Abstract:
Provided is a phantom device having an internal organ simulating phantom. The phantom device comprises: a phantom receiving radiation emitted from a radiation emitting unit and comprising therein a simulant that simulates an internal organ; a lifting unit installed under the phantom to support the phantom and moving the phantom relative to the radiation emitting unit, the lifting unit comprising: a worm shaft axially rotated by an external torque and having a worm formed on an outer circumferential surface thereof, a cylindrical worm wheel having gear grooves formed on an outer circumferential surface thereof to engage with the worm and a female screw formed on an inner circumferential surface thereof, and rotated by the axial rotation of the worm shaft; and a driven screw engaging with the female screw of the worm wheel, and moved up and down by the rotation of the worm wheel to move up and down the phantom; and a horizontal moving unit interlocking with the lifting unit and horizontally moving the phantom. Accordingly, since the phantom device can simulate any movement pattern, even the respiratory movement pattern of a patient&#39;s internal organ to accurately determine a desired dose of radiation to be delivered to the body part, high quality assurance of radiation therapy equipment can be achieved and therapeutic effect can be improved.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2006-0064923, filed on Jul. 11, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a phantom device having an internal organ simulating phantom. 
     2. Description of the Related Art 
     Among various uses of radiation, medical radiation therapy is used to kill cancer cells or alleviate pain for a patient suffering from cancer by emitting radiation to a tumor and preventing the tumor from growing. 
     In particular, radiation therapy is very useful when cancer cells remain after surgery and there is a high risk of cancer recurrence, when surgery cannot be practiced, when radiation therapy is more effective than surgery, when a combination of surgery and radiation therapy improves the quality of life for a cancer patient, or when a combination of drug treatment and radiation therapy maximizes anticancer effect. 
     Meantime, radiation therapy is performed by means of expensive medical equipment called a linear accelerator. Since the linear accelerator cannot only output high-dose-rate X-rays and electron beams but also can finely adjust output energy, it is currently used as standard equipment for radiation therapy. 
     It is essential to radiation therapy that the linear accelerator outputs radiation of appropriate energy. Since radiation conforming to the grade, size, or depth of a tumor results in maximum treatment effect, it is very important to enable the linear accelerator to produce optimal energy radiation. 
     As such, before using the linear accelerator, it is necessary to check whether the linear accelerator can operate normally and, in particular, can emit radiation at desired energy levels after radiation dose adjustment. This process, called quality assurance, is performed in hospitals periodically or non-periodically. 
     Various dosimetric systems are used for quality assurance. In principle, a dosimetric system is located under a radiation emitting unit to receive radiation emitted by the radiation emitting unit, and generates and outputs signals corresponding to the radiation. Since optimal radiation appropriate for a patient&#39;s tumor cannot be measured without the dosimetric system, an optimal dose of radiation cannot be delivered to the tumor, thereby reducing therapeutic anticancer effect and even causing medical malpractice in cases of excessive radiation exposure. 
     Conventional dosimetric systems can measure the dose of radiation while being fixed within a radiation path, but disadvantageously cannot move, for example, in repetitive patterns of internal organs of the human body which move according to respiration. 
     Accordingly, whether accurate or not, information about radiation dosage is obtained from a fixed target, not from a moving one. Since there is a difference between a dose administered to a moving target and a dose administered to a fixed target, it is somewhat difficult to use this information as data for quality assurance of radiation therapy equipment that is to be used to emit radiation to the target moving according to respiration. 
     As described above, in order to emit appropriate energy radiation to a moving target in a patient&#39;s body, that is, to enable the linear accelerator to deliver an accurate dose of radiation to the moving target, quality assurance should be performed by using a phantom simulating the dynamics of the moving target. However, a device that can precisely move a phantom in desired patterns has not yet been developed. 
     SUMMARY OF THE INVENTION 
     The present invention provides a phantom device having a phantom that can simulate any movement pattern, even the respiratory movement pattern of a patient&#39;s internal organ to accurately determine a desired dose of radiation to be delivered to the internal organ, thereby achieving high quality assurance of radiation therapy equipment and improving therapeutic effect. 
     According to an aspect of the present invention, there is provided a phantom device having an internal organ simulating phantom, the phantom device comprising: a phantom receiving radiation emitted from a radiation emitting unit and comprising therein a simulant that simulates an internal organ; a lifting unit installed under the phantom to support the phantom and moving the phantom relative to the radiation emitting unit, the lifting unit comprising: a worm shaft axially rotated by an external torque and having a worm formed on an outer circumferential surface thereof; a cylindrical worm wheel having gear grooves formed on an outer circumferential surface thereof to engage with the worm and a female screw formed on an inner circumferential surface thereof, and rotated by the axial rotation of the worm shaft; and a driven screw engaging with the female screw of the worm wheel, and moved up and down by the rotation of the worm wheel to move up and down the phantom; and a horizontal moving unit interlocking with the lifting unit and horizontally moving the phantom. 
     The lifting unit and the horizontal moving unit may be disposed on a horizontal surface of a base plate. The driven screw engaging with the worm wheel may extend over the worm wheel and a lifting member may be fixed to an upper end of the driven screw. A lift guide member may be disposed between the lifting member and the base plate to guide the lifting movement of the lifting member relative to the base plate and support the driven screw by means of the lifting member. 
     A first plate having a horizontal surface may be disposed on the lifting member. The horizontal moving unit may comprise: a motor mounted on the first plate; a first driven member horizontally and linearly reciprocated by the motor mounted on the first plate; a second plate connected to the first driven member and linearly reciprocated along the driven member; a motor mounted on the second plate; a second driven member linearly reciprocated by the motor in a direction perpendicular to the reciprocating direction of the first driven member; and a phantom fixing plate coupled to the second driven member to be reciprocated along the second driven member, and allowing the phantom to be fixed to a top surface thereof. 
     A lead screw may be connected to the shaft of each of the motors to be axially rotated by the motor. Each of the first and second driven members may be a driven block that engages with the lead screw and is linearly moved in a longitudinal direction of the lead screw by the axial rotation of the lead screw. 
     The phantom device may further comprise phantom fixing means disposed on the phantom fixing plate to fix the phantom to the phantom fixing plate. 
     The phantom fixing means may comprise: support walls fixed to the top surface of the phantom fixing plate and supporting one or more pixels of the phantom; and a phantom fixing unit pressing the phantom against the support walls and fixing the phantom to the phantom fixing plate. 
     The phantom may comprise a phantom body made of acryl and having therein a space simulating the shape of the internal organ. 
     The phantom may further comprise a simulant inserted into the space of the phantom body and simulating the internal organ. 
     The phantom body may be formed by stacking a plurality of acrylic slabs each having a predetermined width. 
     Dosimeter grooves into which dosimeters for measuring the dose of radiation are inserted may be formed in some of the slabs constituting the phantom. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a side view of a phantom device which is applied to a linear accelerator and having an internal organ simulating phantom according to an embodiment of the present invention,; 
         FIG. 2  is a side view of the phantom device of  FIG. 1 , according to an embodiment of the present invention; 
         FIG. 3  is a partially exploded perspective view of the phantom device of  FIG. 2 , according to an embodiment of the present invention; 
         FIG. 4  is a side view of the phantom device of  FIG. 3  when assembled, according to an embodiment of the present invention; 
         FIG. 5  is a partially cutaway perspective view for explaining the drive mechanism of a second plate of the phantom device of  FIG. 2 , according to an embodiment of the present invention; 
         FIG. 6  is a partially cutaway perspective view for explaining the drive mechanism of a phantom fixing plate of the phantom device of  FIG. 2 , according to an embodiment of the present invention; 
         FIG. 7  is a perspective view illustrating a phantom fixing plate and support walls of the phantom device of  FIG. 2 , according to an embodiment of the present invention; 
         FIG. 8  is a side view for explaining the operating principle of a phantom fixing unit of the phantom device of  FIG. 7 , according to an embodiment of the present invention; 
         FIG. 9  is a partially exploded perspective view illustrating the phantom of the phantom device of  FIG. 2 , according to an embodiment of the present invention; 
         FIG. 10  is a partially exploded perspective view of the phantom of  FIG. 9 , according to an embodiment of the present invention; and 
         FIGS. 11 and 12  are perspective views illustrating slabs of the phantom of  FIG. 9 , according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. 
       FIG. 1  is a side view of a phantom device  21  which is applied to a linear accelerator  11  and having an internal organ simulating phantom  23  according to an embodiment of the present invention. 
     Referring to  FIG. 1 , the phantom device  21  is placed on a horizontal bed  19 . The bed  19 , which forms a set with the linear accelerator  11 , is a horizontal table on which a patient lies down. 
     The linear accelerator  11  includes a body  13  and a gantry  15  rotating relative to the body  13 . A high voltage generator or a microwave generator is installed in the body  13 , and an accelerating tube for accelerating electrons, a magnetic field generator, and a radiation emitting unit  17  are installed in the gantry  15 . Radiation output from the radiation emitting unit  17  is emitted to a tumor of the patient lying on the bed  19 . 
     The phantom device  21  having the phantom  23 , which is placed on the bed  19  and located below the radiation emitting unit  17 , receives radiation emitted from the radiation emitting unit  17 . The radiation output from the radiation emitting unit  17  is emitted to the phantom  23  of the phantom device  21  to detect the dose of the emitted radiation. 
     In particular, while the radiation is emitted from the radiation emitting unit  17 , the phantom  23  is moved back and forth, left and right, and up and down by first through third motors which will be explained later. The phantom  23  is designed to resemble the movement pattern of a target body part of the patient. 
     Consequently, the dose and distribution of radiation to be emitted to the target body part, i.e., the tumor, of the patient can be determined in advance by measuring the dose of radiation emitted to a simulant  23   e  inside the phantom  23  that is moved in all directions. In order to measure the dose of radiation, a dose detector should be first located in the phantom  23 . A thermoluminescent dosimeter or a metal oxide semiconductor field effect transistor (MOSFET) dosimeter or film may be used as the dose detector. 
       FIG. 2  is a side view illustrating the entire structure of the phantom device  21  having the phantom  23  of  FIG. 1 , according to an embodiment of the present invention. 
     Referring to  FIG. 2 , the phantom device  21  includes a base plate  27  placed on a flat die, e.g., the bed  19  (see  FIG. 1 ), and having a horizontal support surface, a Z-direction driving unit  91  installed over the base plate  27  and providing a Z-direction force, a Y-direction driving unit  93  installed over the Z-direction driving unit  91  and reciprocating in a Y direction (see  FIG. 5 ), an X-direction driving unit  95  installed over the Y-direction driving unit  93  and reciprocating in an X direction, and the phantom  23  mounted on the X-direction driving unit  95 . A controller  25  is disposed on the base plate  27  to control the movement pattern of the phantom  23 . 
     The X-, Y-, and Z-direction driving units  95 ,  93 , and  91  three-dimensionally move the phantom  23  relative to the radiation emitting unit  17 , such that the phantom  23  can be moved in the same movement pattern as that of the target body part of the patient. 
     The Z-direction driving unit  91  includes a first motor  31  fixed to a side of the base plate  27 , a worm shaft  33  axially rotated by the first motor  31  and having a worm  33   a  (see  FIG. 3 ) formed on an outer circumferential surface thereof, a cylindrical worm wheel  35  disposed on a side of the worm shaft  33  and having a plurality of gear grooves  35   c  formed on an outer circumferential surface thereof and a female screw  35   d  (see  FIG. 3 ) formed on an inner circumferential surface thereof, a driven screw  41  extending upward and engaging with the female screw  35   d  of the worm wheel  35 , a lifting plate  43  fixed to an upper end of the driven screw  41  and kept parallel to the base plate  27 , and a lift guide member  73  disposed between the base plate  27  and the lifting plate  43 . 
     The lift guide member  73  guides the lifting movement of the lifting plate  43  and prevents the lifting plate  43  from being rotated. The lift guide member  73  includes cylindrical vertical guiders  39  fixed to the base plate  27  and having open upper ends, and guide rods  43   a  mounted on a bottom surface of the lifting plate  43  and partially inserted into the vertical guiders  39  to guide the lifting movement of the lifting plate  43 . A bearing  37  rotatably supports the worm wheel  35 . 
     The Z-direction driving unit  91  will be explained later with reference to  FIGS. 3 and 4 . 
     A first plate  45  is disposed on the lifting plate  43 . The first plate  45  has a horizontal surface large enough to support the Y-direction driving unit  93 . If the lifting plate  43  is large enough to support the Y-direction driving unit  93 , the first plate  43  may be omitted. 
     The Y-direction driving unit  93  includes a second motor  49  installed on the first plate  45 , a lead screw  51  (see  FIG. 5 ) axially rotated by the second motor  49 , and a driven block  53  fixed to the second plate  57  by engaging with the lead screw  51 , and linearly moved in a Y direction by the axial rotation of the lead screw  51  to reciprocate the second plate  57  in the Y direction. 
     A plurality of bearings  47  fixed to the first plate  45  are disposed under the second plate  57  and guide the movement of the second plate  57  relative to the first plate  45 . A plurality of bearings  58  are also disposed on the second plate  57  to horizontally support a phantom fixing plate  61  and guide the phantom fixing plate  61  in an X direction. The Y-direction driving unit  93  will be explained again with reference to  FIG. 5 . 
     The X-direction driving unit  95  includes a third motor  63  fixed to the second plate  57 , and the phantom fixing plate  61  is reciprocated in an X direction by the third motor  63 . The X-direction driving unit  95  has a construction as shown in  FIG. 6  and will be explained later with reference to  FIG. 6 . 
     The phantom  23  is disposed on the phantom fixing plate  61 , and fixing means for firmly fixing the phantom  23  to a top surface of the phantom fixing plate  61  is provided. The fixing means includes two support walls  29  facing each other with the phantom  23  therebetween, and a phantom fixing unit  30  passing through one of the two support walls  29  and pressing the phantom  23  in an “f” direction. 
     The phantom  23  installed on the phantom fixing plate  61  is formed by stacking a plurality of acrylic slabs, and includes the simulant  23   e  therein. The simulant  23   e  can simulate an internal organ, such as lung, liver, heart, or stomach, of the human body, which moves according to respiration. 
       FIGS. 3 and 4  are an exploded perspective view and a side view, respectively, illustrating the Z-direction driving unit  91  of the phantom device  21  of  FIG. 2 . according to embodiments of the present invention. 
     Referring to  FIGS. 3 and 4 , the first motor  31  is disposed on a side of a top surface of the base plate  27 , and the worm shaft  33  is connected to the shaft of the first motor  31 . The worm shaft  33  is horizontally supported by a plurality of shaft supports  34  and is axially rotated by the torque of the first motor  31 . The worm shaft  33  is made of synthetic resin or engineering plastic. 
     The worm  33   a  formed on the worm shaft  33  has helical gear teeth formed thereon such that the helical gear teeth engage with the gear grooves  35   c  formed on the outer circumferential surface of the worm wheel  35 . 
     The bearing  37  is disposed beside the worm  33   a . The bearing  37  is a thrust bearing that rotatably supports the worm wheel  35 . The bearing  37  and the worm wheel  35  should be concentric. 
     The worm wheel  35  disposed on the bearing  37  has a sidewall  35   a  and a bottom  35   b , and has a cylindrical shape open at an upper end thereof. The bottom  35   b  is fixed to the bearing  37  to be horizontally supported. The sidewall  35   a  with a predetermined thickness has the gear grooves  35   c  and the female screw  35   d  respectively formed on the outer and inner circumferential surfaces thereof. 
     The gear grooves  35   c  engage with the worm  33   a , and when the worm shaft  33  is axially rotated in an “a” direction, are rotated in a “b” direction to move up and down the driven screw  41 . 
     The driven screw  41  meshes with the worm wheel  35 . The driven screw  41  includes a male screw  41  a partially engaging with the female screw  35   d  and a fixing part  41   b  having a predetermined thickness and integrally formed with an upper end of the male screw  41   a . The fixing part  41   b  is coupled to the square lifting plate  43 . The lifting plate  43 , which is an acrylic plate having a predetermined thickness, horizontally and fixedly supports the driven screw  41  and moves up and down the first plate  45  according to the movement of the driven screw  41 . 
     Three vertical guiders  39  are installed around the worm wheel  35 . The vertical guiders  39  are vertical pipe-shaped members into which the vertical guide rods  43   a  are inserted to guide the lifting movement of the lifting plate  43  and prevent the lifting plate  43  from being rotated. 
     The guide rods  43   a  are annular rods fixed to the bottom surface of the lifting plate  43  and vertically and downwardly extending from the bottom surface of the lifting plate  43 , and correspond to the vertical guiders  39  in a one-to-one manner. The guide rods  43   a  partially inserted into the vertical guiders  39  as shown in  FIG. 2  are vertically driven simultaneously with the movement of the lifting plate  43  to prevent the lifting plate  43  from being shaken or rotated. 
     The first plate  45  is closely fixed to the top of the lifting plate  43 . The first plate  45 , which is a square acrylic plate having a predetermined thickness, has a horizontal surface on which the plurality of bearings  47  are disposed. The Y-direction driving unit  93  is disposed on the first plate  45 . 
       FIG. 5  is a perspective view for explaining the mechanism of driving the second plate  57  by means of the Y-direction driving unit  93  of  FIG. 2 , according to an embodiment of the present invention. 
     Referring to  FIG. 5 , the Y-direction driving unit  93  is disposed on a side of a top surface of the first plate  45 . The Y-direction driving unit  93  horizontally moves the second plate  57  in a Y direction. 
     The Y-direction driving unit  93  includes the second motor  49  fixed to a side on a top surface of the first plate  45 , the lead screw  51  horizontally extending to be connected to the shaft of the second motor  49  and having both ends supported by supporters  54 , and the driven block  53  allowing the lead screw  51  to pass therethrough and reciprocated in a longitudinal direction of the lead screw  51  by the axial rotation of the lead screw  51 . 
     The driven block  53  is fixed to a protrusion  57   a  of the second plate  57 . The protrusion  57   a  is fixed to an end of the second plate  57 , and extends toward the lead screw  51  to be coupled to the driven block  53  to transmit the movement force of the driven block  53  to the second plate  57 . 
     The bearings  47  fixed to the top surface of the first plate  45  are inserted into bearing grooves  57   b  having predetermined widths and depths. The bearings  47  whose upper ends are inserted into the bearing grooves  57   b  support horizontally the second plate  57  such that the second plate  57  can be smoothly moved in the Y direction. 
     The plurality of bearings  58  mounted on the second plate  57  support the phantom fixing plate  61  horizontally (see  FIG. 6 ), and guide the phantom fixing plate  61  in an X direction. 
     A metal piece  56  is disposed on a front end of the protrusion  57   a , and two sensors  55  are disposed on both sides under the metal piece  56 . The sensors  55  are spaced by a predetermined distance from each other, and sense the movement distance of the metal piece  56 . 
     Each of the sensors  55  generates a signal when the metal piece  56  passes through the sensor  55 . Accordingly, when the metal piece  56  moved along the driven block  53  reaches one of the sensors  25 , the sensor  55  generates a signal to the controller  25  to indicate that the metal piece  56  has reached the sensor  55 . Next, the controller  25  reversibly rotates the second motor  49  to move the driven block  53  in the opposite direction. The sensing mechanism is well known. 
     The sensors  55  of the Y-direction driving unit  93  determine the maximum Y-direction reciprocating distance of the second plate  57 . Accordingly, the maximum Y-direction stroke of the second plate  57  can be increased by increasing the distance between the sensors  55 . 
     In practice, however, the metal piece  56  is reciprocated between the sensors  55  without reaching the sensors  55 . The stroke of the metal piece  56 , that is, the stroke of the driven block  53 , is controlled by the controller  25 . 
       FIG. 6  is a detailed perspective view for explaining the mechanism of driving the phantom fixing plate  61  by means of the X-direction driving unit  95 , according to an embodiment of the present invention. The X-direction driving unit  95  horizontally moves the phantom fixing plate  61  in an X direction. 
     Referring to  FIG. 6 , the X-direction driving unit  95  includes the third motor  63  disposed on a side of a top surface of the second plate  57 , a lead screw  69  axially rotated by the torque of the third motor  63 , and a driven block  71  allowing the lead screw  69  to pass therethrough and be reciprocated by the axial rotation of the lead screw  69 . 
     The driven block  71  is coupled to a C-shaped projection  61   b  fixed to an end of the phantom fixing plate  61 . The lead screw  69  is parallel to the shaft of the third motor  63  and has both ends horizontally supported by supporters  72 . 
     In order to transmit the torque of the third motor  63  to the lead screw  69 , a driving pulley  65  is mounted on the shaft of the third motor  63 , a driven pulley  66  is mounted on an end of the lead screw  69 , and the driving pulley  65  and the driven pulley  66  are connected to each other via a belt  67 . Accordingly, the torque of the third motor  63  can be transmitted to the lead screw  69  via the belt  67 . 
     The driven block  71  is reciprocated in a longitudinal direction of the lead screw  69  by the axial rotation of the lead screw  69 , and reciprocates the phantom fixing plate  61  in an X direction by means of the projection  61   b  fixed to the bottom thereof. The phantom fixing plate  61  horizontally supported by the bearings  58  disposed on the second plate  57  is reciprocated within a predetermined range. 
     A plurality of bearing grooves  61   a  into which upper ends of the bearings  58  are inserted are disposed on the phantom fixing plate  61  such that the phantom fixing plate  61  can be linearly moved. The bearing grooves  61  a having predetermined widths and depths are parallel to one another. 
     In order to limit the maximum movement distance of the phantom fixing plate  61 , a metal piece  56  is disposed on an end of the projection  61   b  and a pair of sensors  55  are installed under the metal piece  56 . The operating principles of the metal piece  56  and the sensors  55  are the same as described with reference to  FIG. 5 . 
       FIG. 7  is a perspective view illustrating the phantom fixing plate  61  and the support walls  29  of the phantom device of  FIG. 2 , according to an embodiment of the present invention. 
     Referring to  FIG. 7 , the pair of support walls  29  are disposed at both sides on the top surface of the phantom fixing plate  61 . The support walls  29  face each other to be spaced apart by a predetermined distance, and firmly press the phantom  23  (see  FIG. 2 ) disposed therebetween as shown in  FIG. 2 . The support walls  29  and the phantom fixing unit  30  are made of acryl. The number and structure of the support walls  29  are not limited to the present embodiment. 
     The phantom fixing unit  30  is disposed on one of the support walls  29 . A female screw hole  29   a  into which a pressing screw  30   a  of the phantom fixing unit  30  is inserted is formed in the support wall  29 . 
     The phantom fixing unit  30  includes the pressing screw  30   a  inserted into the female screw hole  29   a , a cylindrical screw connection  30   b  into which an end of the pressing screw  30   a  is fixedly inserted, and a disk-shaped support plate  30   e  integrally formed with the screw connection  30   b.    
     A front end of the pressing screw  30   a  inserted into the screw connection  30   b  is fixed by a fixing screw  30   d . A female screw hole  30   c  into which the fixing screw  30   d  is inserted is formed in a sidewall of the screw connection  30   b.    
       FIG. 8  is a side view for explaining the operating principle of the phantom fixing unit  30  of  FIG. 7 , according to an embodiment of the present invention. 
     Referring to  FIG. 8 , the phantom  23  can be pressed in an “f” direction by rotating the pressing screw  30   a  of the phantom fixing unit  30  mounted on one of the support walls  29 . 
     The phantom  23  mounted on the phantom fixing plate  61  is formed by stacking a plurality of unit slabs  23   a . The structure of the phantom  23  will be explained in detail with reference to  FIG. 9 . 
       FIG. 9  is a partially exploded perspective view of the phantom  23  of  FIG. 2 , and  FIG. 10  is an exploded perspective view illustrating any one of the unit slabs  23   a  constituting a phantom body  23   z  of the phantom  23  of  FIG. 9 , according to embodiments of the present invention. 
     The phantom  23  formed by stacking the plurality of slabs  23   a  includes the phantom body  23   z  having therein a space that simulates the shape of an internal organ, and the simulant  23   e  located in the space inside the phantom body  23   z.    
     Each of the slabs  23   a  constituting the phantom body  23   z  has a predetermined thickness and is made of acryl. Section holes  23   g  are formed in some slabs  23   a  as illustrated in  FIG. 10 . The section holes  23   g  are through-holes representing outlines of the cross-section of the internal organ. 
     That is, the section holes  23   g  represent images of the internal organ tomographed at intervals in a direction from the back to the chest. Accordingly, the section holes  23   g  have different shapes for different slabs  23   a , and the shape of the internal organ can be embodied by sequentially stacking the slabs  23   a.    
     Referring to  FIG. 9 , the plurality of slabs  23   a  are sequentially stacked to form one phantom  23 . Each of the slabs  23   a  is rectangular and has through-holes  23   f  formed in four corners thereof. 
     The through-holes  23   f  permit vertical rods  23   b  to pass therethrough. The vertical rods  23   b  upwardly pass through the through-holes  23   f  of the stack of slabs  23   a  and upper ends of the vertical rods  23   b  are coupled to nuts  23   c  to vertically fasten the slabs  23   a  to one another. 
     In particular, a film  81  (see  FIG. 8 ) may be inserted into the stack of slabs  23   a  fixed by the nuts  23   c  as shown in  FIG. 8  by loosening the nuts  23   c  and slightly lifting the slabs  23   a . The film  81  is used to detect the dose of radiation passing through the simulant  23   e.    
     Simulant pieces  23   d  are inserted into the section holes  23   g  of the slabs  23   a . The simulant pieces  23   d  are automatically stacked when the slabs  23   a  are sequentially stacked, so as to form one simulant  23   e.    
     The simulant  23   e  is made of a tissue-equivalent material for a simulated subject. For example, a simulant  23   e  simulating a lung is made of cork since the density of cork is almost equivalent to that of the lung. 
     The simulant  23   e  is made of a proper material according to the kind of a simulated internal organ. The simulant pieces  23   d  may be made of acryl similarly to the slabs  23   a , or teflon or paraffin. 
     The simulant pieces  23   d  are inserted into the section holes  23   g , the slabs  23   a  are stacked, and radiation is emitted to the phantom  23  in a thickness direction of the simulant pieces  23   d . As a result, the energy level of radiation at a target depth can be obtained and radiation treatment planning can be conducted based on the energy level. 
       FIGS. 11 and 12  are perspective views illustrating some slabs  23   a  of the phantom  23  of  FIG. 9 , according to embodiments of the present invention. The slabs  23  illustrated in  FIGS. 11 and 12  are disposed under the simulant  23   e  as illustrated in  FIG. 8 . 
     Referring to  FIG. 11 , a plurality of dosimeter grooves  23   k  are formed in a top surface of a slab  23   a , according to an embodiment of the present invention. The dosimeter grooves  23   k  are arranged at predetermined intervals and allow thermoluminescent dosimeters  83  to be inserted thereinto. Since the slab  23   a  on which the thermoluminescent dosimeters  83  are installed is disposed under the simulant  23   e  as illustrated in  FIG. 8 , the dose of radiation under the simulant  23   e  can be obtained. 
     Referring to  FIG. 12 , a plurality of dosimeter grooves  23   m  extend longitudinally in a slab  23   a , according to an embodiment of the present invention. The plurality of dosimeter grooves  23   m  are parallel to one another, and allow MOSFET dosimeters to be inserted thereinto. Accordingly, since the slab  23   a  on which the MOSFET dosimeters  85  are installed is disposed under the simulant  23   e  as illustrated in  FIG. 8 , the dose of radiation under the simulant  23   e  can be obtained. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.