Subject positioning method and radiation therapy device using same

Abstract

The brain is slightly off-centered within the skull. In addition, current patient immobilization implements do not provide sufficient position (posture) reproducibility, and aligning a device in order to accurately irradiate a treatment target site in the brain takes a long time.　A subject positioning method according to the present invention includes: a step for obtaining a treatment planning image of a subject immobilized relative to a reference plane in order to make a treatment plan for the subject; a step for obtaining a pre-treatment image of the subject immobilized relative to the reference plane immediately prior to treatment of the subject; a step for determining a posture correction value with which the cerebral sulci in the treatment planning image and the cerebral sulci in the pre-treatment image can be made to overlap; and a step for correcting the posture of the subject during treatment on the basis of the posture correction value. In the subject positioning method, the cerebral sulci in the treatment planning image and the pre-treatment image are adjusted to coincide with each other, whereby radiation can be accurately applied to the treatment target site.

Description

Subject positioning method and radiation therapy device using the method

[0001] The present invention relates to a method for improving the reproducibility of a patient's position during radiation therapy and a radiation therapy apparatus utilizing this method.

[0002] In radiation therapy, various types of high-precision radiation therapy, such as stereotactic radiation therapy, intensity-modulated radiation therapy, rotational intensity-modulated radiation therapy, and particle beam therapy, are becoming increasingly common. While these therapies can deliver high doses of radiation to the target tumor, there is a problem in that deviation from the irradiation position can have a significant impact on normal tissue.

[0003] This problem is one of the unavoidable problems inherent in the radiation therapy procedure. In radiation therapy, the patient is first fixed on a table with a reference surface, and CT images are taken. A treatment plan, including the determination of irradiation angle and dose, is then created based on these images. The actual radiation treatment is then administered.

[0004] However, treatment planning takes several days or more. As a result, the patient's position relative to the reference plane when the first image is taken will be different from when the radiation is actually irradiated. Therefore, an operation called "patient positioning" is required to align the patient's position relative to the reference plane immediately before irradiation with the position when the CT image for the treatment plan was taken.

[0005] Patent Document 1 discloses a subject positioning device comprising: a photographed image acquisition unit that acquires a photographed image, which is photographed using a fluoroscopic imaging device when positioning the subject, and which is a three-dimensional volume image showing a first image of an index portion that serves as an index for positioning the subject, a second image of a non-index portion other than the index portion, and an image in which the first image and the second image are superimposed; a three-dimensional image acquisition unit that acquires a three-dimensional volume image including an image of the subject before positioning the subject; a region identification unit that identifies a specific region in the photographed image in which the second image and the superimposed image are shown based on three-dimensional model information of the non-index portion; an image processing unit that performs image processing to erase the identified second image and the superimposed image from the photographed image based on the specific region; and a positioning unit that performs positioning of the subject by comparing the first image of the photographed image after the image processing with an image of a reference image that is a three-dimensional volume image acquired by the three-dimensional image acquisition unit before positioning the subject.

[0006] This subject positioning device generates a DRR image showing only the patient's bones from the CT images used during treatment planning.Then, the patient table is moved so that the positions of the bones shown in the X-ray images during treatment coincide with the positions of the bones in the DRR image, thereby matching the patient's posture relative to the reference plane used during treatment planning with the patient's posture during treatment.

[0007] Japanese Patent Application Laid-Open No. 2021-94460

[0008] High accuracy is required for positioning the target area for treatment, such as a tumor, in order to minimize damage to normal tissue. Currently, "patient positioning" with an accuracy of 1 mm or less on the scale and 0.5 degrees or less on the angle is required.

[0009] However, the brain is like tofu floating in a solid container, and its position relative to the skull changes daily due to changes in the environment, body size, and fixation, exceeding the range of accuracy described above. Therefore, "patient positioning" based on bones is not sufficient to meet the current required accuracy, and normal tissue will be damaged to the extent that the brain's position differs between when the treatment was planned and when it was actually performed. Furthermore, during current treatment, it is necessary to set a margin that includes normal tissue and takes into account the difference in brain position.

[0010] Furthermore, when there are multiple areas of the brain to be treated, it is extremely difficult to "position the patient" so that all of the treatment areas are accurately aligned. Therefore, it may be necessary to irradiate while aligning each area one by one, and just preparing for treatment irradiation can take an enormous amount of time. This places a heavy burden on the patient receiving treatment.

[0011] The present invention has been devised in view of the above problems, and provides a method that can align the position of the brain at the time of treatment planning relative to a reference plane with the position of the brain during treatment, regardless of the position of the brain in the skull.

[0012] More specifically, the subject positioning method according to the present invention is characterized by comprising the steps of: obtaining a treatment planning image of the subject fixed relative to a reference plane in order to create a treatment plan for the subject; obtaining a pre-treatment image of the subject fixed relative to the reference plane immediately before treatment of the subject; determining a posture correction value such that the cerebral sulci in the treatment planning image and the cerebral sulci in the pre-treatment image overlap; and correcting the posture of the subject during treatment based on the posture correction value.

[0013] Furthermore, a radiation therapy device using the above method comprises a radiation irradiation unit, a couch on which a subject is fixed, a position adjustment unit that adjusts the position of the couch, a guided image capture unit that takes an image of the subject fixed to the couch just before treatment, and a control unit, wherein the control unit comprises an import unit that imports an image at the time of treatment planning, an attitude correction value calculation unit that calculates an attitude correction value for aligning the cerebral sulci between the image just before treatment and the image at the time of treatment planning, and an attitude adjustment unit that transmits the attitude correction value to the position adjustment unit.

[0014] The subject positioning method according to the present invention performs "patient positioning" by matching the cerebral sulci between CT images of the subject's (patient's) brain taken at the time of treatment planning and CT images of the subject's brain taken at the time of treatment. Therefore, accurate positioning of the irradiation position can be performed even if the position of the brain relative to the skull is different between the time of treatment planning and the time of treatment.

[0015] Furthermore, because the subject positioning method of the present invention uses image processing as a means, it is minimally invasive and places little physical strain on the patient. Furthermore, by utilizing today's high-speed computers, positioning can be completed in a very short time, and the mental strain on the patient is also reduced.

[0016] Furthermore, since the position of the brain itself can be reproduced at the time of treatment planning, even if there are multiple areas to be treated within the brain, they can be accurately reproduced, and treatment irradiation can be performed one after another, thereby shortening treatment time.

[0017] Fig. 1 is a diagram showing the configuration of an apparatus for carrying out a subject positioning method according to the present invention. Fig. 2 is a diagram showing a cross-sectional image of the brain. Fig. 3 is a conceptual diagram comparing an image at the time of treatment planning with an image just before treatment. Fig. 4 is a conceptual diagram showing a process of setting an error allowance area in the cerebral sulci of the image at the time of treatment planning. Fig. 5 is a conceptual diagram showing a process of aligning the cerebral sulci of the image at the time of treatment and the image just before treatment.

[0018] The subject positioning method and radiotherapy device using this method according to the present invention will be described below with reference to the drawings and examples. Note that the following description exemplifies one embodiment of the present invention and one example, and the present invention is not limited to the following description. The following description can be modified within the scope of the present invention.

[0019] 1 shows the configuration of an apparatus for carrying out a subject positioning method according to the present invention (hereinafter referred to as "the method"). In this method, the subject K is a patient having a target region to be treated with radiation therapy, such as a tumor in the brain. The subject K may also be referred to as the brain of such a patient.

[0020] This method uses a treatment planning imaging device 50 used when creating a treatment plan and a radiation therapy device 1. The treatment planning imaging device 50 generates an image X to clarify the treatment target area. ０ Currently, image X ０ are images obtained by taking multiple tomographic images, and a three-dimensional image can be formed based on these images.

[0021] The treatment planning imaging device 50 is preferably one that can clearly display the cerebral sulci and the treatment target area. An MRI (Magnetic Resonance Imaging) device is preferably used, but an X-ray device may also be used.

[0022] 1, an MRI apparatus will be described as an example. The treatment planning imaging device 50 includes a magnetic field generating coil and an RF coil 52 for exciting nuclear magnetization, a stage 54 on which the subject K is placed, a controller 56 having a display 56a, and the like.

[0023] The magnetic field generating coil and nuclear magnetization excitation RF coil 52 cause nuclear magnetic resonance in a strong magnetic field and detect the resulting energy. The mounting table 54 has a reference surface 54f, and the subject K is fixed on this reference surface 54f of the mounting table 54 and undergoes imaging. The reference surface 54f is a flat surface without any irregularities or warping. The reference surface 54f can be made to coincide with the horizontal plane, and its tilt and rotation from the horizontal plane can be controlled. The positional relationship of the subject K's brain with respect to this reference surface 54f is called the "posture during treatment planning."

[0024] The controller 56 controls the overall operation of the treatment planning imaging device 50. In particular, it converts the detected energy into an image X ０ Convert to Image X ０ can be confirmed on the display 56a. ０ is treatment planning image X ０ Also called treatment planning image X ０ refers to all images taken during treatment planning, but may also refer to one or more specific images.

[0025] The radiotherapy device 1 is a device that irradiates a treatment target area with radiation. A device called a linac (linear accelerator) that generates high-energy X-rays is widely used. However, other devices may also be used, and the radiation used may suitably be X-rays, electron beams, proton beams, heavy particle beams, gamma rays, neutron beams, or the like.

[0026] The radiation therapy device 1 includes a couch 10, a position adjustment unit 12, a radiation irradiation unit 14, a guided image capture unit 16, and a control unit 20. The couch 10 is a table on which a subject K is placed during treatment. The couch 10 has a reference surface 10f, similar to the table 54 of the treatment planning imaging device 50.

[0027] Like the reference surface 54f of the mounting table 54, the reference surface 10f of the couch 10 is also a flat surface without any irregularities or warping. Therefore, although the devices are different, they can be considered to be the same reference surface. The positional relationship of the brain of the subject K with respect to the reference surface 10f of the couch 10 is called the "posture immediately before treatment." The present invention matches the posture during treatment planning with the posture immediately before treatment.

[0028] The position adjustment unit 12 can adjust the position of the reference surface 10f of the couch 10. For the position adjustment of the reference surface 10f, a device that can adjust six axes, i.e., the x direction, y direction, z direction, pitch angle, roll angle, and yaw angle (rotation angle), can be suitably used.

[0029] The radiation emitting unit 14 is a unit that emits radiation. It is also called a gantry. The guided image capturing unit 16 is used to check the posture of the subject K relative to the reference plane 10f of the couch 10 during treatment (or immediately before treatment) ("posture immediately before treatment"). It is preferable that the unit is capable of tomography. CBCT (Cone Beam Computed Tomography) is usually used, but a device other than one that uses X-rays may also be used. Here, the guided image capturing unit 16 is assumed to be a CBCT, and is configured with an X-ray emitting side 16a and an imaging side 16b that face each other. Furthermore, the radiation emitting unit 14 and the guided image capturing unit 16 may be configured to be rotatable as a single unit.

[0030] The control unit 20 controls the entire radiotherapy apparatus 1. In particular, the device control unit 20a operates the guided image capturing unit 16 and generates an image X from the captured image signal. １ and controls the operation of the radiation irradiation unit 14. １ is the image just before treatment X １ Also called.

[0031] In the radiotherapy device 1 for carrying out this method, the control unit 20 includes a treatment planning image X ０ and image X just before treatment １ The posture adjustment unit 20b adjusts the posture of the treatment planning image X ０ and a treatment planning image X ０ and Immediately before treatment image X １ and an image processing unit 20c for performing image processing appropriate for the treatment planning image X ０ and image X just before treatment １ The posture adjustment unit 20b includes a posture correction value calculation unit 20d that calculates a posture correction value for correcting the posture of the subject K with respect to the reference plane 10f so as to align the cerebral sulci of the subject K with each other. The posture adjustment unit 20b also sends the posture correction value to the position adjustment unit 12 to operate the position adjustment unit 12.

[0032] The implementation of this method will be explained below with a detailed description of each device. In this method, first, a treatment planning image X is generated using a treatment planning image device 50. ０ This is the image acquisition for creating a treatment plan. Treatment planning image X ０ In this case, MRI images and CT (Computed Tomography) images, which show cerebral sulci clearly, are particularly suitable. ０ A schematic diagram of the above is shown.

[0033] 2 shows a cross-sectional image of the head of a subject K lying on the mounting table 54 with his / her head facing upward relative to the reference surface 54f of the mounting table 54. The subject K is fixed in this position with fixing devices such as a fixing shell and a head and neck pillow and is photographed.

[0034] The arrow in Figure 2 indicates the direction in which the face of the subject K is facing. In this cross-sectional view, the cerebral sulci KS can be seen in the skull KB. The view also shows that there are multiple treatment target regions BT in the brain.

[0035] Referring again to FIG. 1, treatment planning image X ０ After the treatment plan is taken, a treatment plan is drawn up. This usually takes several days. ０ The time and equipment change between when the image is taken and when the treatment is actually performed.

[0036] Next, during treatment, the subject K is placed on the couch 10 of the radiation therapy device 1, and the treatment planning image X ０ The patient is fixed in the same position as when the image was taken. In other words, the position at the time of treatment planning is reproduced. However, the treatment planning image X ０ The date, environment such as temperature and humidity, physique, and fixation state may be different from the time of imaging, and the position of the skull KB relative to the reference plane 10f and the position of the brain relative to the skull KB may change. １ Photograph the following.

[0037] In addition, the image just before treatment X １ When taking the images, all the treatment planning images X of the subject K taken at the time of treatment planning are taken. ０may be imported into the posture adjustment unit 20b from the import unit 20bi of the control unit 20 of the radiotherapy apparatus 1. Also, only one or several specific images may be imported.

[0038] Treatment planning image X ０ The method of capturing the treatment planning image X is not particularly limited. The treatment planning image X is transmitted from the treatment planning image device 50 to the radiation therapy device 1 via a wired, wireless or recording medium. ０ In addition, a method such as sending an image X ０ At the same time, information on the imaging conditions, the position of the fixing tool, etc. may be sent to the radiotherapy device 1. １ is sent from the guidance image capturing unit 16 to the posture adjusting unit 20b. １ and treatment planning image X ０ There will be a discrepancy.

[0039] FIG. 3 shows the treatment planning image X ０ (Fig. 3(a)) and the image just before treatment X １ FIG. 3(b) shows a conceptual diagram of the treatment planning image X in which the treatment target region BT is considered during treatment planning. ０ (Fig. 3(a)), an image of almost the same location is taken as an image just before treatment X １ These are selected from the above. In reality, position differences occur across all six axes, but here they are expressed as differences in the roll angle, which is the inclination of the axis AZ in the z-axis direction relative to the cross-sectional view. Note that position differences do not only refer to differences in position within three-dimensional space, but also to the direction of rotation with an axis in either direction. Furthermore, "position differences" will be referred to as "deviations" hereafter.

[0040] That is, the z-axis AZ in FIG. ０ In contrast, the z-axis AZ in FIG. １ Assume that there is a deviation of the posture of the subject K by the roll angle θ. The posture adjustment unit 20b calculates a posture correction value Dcor for correcting this deviation, and moves the couch 10 to which the subject K is fixed, thereby matching the posture at the time of treatment planning with the posture immediately before treatment.

[0041] A specific method for correcting this misalignment will be explained with reference to Figure 4. ０A boundary line KSL is created at the boundary between the cerebral sulcus KS and the cerebrospinal fluid CSD. The cerebral sulcus KS and the cerebrospinal fluid CSD are identified by the image X ０ Since the image appears black and white on the screen, the boundary line KSL can be determined based on the pixel values ​​of the image. Of course, the boundary line KSL may be determined by other methods.

[0042] Next, the treatment planning image X on which the boundary line KSL was created ０ (Fig. 4(a)) is an error allowance area image X ２ (Fig. 4(b)) is created. The error allowance area ae is an area where a margin of 1 mm or less is provided for the boundary line KSL of the cerebral sulcus KS. For example, the area on the boundary line KSL that forms the cerebral sulcus KS is made thicker to a width of 1 mm, and this is the error allowance area ae. Next, the immediately before treatment image X １ and the error tolerance area image X ２ Match.

[0043] This is shown in Figure 5. Figure 5(a) shows the image just before treatment X １ Image X just before treatment １ The treatment target area in the above image is designated as treatment target area BT1. ２ The error tolerance area image X ２ The delayed ejaculation target area above is designated as the treatment target area BT2. ２ The treatment planning image X is the same as the treatment planning image X except that an error tolerance area ae is provided. ０ is the same as

[0044] FIG. 5(b) shows the image X just before treatment of FIG. 5(a). １ 5B shows only the boundary line KSL between the cerebral sulcus KS and the cerebrospinal fluid CSD. Such image processing is performed by the image processing unit 20c in Fig. 1. Note that Fig. 5B also shows the treatment target region BT1.

[0045] FIG. 5(d) shows the error tolerance area image X ２5B and 5C, the error sharing area ae and the treatment target area BT2 are indicated by white lines (white circles). The treatment target area BT1 and the treatment target area BT2 are misaligned. Note that Figures 5B and 5C are shown for ease of explanation, and the image processing unit 20c does not necessarily create such a state.

[0046] Immediately before treatment image X １ The boundary line KSL of the cerebral sulcus KS is the error tolerance area image X ２ The posture correction value Dcor of the six axes is calculated so that the error falls within the error tolerance area ae. This calculation is performed by the posture correction value calculation unit 20d in FIG. 1. FIG. 5(e) shows the posture correction value Dcor of the immediately before treatment image X １ and the error tolerance area image X ２ This shows that the cerebral sulci overlap with an accuracy of the error allowance range ae.

[0047] Referring again to FIG. 1, calculation of the boundary line KSL and setting of the error tolerance area ae can be performed by image processing. Therefore, this is performed by the image processing unit 20c in the posture adjustment unit 20b. The posture correction value Dcor obtained by the posture correction value calculation unit 20d is sent to the position adjustment unit 12. The position adjustment unit 12, which moves the position of the couch 10 along six axes, moves the couch 10 by the posture correction value Dcor.

[0048] By the above procedure, this method produces a treatment planning image X ０ The posture of the subject K when the image was taken and the image just before treatment X １ In other words, the posture at the time of treatment planning can be made to match the posture immediately before treatment, thereby reducing radiation exposure to normal tissue.

[0049] In addition, treatment planning image X ０ Immediately before treatment image X １ The radiation therapy device 1 having the posture correction value calculation unit 20d can also align the posture at the time of treatment planning with the posture immediately before treatment so as to align the cerebral sulci KS, thereby reducing radiation exposure to normal tissue.

[0050] Although the above explanation has been given using radiation therapy for the brain as an example, it can also be applied to other organs by replacing "cerebral sulci" with "organs."０ The characteristic part of the organ (if the tumor is directly visible, the tumor itself is acceptable) is photographed with the X-ray, and the characteristic part is photographed just before treatment. ０ and image X just before treatment １ A posture correction value is calculated so that the characteristic portions of the patient's posture are matched, and the couch 10 on which the patient is fixed is moved.

[0051] For four patients with treatment areas in the brain, the average difference between alignment based on the cerebral sulci and alignment based on the skull was measured. The results are shown in Table 1. The purpose of this alignment is to reproduce the irradiation position relative to the treatment area in the brain.

[0052] Therefore, when the position is aligned with the cerebral sulci, which are the actual structure of the brain, the position of the treatment target area is ０ Image taken at the time of shooting and immediately before treatment X １ It is believed that the positions match when the images are taken. In addition, it was confirmed that accurate positioning is possible when the cerebral sulci are used as the reference point, even if there are multiple treatment target areas.

[0053]

[0054] Table 1 shows the average difference between translational and rotational components of three to five averages taken for each of four patients, Pt. 1 to Pt. 4. The goal during treatment is to align the patient to within 1 mm or 0.5°, so if the patient is aligned based on the skull, this much positional difference occurs, causing damage to healthy tissue areas.

[0055] The subject positioning method according to the present invention can be suitably used in radiation therapy for irradiating a target area in the brain with radiation. Furthermore, a radiation therapy device that can implement this method can reduce the physical and mental burden on the patient and minimize damage to normal tissue. Furthermore, the present invention can be suitably used in radiation therapy for other organs in addition to the brain.

[0056] REFERENCE SIGNS LIST 1 Radiation therapy device 10 Couch 10f Reference plane 12 Position adjustment unit 14 Radiation irradiation unit 16 Guided image acquisition unit 16a X-ray irradiation side 16b Image acquisition side 20 Control unit 20a Equipment control unit 20b Posture adjustment unit 20bi Import unit 20c Image processing unit 20d Posture correction value calculation unit 50 Treatment planning imaging device 52 Magnetic field generating coil and RF coil for nuclear magnetization excitation 54 Placement table 54f Reference plane 56 Controller 56a Display K Subject KB Skull KS Cerebral sulcus CSD Cerebrospinal fluid KSL Boundary line X ０ Treatment planning image X １ Immediately before treatment image X ２ Error tolerance area image 　 BT Treatment target area Dcor Posture correction value ae Error tolerance area

Claims

1. A method for positioning a subject, comprising the steps of: obtaining a treatment planning image of the subject fixed relative to a reference plane in order to create a treatment plan for the subject; obtaining a pre-treatment image of the subject fixed relative to the reference plane immediately before treatment of the subject; determining a posture correction value such that the cerebral sulci in the treatment planning image and the cerebral sulci in the pre-treatment image overlap; and correcting the posture of the subject during treatment based on the posture correction value.

2. A radiation therapy device having a radiation irradiation unit, a couch on which a subject is fixed, a position adjustment unit that adjusts the position of the couch, a guided image capture unit that takes an image of the subject fixed to the couch just before treatment, and a control unit, wherein the control unit has: an import unit that imports an image at the time of treatment planning; an attitude correction value calculation unit that calculates an attitude correction value for aligning the cerebral sulci in the image just before treatment and the image at the time of treatment planning; and an attitude adjustment unit that transmits the attitude correction value to the position adjustment unit.

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