Radiation therapy apparatus

Abstract

The invention provides a radiation therapy device capable of suppressing the influence of radiation on an imaging device. An X-ray imaging device is provided with an X-ray tube (7) that irradiates a patient (6) with X-rays, which are light for imaging, and an FPD (2) that detects the X-rays via the patient (6). The X-ray tube (7) and the FPD (2) are disposed at positions offset from a line connecting an isocenter (8) of radiation from the irradiation nozzle (1) and the irradiation nozzle (1). Furthermore, the FPD (2) is disposed on a reference surface (S), which passes through the isocenter (8) and is orthogonal to a line connecting the isocenter (8) and the irradiation nozzle (1), or at a position closer to the irradiation nozzle than the reference surface (S).

Description

Technical Field

[0001] The present disclosure relates to a radiation therapy device. Background Art

[0002] In patent document 1, as a radiotherapy device for treating cancer by irradiating radiation to cancer lesions, a particle beam therapy device capable of irradiating a patient with particle beams from three directions is disclosed. The particle beam therapy device has an irradiation port through which the particle beam passes, an irradiation nozzle for irradiating the patient with the particle beam from the irradiation port, and a moving mechanism for moving the irradiation nozzle. In addition, there are three irradiation ports, which are respectively arranged in a vertical direction, a horizontal direction, and an inclined direction. The particle beam therapy device switches the irradiation port for guiding the particle beam while using a moving mechanism to move the irradiation nozzle so as to be connected to the irradiation port for guiding the particle beam. Thus, the patient can be irradiated with radiation from three directions.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2017-153908 Summary of the invention

[0006] Problems to be solved by the invention

[0007] In a radiotherapy apparatus, in addition to an irradiation nozzle for irradiating radiation, an imaging device for acquiring an image of the patient is provided in order to determine the position of the patient. For example, as an imaging device, a particle beam therapy apparatus described in Patent Document 1 includes an X-ray generator and an FPD (Flat Panel Detector) for detecting X-rays from the X-ray generator via the patient.

[0008] When the imaging device and the irradiation nozzle are arranged independently of each other, the radiation irradiated from the irradiation nozzle and the X-ray irradiated from the imaging device interfere with each other, and as a result, the imaging device may be affected. For example, in the case where it is necessary to acquire an image of a patient while irradiating radiation, such as in mobile tracking irradiation to accurately irradiate an organ that moves with the patient's breathing, the interference between the radiation and the X-ray may affect the image of the patient generated by the X-ray, resulting in a decrease in the accuracy of the image.

[0009] However, Patent Document 1 does not describe the positional relationship between the X-ray imaging device and the irradiation nozzle, and cannot suppress the influence of radiation on the imaging device.

[0010] An object of the present disclosure is to provide a radiotherapy apparatus capable of suppressing the influence of radiation on an imaging device.

[0011] Solutions to Solve Problems

[0012] A radiotherapy device based on one embodiment of the present disclosure comprises: an irradiation unit that irradiates radiation to an irradiation object; and a photographing device that photographs the irradiation object, the photographing device comprising a light source unit that irradiates the irradiation object with light for photographing and a detection unit that detects the light via the irradiation object, the light source unit and the detection unit being arranged at positions deviated from a line connecting the isocenter of the radiation and the irradiation unit, the detection unit being arranged on a reference plane or at a position closer to the irradiation unit than the reference plane, the reference plane being a plane that passes through the isocenter and is orthogonal to the line connecting the isocenter and the irradiation unit.

[0013] The effects of the invention are as follows.

[0014] According to the present invention, it is possible to suppress the influence of radiation on the imaging device. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a diagram schematically showing the appearance of the irradiation device according to the first embodiment of the present disclosure.

[0016] Figure 2 This is a diagram showing an example of the structure of the radiotherapy apparatus according to the first embodiment of the present disclosure.

[0017] Figure 3 It is a diagram showing a configuration example of an X-ray imaging device according to the first embodiment of the present disclosure.

[0018] Figure 4 It is a diagram showing another configuration example of the X-ray imaging device according to the first embodiment of the present disclosure.

[0019] Figure 5 1 is a diagram showing an angle range in which the FPD according to the first embodiment of the present disclosure can be set.

[0020] Figure 6 1 is a diagram showing an angle range in which the FPD according to the second embodiment of the present disclosure can be set.

[0021] Figure 7 It is a diagram showing a configuration example of an X-ray imaging device according to a third embodiment of the present disclosure.

[0022] Figure 8 1 is a diagram showing an angle range in which the FPD according to the fourth embodiment of the present disclosure can be set. DETAILED DESCRIPTION

[0023] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0024] (First embodiment)

[0025] Figure 1 This is a diagram schematically showing the appearance of an irradiation device included in the radiotherapy apparatus according to the first embodiment of the present disclosure. Figure 1 The irradiation device 10 shown is arranged in a treatment room R where radiation therapy is performed, and includes an irradiation nozzle 1 , an FPD 2 , a nozzle rotating mechanism 3 , and a treatment table 4 .

[0026] The irradiation nozzle 1 is directed to a patient ( Figure 1 The type of radiation is not particularly limited, but in this embodiment, the radiation is a particle beam, more specifically a carbon beam.

[0027] The FPD2 is a part of an imaging device that captures a patient and obtains an image of the patient. In this embodiment, the imaging device is an X-ray imaging device that irradiates the patient with X-rays as imaging light and detects the X-rays through the patient to capture the patient. Figure 1 The X-ray tube (not shown) that functions as a light source of X-rays (see Figure 3 and Figure 4 The X-ray tube 7 is an X-ray detection unit (flat panel detector). The number of FPDs 2 is not limited, but in the present embodiment, two FPDs 2A and 2B are provided as FPDs 2.

[0028] The nozzle rotating mechanism 3 is a moving mechanism that moves the irradiation nozzle 1 to place the irradiation nozzle 1 at any one of a plurality of irradiation start positions for irradiating radiation.

[0029] The treatment table 4 has a top plate 4A as a bed on which a patient is placed and an arm 4B for moving the top plate 4A. The arm 4B can perform translational movement along three different axial directions and rotational movement with the three axial directions as rotation axes relative to the top plate 4A. The arm 4B is controlled, for example, based on an image of the patient acquired by the above-mentioned X-ray imaging device so that the affected part of the patient placed on the top plate 4A coincides with the isocenter of the radiation from the irradiation nozzle 1. The isocenter is the position where the radiation is irradiated most concentratedly.

[0030] Figure 2 This is a diagram showing an example of the structure of a radiotherapy apparatus. Figure 2 The radiation therapy apparatus 100 shown includes an irradiation device 10 , an accelerator 20 , and a beam transport system 30 .

[0031] The accelerator 20 accelerates charged particles and emits them as a particle beam. The type of the accelerator 20 is not particularly limited, but in the present embodiment, the accelerator 20 includes a linear accelerator 21 and a synchrotron 22. The linear accelerator 21 is an injection unit into which charged particles are injected into the synchrotron 22 with acceleration. The synchrotron 22 further accelerates the charged particles injected from the linear accelerator 21 and emits them as a particle beam (charged particle beam).

[0032] The beam transport system 30 is a transport device that transports the particle beam emitted from the accelerator 20 to the irradiation device 10. The beam transport system 30 includes a plurality of deflection electromagnets 31 that deflect the particle beam to change the advancing direction of the particle beam. Figure 2 In the example of FIG. 1 , four deflection magnets 31A to 31D are provided in the beam transport system 30 as the deflection electromagnets 31 .

[0033] The irradiation device 10 includes Figure 1 In addition to the structure shown in the figure, a plurality of irradiation ports 5 are provided. The irradiation port 5 is a vacuum pipe for guiding the particle beam delivered by the beam delivery system 30 to the irradiation nozzle 1. Figure 2 In the example, three irradiation ports 5A to 5C are provided as irradiation ports 5. The irradiation port 5A is provided substantially in the horizontal direction, the irradiation port 5B is provided substantially in the vertical direction, and the irradiation port 5C is provided in the inclined direction (specifically, in the direction forming an angle of substantially 45 degrees with respect to the horizontal direction).

[0034] The irradiation ports 5A to 5C are connected to a beam transport system 30 , and a deflection electromagnet 31 of the beam transport system 30 is controlled so as to guide the particle beam to any one of the irradiation ports 5A to 5C.

[0035] Figure 1 The nozzle rotation mechanism 3 shown moves the irradiation nozzle 1 so as to connect it to any one of the three irradiation ports 5A to 5C. The positions connected to the irradiation ports 5A to 5C respectively become the irradiation start positions. In the present embodiment, the nozzle rotation mechanism 3 rotates the irradiation nozzle 1 around a predetermined rotation axis so that the irradiation nozzle 1 rotates around the patient 6 placed on the treatment table 4. The predetermined rotation axis is the axis of the isocenter 8 of the radiation irradiated by the irradiation nozzle 1, and is roughly oriented in the horizontal direction in the present embodiment. Furthermore, in the present embodiment, the nozzle rotation mechanism 3 rotates the irradiation nozzle 1 by 90° from the horizontal direction to the vertical direction to connect the irradiation nozzle 1 to any one of the three irradiation ports 5A to 5C.

[0036] According to the above configuration, the radiotherapy apparatus 100 uses the nozzle rotating mechanism 3 to move the irradiation nozzle 1 so as to be connected to any one of the irradiation ports 5A to 5C, and uses the deflection electromagnet 31 of the beam transport system 30 to guide the particle beam to the irradiation port connected to the irradiation nozzle 1. Thus, the particle beam can be irradiated from three different directions to the isocenter 8 where the affected part of the patient 6 lying on the top plate 4A of the treatment table 4 exists.

[0037] In addition, the moving mechanism for moving the irradiation nozzle 1 is not limited to the nozzle rotating mechanism 3. For example, the moving mechanism may be a rotating frame or the like.

[0038] The following describes the configuration of the X-ray imaging device of the radiotherapy apparatus 100. In the following description, the vertical direction is referred to as the Z direction, the direction along the rotation axis of the irradiation nozzle 1 in the horizontal direction is referred to as the Y direction, and the direction orthogonal to the Y direction in the horizontal direction is referred to as the X direction. In this case, the X direction is the direction along the straight line connecting the isocenter 8 and the irradiation port 5A (the irradiation nozzle 1 arranged in the horizontal direction) when viewed from the Z direction. Furthermore, the direction from the isocenter 8 toward the irradiation port 5A is referred to as the positive direction of the X direction, and the upward direction in the vertical direction is referred to as the positive direction of the Z direction. Furthermore, the positive direction of the Y direction is the direction in which the XYZ directions constitute a right-handed system.

[0039] Figure 3 : is a diagram showing an example of the configuration of an X-ray imaging device. Specifically, Figure 3 (a) schematically shows a cross section of the irradiation device 10 along the ZX plane passing through the isocenter 8, Figure 3 (b) schematically shows a cross section of the irradiation device 10 taken along a YZ plane passing through the isocenter 8 .

[0040] As described above, the X-ray imaging device includes an X-ray tube 7, which is a light source unit for irradiating X-rays as imaging light to the patient 6, and an FPD 2, which is a detection unit for detecting X-rays from the X-ray tube 7 via the patient 6. There may be multiple combinations of FPD 2 and X-ray tube 7. In the present embodiment, there are two combinations of FPD 2 and X-ray tube 7. Specifically, two FPDs 2A and 2B are provided as FPD 2, and two X-ray tubes 7A and 7B are provided as X-ray tube 7.

[0041] The FPD2A is disposed at a position opposite to the X-ray tube 7A across the isocenter 8, and the FPD2B is disposed at a position opposite to the X-ray tube 7B across the isocenter 8. Thus, the FPD2A detects X-rays emitted from the X-ray tube 7A via the patient 6, and detects X-rays emitted from the X-ray tube 7B via the patient 6. Furthermore, the X-ray imaging device is configured so that a line connecting the FPD2A and the X-ray tube 7A and a line connecting the FPD2B and the X-ray tube 7B, that is, a traveling direction of the X-rays from the X-ray tube 7A and a traveling direction of the X-rays from the X-ray tube 7B intersect each other.

[0042] The X-ray imaging device composed of the FPD 2 and the X-ray tube 7 is arranged at a position deviated from the line connecting the irradiation nozzle 1 and the isocenter 8 relative to each irradiation start position of the irradiation nozzle 1. In the case of the present embodiment, it is arranged at a position deviated from the moving plane M on which the irradiation nozzle 1 moves. In the present embodiment, the moving plane M is a plane along the ZX plane.

[0043] Furthermore, the X-ray imaging device is configured such that the FPD 2 is disposed on the upstream side of the isocenter 8 in the trajectory of the particle beam relative to each irradiation start position of the irradiation nozzle 1. Specifically, the upstream side of the isocenter 8 refers to a position on the reference plane S or closer to the irradiation nozzle 1 than the reference plane S, the reference plane S being a plane passing through the isocenter 8 and being orthogonal to the line I connecting the isocenter 8 and the irradiation nozzle 1. Figure 3 (a) shows the line I and the reference plane S when the irradiation nozzle 1 is oriented substantially in the horizontal direction.

[0044] exist Figure 3 In the example of , FPD2A and 2B and X-ray tubes 7A and 7B are arranged on the reference plane S when the irradiation nozzle 1 is generally oriented in the horizontal direction. In addition, the X-ray tubes 7A and 7B are set at a position lower than the isocenter 8, and the FPD2A and 2B are arranged at a position higher than the isocenter 8. In addition, the X-ray imaging device is arranged so that the line connecting the FPD2A and the X-ray tube 7A and the line connecting the FPD2B and the X-ray tube 7B are substantially orthogonal to each other.

[0045] Figure 4 FIG. 2 is a diagram showing another example of arrangement of the X-ray imaging device in the radiation therapy apparatus 100 .

[0046] exist Figure 4 In the example, also with Figure 3 Similar to the example, the X-ray imaging device is arranged at a position deviated from the line connecting the irradiation nozzle 1 and the isocenter 8 relative to each irradiation start position of the irradiation nozzle 1, and is arranged so that the FPD2 is set on the upstream side of the isocenter 8 in the trajectory of the particle beam.

[0047] Among them, Figure 4In the example, Figure 3 Unlike the example of , the X-ray imaging device is arranged on the reference plane S when the irradiation nozzle 1 is oriented substantially in the vertical direction. That is, the FPD 2 and the X-ray tube 7 are all arranged on a plane at the same height as the isocenter 8 .

[0048] Furthermore, the X-ray imaging device may be disposed on the reference plane S when the irradiation nozzle 1 is oriented in an inclined direction.

[0049] Figure 5 : is a diagram showing the FPD installation angle range as the range in which the FPD 2 can be configured in this embodiment. Specifically, Figure 5 (a) shows the FPD setting angle range on the XY plane, Figure 5 (b) shows the FPD setting angle range on the XZ plane, Figure 5 (c) shows the FPD settable angle range on the YZ plane. In addition, the FPD settable angle range is represented by, for example, the range of the deflection angle on each plane.

[0050] In the XY plane direction, if Figure 5 As shown in (a), the range of the deflection angle from -90° to 90° (that is, the range in which the X direction is positive) becomes the FPD setting angle range. And, in the XZ plane direction, as Figure 5 As shown in (b), the range of the deflection angle from 0° to 90° (that is, the range where the X direction is positive and the Z direction is positive) becomes the FPD setting angle range. And, in the YZ plane direction, as Figure 5 As shown in (c), the range of the off-angle of 0° to 180° (that is, the range in which the Z direction is positive) becomes the FPD installable angle range.

[0051] The radiotherapy apparatus 100 described above may also irradiate the patient 6 with X-rays from the X-ray tube 7 of the X-ray imaging device while the irradiation nozzle 1 is irradiating radiation in order to perform moving body tracking irradiation for accurately irradiating organs that move with the patient's breathing, etc.

[0052] As described above, according to the present embodiment, the X-ray imaging device includes the X-ray tube 7 for irradiating the patient 6 with X-rays as light for imaging, and the FPD 2 for detecting the X-rays via the patient 6. The X-ray tube 7 and the FPD 2 are arranged at positions deviated from the line connecting the isocenter 8 of the radiation from the irradiation nozzle 1 and the irradiation nozzle 1. Furthermore, the FPD 2 is arranged on the reference plane S or at a position closer to the irradiation nozzle side than the reference plane S, and the reference plane S is a plane passing through the isocenter 8 and orthogonal to the line connecting the isocenter 8 and the irradiation nozzle 1. Therefore, it is possible to suppress the detection of the secondary particle beam scattered by the radiation by the FPD 2, and thus it is possible to suppress the influence of the radiation on the X-ray imaging device.

[0053] Furthermore, in the present embodiment, the nozzle rotating mechanism 3 moves the irradiation nozzle 1 and places it at any one of a plurality of irradiation start positions. The FPD 2 is arranged on the reference plane S or at a position closer to the irradiation nozzle portion than the reference plane S relative to all irradiation start positions. Therefore, no matter from which irradiation start position the radiation is irradiated, it is possible to suppress the X-rays that interfere with the radiation detected by the FPD 2. Therefore, even when the irradiation nozzle 1 is moved, it is possible to suppress the influence of the radiation on the X-ray imaging device.

[0054] Furthermore, in this embodiment, the X-ray imaging device is arranged so that the line connecting the FPD2A and the X-ray tube 7A and the line connecting the FPD2B and the X-ray tube 7B are substantially orthogonal to each other. Furthermore, the FPD2A and 2B and the X-ray tubes 7A and 7B are arranged on the reference plane S when the irradiation nozzle 1 is set at any one of the irradiation start positions. In this case, the influence of radiation on the X-ray imaging device can be more appropriately suppressed.

[0055] Furthermore, in this embodiment, while the irradiation nozzle 1 irradiates radiation, the X-ray tube of the X-ray imaging device irradiates X-rays to the patient 6. Therefore, detection of secondary particle beams scattered by radiation by the FPD 2 can be suppressed, and moving body tracking irradiation etc. can be performed with high accuracy.

[0056] Furthermore, in the present embodiment, the radiation is a carbon beam. Since the carbon beam has a greater influence on X-rays than other radiations, the effect of suppressing the influence on the X-ray imaging device is also greater.

[0057] (Second embodiment)

[0058] In the first embodiment, the irradiation nozzle 1 is rotated 90°, but in the present embodiment, the irradiation nozzle 1 is fixed. In addition, the X-ray imaging device is arranged at a position deviated from the line connecting the irradiation nozzle 1 and the isocenter 8 relative to the fixed irradiation nozzle 1, and the FPD 2 is arranged on the upstream side of the isocenter 8 in the trajectory of the particle beam.

[0059] Figure 6 1 is a diagram showing the FPD installation angle range of the FPD 2 when the irradiation nozzle 1 is fixed. Specifically, Figure 6 (a) shows the FPD setting angle range on the XY plane, Figure 6 (b) shows the FPD setting angle range on the XZ plane, Figure 6 (c) shows the FPD setting angle range on the YZ plane. Figure 6 In the example shown in FIG. 1 , the irradiation nozzle 1 is fixed in the horizontal direction.

[0060] In the XY plane direction, if Figure 6 As shown in (a), the range of the deflection angle from -90° to 90° (that is, the range in which the X direction is positive) becomes the FPD setting angle range. And, in the XZ plane direction, as Figure 6 As shown in (b), the range of the deflection angle from -90° to 90° (that is, the range in the positive direction of the X direction) becomes the FPD setting angle range. And, in the YZ plane direction, as Figure 5 As shown in (c), the range of the deflection angle from 0° to 360° (that is, the entire range in the Z direction) becomes the FPD installable angle range.

[0061] In the present embodiment as well, it is possible to suppress the detection of a secondary particle beam scattered by radiation by the FPD 2, and thus it is possible to suppress the influence of radiation on the X-ray imaging device.

[0062] (Third Embodiment)

[0063] In the present embodiment, an example in which a plurality of fixed irradiation nozzles 1 are provided will be described.

[0064] Figure 7 : is a diagram showing an example of the configuration of an X-ray imaging device. Specifically, Figure 7 (a) schematically shows a cross section of the irradiation device 10 along the ZX plane passing through the isocenter 8 of the patient 6 , Figure 7 (b) schematically shows a cross section of the irradiation device 10 along a YZ plane passing through the isocenter 8 of the patient 6 .

[0065] Figure 7 The irradiation device 10 shown is Figure 2 The irradiation device 10 shown in FIG. 1 is different in that it includes a plurality of irradiation nozzles 1 . Figure 7 In the example of FIG. 1 , two irradiation nozzles 1A to 1B are provided as the irradiation nozzle 1 .

[0066] The irradiation nozzles 1A to 1C are disposed at the same positions as the plurality of irradiation start positions in the first embodiment. Figure 2 The irradiation port 5A is connected to the irradiation nozzle 1B. Figure 2 The irradiation port 5B is connected to the irradiation nozzle 1C. Figure 2 Connect the irradiation port 5C.

[0067] The X-ray imaging device is arranged at a position deviated from the line connecting the irradiation nozzle 1 and the isocenter 8 with respect to each irradiation nozzle 1, and the FPD 2 is arranged upstream of the isocenter 8 in the trajectory of the particle beam. In this case, the FPD can be set at an angle range of 100° to 100°, which is the range in which the FPD 2 can be arranged. Figure 5The FPDs of the first embodiment shown have the same settable angle range.

[0068] In addition, the number of the irradiation nozzles 1 is not particularly limited, and for example, there may be two irradiation nozzles.

[0069] In the present embodiment as well, it is possible to suppress the detection of a secondary particle beam scattered by radiation by the FPD 2, and thus it is possible to suppress the influence of radiation on the X-ray imaging device.

[0070] (Fourth Embodiment)

[0071] In the first embodiment, the irradiation nozzle 1 is rotated by 90°, but in the present embodiment, the irradiation nozzle 1 is rotated by 180°.

[0072] Figure 8 : is a diagram showing the FPD installation angle range of the FPD 2 when the irradiation nozzle 1 is rotated 180 degrees. Specifically, Figure 8 (a) shows the FPD setting angle range on the XY plane, Figure 8 (b) shows the FPD setting angle range on the XZ plane, Figure 8 (c) shows the FPD settable angle range on the YZ plane.

[0073] exist Figure 8 In the example, the irradiation nozzle 1 is rotated 180° from the vertical upper direction (Z direction positive direction) to the vertical lower direction (Z direction negative direction). Figure 7 Although not shown in the figure, there are five irradiation ports 5, which are respectively oriented vertically downward, in a direction approximately at an angle of 45 degrees relative to the horizontal direction, in a substantially horizontal direction, in a direction approximately at an angle of -45 degrees relative to the horizontal direction, and vertically upward. The irradiation nozzle 1 is moved by the nozzle rotating mechanism 3 so as to be connected to any of the five irradiation ports 5.

[0074] exist Figure 8 In the case of XY plane direction, Figure 8 As shown in (a), the range of the deflection angle from -90° to 90° (that is, the range in which the X direction is positive) becomes the FPD setting angle range. And, in the XZ plane direction, as Figure 8 As shown in (b), only the position with a deflection angle of 0° is within the FPD setting angle range. Figure 8 As shown in (c), only the position with a deviation angle of 0° is within the FPD installable angle range.

[0075] In the present embodiment as well, it is possible to suppress the detection of a secondary particle beam scattered by radiation by the FPD 2, and thus it is possible to suppress the influence of radiation on the X-ray imaging device.

[0076] The above-mentioned embodiments of the present disclosure are examples for explaining the present disclosure, and are not intended to limit the scope of the present disclosure to the above-mentioned embodiments. A person skilled in the art can implement the present disclosure in various ways without departing from the scope of the present disclosure.

[0077] Explanation of symbols

[0078] 1, 1A, 1B, 1C—irradiation nozzle, 2, 2A, 2B—FPA, 3—nozzle rotation mechanism, 4—treatment table, 4A—top plate, 4B—arm, 5, 5A, 5B, 5C—irradiation port, 6—patient, 7, 7A, 7B—X-ray tube, 8—isocenter, 10—irradiation device, 20—accelerator, 21—linear accelerator, 22—synchrotron, 30—beam delivery system, 31, 31A—deflection magnets, 100—radiotherapy device.

Claims

1. A radiotherapy device, characterized in that: have: an irradiation unit that irradiates radiation to an irradiation object; and a photographing device for photographing the irradiated object; The imaging device includes a light source unit for irradiating the illumination object with light for imaging, and a detection unit for detecting the light via the illumination object. The light source unit and the detection unit are arranged at positions offset from a line connecting the isocenter of the radiation and the irradiation unit. The detection unit is arranged on a reference plane or at a position closer to the irradiation unit than the reference plane. The reference plane is a plane that passes through the isocenter and is orthogonal to a line connecting the isocenter and the irradiation unit.

2. The radiotherapy apparatus according to claim 1, wherein: The device further comprises a moving mechanism for moving the irradiation unit to be placed at any one of a plurality of irradiation start positions. The detection unit is disposed on the reference plane or at a position closer to the irradiation unit than the reference plane with respect to all of the plurality of irradiation start positions.

3. The radiotherapy apparatus according to claim 1, wherein: There are multiple irradiation parts. The detection unit is disposed on the reference plane or at a position closer to the irradiation unit than the reference plane with respect to each of the plurality of irradiation units.

4. The radiotherapy apparatus according to claim 1, wherein: The above-mentioned photographing device comprises a combination of two above-mentioned light source units and the above-mentioned detection unit, Two lines connecting the light source unit and the detection unit of each of the two combinations are substantially perpendicular to each other, and the imaging device is arranged on the reference plane.

5. The radiotherapy apparatus according to claim 1, wherein: The light source section irradiates the light while the irradiation section irradiates the radiation.

6. The radiotherapy apparatus according to claim 1, wherein: The above-mentioned radiation is a carbon beam.

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