis  22 . 
         [0048]    The therapeutic radiation irradiation device  16  radiates a therapeutic radiation  23  under the control of the radiotherapy apparatus controller  2 . The therapeutic radiation  23  is radiated almost along a straight line running on the intersection where the pan axis  21  and the tilt axis  22  intersect each other. Since a part of the therapeutic radiation  23  is blocked, a shape of its irradiation field is controlled when the therapeutic radiation  23  is radiated to a patient. In addition, the therapeutic radiation  23  is formed so as to have a uniform distribution of intensity in the irradiation field. 
         [0049]    Since the therapeutic radiation irradiation device  16  is supported by the traveling gantry  14 , the therapeutic radiation  23  always and almost passes the isocenter  19  when the therapeutic radiation irradiation device  16  is once adjusted so as to face the isocenter  19  by the head swing mechanism  15 , even when the O-ring  12  is rotated by the rotation drive device  11  or the traveling gantry  14  is rotated by the traveling driving device. That is to say, the therapeutic radiation  23  can be radiated to the isocenter  19  from an arbitrary direction through the traveling and the rotating. 
         [0050]    The radiotherapy apparatus  3  further includes a plurality of imager systems. Concretely, the radiotherapy apparatus  3  includes diagnostic x-ray sources  24  and  25  and sensor arrays  32  and  33 . The diagnostic X-ray source  24  is supported by the traveling gantry  14 . The diagnostic X-ray source  24  is arranged inside the ring of the traveling gantry  14 , and arranged at a position where an angle formed by a line segment connecting the isocenter  19  with the diagnostic X-ray source  24  and a line segment connecting the isocenter  19  with the therapeutic radiation irradiation device  16  is an acute angle. The diagnostic X-ray source  24  radiates a diagnostic X-ray  35  to the isocenter  19  under the control by the radiotherapy apparatus controller  2 . The diagnostic X-ray  35  is a conical corn beam that is radiated from one point included in the diagnostic X-ray source  24  and whose cone point is the one point. The diagnostic X-ray source  25  is supported by the traveling gantry  14 . The diagnostic X-ray source  25  is arranged inside the ring of the traveling gantry  14 , and arranged at a position where an angle formed by a line segment connecting the isocenter  19  with the diagnostic X-ray source  25  and a line segment connecting the isocenter  19  with the therapeutic radiation irradiation device  16  is an acute angle. The diagnostic X-ray source  25  radiates a diagnostic X-ray  36  to the isocenter  19  under the control of the radiotherapy apparatus controller  2 . The diagnostic X-ray  36  is a conical corn beam that is radiated from one point of the diagnostic X-ray source  25  and whose cone point is the one point. 
         [0051]    The sensor array  32  is supported by the traveling gantry  14 . The sensor array  32  receives the diagnostic X-ray  35  that is radiated by the diagnostic X-ray source  24  and transmits a subject around the isocenter  19 , and produces a transfer image of the subject. The sensor array  33  is supported by the traveling gantry  14 . The sensor array  33  receives the diagnostic X-ray  36  that is radiated by the diagnostic X-ray source  25  and transmits a subject around the isocenter  19 , and produces a transfer image of the subject. Each of the sensor arrays  32  and  33  is exemplified in a FPD (Flat Panel Detector) or an X-ray II (Image Intensifier). 
         [0052]    The radiotherapy apparatus  3  further includes a sensor array  31 . The sensor array  31  is arranged so that a line segment connecting the sensor array  31  with the therapeutic radiation irradiation device  16  runs on the isocenter  19 , and is secured inside the ring of the traveling gantry  14 . The sensor array  31  receives the diagnostic x-ray  23  that is radiated by the therapeutic radiation irradiation device  16  and transmits a subject around the isocenter  19 , and produces a transfer image of the subject. The sensor array  31  is exemplified in a FPD (Flat Panel Detector) or an X-ray II (Image Intensifier). 
         [0053]    According to such imager systems, a transfer image centered around the isocenter  19  can be produced on the basis of image signals obtained by the sensor arrays  31 ,  32 , and  33 . 
         [0054]    The radiotherapy apparatus  3  further include a couch  41  and a couch driving device  42 . The couch  41  is used when a patient  43  to be treated by the radiotherapy system  1  lies down. The couch  41  includes holding fixtures that are not shown in  FIG. 2 . The holding fixtures keep the patient from moving, and fix the patient to the couch  41 . The couch driving device  42  supports the couch  41  on a base, and moves the couch  41  under the control by the radiotherapy apparatus controller  2 . 
         [0055]      FIG. 3  shows the therapeutic radiation irradiation device  16 . The therapeutic radiation irradiation device  16  includes an electron beam accelerator  51 , an X-ray target  52 , a primary collimator  53 , a flattening filter  54 , a dosimeter  61 , a secondary collimator  55 , and a multi-leaf collimator  56 . The electron beam accelerator  51  emits an electron beam  57  generated by accelerated electrons to the X-ray target  52 . The X-ray target  52  is composed of a material of higher atomic number (tungsten, tungsten alloy, and so on), and radiates a radiation  59  produced by the bremsstrahlung in emission of the electron beam  57 . A radiation point of the radiation  59  has a constant distribution (area) depending on energy and property of the electron beam  57  emitted to the X-ray target  52 . However, dimensions of the area are much smaller than the distance from the X-ray target  52  to the isocenter  19 . Therefore, the position of radiating the radiation  59  can be treated as a point source for convenience. Hereinafter, this point source is referred to as a hypothetical point radiation source  58 . The radiation  59  is radiated almost along a straight line running on the hypothetical point radiation source  58  that the X-ray target  52  includes internally. That is to say, the radiation  59  is a conical corn beam that is radiated from hypothetical point radiation source  58  in a radial pattern and whose cone point is the hypothetical point radiation source  58 . The primary collimator  53  is composed of a material of higher atomic number (lead, tungsten, and so on), and shields against the radiation  59  so that an area other than the desired area is not irradiated with the radiation  59 . The flattening filter  54  is, for example, composed of aluminum, and is formed in a plate having an approximately conical projection. The flattening filter  54  is arranged so that its projection faces the X-ray target side. A shape of the flattening filter is formed so that, after passing the flattening filter, dose in predetermined area of a plane perpendicular to its radiation direction is distributed almost uniformly. The secondary collimator  55  is composed of a material of higher atomic number (lead, tungsten, and so on), and shields against the radiation  60  so that an area other than the desired area is not irradiated with the radiation  60 . The multi-leaf collimator  56  has a plurality of leaves for shielding against a part of the radiation  60 . Each of the plurality of leaves is arranged along a plane including the hypothetical point radiation source  58 , and is supported along the plane in a movable condition. The multi-leaf collimator  56  moves each of the plurality of leaves to arbitrary position under the control of radiotherapy apparatus controller  2 . That is to say, when the therapeutic radiation  23  is radiated to the patient, the multi-leaf collimator  56  controls the shape of the irradiation field by shielding against a part of the radiation  60  under the control of the radiotherapy apparatus controller  2 . In addition, the multi-leaf collimator  56  can be replaced by an irradiation field shape controller for controlling a shape of an irradiation field without equipping the plurality of leaves. Both may be called the irradiation field shape controlling device. 
         [0056]    The dosimeter  61  is a transmission ionization chamber for measuring intensity of penetrating radiation, and is arranged in a position between the primary collimator  53  and the secondary collimator  55  so that the radiation  60  penetrates. The dosimeter  61  measures dose of the penetrating radiation  60 , and outputs the dose to the radiotherapy apparatus controller  2 . Such dosimeter  61  is preferable because non-destructive examination can be achieved. Other X-ray intensity detector different from the transmission ionization chamber can be used as the dosimeter  61 . The X-ray intensity detector is exemplified in a semiconductor detector or a scintillation detector. Since it is preferable to arrange the semiconductor detector or the scintillation detector out of a radiation path because it is difficult to arrange them on the path as an alternative for the transmission ionization chamber. The semiconductor detector or the scintillation detector is, for example, secured on the traveling gantry  14  so as to be arranged in a position facing the therapeutic radiation irradiation device  16  at a distance from the isocenter  19 . The ionization chamber is inferior in a responsibility because its time constant is a few seconds. The semiconductor detector and the scintillation detector have disadvantages that signal intensity is lower than that of the ionization chamber when being arranged out of the radiation path. However, they are preferable to the ionization chamber because a responsibility is improved. 
         [0057]    The electron beam accelerating device  51  includes an electron beam generator  63  and an acceleration tube  64 . The electron beam generator  63  includes a cathode  66  and a grid  67 . The acceleration tube  64  is formed in cylindrical shape, and includes a plurality of electrodes  68  lining up at appropriate intervals inside the cylinder. The radiotherapy apparatus  3  further includes a cathode power source  70  and a grid power source  69 . The cathode power source  70  supplies, under the control of the radiotherapy apparatus controller  2 , electric power to the cathode  66  so that the predetermined amount of electrons are emitted from the cathode  66  by heating the cathode  66  (that is to say, so that a predetermined temperature of the cathode  66  is maintained). The grid power source  69  supplies, under the control of the radiotherapy apparatus controller  2 , voltage between the grid  67  and the cathode  66  so that the predetermined amount of electrons are emitted from the electron beam generator  63 . A klystron  5  is connected to the acceleration tube  64  via a waveguide tube  8 . The klystron  5  emits, under the control of the radiotherapy apparatus controller  2 , a micro wave to the acceleration tube  64  via the waveguide tube  8  so that the acceleration tube  64  accelerates electrons emitted from the electron beam generator  63  such that the electrons have predetermined energy. 
         [0058]      FIG. 4  shows the head swing mechanism  15 . The head swing mechanism  15  includes a radiation device support member  81  and an intermediate member  82 . The radiation device support member  81  is supported by the traveling gantry  14 , and moves with the traveling gantry  14 . The tilt axis  22  is fixed to the radiation device support member  81 . The intermediate member  82  is rotatably supported by the radiation device support member  81  centering around the tilt axis  22 . Since the intermediate member  82  contacts a part of the radiation device support member  81  when rotating centering around the tilt axis  22 , a range of the rotation is limited. The pan axis  21  is fixed to the intermediate member  82 . The therapeutic radiation irradiation device  16  is rotatably supported by the intermediate member  82  centering around the pan axis  21 . Since the therapeutic radiation irradiation device  16  contacts a part of the intermediate member  82  when rotating centering around the pan axis  21 , a range of the rotation is limited. 
         [0059]    The head swing mechanism  15  further includes a pan axis driving device and a tilt axis driving device that are not shown in  FIG. 4 . The pan axis driving device rotates the therapeutic radiation irradiation device  16  centering around the pan axis  21  under the control of the radiotherapy apparatus controller  2 . The tilt axis driving device rotates the intermediate member  82  centering around the tilt axis  22  under the control of the radiotherapy apparatus controller  2 . 
         [0060]    The head swing mechanism  15  further supports the therapeutic radiation irradiation device  16  so that an intersection of the pan axis  21  and the tilt axis  22  conforms with the hypothetical point radiation source  58  of the therapeutic radiation irradiation device  16 . In such radiotherapy apparatus  3 , when the couch  41 , the O-ring  12 , and the traveling gantry  14  are secured, the hypothetical point radiation source  58  of the therapeutic radiation irradiation device  16  is secured against the patient  43 . In this case, when radiating the therapeutic radiation  23  respectively to a plurality of areas of the patient  43  by moving the therapeutic radiation irradiation device  16  using the head swing mechanism  15 , the radiotherapy apparatus  3  can radiate the therapeutic radiation  23  from the same point to a plurality of the areas, respectively. 
         [0061]      FIG. 5  shows the radiotherapy apparatus controller  2 . The radiotherapy apparatus controller  2  is a computer, and includes a CPU, a storage device, an input device, an output device, and an interface that are not shown in  FIG. 5 . The CPU executes computer programs installed in the radiotherapy apparatus controller  2 , and controls the storage device, the input device, the output device, and the interface. The storage device stores the computer programs, stores information used by the CPU, and stores information created by the CPU. The input device supplies information created by a user&#39;s operation to the CPU. As the input device, a keyboard and a mouse are shown as examples. The output device outputs the information created by the CPU so as to be recognized by the user. As the output device, a display for showing images created by the CPU is shown as an example. The interface outputs information created by an outside device connected with the radiotherapy apparatus controller  2  to the CPU, and outputs information created by the CPU to the outside device. The outside device includes the radiotherapy apparatus  3 . 
         [0062]    The radiotherapy apparatus controller  2  includes a treatment planning portion  91 , an irradiation planning portion  92 , an irradiation position controller  93 , an head swing portion  94 , an irradiation field shape controller  95 , a motion collecting portion  96 , a moving body tracking portion  97 , and a therapeutic radiation radiating portion  98 . 
         [0063]    The treatment planning portion  91  shows three dimensional data, which are created by a computer tomography apparatus, indicating a positional relation between an affected area of the patient  43  and internal organs (including a risk part) around the affected area so as to be browsed by a user. The treatment planning portion  91  further creates a treatment plan on the basis of the three dimensional data and information supplied by using the input device. The treatment plan shows three dimensional data of the affected area of the patient  43 , and shows a combination of an irradiation angle and a radiation dose. The irradiation angle shows a direction of radiating the therapeutic radiation  23  to the affected area of the patient  43  (that is, a relative position of the patient  43  and the hypothetical point radiation source  58  of the therapeutic radiation irradiation device  16 ), and shows a traveling angle and a rotational angle. The traveling angle shows a direction of the traveling gantry  14  when the traveling gantry  14  is rotated by the traveling driving device. The rotational angle shows a direction of the O-ring  12  when the O-ring  12  is rotated by the rotation drive device  11 . The radiation dose shows a dose of the therapeutic radiation  23  radiated to an affected area from the respective irradiation angles. 
         [0064]    The irradiation planning portion  92  creates an irradiation plan for each of combinations of the irradiation and the radiation dose angle shown by the treatment plan created by the treatment planning portion  91 . The irradiation plan shows three-dimensional data of a plurality of areas obtained by dividing the affected area of the patient  43  by planes including the hypothetical point radiation source  58 , and shows combinations of a head swing angle, a shape of an irradiation field, and a radiation dose for each of the plurality of areas. The head swing angle shows a direction of the therapeutic radiation irradiation device  16  when the area is irradiated with the therapeutic radiation  23 , and shows a pan angle and a tilt angle. The pan angle shows a direction of the therapeutic radiation irradiation device  16  when the therapeutic radiation irradiation device  16  rotates centering around the pan axis  21  against the intermediate member  82 . The tilt angle shows a direction of the intermediate member  82  when the intermediate member  82  rotates centering around the tilt axis  22  against the radiation device support member  81 . The shape of an irradiation field shows a sectional shape of the therapeutic radiation  23  radiated to the area. The radiation dose shows a dose of the therapeutic radiation  23  radiated to the area. 
         [0065]    The irradiation position controller  93  moves the couch  41  by using the couch driving device  42 , and moves the therapeutic radiation irradiation device  16  by using the rotation driving device  11  or the traveling driving device so that a relative position of the patient  43  and the hypothetic point source  58  of the therapeutic radiation irradiation device  16  can meet the irradiation angle shown by the treatment plan created by the treatment planning portion  91 . 
         [0066]    The head swing portion  94  moves the therapeutic radiation irradiation device  16  by using the head swing mechanism  15  so that a relative position of the patient  43  and the therapeutic radiation irradiation device  16  can meet an irradiation angle shown by an irradiation plan created by the irradiation planning portion  92 . 
         [0067]    The irradiation field shape controller  95  controls the multi-leaf collimator  56  so that a sectional shape of the therapeutic radiation  23  can meet a shape of an irradiation field shown by an irradiation plan created by the irradiation planning portion  92 . 
         [0068]    The motion collecting portion  96  detects a motion of the patient  43  by using the imager system of the radiotherapy apparatus  3 . That is to say, the motion collecting portion  96  radiates the diagnostic X-ray  35  by using the diagnostic X-ray source  24 , and takes a transfer image of the patient  43  produced by using the sensor array  32  on the basis of the diagnostic X-ray  35 . Further, the motion collecting portion  96  radiates the diagnostic X-ray  36  by using the diagnostic X-ray source  25 , and takes a transfer image of the patient  43  produced by using the sensor array  33  on the basis of the diagnostic X-ray  36 . Further, the motion collecting portion  96  radiates the therapeutic radiation  23  by using the therapeutic radiation irradiation device  16 , and takes a transfer image of the patient  43  produced by using the sensor array  31  on the basis of the therapeutic radiation  23 . The motion collecting portion  96  calculates a marker position by using a plurality of the transfer images taken in such manner. The marker position shows a value indicating a position of a landmark inside the patient  43  in the image when the patient  43  is imaged by the imager system, and shows a motion of the patient  43 . As the landmark, the affected area of the patient  43 , a bone (a rib) of the patient  43 , a diaphragm, a bladder, and an object embedded in the body of the patient  43  so as to move with the affected area are shown as examples. The object is something to be detected by the imager system and a spherical gold marker made of gold is shown as an example. 
         [0069]    The moving body tracking portion  97  stores a table for relating a motion detected by the motion collecting portion  96  to a position of the affected area in the patient  43 . The moving body tracking portion  97  refers to the table, and calculates the position of the affected area relating to the motion detected by the motion collecting portion  96 . The moving body tracking portion  97  moves the therapeutic radiation irradiation device  16  by using the head swing mechanism  15  so that the position of the affected area can be irradiated with the therapeutic radiation  23 . 
         [0070]    The therapeutic radiation radiating portion  98  radiates the therapeutic radiation  23  to the position of the affected area by using the therapeutic radiation irradiation device  16  after the therapeutic radiation irradiation device  16  is moved by the moving body tracking portion  97 . 
         [0071]      FIG. 6  shows the affected area of the patient  43 . The affected area  101  is divided in a plurality of parts  102 - 1  to  102 - 4  by planes including the hypothetic point source  58 . The part  102 - i  (i=1, 2, 3, and 4) is included in a patch area  103 - i . A plurality of the patch areas  103 - 1  to  103 - 4  respectively shows areas which are irradiated with the therapeutic radiation  23  when the multi-leaf collimator  56  controls a shape of the irradiation field so that a sectional shape of the therapeutic radiation  23  can be maximum. The plurality of the patch areas  103 - 1  to  103 - 4  does not overlap each other. The patch area  103 - i  includes an irradiation field  104 - i . The irradiation field  104 - i  shows a sectional shape of the therapeutic radiation  23 . The irradiation field  104 - i  is controlled so that the whole part  102 - i  can be irradiated with the therapeutic radiation  23  and a part irradiated with the therapeutic radiation  23  other than the part  102 - i  can be as small as possible. 
         [0072]    Respective parts  102 - i  are not necessarily irradiated at same time and in the same shape. For example, in the same head swing angle, each part  102 - i  may be composed of a combination of a plurality of minute parts which are formed by controlling the shape of the multi-leaf collimator  56 . In addition, an irradiation time may be changed for every irradiation of respective minute parts at that time. In such case, this embodiment can be applied to an intensity-modulated irradiation. Only a case of collectively and homogeneously irradiating of respective parts  102 - i  in a specific shape is shown to simply explain below. 
         [0073]      FIG. 7  shows parts irradiated with the therapeutic radiation  23 , when a plurality of the parts  102 - 1  to  102 - 2  are irradiated with the therapeutic radiation  23 . The area  111 - 1  shows an area irradiated with the therapeutic radiation  23  with which the part  102 - 1  is irradiated. The area  111 - 2  shows an area irradiated with the therapeutic radiation  23  with which the part  102 - 2  is irradiated. The area  111 - 1  includes an irradiation field  104 - 1 , and is formed in a corn shape whose apex is arranged at a position  112 . The position of the apex meets a position of the hypothetic point source  58  that is made when the therapeutic radiation irradiation device  16  radiates the therapeutic radiation  23  to the part  102 - 1 . The area  111 - 2  includes an irradiation field  104 - 2 , and is formed in a cone shape whose apex is arranged at the position  112 . The position of the apex meets a position of the hypothetic point source  58  that is made when the therapeutic radiation irradiation device  16  radiates the therapeutic radiation  23  to the part  102 - 2 . That is to say, the apex of the cone of the area  111 - 1  and the apex of the cone of the area  111 - 2  meet at the position  112 , and positions of the hypothetic point source  58  meet at the same point when the therapeutic radiation irradiation device  16  radiates the therapeutic radiation  23  to the part  102 - 1  and when the therapeutic radiation irradiation device  16  radiates the therapeutic radiation  23  to the part  102 - 2 . 
         [0074]    In this time, for the purpose of reducing radiation dose to healthy tissue, it is preferable that there is no overlapping of the area  111 - 1  and the area  111 - 2 . However, in the case of applying the aforementioned intensity-modulated irradiation, it is permissible to have the overlapping within a degree determined by a treatment plan created by the irradiation planning portion  92 . 
         [0075]    As a result, for the purpose of making possible to control the overlapping, it is preferable that the apex of the cone meets to the hypothetic point source  58 . In order to do this, it is preferable to be configured so that the intersection of the pan axis  21  and the tilt axis  22  can meet to the hypothetic point source  58 . 
         [0076]    That is, the irradiation planning portion  92  divides the affected area  101  into a plurality of the parts  102 - 1  to  102 - 4  for every combination of an irradiation angle and a radiation dose shown by a treatment plan created by the treatment planning portion  91 , calculates the patch area  103 - i  including the part  102 - i , and calculates an head swing angle when the therapeutic radiation irradiation device  16  turns on the patch area  103 - i . The irradiation planning portion  92  further calculates a shape of the irradiation field  104 - i  so that the whole part  102 - i  can be irradiated with the therapeutic radiation  23  and a part irradiated with the therapeutic radiation  23  other than the part  102 - i  can be as small as possible. 
         [0077]    The embodiment of the radiation irradiation method according to the present invention is carried out by using the radiotherapy system  1 . A user creates a treatment plan by using the radiotherapy apparatus controller  2  at first. The treatment plan shows an irradiation angle in irradiating the affected area of the patient  43  with the therapeutic radiation  23 , and shows a radiation dose and a property of the therapeutic radiation  23  radiated from the respective irradiation angles. Next, the radiotherapy apparatus controller  2  creates irradiation plans for every combination of the irradiation angle and the radiation dose shown by the treatment plan. The irradiation plan shows three dimensional data of a plurality of parts formed by dividing the affected area of the patient  43  by a plane including the hypothetic point source  58 , and shows combinations of an head swing angle, a shape of the irradiation field and a radiation dose for each of the plurality of the parts. The head swing angle shows a direction of the therapeutic radiation irradiation device  16  when the parts are irradiated with the therapeutic radiation  23 , and shows a pan angle and a tilt angle. The shape of the irradiation field shows a sectional shape of the therapeutic radiation  23  with which the parts are irradiated. The radiation dose shows a dose of the therapeutic radiation  23  with which the parts are irradiated, and meets a radiation dose shown by the treatment plan. 
         [0078]    A user secures the patient  43  to the couch  41  of the radiotherapy apparatus  3 . The radiotherapy apparatus controller  2  moves the couch  41  by using the couch driving device  42  so that the affected area  101  of the patient  43  can be irradiated with the therapeutic radiation  23  at the irradiation angle shown by the treatment plan, rotates the O-ring  12  by using the rotation driving device  11 , and rotates the traveling gantry  14  by using the traveling driving device. The radiotherapy apparatus controller  2  moves the therapeutic radiation irradiation device  16  by using the head swing mechanism  15  so that the part  102 - i  in the affected area  101  of the patient  43  can be irradiated with the therapeutic radiation  23 . 
         [0079]    In addition, the radiotherapy apparatus controller  2  is also able to irradiate the respective parts  102 - i  in the affected area  101  of the patient  43  with the therapeutic radiation  23  without using the head swing mechanism  15 . For example, the radiotherapy apparatus controller  2  controls an irradiation field by using the multi-leaf collimator  56  so that the part  102 - i  in the affected area  101  of the patient  43  can be irradiated with the therapeutic radiation  23  after moving the therapeutic radiation irradiation device  16  by using the head swing mechanism  15  so that the therapeutic radiation irradiation device  16  can face the affected area  101  of the patient  43 . 
         [0080]    Subsequently, the radiotherapy device controller  2  repeats a tracking operation and an irradiation operation for every part  102 - i . In the tracking operation, the radiotherapy apparatus controller  2  calculates a position of an affected area on the basis of a position of a landmark detected by the imager system of the radiotherapy apparatus  3 . The radiotherapy apparatus controller  2  moves the therapeutic radiation irradiation device  16  by using the head swing mechanism  15  so that the therapeutic radiation  23  can penetrate the position of the affected area. In the irradiation operation, the radiotherapy apparatus controller  2  irradiates the affected area with the therapeutic radiation  23  by using the therapeutic radiation irradiation device  16  just after the therapeutic radiation irradiation device  16  is moved in the tracking operation. Here, an evaluation object of the position of the affected area may be the affected area  101 , and may be a center of each part  102 - i . However, since the shape of the irradiation field is controlled for each part  102 - i , it is preferable to set each part  102 - i  as an evaluation object. 
         [0081]      FIG. 8  shows an intensity distribution of the therapeutic radiation  23  with which a predetermined plane is irradiated. The plane is perpendicular to a radiation direction of the therapeutic radiation  23 , and is at the position equivalent to the depth of 10 cm in water. The distribution  106  shows that, with respect to a width direction that is perpendicular to the radiation direction, intensity within an irradiation range included in a part irradiated with the therapeutic radiation  23  is almost constant. The distribution  106  further shows that intensity in a non-irradiation range except the irradiation range is sufficiently low in comparison with intensity within the irradiation range. In Japan, the intensity in the non-irradiation range is regulated so as to be equal to or less than one-thousandth of the intensity within the irradiation range by the Enforcement Regulations of Medical Law. 
         [0082]      FIG. 9  shows a distribution of dose of the therapeutic radiation  23  with which the plurality of the parts  102 - 1  to  102 - 2  are irradiated with executing the radiation irradiation method according to the present invention. The distribution  107  shows a dose of the therapeutic radiation  23  with which a minute part on a plane is irradiated, when the therapeutic radiation  23  with the intensity of the distribution  106  is used, in a case where there is no overlapping area between the area  111 - 1  and the area  111 - 2 . The plane is perpendicular to the radiation direction of the therapeutic radiation  23  in the plurality of the parts  102 - 1  to  102 - 2 , and is at the position equivalent to the depth of 10 cm in water. The distribution  107  shows that, with respect to the width direction that is perpendicular to the radiation direction, a radiation dose is almost constant value in a range  108 - 1  corresponding to the part  102 - 1 , and shows that a radiation dose is almost constant value in a range  108 - 2  corresponding to the part  102 - 2 . The distribution  107  further shows that the radiation dose in the range  108 - 1  is almost equal to that in the range  108 - 2 . The distribution  107  further shows that a radiation dose in a range except for the range  108 - 1  and the range  108 - 2  is sufficiently smaller than those in the range  108 - 1  and the range  108 - 2 . According to the present invention, a distribution of a dose of the therapeutic radiation  23  with which a minute part on a plane differently positioned to the radiation direction is similar to the distribution  107 , and a dose of the therapeutic radiation  23  with which a plurality of the parts  102 - 1  to  102 - 4  is irradiated can be controlled in a similar way of other radiation irradiation apparatus irradiating a plurality of the parts  102 - 1  to  102 - 2  at a time. 
         [0083]    Incidentally,  FIG. 9  is explained regarding a simply explained case where the distribution of the dose of the therapeutic radiation  23  is in a top-flatted shape as shown in  FIG. 8 . However, since this flatted part is in the case that the position equivalent to the depth of 10 cm in water when the pan angle and the tilt angle is adjusted at 0 degrees, and a flatted part will be generally different from this part in a case of other head swing angle and depth. The greater a difference between the head swing angle and the depth becomes, the greater an extent of the difference becomes. For this reason, its influence is not a problem when a dimension of the depth direction in the affected area  101  is sufficiently small. 
         [0084]    In addition, an irradiation condition of a treatment plan is set including this influence. For this reason, when such influence is noticeable depending on a property of an affected area (for example, when a dimension of a depth direction in an affected area is large), it is especially effective to execute aforementioned intensity-modulated irradiation. In addition, since the present invention is not limited to only a case where a distribution of a radiation dose in a specific position becomes top-flatted shape by using the flattening filter  54 , it is possible, by optimizing an irradiation condition in a similar treatment plan, to address a case where a distribution of a radiation dose accordingly shows the Gaussian distribution without using the flattening filter  54 . 
         [0085]      FIG. 10  shows a comparative example of an area irradiated with the therapeutic radiation  23  when a plurality of the parts  102 - 1  to  102 - 2  is irradiated with the therapeutic radiation  23 . The area  121 - 1  shows an area irradiated with the therapeutic radiation  23  radiated to the part  102 - 1 . The area  121 - 2  shows an area irradiated with the therapeutic radiation  23  radiated to the part  102 - 2 . The area  121 - 1  includes the irradiation field  104 - 1 , and formed in a cone shape whose apex is arranged at a position  122 - 1 . The area  121 - 2  includes the irradiation field  104 - 2 , and formed in a cone shape whose apex is arranged at a position  122 - 2 . The position  122 - 2  is different from the position  122 - 1 . At this time, in the affected area of the patient  43 , an area  123  that is included in both of the area  121 - 1  and the area  121 - 2  exists and an area  124  that is not included in both of the area  121 - 1  and the area  121 - 2  exists. That is to say, a distribution of the therapeutic radiation  23  with which a plane perpendicular to its radiation direction is irradiated varies depending on a distance from the position  122 - 1  (or the position  122 - 2 ) of the plane. 
         [0086]    That is to say, according to the radiation irradiation method of the present invention, by radiating every part of the affected area of the patient  43  respectively, a predetermined dose of the therapeutic radiation  23  can be radiated to the affected area of the patient  43  with high precision, similar to the case that whole of the affected area of the patient  43  is irradiated at a time. For this reason, since the therapeutic radiation irradiation device  16  is not required to radiate the therapeutic radiation  23  to the whole of the affected area of the patient  43 , the therapeutic radiation irradiation device  16  can be designed for radiating the therapeutic radiation  23  only to narrower range, and dimensions of the multi-leaf collimator  56  can be minimized. As a result, since the deflection of the traveling gantry  12  caused by weight of the therapeutic radiation irradiation device  16  decreases, the therapeutic radiation irradiation device  16  is positioned with higher-precision than ever and can radiate the therapeutic radiation  23  to the affected area of the patient  43  with higher-precision than ever. Further, at this time, the multi-leaf collimator  56  can control the irradiation field of the therapeutic radiation  23  with higher-precision than ever, since the plurality of the leaves for shielding against a part of the radiation  60  can be designed so as to be small and the deflection of the leaf caused by its own weight is avoided. The multi-leaf collimator  56  can be further designed so that a thickness of the leaf can be thin more than ever, and resolution of the irradiation field of the therapeutic radiation  23  can be further improved at this time. 
         [0087]    A volume of the hypothetic point source  58  is not generally 0, and indicates a positive quantity. The radiation irradiation method of the present invention respectively radiates the therapeutic radiation  23  to a plurality of parts of an affected area of the patient  43  by moving the therapeutic radiation irradiation device  16  so that a point included in an area occupied by the hypothetic point source  58  cannot move against the patient  43 . According to such radiation irradiation method, since a part irradiated with the therapeutic radiation  23  more than once and a part that is not irradiated with the therapeutic radiation  23  in the affected area of the patient  43  are sufficiently small when the volume of the hypothetic point source  58  is sufficiently small, a predetermined dose of the therapeutic radiation  23  can be radiated to the affected area of the patient  43  with high precision in a similar way of irradiating the whole of the affected area of the patient  43  at a time. 
         [0088]    In addition, the radiation irradiation method of the present invention can be carried out even when other radiotherapy apparatus different from the radiotherapy apparatus  3  in the above-mentioned embodiment is used. In the radiotherapy apparatus, the therapeutic radiation irradiation device  16  in the above-mentioned embodiment is supported so as to be able to move by other driving mechanism. As the driving mechanism, a robot arm is shown as an example. In the radiation irradiation method of the present invention, the therapeutic radiation  23  is radiated respectively to the plurality of the parts  102 - 1  to  102 - 4  of the affected area  101  when the plurality of the parts  102 - 1  to  102 - 4  is respectively irradiated so that a relative position of the hypothetic point source  58  of the therapeutic radiation irradiation device  16  against the patient  43  cannot change when the plurality of the parts  102 - 1  to  102 - 4  of the affected part  101  is respectively irradiated. According to such radiation irradiation method, the therapeutic radiation  23  can be radiated to the affected area of the patient  43  with higher precision than ever, dimensions of the multi-leaf collimator  56  can be minimized, and a resolution of the therapeutic radiation  23  in the irradiation field can be improved in a similar way of the radiation irradiation method in the above-mentioned embodiment. 
         [0089]    In addition, the radiation irradiation method of the present invention can abbreviate the tracking operation. At this time, the radiotherapy apparatus controller  2  moves the therapeutic radiation irradiation device  16  by using the head swing mechanism  15  so that the therapeutic radiation irradiation device  16  can face the part  102 - i  of the affected part  101  in the patient  43 , and radiates only a predetermined dose of the therapeutic radiation  23  to the part  102 - i  by using the therapeutic radiation irradiation device  16  after controlling the irradiation field of the therapeutic radiation  23  by using the multi-leaf collimator  56 . 
         [0090]    According to such radiation irradiation method, the therapeutic radiation  23  can be radiated to the affected area of the patient  43  with higher precision than ever, dimensions of the multi-leaf collimator  56  can be minimized, and a resolution of the therapeutic radiation in the irradiation field can be further improved in a similar way of the radiation irradiation method in the above-mentioned embodiment. Further, such radiation irradiation method is desirable because it is not required for the imager system to be frequently operated for tracking. 
         [0091]    In addition, when the therapeutic radiation  23  is radiated to the plurality of the parts  102 - 1  to  102 - 2 , the radiation irradiation method of the present invention also can radiate the therapeutic radiation  23  so that an overlapping in an area irradiated with the radiation  23  can exist. According to such radiation irradiation method, a situation that the therapeutic radiation  23  is not radiated to a part between the part  102 - 1  and the part  102 - 2  certainly can be avoided, or a dose of the therapeutic radiation  23  larger than ever can be radiated to a desired part of the affected area  101 . 
         [0092]    In addition, the radiation irradiation method of the present invention can radiate the therapeutic radiation  23  so that doses of the therapeutic radiation  23  radiated to the plurality of the parts  102 - 1  to  102 - 2  can be different from each other. Such radiation can be operated by changing irradiation times for the plurality of the parts  102 - 1  to  102 - n , respectively, and by changing radiation intensities for the plurality of the parts  102 - 1  to  102 - n , respectively, when the therapeutic radiation  23  is radiated. According to such radiation irradiation method, dose of the therapeutic radiation  23  larger than ever can be radiated to a desired part of the affected area  101 . 
         [0093]    On equal terms with other radiation irradiation device which irradiates an irradiation area including a plurality of parts at one time, the radiation irradiation method and the radiotherapy apparatus controller according to the present invention can control the radiation dose with which the plurality of the parts is irradiated, by irradiating the plurality of parts of the subject with radiation radiated from the same one point. Further, the radiation irradiation method and the radiotherapy apparatus controller according to the present invention can design the radiation irradiation device in more miniature size in comparison with other radiation irradiation device which irradiates the irradiation area including the plurality of the parts at one time. For this reason, in a support member for supporting the radiation irradiation device, deflection of the support member caused by weight of the radiation irradiation device is reduced, the radiation irradiation device is positioned with higher precision than ever, and a position of a part irradiated with radiation in the subject can be controlled with higher precision than ever. 
         [0094]    It is apparent that the present invention is not limited to the above embodiment that may be modified and changed without departing from the scope and spirit of the invention.