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 . 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 fig1 . 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 . fig2 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 fig2 . 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 . 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 . 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 . 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 . 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 . 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 ). 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 ). 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 . 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 fig2 . 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 . fig3 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 . 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 . 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 . fig4 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 . the head swing mechanism 15 further includes a pan axis driving device and a tilt axis driving device that are not shown in fig4 . 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 . 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 . fig5 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 fig5 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . fig6 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 . 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 . fig7 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . fig8 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 . fig9 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 . incidentally , fig9 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 fig8 . 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 . 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 . fig1 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 .
a radiation irradiation method includes the steps and . the step 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 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 .