Patent Publication Number: US-7212609-B2

Title: Patient positioning device and patient positioning method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of U.S. patent application Ser. No. 10/767,330, filed Jan. 30, 2004, which claims priority under 35 USC 119 to Japanese Application No. 2003-058199, dated Mar. 5, 2003, which are incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a patient positioning device and a patient positioning method. More particularly, the present invention relates to a patient positioning device and a patient positioning method, which are suitably employed in a particle beam treatment system for irradiating a charged particle beam (ion beam), such as a proton and a carbon ion, to a tumor for treatment. 
   2. Description of the Related Art 
   There is known a treatment method of setting an isocenter (irradiation target center) at a tumor, e.g., a cancer, in the body of a patient and irradiating an ion beam, such as a proton, to the tumor. An apparatus for use with such a treatment method comprises a charged particle beam generator, a beam transport system, and a rotating gantry. An ion beam accelerated by the charged particle beam generator reaches the rotating gantry through a first beam transport system, and is irradiated to the tumor from an irradiation nozzle after having passed through a second beam transport system provided in the rotating gantry. 
   In the apparatus thus constructed, the patient must be caused to lie in a proper position relative to the irradiation nozzle so that the ion beam is irradiated to only the isocenter without damaging normal cells. A patient positioning device for use with irradiation of the particle beam is a device for positioning a patient couch to make the patient lie in the proper position (see, e.g., Patent Reference 1, JP,A 2000-510023 (pages 27–31 and FIGS. 1, 6, 7A and 7B)). Particularly, in the case of irradiating the ion beam, for example, a proton beam, activation energy for the proton beam is selected so as to stop protons at the isocenter and apply most of the proton energy to only cells in the tumor, which is positioned at the isocenter, by utilizing a characteristic that most of the proton energy is released upon the stop of protons (this phenomenon is called “Brag peak”). Therefore, the alignment of the ion beam with the isocenter is very important. 
   In a known patient positioning device, to ensure accurate positioning of the patient relative to the irradiation nozzle, the position of the isocenter is decided beforehand relative to monuments (or landmarks, i.e., anatomical base points; for example, portions of the patient&#39;s skeleton), which are set in the patient body. Usually, the position of the isocenter including a diseased tissue, e.g., a tumor, is marked on a DRR (digitally reconstructed radiograph). Then, display images looking from other directions are edited as required. 
   In a state where the patient lies on a patient couch prior to the irradiation of a proton beam, an X-ray source is disposed on a path of the proton beam, and an X-ray receiver is disposed on the side opposed to the X-ray source with respect to the patient along the path of the proton beam. The X-ray receiver produces an X-ray image of the tumor and its surroundings in the patient body. On this occasion, in order to align the isocenter on a beam line, through which the proton beam passes in the irradiation nozzle, with the tumor, the direction in and the distance by which the patient couch is moved relative to the irradiation nozzle must be determined by employing the offset distance on an X-ray image from each of the particular monuments to the center of the X-ray beam and the offset distance on the DRR from the same particular monument to the isocenter. Positioning control of the patient couch is performed based on the thus-determined direction and distance of movement of the patient couch. 
   SUMMARY OF THE INVENTION 
   In the prior art described above, an operator, e.g., a doctor, designates plural monument positions on the skeleton of the patient on a DRR as a reference image, displayed on a display unit, and also designates the same positions of the same plural monuments on a captured image as an X-ray image obtained by the X-ray receiver, displayed on the display unit. In spite of the operator having intended to designate the same positions of the same plural monuments on both the screen images, therefore, there is a fear that the respective corresponding positions designated on the DRR and the captured image are not in alignment and offset from each other. If the respective designated positions to be kept in alignment on the DRR and the captured image are offset from each other, deterioration of accuracy occurs in aligning the patient couch (particularly the tumor), which should be properly positioned based on both the designated positions, with the beam line. 
   Accordingly, it is an object of the present invention to provide a patient positioning device and a patient positioning method, which can increase the accuracy in positioning of a patient. 
   To achieve the above object, the present invention is featured in that a processing unit executes pattern matching between a part of first image information in a first set area including an isocenter, the first image information representing a tumor in the body of the patient and serving as a reference including the isocenter, and a part of second image information in a second set area including a position corresponding to a path of a charged particle beam, the second image information representing a portion of the patient lying across the path of the charged particle beam, thereby producing information used for positioning of the patient (couch). Since the positioning information is produced through the pattern matching between the first image information in the first set area and the second image information in the second set area, accuracy in producing the positioning information is avoided from being affected by the skill of an operator, such as required when designating the positions of monuments, unlike the case of producing the positioning information based on the positions of monuments designated by the operator. As a result, the positioning accuracy can be increased regardless of the skills of individual operators. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an overall view showing a construction of a medical particle beam irradiation system to which a patient positioning device according to one preferred embodiment of the present invention is applied; 
       FIG. 2  is a perspective view of a rotating gantry shown in  FIG. 1 ; 
       FIG. 3  is a front view of the rotating gantry shown in  FIG. 1 ; 
       FIG. 4  is a schematic view showing a vertical sectional structure of a particle beam irradiation section shown in  FIG. 1 ; 
       FIG. 5  is a conceptual view showing detailed functions of a couch driver for driving a patient couch shown in  FIG. 1 ; 
       FIG. 6  is a schematic view showing a construction of the patient positioning device according to the one preferred embodiment of the present invention; 
       FIG. 7  is a detailed sectional view showing a structure of an X-ray fluorescence multiplier shown in  FIG. 6 ; 
       FIG. 8  is a flowchart showing a processing sequence executed by a positioning data generator shown in  FIG. 6 ; 
       FIGS. 9(A) ,  9 (B) and  9 (C) show examples of screen images displayed on display units shown in  FIG. 6 ; 
       FIGS. 10(A) and 10(B)  show other examples of screen images displayed on the display units shown in  FIG. 6 ; 
       FIG. 11  is a flowchart showing a detailed processing sequence of step  79  shown in  FIG. 8 ; 
       FIG. 12  is a flowchart showing a detailed processing sequence of step  81  shown in  FIG. 8 ; and 
       FIG. 13  is a schematic view showing a construction of a modification of the patient positioning device according to the one preferred embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   One embodiment of the present invention will be described below with reference to the drawings. 
   With reference to  FIGS. 1 and 2 , a description is first made of a medical particle beam irradiation system to which a patient positioning device of this embodiment is applied. 
   A medical particle beam irradiation system  40  comprises a charged particle beam generator  41  and a rotating gantry  1 . The charged particle beam generator (also called a particle beam generator)  41 , an ion source (not shown), a pre-stage accelerator  42 , and a synchrotron  43 . Ions (e.g., proton ions or carbon ions) generated from the ion source are accelerated by the pre-stage accelerator (e.g., a linear accelerator)  42 . An ion beam (proton beam) accelerated by the pre-stage accelerator  42  enters the synchrotron  43 . In this embodiment, a proton beam is employed as the ion beam. The ion beam in the form of a charged particle beam (also called a particle beam) is accelerated by being given with energy applied as high-frequency electric power from a high-frequency accelerator cavity  44  in the synchrotron  43 . After the energy of the ion beam circling in the synchrotron  43  has been increased up to a preset level of energy (usually 100 to 200 MeV), a high frequency wave is applied to the ion beam from a high-frequency applying device  45  for exiting of the ion beam. With the application of that high frequency wave, the ion beam circling within a stable limit high frequency wave is caused to shift out of the stable limit and to exit from the synchrotron  43  through an exit deflector  50 . Upon the exiting of the ion beam, currents supplied to electromagnets, i.e., quadrupole electromagnets  46  and deflection electromagnets  47 , disposed in the synchrotron  43  are held at respective setting values and the stable limit is also held substantially constant. By stopping the application of high-frequency electric power to the high-frequency applying device  45 , the exiting of the ion beam from the synchrotron  43  is stopped. 
   The ion beam having exited from the synchrotron  43  reaches, through a beam transport system  49 , a particle beam irradiation section (also called a particle beam irradiator)  4  for irradiating the ion beam. The ion beam is irradiated from the particle beam irradiation section  4  to a tumor (cancer) in the body of a patient  8  lying on a treatment couch (patient couch)  59 . The particle beam irradiation section  4  generates the ion beam providing a dose distribution optimum for the treatment utilizing the particle beam. 
   The rotating gantry  1  comprises a substantially cylindrical rotating drum (rotating body)  3  having a front ring  2 , and a motor (rotating device), not shown, for rotating the rotating drum  3 . The front ring  2  provided at one end of the rotating drum  3  is supported by a plurality of rotatable support rolls  6 . As shown in  FIG. 3 , the support rolls  6  are rotatably mounted to a support unit  10  installed on a rotating gantry installation area (building base)  9 . Though not shown, the other ring (having an outer diameter equal to that of the front ring  2 ) provided at the other end of the rotating drum  3  is similarly supported by a plurality of support rolls  6  which are rotatably mounted to the other support unit  10 . An inverted U-shaped beam transport system  5  serving as a part of the beam transport system  49  and the particle beam irradiation section  4  are mounted on the rotating drum  3  and are rotated with the rotation of the rotating gantry  1 . The beam transport system  5  includes electromagnets, such as deflecting electromagnets  51 ,  52 . A treatment gauge (treatment chamber)  14  is formed inside the rotating drum  3 . 
     FIG. 4  is a schematic view showing a vertical sectional structure of the particle beam irradiation section  4 . In  FIG. 4 , the particle beam irradiation section  4  comprises a casing  90  mounted to the rotating drum  3  and coupled to the inverted U-shaped beam transport system  5 , and a snout  21  provided at one end of the casing  90 , i.e., on the side nearer to the nozzle end. Inside the casing  90  and the snout  21 , a scatterer (not shown), a ring collimator  22 , a patient collimator  23 , and a bolus  25  are disposed, by way of example, in this order from the upstream side in the direction of advance of the ion beam introduced from the beam transport system  5 . Those components are successively arranged to lie on a beam line m along which the ion beam passes. Additional units, such as an SOBP forming unit of ridge filter type and a range adjusting unit having a pair of wedge-shaped blocks, may also be disposed to lie on the beam line m. 
   The ring collimator  22  is to roughly collimate an irradiation field of the ion beam and is mounted to the snout  21  through a mounting member (not shown). The patient collimator  23  is to shape the ion beam in match with the tumor shape in the direction perpendicular to the beam line m, and it is also mounted to the snout  21  through a mounting member (not shown). 
   The ion beam formed by the particle beam irradiation section  4  of the above-described construction and having the proper irradiation field releases its energy in the tumor in the body of the patient  8 , thereby forming a high-dose area. 
   Incidentally, an X-ray emission device (X-ray tube)  26  serving as an X-ray source will be described later. 
   Returning to  FIGS. 2 and 3 , the medical particle beam irradiation system  40  includes an irradiation chamber  55  for the particle beam treatment in the rotating drum  3  of the rotating gantry  1 . The irradiation chamber  55  for the particle beam treatment is provided with a fixed annular frame (ring member)  15 . The annular frame  15  is disposed on one end side of the rotating drum  3 , i.e., on the same side as the front ring  2 , and is fixed to a mount base  18  installed in the rotating gantry installation area  9 . In addition, the other annular frame (not shown) is disposed on the other end side of the rotating drum  3  so as to sandwich a path of movement of the particle beam irradiation section  4  between itself and the annular frame  15 . The other annular frame is supported by a plurality of support rolls  20  which are rotatably held by a support frame  19  fixed to an inner surface of the rotating drum  3 . In other words, the other annular frame is rotatable relative to the rotating drum  3  through the support rolls  20 . These annular frames including the one  15  have guide grooves (not shown) each comprising a lower horizontal portion and an upper arc-shaped portion, which are formed in respective side surfaces of the annular frames in an opposed relation to each other. Each of the guide grooves has a substantially semi-cylindrical shape defined by the lower horizontal portion and the upper arc-shaped portion. 
   The irradiation chamber  55  for the particle beam treatment is further provided with a movable floor  17 . The movable floor  17  has a freely bendable articulated structure such that it comprises a number of plates  24  and every adjacent two of the plates  24  are coupled to each other by links (not shown). One end of the movable floor  17  is engaged in the guide groove of the annular frame  15 , and the other end of the movable floor  17  is engaged in the guide groove of the other annular frame. Further, circumferential opposite ends of the movable floor  17  are connected to the particle beam irradiation section  4 . When the motor is driven to rotate the rotating gantry  1 , the particle beam irradiation section  4  is also rotated in the same rotating direction as the rotating gantry  1 . Correspondingly, the movable floor  17  connected to the particle beam irradiation section  4  is pulled together and moved in the same rotating direction. The movement of the movable floor  17  is smoothly performed along the guide grooves of the annular frames including the one  15 . The movable floor  17  is made up of a horizontal floor portion  57  formed by the horizontal portions of the guide grooves in the lower side of the annular frames including the one  15 , and an arc-shaped wall portion  58  formed by the arc-shaped portions of the guide grooves in the upper side of the annular frames including the one  15 . The treatment gauge  14  is formed within the movable floor  17 . The treatment couch  59  is inserted in the treatment gauge  14  when the ion beam is irradiated to the patient from the particle beam irradiation section  4 . 
   As shown in  FIG. 5 , a treatment bench  7  comprises a couch driver  12  and the treatment couch  59  installed on the couch driver  12 . The treatment bench  7  is installed outside the rotating gantry  1  in an opposed relation to the front ring  2  within a treatment couch installation area (not shown) located at a level elevated one step from the rotating gantry installation area  9  (see  FIG. 3 ). As seen from a conceptual view of  FIG. 5 , the couch driver  12  has four articulation axes  12 A,  12 B,  12 C and  12 D, and includes motors  11   a ,  11   b ,  11   c  and  11   d  for driving the treatment couch  59 . Driving of the motor  11   a  moves the treatment couch  59  in the direction of the articulation axis  12 A (X-axis) that is horizontally extended parallel to the front ring  2 . Driving of the motor  11   b  moves the treatment couch  59  in the direction of the articulation axis  12 B (Z-axis) that is perpendicular to the articulation axis  12 A. Driving of the motor  11   c  moves the treatment couch  59  in the direction of the articulation axis  12 C (Y-axis) that is perpendicular to both the articulation axis  12 A (X-axis) and the articulation axis  12 B (Z-axis) and is extended in the direction of a rotation axis of the rotating gantry  1 . Thus, the treatment couch  59  is moved into and out of the treatment gauge  14  with the driving of the motor  11   c . Furthermore, driving of the motor  11   d  rotates the treatment couch  59  about the articulation axis  12 D (ψ-axis) that is perpendicular to the articulation axis  12 C (Y-axis). 
   The patient positioning device of this embodiment is provided in the medical particle beam irradiation system  40  having the basic construction described above. The construction and functions of the patient positioning device will be described in detail below. 
   As shown in  FIG. 6 , a patient positioning device  28  comprises an X-ray emission device (X-ray tube or source)  26 , an X-ray image capturing device (image information generator)  29 , an X-ray tube controller  36 , a positioning data generator (positioning information generator)  37  having not-shown input means (such as a keyboard and a mouse), a medical image archive server  17 , a couch controller  38 , and display units  39 A,  39 B. The positioning data generator  37  is constituted a work station (processing unit). 
   The X-ray image capturing device  29  comprises an X-ray fluorescence multiplier (X-ray image intensifier)  30 , an optical system  33 , and a CCD camera (image information producing unit)  34 . Inside a vacuum vessel  31 , as shown in  FIG. 7 , a fluorescence film board  32  is disposed on the side nearer to an inlet window  64 , and an output fluorescence film  53  is disposed on the side nearer to an outlet window  63 . The fluorescence film board  32  has an input fluorescence film (X-ray entry device or X-ray transducer)  48  disposed on its rear side (i.e., on the side opposed to the inlet window  64 ). The output fluorescence film  53  has a smaller diameter than the input fluorescence film  48 . A photocathode  50  is disposed in contact with the input fluorescence film  48 . A converging electrode  54  is disposed in the vacuum vessel  31  so as to surround a photoelectron path  65 . An anode  60  surrounding the output fluorescence film  53  is also disposed in the vacuum vessel  31 . A voltage is applied between the photocathode  50  and the converging electrode  54  from a convergence power supply  56 . Further, a voltage is applied between the photocathode  50  and the anode  60  from an anode power supply  61 . 
   The X-ray image capturing device  29  is mounted to the rotating drum  3  of the rotating gantry  1  and is rotated together with the rotation of the rotating gantry  1 . The X-ray image capturing device  29  is positioned on the beam line m on the side opposed to the particle beam irradiation section  4  with respect to the treatment couch  59 . 
   As shown in  FIG. 4 , the X-ray emission device  26  is provided on a support member  16 , which is mounted to the snout  21 , to be movable in a direction perpendicular to the beam line m. The support member  16  has an opening through which the ion beam and the X-ray pass. Usually (other than the time for the positioning of the treatment couch  59 , e.g., during the irradiation of the ion beam), the X-ray emission device  26  is retreated to a position P 1  away from the beam line m. 
   When the patient  8  lies down on the treatment couch  59  for starting the treatment with the irradiation of the ion beam, an operator, e.g., a doctor, inputs a command for movement of the treatment couch  59  to the couch controller  38  by using an input device (not shown) of the couch controller  38  so that a cross mark drawn on the body surface of the patient  8  (the cross mark being displayed by a laser so as to locate right above a tumor) is positioned on the beam line m. Thus, in accordance with the movement command, the couch controller  38  controls the couch driver  12  to move the treatment couch  59  so that the cross mark on the patient&#39;s body surface is aligned with the beam line m. With this alignment, an offset between the tumor and the beam line m is held within the range on the order of millimeter. 
   Further, the operator inputs a command for starting advance of the X-ray emission device  26  to an X-ray tube controller  36 , e.g., a personal computer, through an input means (not shown). The X-ray tube controller  36  having received the start command outputs an X-ray tube movement signal to a not-shown driver (e.g., a motor) for the X-ray emission device  26 . In response to the X-ray tube movement signal, the X-ray emission device  26  is advanced to a position P 2  on the beam line m. Then, when the operator inputs a command for starting the irradiation of an X-ray to the X-ray tube controller  36 , an X-ray irradiation start signal outputted from the X-ray tube controller  36  is inputted to the X-ray emission device  26 . Correspondingly, the X-ray emission device  26  irradiates an X-ray beam toward the patient  8  along the beam line m. 
   The X-ray having penetrated the patient  8  is inputted to the vacuum vessel  31  through the inlet window  64  and then reaches the input fluorescence film  48  through the fluorescence film board  32  for conversion into a visible image. Light of the visible image is converted into photoelectrons by the photocathode  50 . The photoelectrons are converged by the converging electrode  54  and then reach the output fluorescence film  53  through the anode  60  along the photoelectron path  65  for conversion into a bright visible image. This bright visible image is captured by the CCD camera  34  through lenses  62  in the optical system  33 . The image captured by the CCD camera  34  is inputted to a personal computer (image processing unit)  35  serving as a first processing unit. The image processing unit  35  executes predetermined processing on the input image for the purpose of image processing (such as color correction and blur correction). Image data (also called current image data or captured image data), including a tumor image, which has been subjected to the image processing, is inputted to the positioning data generator  37  from the image processing unit  35 . 
   The positioning data generator  37  produces positioning data for the treatment couch  59  based on the current image data outputted from the X-ray image capturing device  29  and image data stored in the medical image archive server  17 , and then outputs the produced positioning data to the couch controller  38 . A sequence of processing executed by the positioning data generator  37  to produce the positioning data will be described below with reference to  FIG. 8 . This processing sequence is stored, as a program, in a memory (e.g., a not-shown ROM or other storage medium) provided in the positioning data generator  37 . 
   The medical image archive server  17  accumulates and stores, as reference image data (control image data) serving as a positioning reference, data of a tomographic image of the relevant patient  8  captured by X-ray CT (e.g., a DRR image, or an X-ray image captured by the patient positioning device shown in  FIG. 6  in advance, for example, until the day before the treatment day, or an image obtained by editing such an image using the known method in match with the direction in which the ion beam is now to be irradiated). When aligning the tumor in the body of the patient  8  with the beam line m, the reference image data is first loaded into a memory (not shown) of the positioning data generator  37  from medical image archive server  17  (step  71 ). In the following description, the expression “data (or information) is inputted to the positioning data generator  37 ” means that “the data (or information) is stored in the above-mentioned memory in the positioning data generator  37 ”. 
   Then, the current image data of the tumor, which is outputted from the image processing unit  35  after being subjected to the above-mentioned image processing, is also inputted to the positioning data generator  37  (step  72 ). 
   Subsequently, the reference image data taken into the positioning data generator  37  is outputted to the display unit (second display unit)  39 A (step  73 ), and the current image data taken into the positioning data generator  37  is outputted to the display unit (first display units)  39 B (step  74 ). With these steps, a reference image is displayed on the display unit  39 A and a current image is displayed on the display unit  39 B.  FIG. 9(A)  shows an example of a screen image of the reference image displayed on the display unit  39 A, and  FIG. 9(B)  shows an example of a screen image of the current image displayed on the display unit  39 B. At this time, the reference image displayed on the display unit  39 A in step  73  does not yet indicate a frame of a comparison area A. Also, the current image displayed on the display unit  39 B in step  74  does not yet indicate a frame of a comparison area B. The reference image and the current image may be displayed on one display unit side by side or in a superposed relation instead of separately displaying them on the respective display units  39 A,  39 B. As an alternative, the reference image and the current image may be displayed on a display of the image processing unit  35 . 
   Thereafter, while looking at the reference image and the current image displayed on the display units  39 A,  39 B, the operator sets a predetermined comparison area (clipping area) A in the reference image displayed on the display unit  39 A with the isocenter positioned at the center. The comparison area A (more exactly speaking, the frame of the comparison area A) is inputted for setting (clipping) by using the input unit of the positioning data generator  37 . The comparison area A is employed as an area for comparison with the current image having the center aligned with the beam line m through pattern matching. The input data for setting the comparison area A is taken into the positioning data generator  37  (step  75 ). Then, display information of the set comparison area A (more exactly speaking, the frame of the set comparison area A), i.e., display information of the frame of the comparison area A, is outputted to the display unit  39 A (step  76 ). As a result, the data of the frame of the comparison area A is displayed on the display unit  39 A in a superposed relation to the reference image while the center of the comparison area A is aligned with the isocenter.  FIG. 9(A)  shows one practical example in which the data of the frame of the comparison area A is displayed on the reference image. A region inside the frame of the comparison area A defines the comparison area A. Instead of manually setting the comparison area A by the operator as described above, it is also possible to automatically set the comparison area A by the positioning data generator  37  (for example, through a step of automatically setting a preset area of a predetermined size with the isocener positioned at the center, or an area of a size variable depending on a treatment plan supplied from the medical image archive server  17 ). 
   Corresponding to the setting of the comparison area A, the positioning data generator  37  sets a comparison area B (more exactly speaking, a frame of the comparison area B), which has the same size as the comparison area A, on the current image displayed on the display unit  39 B with the origin defined at the center (beam line m) of the current image (step  77 ). The setting of the size of the comparison area B is automatically performed using the setting input data that has been entered through the input unit of the positioning data generator  37  to set the comparison area A. The data of the comparison area B (more exactly speaking, the frame of the comparison area B) thus set is outputted to the display unit  39 B (step  78 ). As a result, the data of the frame of the comparison area B is displayed on the display unit  39 B in a superposed relation to the current image while the center of the comparison area B is aligned with the center of the current image.  FIG. 9(B)  shows one practical example in which the frame of the comparison area B is displayed on the current image. A region inside the frame of the comparison area B defines the comparison area B. Note that the comparison area B may be set with manual setting made by the operator. 
   Then, the positioning data generator  37  executes primary pattern matching between the comparison area A and the comparison area B based on image similarity searching (e.g., pattern matching through comparison of pixel information) utilizing correlation between two images (step  79 ). The comparison area A and the comparison area B have the same number of pixels in each of the X- and Y-directions, and also have the same total number of pixels in the respective entire areas. Detailed processing of step  79  will be described below with reference to  FIG. 11 . First, a search area  70  (see  FIG. 9(B) ) is set which is smaller than the current image, but larger than the comparison area B (step  79 A). Then, pattern matching is executed through comparison between pixel information of a reference image present inside the frame of the comparison area A (referred to as the reference image in the comparison area A) and pixel information of a current image present inside the frame of the comparison area B (referred to as the current image in the comparison area B) (step  79 B). It is generally thought that an image is made up of a large number of pixels (see  FIGS. 10(A) and 10(B) ) two-dimensionally arrayed in a mesh-like pattern, and pixel information (pixel value) is stored in each of the pixels. In this embodiment, the pattern matching between the current image and the reference image is executed by utilizing those pixel values. In step  79 B, the pattern matching is first executed on the pixel values (scalar quantities) of all pixels of the current image included within the frame of the comparison area B and the pixel values of all pixels of the reference image included within the frame of the comparison area A while successively moving, e.g., translating, the frame of the comparison area B in the search area  70  in each of the X- and Y-directions. More specifically, in  FIG. 9(B) , an upper end of the frame of the comparison area B is aligned with an upper end of the search area  70 , and an upper left corner of the frame of the comparison area B is aligned with an upper left corner of the search area  70 . In this state, the pixel value for each of the pixels of the reference image in the comparison area A and the pixel value for each of the pixels of the current image in the comparison area B are compared with each other while the pixels in both the images are made correspondent to each other in a one-to-one relation. This comparison is performed through steps of computing a square value of a difference between the pixel value of each pixel of the reference image in the comparison area A and the pixel value of each pixel, corresponding to the above each pixel of the reference image, of the current image in the comparison area B for all the corresponding pixels in both the comparison areas, and then adding the thus-computed square values. The total sum resulting from the above addition represents a deviation between the reference image in the comparison area A and the current image in the comparison area B set in the aforesaid position, and the aforesaid comparison represents an arithmetic operation for computing a deviation between the pixel values of all the corresponding pixels included in both the images and compared with each other. After translating the frame of the comparison area B to the right by a distance of one pixel, the above-described arithmetic operation is repeated on each pixel of the current image in the comparison area B having been translated and on each pixel, corresponding to the above each pixel of the current image, of the reference image in the comparison area A, thereby computing a deviation similar to that described above. Such a deviation is repeatedly computed for each position of the comparison area B while successively translating the frame of the comparison area B to the right (in the X-direction) on the one-pixel by one-pixel basis. When the right end of the frame of the comparison area B reaches the right end of the search area  70  with the movement of the frame of the comparison area B in the X-direction, the upper end of the frame of the comparison area B is translated by a distance of one pixel downward (in the Y-direction). Then, a similar deviation is computed in the same manner as described above for each position of the comparison area B while successively translating the frame of the comparison area B to the right (in the X-direction) on the one-pixel by one-pixel basis. Further, the movement of the frame of the comparison area B in the Y-axis is repeated. Eventually, the movement of the frame of the comparison area B is performed until the lower end and the lower right corner of the frame of the comparison area B are aligned respectively with the lower end and the lower right corner of the search area  70 , whereby the above-described deviation is computed for each position of the frame of the comparison area B. 
   Subsequently, a primary matching area having an image similar to the reference image in the comparison area A is extracted (step  79 C). More specifically, the comparison area B is extracted of which deviation has the smallest value among all of the deviations computed in step  79 B through the pattern matching performed for each position of the frame of the comparison area B. Hereinafter, the extracted comparison area B will be referred to as a final comparison area B. In other words, the current image in the final comparison area B is most similar to the reference image in the comparison area A. The final comparison area B is the primary matching area. A position offset between the center (beam line m) of the current image and the center of the final comparison area B (primary matching area) is then computed (step  79 D). More specifically, such a position offset is computed by using coordinate values (X a , Y c ) of the center of the current image and coordinate values (X rc , Y rc ) of the center of the final comparison area B to obtain a position offset ΔX 1  in the X-direction between the center of the current image and the center of the final comparison area B and a position offset ΔY 1  in the Y-direction between the center of the current image and the center of the final comparison area B. The position offsets ΔX 1 , ΔY 1  are stored in the memory provided in the positioning data generator  37 . 
   In this embodiment, since the primary pattern matching is performed based on the reference image in the comparison area A and the current image in the comparison area B each having a restricted two-dimensional range, the time required for the pattern matching can be cut down. Particularly, the primary pattern matching is performed by linearly moving the comparison area B in the X- and Y-directions without rotating the comparison area B, and this pattern matching method also contributes to cutting down the time required for the pattern matching. 
   While the frame of the comparison area B is translated in the X- and Y-directions in this embodiment, it is also possible to rotate the frame of the comparison area B for the purpose of pattern matching. 
   As practical pattern matching methods, there are known six methods (1) to (6), given below, in addition to the one described above in the embodiment. Any of the methods (1) to (6) can be used to implement the present invention. 
   (1) Residual Error Matching 
   For the comparison area B (target pattern) and the comparison area A (master pattern), a superposition deviation (residual error) is computed from pixel information of all meshes. Then, the position of the comparison area B where the computed residual error is minimum is determined while moving the comparison area B in the up-and-down direction and the left-and-right direction. 
   (2) Correlation Coefficient Method 
   For the comparison area B (target pattern) and the comparison area A (master pattern), normalized distributions of pixel information of all meshes are separately computed. Then, the position of the comparison area B where a value of the correlation coefficient between the two computed distributions is maximum is determined while moving the comparison area B in the up-and-down direction and the left-and-right direction. This method requires a longer computing time than the residual error matching of above (1), but practical processing can be performed with speed-up through division of the distribution into layers. 
   (3) Phase-Only Correlation 
   For the comparison area B (target pattern) and the comparison area A (master pattern), pixel information patterns of all meshes are separately subjected to Fourier transformation. Then, phase-only processing is performed on the Fourier transformation plane to determine a matching point between both the patterns. 
   (4) Geometry Matching 
   This is a recently proposed matching method utilizing a series of edge points. This method enables the matching to be performed without being affected by rotation and resizing of the comparison area A (master pattern). 
   (5) Vector Correlation 
   Similarly to the geometry matching of above (4), this is a matching method utilizing a series of edge points. This method enables the matching to be performed without being affected by overlapping and hiding. 
   (6) Generalized Hough Transformation 
   This is a method obtained by extending and generalizing Hough transformation for detection of a straight line, and is primarily applied to geometrical figures. This matching method utilizes a series of edge points similarly to the above methods (4) and (5), and enables the matching to be performed without being affected by rotation and resizing, as well as by overlapping and hiding. 
   Note that, instead of the above methods (1) to (6), any other suitable one, e.g., the least square method used in step  81  described later, may also be used to perform the primary pattern matching. 
   The data of the frame of the final comparison area B extracted through the primary pattern matching is outputted to the display unit  39 B (step  80 ). With this step, the frame of the final comparison area B is displayed on the display unit  39 B together with the information of the current image (see  FIG. 9C ). 
   Secondary pattern matching for the current image in the final comparison area B is executed by employing just the reference image in the comparison area A and the current image in the final comparison area B (step  81 ). In other words, the entire regions of the reference image and the current image are not used here. In the secondary pattern matching, the primary matching area (final comparison area B) obtained through the primary pattern matching is employed as a secondary matching candidate area. Then, based on the reference image in the comparison area A and the current image in the secondary matching candidate area (final comparison area B), the positioning data generator  37  executes coordinate transformation of the current image in the final comparison area B and finely determines the amounts of translation in the X- and Y-directions and the amount of a rotational angle at which both the images are most matched with each other. Practically, the secondary pattern matching is performed in this embodiment by using the least square method. 
   Detailed processing of step  81  will be described below with reference to  FIG. 12 . First, a similar area, i.e., the current image in the comparison area B, is moved and rotated (step  81 A). In practice, the current image in the comparison area B is subjected to coordinate transformation by using coordinate transformation coefficients. The amount of translation and the amount of a rotational angle can be designated as the coordinate transformation coefficients. Stated another way, the movement of the comparison area B is performed by translating the current image in the final comparison area B in the X- and Y-directions and rotating it until the center of the final comparison area B (i.e., the position at which two diagonals of the final comparison area B cross each other) (see  FIG. 9(C) ) is aligned with the center of the current image (i.e., the beam line m) (see  FIG. 10(B) ). Then, pattern matching is executed (step  81 B). In this pattern matching, the least square method is employed to evaluate similarity (degree of matching) between the reference image in the comparison area A the current image in the final comparison area B. More specifically, in a state of  FIG. 10(B) , the current image in the final comparison area B is translated in the X- and Y-directions and rotated in step  81 A with respect to the reference image in the comparison area A, and the degree of matching between the moved current image in the final comparison area B and the reference image in the comparison area A is evaluated. In this embodiment, since the pattern matching is made on the reference image in the comparison area A and the current image in the comparison area B (final comparison area B) each having a restricted two-dimensional range, processing for the pattern matching can be executed in a non-wasteful manner and hence the processing time required for the pattern matching can be cut down. The processing for the pattern matching in step  81 A will be described below. It is here assumed that the position of a pixel of the reference image in the comparison area A is A(X, Y) and the position of a pixel, corresponding to the above pixel of the reference image, of the current image in the final comparison area B is B(X′, Y′). Thus, the position of each pixel is expressed, by way of example, as follows. The position of a pixel locating at an upper left corner of the reference image in the comparison area A is expressed by coordinate values of A(1, 1), and the position of a pixel locating at an upper left corner of the current image in the final comparison area B is expressed by coordinate values of B(1, 1). Because (X, Y) and (X′, Y′) representing pixels are given as coordinate information, the pixels of the reference image in the comparison area A can be made respectively correspondent to the pixels of the current image in the final comparison area B by using a coordinate transformation formula, such as an Affine transformation formula, and the current image in the final comparison area B can be translated in the X- and Y-directions and rotated in accordance with the coordinate transformation formula. A description is now made of step  81 B. A square value of a difference (deviation) between the pixel value of each pixel A(X, Y) and the pixel value of each corresponding pixel B(X′, Y′) is computed for each pair of all the corresponding pixels in both the reference image in the comparison area A and the current image in the final comparison area B, and the thus-computed square values are added to determine the total sum. Then, while repeating the processing sequence of step  81 A, i.e., translating the current image in the final comparison area B in the X- and Y-directions and rotating it with respect to the reference image in the comparison area A, the above-mentioned total sum is successively computed in step  81 B. After repeating above two steps  81 A and  81 B, the coordinate transformation coefficients providing the minimum total sum are obtained. The thus-obtained coordinate transformation coefficients represent a position offset of the final position of the current image in the final comparison area B with respect to the reference image in the comparison area A, i.e., a position offset ΔX 2  in the X-direction, a position offset ΔY 2  in the Y-direction, and a rotation amount (angle) Δθ. The position offsets ΔX 2 , ΔY 2  and the rotation amount Δθ are all stored in the memory provided in the positioning data generator  37 . 
   Thus, in the secondary pattern matching, the pattern matching is performed on the current image in the comparison area B having a restricted two-dimensional range and the reference image in the comparison area A also having a restricted two-dimensional range while translating the current image in the primary matching area (final comparison area B) in the X- and Y-directions and rotating it. Hence, the time required for the pattern matching can be cut down even with the matching process including the image rotation. 
   Note that the method used for executing the secondary pattern matching is not limited to the least square method described above, and the secondary pattern matching may be performed by using any other suitable method, for example, by executing one of the above-mentioned methods (1) to (6) again. 
   The data of the current image in the final comparison area B, which is located in the final position of the current image determined through the secondary pattern matching, is outputted to the display unit  39 A (step  82 ). The current image in that final position is displayed (though not shown) on the display unit  39 A in a superposed relation to the reference image in the comparison area A. By displaying the current image in that final position and the reference image on the display unit in a superposed relation to each other as described above, the operator, such as the doctor, can visually confirm the aligned state of the tumor. Then, couch (patient) positioning data is produced (step  83 ). Couch movement amounts (couch movement information) constituting the couch positioning data are computed by using the position offsets ΔX 1 , ΔY 1 , ΔX 2  and ΔY 2  and the rotation amount Δθ which are all stored in the memory provided in the positioning data generator  37 . More specifically, a couch movement amount ΔX in the X-direction is computed as (ΔX 1 +ΔX 2 ), a couch movement amount ΔY in the Y-direction is computed as (ΔY 1 +ΔY 2 ), and a couch movement amount (couch rotation amount) ΔΘ in the rotating direction is computed as Δθ. These couch movement amounts ΔX, ΔY and ΔΘ constitute couch positioning information used for the positioning of the couch. This couch positioning information serves also as the couch movement information. Subsequently, in step  83 , the couch movement amounts ΔX, ΔY and Δθ are outputted to and displayed on the display unit  39 A. 
   By looking at the displayed couch movement amounts ΔX, ΔY and ΔΘ, the doctor determines whether the treatment couch  59  is to be moved to execute again for alignment of the tumor. If the doctor determines that the operation for alignment of the tumor is required with the movement of the treatment couch  59 , the doctor inputs information indicative of “necessity of couch movement” to the positioning data generator  37  by using the input unit (not shown), the input information being separated into data per X-direction, Y-direction and rotating direction. On the other hand, if the doctor determines that the operation for aligning the tumor is not required with the movement of the treatment couch  59 , the doctor inputs information indicative of “non-necessity of couch movement” to the positioning data generator  37  by using the input unit. 
   The positioning data generator  37  determines whether the “couch is to be moved” (step  84 ). More specifically, if the information inputted from the input unit indicates “non-necessity of couch movement”, this means that the tumor is positioned on the beam line m. Hence, the movement of the treatment couch  59 , i.e., the alignment of the tumor in the body of the patient  8  with the beam line m, is not performed by the couch driver  12 , and the couch positioning process is completed. On the other hand, if the information inputted from the input unit indicates “necessity of couch movement”, the couch positioning information is outputted to the couch controller  38  (step  85 ). Practically, the couch movement amounts ΔX, ΔY and ΔΘ obtained in above step  83  are sent to the couch controller  38 . The couch movement amounts ΔX, ΔY and ΔΘ constitute information used for the positioning of the treatment couch  59 . Thereafter, the alignment of the tumor is performed through the movement of the treatment couch  59  as described later. 
   While whether to move the treatment couch  59  or not is determined by the doctor in this embodiment, such a determination may be made by the positioning data generator  37 . In other words, it is also possible to determine in step  84  as to “whether the couch movement amount is equal to a preset movement value (e.g., a movement value 0)” instead of “whether the couch is to be moved”, and to instruct the positioning data generator  37  to carry out the movement of the couch. In this modification, more specifically, if the couch movement amounts ΔX, ΔY and ΔΘ obtained in step  83  are each equal to the preset movement value, e.g., the movement value 0 (namely, in the case of “YES” in the determination of modified step  84 ), this means that the tumor is positioned on the beam line m. Hence, the movement of the treatment couch  59 , i.e., the alignment of the tumor in the body of the patient  8  with the beam line m, is not performed by the couch driver  12 , and the couch positioning process is completed. On the other hand, in the case of “NO” in the determination of modified step  84  (namely, if the couch movement amounts ΔX, ΔY and ΔΘ are each not equal to the preset movement value, e.g., the movement value 0), the processing of step  85  is performed and the couch positioning information is outputted to the couch controller  38 . Thus, the couch movement amounts ΔX, ΔY and ΔΘ obtained in step  83  are sent to the couch controller  38 . Additionally, in modified step  84 , information indicating the determination result, i.e., “completion of the patient positioning” or “re-execution of the patient positioning” is outputted to and displayed on, for example, the display unit  39 A. In the case of “re-execution of the patient positioning”, the couch movement amounts ΔX, ΔY and ΔΘ are outputted to and displayed on the display unit  39 A. 
   The couch controller  38  receives respective detected data regarding X- and Y-directional positions (X 0 , Y 0 ) of the treatment couch  59  and a rotational angle (e.g., Θ0) thereof in the rotating direction in the state before the X-ray is irradiated from the X-ray emission device  26  as described above. Those data are detected by respective sensors (not shown) disposed on the couch driver  12 . Also, the couch controller  38  receives the couch movement amounts ΔX, ΔY and ΔΘ and compute the position of the treatment couch  59 , i.e., (X 0 +ΔX), (Y 0 +ΔY) and (Θ0+ΔΘ), to which it is to be moved. Then, the couch controller  38  drives the motors  11   a ,  11   c  and  11   d  to move the treatment couch  59  so that the position of the tumor in the body of the patient  8  lying on the treatment couch  59  is aligned with the computed position. 
   After moving the treatment couch  59  in such a manner, the X-ray irradiation along the beam line m is performed on the patient  8  again, and the processing of steps  72  to  84  are repeated by the positioning data generator  37  using the current image captured by the X-ray image capturing device  29  until the information “non-necessity of couch movement” is inputted in step  84 . 
   With the patient positioning device of this embodiment, as described above, pattern matching is performed on the reference image in the set comparison area A and the current image in the set comparison area B to produce information for the positioning of the patient (couch). In the prior-art case of requiring the operator to set particular monuments, landmarks, anatomical base points, or the likes to produce patient positioning data based on them, the positions of the monuments or the likes must be designated on each of the reference image and the current image at high accuracy without an offset between the reference image and the current image. However, it is difficult, as mentioned before, to designate corresponding positions on the reference image and the current image without an offset between them. With this embodiment, since the reference image in the set comparison area A and the current image in the set comparison area B are subjected to the pattern matching, the operator is not required to designate the positions of the monuments or the likes, and hence the accuracy in producing the patient positioning data is avoided from being affected by the skills of individual operators. Accordingly, the patient positioning accuracy can be increased regardless of the skills of individual operators. As a result, a patient positioning device can be constructed of which operation does not depend upon amounts of the skills of individual operators. Further, it is possible to cut the time and labor required for setting the monuments or the likes, and to quickly and smoothly carry out the positioning operation. 
   With this embodiment, since the movement amount of the treatment couch  59  (specifically the movement amount of the tumor in the body of the patient  8  lying on the treatment couch  59 ) is determined through pattern matching made on a plurality of corresponding areas (e.g., pixels) in both the above-mentioned images, the positioning accuracy of the treatment couch  59  with respect to the beam line m is further increased. In addition, with this embodiment, since the pattern matching between the reference image and the current image is performed by using respective image information (pixel values of respective pixels) specific to the reference image and the current image, there is no need of adding new information for the pattern matching. 
   While the above embodiment has been described as using the X-ray image capturing device  29  including the X-ray fluorescence multiplier  30 , an X-ray image capturing device (image information generator)  29 A may be used instead of the X-ray image capturing device  29  shown in  FIG. 13 . 
   A patient positioning device  28 A using the X-ray image capturing device  29 A, according to another embodiment of the present invention, will be described below with reference to  FIG. 13 . The patient positioning device  28 A differs from the above-described patient positioning device  28  in using the X-ray image capturing device  29 A. More specifically, the X-ray image capturing device  29 A comprises a plurality of semiconductor radiation detectors (X-ray entry devices or flat panel detector)  66 , a plurality of signal amplifiers  67 , a plurality of signal processors  68 , and an image processing unit (image information producing unit)  69 . Looking from the direction along the beam line m, the plurality of semiconductor radiation detectors  66  are arranged in a grid pattern comprising a plurality of rows in the X-direction and a plurality of columns in the Y-direction, which are arrayed in a closely contacted state with each other. The signal amplifiers  67  and the signal processors  68  are disposed in a one-to-one relation to the semiconductor radiation detectors  66  and are serially connected to corresponding ones of the semiconductor radiation detectors  66 . Information outputted from the individual signal processors  68  and indicating the intensity of X-ray is sent to the image processing unit  69 . 
   An X-ray beam for detecting the tumor in the body of the patient  8  is emitted from the X-ray emission device  26 , which has been moved to position on the beam line m, and penetrates the tumor and the surroundings thereof. Then, the X-ray beam enters the flat panel detector (all the semiconductor radiation detectors  66 ) disposed on the side of the treatment couch  59  away from the patient  8  for conversion into electrical signals. The electrical signal outputted from each of the semiconductor radiation detectors  66  is amplified by the corresponding signal amplifier  67  and is integrated by the corresponding signal processor  68  for a preset interval of time. As a result of integrating the electrical signal, X-ray intensity information is obtained. The image processing unit  69  produces image information (information of a current image or a captured image) by using the X-ray intensity information outputted from each signal processor  68 . The information of the current image is taken into the positioning data generator  37 , which executes similar processing to that described in the above embodiment. 
   This modified embodiment can also provide similar advantages as those obtained with the above embodiment. 
   According to the present invention, as will be seen from the above description, a sufficient level of patient positioning accuracy can always be ensured regardless of the skills of individual operators.