JP2011189016A - Radiotherapy apparatus and method of acquiring irradiation field confirmation image of radiotherapy apparatus - Google Patents

Abstract

An object of the present invention is to increase the contrast of only a region serving as a reference necessary for comparison with an X-ray CT image taken in a treatment plan in an irradiation field confirmation image.
A radiation therapy apparatus includes a radiation irradiation means for irradiating radiation for radiation field confirmation, a patient support for supporting a patient, a radiation image detector for outputting a radiation field confirmation image, and a radiation image detector for a patient. The detector moving means that moves so as to come in contact with and away from the support base and the contrast of the irradiation field confirmation image are obtained, and the detector is moved so that the contrast of the contour portion of the body tissue included in the irradiation field confirmation image is maximized. Control means for driving the means to move the radiation image detector.
[Selection] Figure 1

Description

  The present invention relates to a radiotherapy apparatus that irradiates an affected area of a patient with therapeutic radiation, a radiotherapy apparatus that acquires an irradiation field confirmation image used for confirming the position of the affected area, and a method for acquiring the irradiation field confirmation image.

  Conventionally, radiation that is treated by irradiating an affected area of a patient with an X-ray or electron beam emitted from a radiation generator using an electron accelerator such as a linear accelerator or a microtron, or a particle beam emitted from a cyclotron or a synchrotron A therapeutic device is used. Radiation therapy is performed by damaging cells in an affected area of a patient with therapeutic radiation, and it is necessary to accurately irradiate the affected area with radiation so as not to damage normal cells.

  In radiotherapy, the position and shape of the affected area are imaged in advance by diagnostic X-ray CT to prepare a treatment plan. Prior to the treatment by the radiotherapy apparatus, the therapeutic radiation having a reduced intensity so as not to damage normal cells is irradiated to the region including the affected area, and the transmitted radiation is photographed to obtain an irradiation field confirmation image. To get. The irradiation field confirmation image is an image used for matching the irradiation position of the therapeutic radiation with the position of the affected part. Specifically, the irradiation field confirmation image is compared with the image obtained by the X-ray CT taken in the treatment plan. However, the patient is moved and aligned so that both images match. Radiotherapy (irradiation of therapeutic radiation with a normal intensity for treatment) is performed after accurately positioning the affected part and the therapeutic radiation (for example, Patent Document 1).

  When comparing the irradiation field confirmation image and the X-ray CT image taken in the treatment plan, the comparison is made by comparing the position of a body tissue (for example, bone) that is easily checked on the irradiation field confirmation image. In other words, the position of the patient is moved so that the position of the reference internal tissue exactly matches between these images. Since the correspondence between the images matches, the position of the affected part obtained by the treatment plan can be specified also in the radiotherapy apparatus, so that it is possible to accurately irradiate the affected part with the therapeutic radiation.

The accuracy of the irradiation position on the affected part of the therapeutic radiation is directly affected by the accuracy of matching between the irradiation field confirmation image and the X-ray CT image taken in the treatment plan. Therefore, a clear image is required for the irradiation field confirmation image to be compared with the X-ray CT image. However, as will be described later, the contrast of the irradiation field confirmation image is lower than that of the X-ray CT image. A high irradiation field confirmation image is required.

  As a technique for increasing the contrast of an X-ray image, there is known a method of enhancing the contour of an affected area by utilizing the bending of the X-ray at the boundary surface when there is a density difference between the affected area and its surrounding substances. (For example, Patent Document 2).

JP 2007-61438 A JP 2006-95327 A

  Conventional radiation field confirmation images use therapeutic radiation with reduced intensity, but generally its radiation energy is 10 times higher than diagnostic radiation. Therefore, most of the radiation passes through the patient's body, and it is difficult to observe the difference in radiation absorption rate between the affected area and the surrounding body tissue. That is, the irradiation field confirmation image is an image having a low contrast as compared with the diagnostic image. In addition, when the patient is irradiated with high-energy radiation, the intensity of the radiation scattered inside the patient's body also increases dramatically, and this scattered radiation further reduces the contrast of the irradiation field confirmation image and lowers the resolution. It will also be a factor.

  If the contrast of the irradiation field confirmation image is low, it becomes difficult to compare the image with the X-ray CT image taken in the treatment plan, and the patient's affected area and the therapeutic radiation cannot be accurately aligned. In such a case, in conventional radiotherapy, an irradiation region is defined with a certain margin around the affected area and irradiated with therapeutic radiation. In such a method, normal cells around the affected area are damaged. There is a problem that side effects on patients are increased.

  As a technique for increasing the contrast of an X-ray image, techniques such as Patent Document 2 are known as described above, but these are effective when using diagnostic radiation with relatively low energy, For example, when it is applied as a means for obtaining an irradiation field confirmation image, not only the affected part but also the outline of the surrounding body tissue is enhanced, resulting in an irradiation field confirmation image that is difficult to compare with an image by X-ray CT.

  The present invention has been made to solve the above problems. That is, according to the present invention, in the irradiation field confirmation image by the therapeutic radiation, the contrast of only the internal tissue that is a reference necessary for comparison with the image by the X-ray CT imaged by the treatment plan is increased, and the X-ray imaged by the treatment plan is obtained. It is an object to make comparison with an image by CT easy and accurate.

  In order to achieve the above object, a radiotherapy apparatus according to the present invention comprises a radiation irradiation means for irradiating an affected area with radiation for confirming an irradiation field having a lower intensity than therapeutic radiation, a patient support table for supporting a patient, a patient and A radiation image detector that detects radiation for confirming the irradiation field transmitted through the patient support table and outputs an irradiation field confirmation image, and the radiation image detector to the patient support table along the optical axis of the radiation for radiation confirmation The detector moving means that moves so as to come in contact with and away from each other and the contrast of the irradiation field confirmation image are obtained, and the detector moving means is driven so that the contrast of the contour portion of the body tissue included in the irradiation field confirmation image is maximized. Control means for moving the radiation image detector. With such a configuration, it is possible to increase the contrast of only the desired in-vivo tissue in the irradiation field confirmation image, and it is possible to easily and accurately compare the image with the X-ray CT image captured in the treatment plan.

  The radiotherapy apparatus further includes patient support table moving means for moving the patient support table in a direction perpendicular to the optical axis of radiation for confirming the radiation field, and the control means includes in-vivo tissue included in a reference image created in advance. It is preferable to move the patient support moving means so that the position of the body and the position of the body tissue included in the irradiation field confirmation image coincide with each other. With such a configuration, it is possible to accurately perform the matching between the irradiation field confirmation image and the X-ray CT image captured in the treatment plan.

  The therapeutic radiation and the radiation for confirming the irradiation field are preferably synchrotron radiation having a critical energy value of 15 keV or more. With such a configuration, it is possible to use both therapeutic radiation and radiation for confirming the irradiation field.

  The radiation irradiating means includes an electron accelerator for accelerating electrons, an X-ray conversion target for irradiating X-rays when the accelerated electrons collide, and a cooling means for cooling the X-ray conversion target. The beam diameter is preferably larger than 0.1 mm and smaller than 0.5 mm. With such a configuration, it is possible to obtain an irradiation field confirmation image having a resolution substantially equal to the resolution of the image obtained by the X-ray CT imaged in the treatment plan.

  From another point of view, the radiation field image acquisition method of the radiotherapy apparatus of the present invention includes a step of irradiating an affected area with radiation for confirming an irradiation field having a lower intensity than the therapeutic radiation, and the patient and the patient support base. Detecting the irradiation field confirmation radiation with a radiation detector to obtain an irradiation field confirmation image, and bringing the radiation image detector into and out of contact with the patient support table along the optical axis of the radiation field confirmation radiation And a step of obtaining a contrast of the irradiation field confirmation image, and a step of moving the radiation image detector so that the contrast of the contour portion of the in-vivo tissue included in the irradiation field confirmation image is maximized.

  As described above, according to the present invention, in the irradiation field confirmation image, the contrast of only the internal body part that is a reference necessary for comparison with the X-ray CT image captured in the treatment plan is increased, and the irradiation field confirmation image and the X Comparison with an image by line CT can be easily and accurately performed.

It is a schematic block diagram which shows the structure of the radiotherapy apparatus which concerns on the 1st Embodiment of this invention. It is a figure explaining a mode that the radiation for treatment of the radiotherapy apparatus concerning a 1st embodiment of the present invention is bent in a patient's body, and a relation between a position of an X-ray image sensor, and radiation intensity. It is a flowchart of the irradiation field confirmation image acquisition routine of the radiotherapy apparatus which concerns on the 1st Embodiment of this invention. It is a schematic block diagram which shows the structure of the radiotherapy apparatus which concerns on the 2nd Embodiment of this invention.

  A radiotherapy apparatus according to an embodiment of the present invention will be described below. FIG. 1 is a schematic configuration diagram of a radiation therapy apparatus 1 according to the first embodiment of the present invention.

  The radiotherapy apparatus 1 according to the present embodiment includes a radiation generator 10, an absorber 21, an X-ray shutter 22, a multi-leaf collimator 30, a patient support base 50, an X-ray image sensor 60, a controller 70, a display device 80, and the like. . The patient 40 who receives radiation therapy is supported and fixed on the patient support base 50. In FIG. 1, for convenience of explanation, the patient 40 and the patient support base 50 are illustrated separately from each other, but the patient 40 is actually supported in close contact with the patient support base 50.

  The radiation generator 10 includes a storage ring (synchrotron) 11 and a deflecting electromagnet 12 that store high-energy electrons or positrons. By generating a magnetic field in the deflection electromagnet 12, the trajectory of high energy electrons or positrons stored in the storage ring 11 is bent, and high intensity emitted light 14 is emitted from the light source 13 in the tangential direction of the storage ring 11. . The emitted light 14 is an electromagnetic wave that has a band from visible light to an X-ray region, has high directivity like a laser beam, and travels almost in parallel. In the present embodiment, the emitted light 14 has an energy spectrum with a critical energy value of 15 keV or more.

  The absorber 21 is disposed on the optical axis of the radiated light 14 emitted from the light source 13 of the radiation generator 10, and has a low energy component (that is, a component having a long wavelength in the X-ray) in the X-ray region from the radiated light 14. The therapeutic radiation 15 which consists of only the X-ray area | region of the component which absorbs and has high energy is radiate | emitted. Since the radiotherapy apparatus 1 of the present embodiment uses X-rays having energy of about 80 keV or more, the absorber 21 of the present embodiment also absorbs X-ray components of 80 keV or less from the emitted light 14.

  The X-ray shutter 22 is a mechanical shutter composed of shutter blades such as tungsten, and is disposed on the optical axis of the therapeutic radiation 15 emitted from the absorber 21 and connected to a controller 70 described later. The X-ray shutter 22 controls the irradiation time of the therapeutic radiation 15 in accordance with instructions from the controller 70.

  The multi-leaf collimator 30 includes leaves 31 to 34 that are shielding plates such as tungsten. A horizontal beam width of the therapeutic radiation 15 is defined by a slit composed of the leaf 31 and the leaf 32 arranged in the horizontal direction (in FIG. 1), and the leaf 33 arranged in the vertical direction (in FIG. 1). And the vertical beam width of the therapeutic radiation 15 is defined by the slit formed by the leaf 34. The multi-leaf collimator 30 is connected to a controller 70 which will be described later, and drives a drive unit (not shown) according to an instruction from the controller 70 to control the interval between the leaf 31 and the leaf 32 (slit width) and the interval between the leaf 33 and the leaf 34. . By controlling the distance between the leaf 31 and the leaf 32 and the distance between the leaf 33 and the leaf 34, the irradiation field (irradiation region) of the therapeutic radiation 15 is determined.

  The patient support 50 is made of carbon fiber or the like so as not to absorb radiation, and supports and fixes the patient 40. The patient support base 50 has a motor 55 connected to the controller 70, and the motor 55 moves in the horizontal direction and the vertical direction in FIG. By moving the patient support 50 that supports the patient 40, the irradiation position of the therapeutic radiation 15 and the position of the affected part are adjusted.

  The X-ray image sensor 60 has an X-ray detection surface in which pixels are two-dimensionally arranged on the side facing the patient support base 50, and the therapeutic radiation 15 transmitted through the patient 40 and the patient support base 50 is detected on the X-ray detection surface. This is an image sensor that detects and outputs an irradiation field confirmation image to the controller 70. The X-ray image sensor 60 has a motor 65 connected to the controller 70, and the motor 65 moves in a direction approaching or separating from the patient support base 50 by driving a moving mechanism (not shown) according to an instruction from the controller 70. The X-ray image sensor 60 moves while outputting the irradiation field confirmation image, and is arranged at a position where the contrast of the contour portion of the body tissue included in the irradiation field confirmation image is maximized as will be described later.

  The display device 80 is connected to the controller 70 and displays an irradiation field confirmation image output from the X-ray image sensor 60 in accordance with an instruction from the controller 70.

  As described above, the controller 70 is connected to the X-ray shutter 22, the multi-leaf collimator 30, the motor 55 of the patient support base 50, the X-ray image sensor 60, the motor 65 of the X-ray image sensor 60, and the display device 80. To control. Further, as will be described later, the contrast of the irradiation field confirmation image output from the X-ray image sensor 60 is obtained, and the X-ray image sensor 60 is set so that the contrast of the contour portion of the body tissue included in the irradiation field confirmation image is maximized. The motor 65 is driven.

  FIG. 2 is a diagram for explaining the relationship between the manner in which the therapeutic radiation of the radiation therapy apparatus according to the first embodiment of the present invention bends within the patient and the position of the X-ray image sensor and the radiation intensity. FIG. 2A is a view schematically showing a state in which the therapeutic radiation 15 in FIG. 1 is bent in the body of the patient 40, and shows a horizontal section in FIG. In FIG. 2A, the in-vivo tissue 42 is a tissue in the body of the patient 40 that is used as a reference when comparing the irradiation field confirmation image with the image obtained by the X-ray CT taken in the treatment plan. For example, a bone having a high tissue density. Position A, position B, and position C indicate the position of the light receiving surface of the X-ray image sensor 60, and the radiation intensity I received by the X-ray image sensor 60 when the X-ray image sensor 60 is disposed at each position. (B), (c) and (d) of FIG. Here, in FIGS. 2B, 2C, and 2D, it is assumed that the radiation intensity I is higher toward the left side in the figure. In FIG. 2A, the patient support base 50 is omitted for convenience of explanation.

  The therapeutic radiation 15 emitted from the multi-leaf collimator 30 is substantially parallel radiation. When the therapeutic radiation 15 is irradiated to the patient 40, the therapeutic radiation 15 proceeds while being absorbed by the body tissue 42 of the patient 40, and the therapeutic radiation 15 that could not be absorbed by the body tissue 42 passes through the body of the patient 40. To Penetrate. And the therapeutic radiation 15 which permeate | transmitted the inside of the patient 40 is detected by the X-ray image sensor 60 installed outside the body. The amount of therapeutic radiation 15 absorbed in the body of the patient 40 varies depending on the body tissue of the patient 40 through which the therapeutic radiation 15 passes. In particular, the body tissue 42 having a high tissue density absorbs much more radiation than other tissues. Therefore, the body tissue 42 is imaged by imaging the distribution of the radiation intensity detected by the X-ray image sensor 60. It becomes possible.

  When the body tissue 42 is a bone, the shape thereof is a substantially cylindrical shape, and the cross section thereof is a substantially elliptical shape. In addition, the bone has a higher density than the surrounding soft tissue, and the refractive index for X-rays is smaller than 1. Therefore, when the therapeutic radiation 15 passes through the body tissue 42 (bone), the bone functions as a kind of lens, and as shown in FIG. The bending radiation 16 is bent in the direction.

  Here, when the X-ray image sensor 60 is disposed at the position A, the radiation detected by the X-ray image sensor 60 is the therapeutic radiation 15 and the bending radiation 16 that pass straight through the body of the patient 40. Since the bending amount of the bending radiation 16 at A (the shift amount with respect to the case where the radiation goes straight) is small, it is observed as substantially parallel radiation. Therefore, the distribution of the radiation intensity I detected by the X-ray image sensor 60 is substantially the same as the transmission amount of the therapeutic radiation 15 that passes straight through. In the case where the thickness of the body tissue 42 is gradually reduced from the center to the periphery, the radiation intensity I corresponding to the periphery of the body tissue 42 is a gentle curve as shown in FIG. (Inside arrow 72). As a result, the irradiation field confirmation image obtained from this radiation distribution is a blurred image in which the contour portion (arrow 72) of the body tissue 42 is blurred.

  Further, when the X-ray image sensor 60 is arranged at the position B, unlike the case where the X-ray image sensor 60 is arranged at the position A, the bending amount of the bending radiation 16 at the position B becomes sufficiently large. Accordingly, in the distribution of the radiation intensity I received by the X-ray image sensor 60, as shown in FIG. 2C, the therapeutic radiation 15 that passes straight through the outside of the body tissue 42 and the bending radiation 16 overlap. The intensity is increased at the portion (arrow 74), and the intensity is decreased at the portion where the bending radiation 16 is generated (arrow 75). The position B is a position where all the generated bending radiation 16 and the therapeutic radiation 15 that travels straight through the outside of the body tissue 42 overlap each other outside the contour portion (arrow 72) of the body tissue 42. Since the bending radiation 16 is generated inside the peripheral portion of the body tissue 42, the distribution of the radiation intensity I received by the X-ray image sensor 60 is bordered by the contour portion (arrow 72) of the body tissue 42. It is observed that the strength is strong outside the contour portion and the strength is weak inside the contour portion. As a result, the irradiation field confirmation image obtained from this radiation distribution is an image in which the contour portion (arrow 72) of the body tissue 42 is clearly emphasized.

  Further, when the X-ray image sensor 60 is disposed at the position C, the bending amount of the bending radiation 16 at the position C is further larger than the bending amount of the bending radiation 16 at the position B. Therefore, the position of the portion (arrow 74) where the therapeutic radiation 15 and the bending radiation 16 that pass straight through the outside of the body tissue 42 overlap is moved away from the contour portion (arrow 72) of the body tissue 42, and FIG. The radiation intensity distribution as shown in FIG. That is, the therapeutic radiation 15 that passes straight outside the body tissue 42 and the bending radiation 16 overlap with each other and the strength is increased (arrow 74), and the bending radiation 16 is generated and the strength is decreased (arrow 75). ), And the radiation intensity I corresponding to the outer periphery of the contour portion (arrow 72) of the body tissue 42 is a gentle curve (outside the arrow 72). Here, the therapeutic radiation 15 that passes straight outside the body tissue 42 and the bending radiation 16 overlap each other and the strength is increased (arrow 74), and the bending radiation 16 is generated and the strength is decreased (arrow). 75) is observed as a line width indicating the outline of the body tissue 42 on the irradiation field confirmation image, the irradiation field confirmation image obtained from the radiation distribution at position C is the radiation distribution at position B. Compared with the irradiation field confirmation image obtained from the above, the emphasis of the contour portion (arrow 72) of the in-vivo tissue 42 is weak, and the image becomes unclear with a wide contour line width.

  As described above, when the X-ray image sensor 60 is arranged at the position B, the contour portion (arrow 72) of the body tissue 42 in the irradiation field confirmation image is most emphasized, and the contrast (arrow 72) of the contour portion of the body tissue 42 is shown. (The difference between the maximum value and the minimum value of the radiation intensity I on the line indicated by) is also maximum.

  According to the experiment by the inventors of the present invention, the bending amount of the bending radiation 16 depends on the shape of the body tissue 42 but is proportional to the distance between the body tissue 42 and the X-ray image sensor 60 and is several tens of μm / m. It is as follows. Further, the sensor resolution of the X-ray image sensor 60 of the present embodiment is about 20 to 30 μm. Therefore, if the contour enhancement effect of the body tissue 42 by the bending radiation 16 is to be obtained, at least the amount of bending needs to exceed the sensor resolution, and therefore the distance between the body tissue 42 and the X-ray image sensor 60 is 1 m or more. Become. However, for example, if the sensor resolution of the X-ray image sensor 60 is higher, the distance between the in-vivo tissue 42 and the X-ray image sensor 60 can be shortened.

  The radiotherapy apparatus 1 according to the present embodiment is configured to place the X-ray image sensor 60 at the position B and to emphasize the contour of the body tissue 42 on the irradiation field confirmation image by using the bending radiation 16 described above. Has been.

  FIG. 3 is a flowchart of an irradiation field confirmation image acquisition routine executed by the controller 70 of the radiation therapy apparatus 1 according to this embodiment.

  When the irradiation field confirmation image acquisition routine starts, the controller 70 initializes the position of the X-ray image sensor 60 (S101). Specifically, the controller 70 drives the motor 65 of the X-ray image sensor 60 to bring the X-ray image sensor 60 to a predetermined position closest to the patient support base 50 (for example, a position 50 cm away from the patient support base 50). Stop.

  Next, the controller 70 controls the X-ray shutter 22 so that the intensity of the therapeutic radiation 15 becomes a necessary intensity for obtaining a predetermined irradiation field confirmation image (S103).

  Next, the controller 70 controls the leaves 31 to 34 of the multi-leaf collimator 30 so that the irradiation field is in a predetermined range, and determines the horizontal and vertical beam widths of the therapeutic radiation 15 (S105). ).

  Next, the controller 70 drives the motor 55 of the patient support base 50 so that the affected part of the patient 40 enters the irradiation field determined in step S105, and moves the patient support base 50 in the horizontal direction and the vertical direction (S107). .

  Next, the controller 70 acquires image data (pixel luminance data) for one screen output from the X-ray image sensor 60 (S109), and performs contrast calculation (S111). In step S111, the controller 70 obtains the maximum value (maximum luminance value) and minimum value (minimum luminance value) of the luminance value from the image data acquired in S109, and has the position of the pixel having the maximum luminance value and the minimum luminance value. The position of the pixel is specified, and the contrast value in one screen is obtained from the difference between the maximum value and the minimum value of the luminance values. Then, the position of the pixel having the maximum luminance value, the position of the pixel having the minimum luminance value, and the contrast value are stored in a memory (not shown) in the controller 70 in association with the information on the moving distance of the X-ray image sensor 60. (S111).

  Next, the controller 70 drives the motor 65 of the X-ray image sensor 60 to move the X-ray image sensor 60 by a predetermined amount (for example, 10 cm) in a direction away from the patient support base 50. Then, it is determined whether or not the movement of a predetermined distance (for example, 1 m) is completed (S115). If it is determined that the movement of the predetermined distance has been completed, the process proceeds to step S117 (S115: YES). If it is determined that the movement of the predetermined distance has not been completed, the process returns to S109, and the predetermined distance is reached. Steps S109 to S115 are repeated until the movement is completed (S115: NO).

  When the X-ray image sensor 60 completes the movement of the predetermined distance, the controller 70 reads the position of the pixel having the maximum luminance value, the position of the pixel having the minimum luminance value, and the contrast value stored in the memory in step S111, and the contrast value. Is the maximum and the moving distance of the X-ray image sensor 60 when the distance between the pixel having the maximum luminance value and the pixel having the minimum luminance value is the shortest is obtained (S117). Then, the controller 70 moves the X-ray image sensor 60 again to the moving distance of the X-ray image sensor 60 obtained in S117 (S119), and ends the irradiation field confirmation image acquisition routine.

  The stop position of the X-ray image sensor 60 after completion of the irradiation field confirmation image acquisition routine corresponds to the position B in FIG. 2A, the contour portion of the body tissue 42 is most emphasized, and the contrast of the contour portion of the body tissue 42 is contrasted. Is the position where an irradiation field visual field confirmation image with the maximum can be obtained. The controller 70 compares the position of the in-vivo tissue 42 of the irradiation field confirmation image acquired at this position with the position of the in-vivo tissue 42 of the image obtained by the X-ray CT imaged in the treatment plan so that the positions of both coincide with each other. The motor 55 of the patient support base 50 is driven. Then, after matching the position of the in-vivo tissue 42 in the irradiation field confirmation image with the position of the in-vivo tissue 42 in the image obtained by the X-ray CT taken in the treatment plan, the controller 70 adds the position information of the affected part obtained in the treatment plan. Based on this, the therapeutic radiation 15 is applied to the affected area. Specifically, the multi-leaf collimator 30 is controlled so that the position of the affected part determined in the treatment plan becomes an irradiation field, and the X-ray shutter 22 is controlled to output the therapeutic radiation 15 having the intensity necessary for the treatment. .

  As described above, according to the radiation therapy apparatus 1 of the present embodiment, an image of the in-vivo tissue 42 with high contrast can be obtained in the irradiation field confirmation image. Comparison with an image by CT can be performed easily and accurately. Therefore, alignment between the affected part of the patient 40 and the therapeutic radiation 15 can be performed accurately.

  Although the radiation generator 10 of this embodiment was demonstrated as the storage ring (synchrotron) 11 which accumulate | stores a high energy electron or a positron, this invention is not limited to this embodiment. For example, the radiation generator 10 can be a radiation generator using an electron accelerator such as a linear accelerator or a microtron.

  FIG. 4 is a schematic configuration diagram showing a configuration of a radiation therapy apparatus 1 ′ according to the second embodiment of the present invention. The radiation generator 10 ′ is different from the radiation therapy apparatus 1 according to the first embodiment of the present invention in that an electron accelerator 110 and an X-ray conversion target 120 are used.

  Electrons are accelerated to an energy of 1 MeV or more and output by the electron accelerator 110. Then, the electrons output from the electron accelerator 110 collide with the X-ray conversion target 120, so that X-rays are irradiated. Here, the size of the X-ray light source 13 ′ is substantially the same as the beam diameter of the X-ray conversion target 120.

  In conventional radiotherapy, the beam diameter of an X-ray light source is generally about 2 mm. This is because, in order to obtain a sufficient radiation intensity, it is necessary to make electrons having a somewhat large beam diameter incident on the X-ray conversion target. On the other hand, in the field of radiation diagnosis, the beam diameter of an X-ray light source is generally about 0.5 mm. This is because the radiation intensity is not as high as that of therapeutic radiation, and the influence of penumbra increases as the size of the light source increases and the sharpness of the image (the degree of blurring of the outline) deteriorates.

  In the radiotherapy apparatus 1 ′ according to the present embodiment, the electron accelerator 110 allows the resolution of the irradiation field confirmation image to be equal to or higher than the resolution of the radiation diagnosis image (approximately 0.1 mm) by the electron accelerator 110. Electrons accelerated by energy are made to enter the X-ray conversion target 120 with a beam diameter of 0.5 mm or less. However, when the beam diameter of the accelerated electrons is reduced, the intensity of the therapeutic radiation 15 is lowered, so that the beam diameter needs to be 0.1 mm or more. With such a configuration, the radiation intensity for performing radiotherapy is maintained, and the deterioration of contrast when acquiring an irradiation field image is prevented. Note that when high-energy electrons with a narrowed beam diameter are incident on the X-ray conversion target 120, the X-ray conversion target 120 generates heat. Therefore, it is necessary to attach a cooling device 130 to the X-ray conversion target 120.

DESCRIPTION OF SYMBOLS 1, 1 'Radiation therapy apparatus 10, 10' Radiation generator 11 Accumulation ring 12 Bending electromagnet 13, 13 'X-ray light source 14 Radiation light 15 Treatment radiation 21 Absorber 22 X-ray shutter 30 Multi-leaf collimator 40 Patient 50 Patient support Table 55, 65 Motor 60 X-ray image sensor 70 Controller 80 Display device 110 Electron accelerator 120 X-ray conversion target 130 Cooling device

Claims (5)

In a radiotherapy apparatus that performs treatment by irradiating therapeutic radiation to an affected area of a patient,
Radiation irradiating means for irradiating the affected area with radiation for radiation field confirmation having a lower intensity than the therapeutic radiation;
A patient support for supporting the patient;
A radiation image detector that detects the radiation for confirming the irradiation field transmitted through the patient and the patient support, and outputs an irradiation field confirmation image;
Detector moving means for moving the radiological image detector so as to be in contact with and away from the patient support along the optical axis of the radiation for confirming the irradiation field;
Control means for obtaining the contrast of the irradiation field confirmation image and driving the detector moving means to move the radiation image detector so that the contrast of the contour portion of the body tissue included in the irradiation field confirmation image is maximized. When,
A radiation therapy apparatus comprising: The radiotherapy apparatus further comprises patient support table moving means for moving the patient support table in a direction perpendicular to the optical axis of the radiation field confirmation radiation,
The control means moves the patient support stage moving means so that the position of the in-vivo tissue included in the reference image prepared in advance matches the position of the in-vivo tissue included in the irradiation field confirmation image. The radiotherapy apparatus according to claim 1.   The radiotherapy apparatus according to claim 1 or 2, wherein the therapeutic radiation and radiation for confirming the irradiation field are synchrotron radiation having a critical energy value of 15 keV or more. The radiation irradiating means includes an electron accelerator that accelerates electrons, an X-ray conversion target that irradiates X-rays when the accelerated electrons collide, and a cooling means that cools the X-ray conversion target.
The radiotherapy apparatus according to claim 1 or 2, wherein a beam diameter of the accelerated electrons is larger than 0.1 mm and smaller than 0.5 mm. An irradiation field image acquisition method for a radiotherapy apparatus that performs treatment by irradiating therapeutic radiation to an affected area of a patient supported on a patient support table,
Irradiating the affected area with radiation for confirming an irradiation field having a lower intensity than the therapeutic radiation; and
Detecting the radiation for confirming the irradiation field transmitted through the patient and the patient support with a radiation detector to obtain an irradiation field confirmation image;
Moving the radiation image detector so as to be in contact with and away from the patient support along the optical axis of the radiation for confirming the irradiation field;
Determining the contrast of the irradiation field confirmation image, and moving the radiation image detector so that the contrast of the contour portion of the body tissue included in the irradiation field confirmation image is maximized;
An irradiation field image acquisition method for a radiation therapy apparatus.

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