Positioning device, radiation therapy device, and positioning method

Abstract

To provide a positioning apparatus, a radiation therapy apparatus and a positioning method which can perform highly accurate positioning of a patient while reducing a calculation time.SOLUTION: An image acquisition unit 21 acquires a plurality of perspective X-ray images obtained by imaging a subject. A pseudo perspective X-ray image creation unit 22 creates a pseudo perspective image obtained by projecting a three-dimensional perspective image of the subject on a detection surface with respect to an imaging axis for each imaging axis of the perspective X-ray image. An image collation unit 24 obtains a correction axis that corrects the imaging axis on the basis of a two-dimensional movement amount being a deviation amount between the perspective X-ray image and the pseudo perspective X-ray image according to the imaging axis for each of the plurality of imaging axes, and calculates a movement amount from an intersection of each imaging axis to a middle point on a common perpendicular of each correction axis as a bed movement amount of moving a bed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a positioning device, a radiation therapy device, and a positioning method. [Background technology]

[0002] Radiation therapy, which irradiates patients with radiation, is known as one of the cancer treatment methods. The radiation used in radiation therapy is broadly divided into uncharged particle beams such as X-rays or gamma rays, and charged particle beams such as proton beams or carbon ions. Radiation therapy using the latter type of charged particle beam is generally called particle beam therapy.

[0003] With uncharged particle beams, the dose decreases at a constant rate from shallow to deep positions within the body. On the other hand, with charged particle beams, it is possible to form a dose distribution (Brugh curve) with a peak in energy loss at a specific depth. Therefore, by aligning the peak in energy loss of charged particle beams with the position of the tumor, it is possible to significantly reduce the dose of charged particle beams irradiated to normal tissue located deeper than the tumor.

[0004] Therefore, in radiation therapy, it is important to accurately deliver the desired dose of radiation to the target tumor in order to improve the therapeutic effect. To achieve accurate irradiation of the tumor with radiation, it is necessary to position the patient at the same position as the planned position determined by the pre-created treatment plan. This positioning of the patient is called patient positioning.

[0005] One method for positioning a patient in radiation therapy is to use fluoroscopic X-ray images (Digital Radiography: DR) of a patient lying on a bed, taken from two different directions using two sets of X-ray tubes and flat panel detectors (FPDs).In this method, the fluoroscopic X-ray images taken of the patient during radiation therapy are compared with pseudo-fluoroscopic X-ray images created from CT (Computed Tomography) images used to create the treatment plan, and the patient is positioned so that the positions of structures to be positioned, such as bones, match between the fluoroscopic X-ray images and the pseudo-fluoroscopic X-ray images.

[0006] In addition, fluoroscopic X-ray images generally include structures other than the target structure to be positioned, such as the patient's fixation devices and soft tissue, and the position of the bone, which is the target structure to be positioned, may change from the time of treatment planning. In such a situation, the structures captured in the fluoroscopic X-ray image and the pseudo-fluoroscopic X-ray image do not match across the entire image. In this case, patient positioning is performed using a region of interest (ROI) set on the fluoroscopic X-ray image as the area where the target structure to be positioned exists. Note that the ROI is usually set by a medical professional by drawing the ROI on the image.

[0007] Automatic patient alignment is performed by using the translation and rotation of the patient's bed as parameters and calculating the optimal values ​​of these parameters through optimization calculations. Typically, translation has three components along three mutually orthogonal axes (x, y, z), and rotation has three components (pitch, roll, yaw) around the three axes. Therefore, the optimization calculation iterates the optimization process for each of the six components to calculate the optimal parameter values. The three axes defining the translation coincide with the axes of movement of the bed to position the patient in the planned position. The x-axis is oriented from right to left (Right-Left direction, RL) as seen from the patient lying supine on the bed, the y-axis is oriented from the feet to the head (Superior-Inferior direction, SI), and the z-axis is oriented from the back to the abdomen (Anterior-Posterior direction, AP).

[0008] However, if the patient's position at the start of positioning is far from the planned position, the change in the similarity between images, which serves as the judgment index in the optimization calculation, becomes small, and it is not possible to utilize features that increase the similarity toward the optimal position, which may result in the parameter not reaching the optimal value or an increase in calculation time due to an increase in the number of iterative calculations in the optimization calculation.

[0009] In response to this, Patent Documents 1 and 2 disclose techniques for reaching an optimum value with fewer iterative calculations. These techniques aim to reduce the number of times the optimization process is repeated in the optimization calculation by adding an optimization process in a one-dimensional direction along the imaging axis for capturing a fluoroscopic X-ray image after the optimization process for each component is completed.

[0010] Furthermore, Patent Document 3 discloses a technology that reduces the number of fluoroscopic X-ray images and shortens the time required for patient positioning by evaluating the optimization of the translation amount in the direction along the imaging axis only in one direction perpendicular to the fluoroscopic imaging axis. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent No. 6668902 [Patent Document 2] International Publication No. 2018 / 225234 [Patent Document 3] JP 2013-99431 A Summary of the Invention [Problem to be solved by the invention]

[0012] However, in the technologies described in Patent Documents 1 to 3, optimization is still performed using image similarity, so in cases where the patient's position at the start of positioning is significantly different from the planned position and the change in similarity between images is small, it may not be possible to prevent an increase in calculation time due to an increase in the number of iterative calculations in the optimization calculation.

[0013] An object of the present disclosure is to provide a positioning device, a radiation therapy device, and a positioning method that can further reduce calculation time. [Means for solving the problem]

[0014] A positioning device according to one aspect of the present disclosure is a positioning device that controls the position of a bed on which a subject is placed, and includes: an image acquisition unit that acquires a plurality of fluoroscopic images of the subject by detecting light from a light source through a detection surface via the subject for each of a plurality of imaging axes; The apparatus includes a creating unit that creates a pseudo-perspective image for each of the plurality of imaging axes by projecting a three-dimensional perspective image of the subject onto a detection plane for that imaging axis, and a calculation processing unit that determines a correction axis for each of the plurality of imaging axes by correcting that imaging axis based on the amount of deviation between the perspective image and the pseudo-perspective image corresponding to that imaging axis, and calculates the amount of movement from the intersection of the plurality of imaging axes to the midpoint of a common perpendicular line of each correction axis as the bed movement amount for moving the bed. [Effects of the Invention]

[0015] According to the present invention, it is possible to further reduce the calculation time. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a diagram illustrating an overall configuration of a particle beam therapy system according to an embodiment of the present disclosure. [Figure 2] 10 is a flowchart illustrating an example of a patient positioning process. [Figure 3] 10A and 10B are diagrams for explaining a process of obtaining a correction axis from a two-dimensional movement amount. [Figure 4] 10A and 10B are diagrams for explaining a process of calculating a three-dimensional movement amount from a correction axis. [Figure 5] FIG. 5 is an enlarged view of the common perpendicular line shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0018] The following description and drawings are merely illustrative of the present invention, and have been omitted or simplified as appropriate for clarity of explanation. The present invention can be implemented in various other forms. Unless otherwise specified, each component may be singular or plural. In addition, in the drawings illustrating the embodiments, parts having the same function are given the same reference numerals, and repeated description thereof may be omitted. In addition, the position, size, shape, range, etc. of each component shown in the drawings may not represent the actual position, size, shape, range, etc., in order to facilitate understanding of the invention. Therefore, the present invention is not limited to the position, size, shape, range, etc. disclosed in the drawings. In addition, when there are multiple identical or similar components, they may be described using the same reference numerals with different subscripts. However, when it is not necessary to distinguish between these multiple components, the subscripts may be omitted.

[0019] Fig. 1 is a diagram showing the overall configuration of a particle therapy system according to an embodiment of the present disclosure. The particle therapy system A shown in Fig. 1 is a radiation therapy apparatus having a group of devices for irradiating a patient B, who is an examinee, with particle beams. The particle therapy system A includes an accelerator 1, a beam transport device 2, a gantry 3, an irradiation nozzle 4, FPDs 5A and 5B, X-ray tubes 6A and 6B, a bed 7, a robot arm 8, a communication device 9, a data server 10, a treatment planning device 11, a fluoroscopic X-ray imaging device 12, a bed control device 13, and a patient positioning device 20.

[0020] The accelerator 1 is a particle beam generator that generates a particle beam to be irradiated onto a patient B, and accelerates and outputs the particle beam until it reaches an energy level suitable for treating the patient B. The beam transport device 2 transports the particle beam output from the accelerator 1 to a gantry 3. The type of particle beam is not particularly limited, and may be, for example, a proton beam or a carbon beam.

[0021] The gantry 3 and irradiation nozzle 4 are irradiation devices that irradiate patient B with the particle beam transported from the accelerator 1. The gantry 3 adjusts the irradiation angle at which the particle beam transported from the accelerator 1 is irradiated onto patient B. Specifically, the gantry 3 has a rotation mechanism that can rotate 360° around patient B, and adjusts the irradiation angle by rotating. The irradiation nozzle 4 is provided on the gantry 3, and irradiates patient B with the particle beam transported to the gantry 3. The irradiation nozzle 4 may incorporate a mechanism that adjusts the shape of the particle beam to match the shape of the affected area of ​​the patient.

[0022] The FPDs 5A and 5B and the X-ray tubes 6A and 6B constitute an imaging system for performing fluoroscopic imaging of patient B. The FPDs 5A and 5B are flat panel detectors that image patient B by detecting X-rays, which are imaging light, on their detection surfaces. The X-ray tubes 6A and 6B are light sources that output X-rays. The FPD 5A and the X-ray tube 6A are arranged opposite each other so that the X-rays output from the X-ray tube 6A are detected by the FPD 5A via the patient B, and the FPD 5B and the X-ray tube 6B are arranged opposite each other so that the X-rays output from the X-ray tube 6B are detected by the FPD 5B via the patient B. An axis connecting the center of the FPD 5A and the X-ray tube 6A and an axis connecting the center of the FPD 5B and the X-ray tube 6B are two imaging axes for imaging patient B. The two imaging axes are preferably orthogonal to each other, but do not have to be orthogonal to each other. The particle beam therapy system A may also include three or more FPDs and three or more X-ray tubes. In this case, the number of imaging axes is also three or more.

[0023] The bed 7 is a platform on which patient B rests when irradiating patient B with a particle beam. The robot arm 8 is a device for moving the bed 7. Specifically, the robot arm 8 performs translational movement in multiple translational directions along multiple movement axes and rotational movement in multiple rotational directions around multiple rotation axes relative to the bed 7. In this embodiment, the movement axes and the rotation axes are identical, and there are three movement axes (rotation axes). Furthermore, each movement axis points in a direction from right to left (RL direction) as seen from patient B lying supine on the bed 7, a direction from patient B's feet to head (SI direction), and a direction from the back to the abdomen (AP direction).

[0024] The communication device 9 communicatively connects the data server 10, the treatment planning device 11 and the patient positioning device 20 with each other.

[0025] The data server 10 is a storage device that stores various information related to particle beam therapy for patient B. The data server 10 stores, for example, three-dimensional fluoroscopic images of patient B and treatment plan information that indicates a treatment plan for patient B. The three-dimensional fluoroscopic images include information that indicates the shape and electron density of the patient in voxel units. The three-dimensional fluoroscopic images are, for example, computed tomography (CT) images, and are generated in advance (before creating treatment plan information for patient B). The treatment plan information is generated based on the three-dimensional fluoroscopic images. The treatment plan information also includes planned arrangement information that indicates a planned arrangement, which is the arrangement of patient B during treatment. The arrangement of patient B indicates the position and angle (posture) of patient B, and is determined by the position and angle of the bed 7.

[0026] The treatment planning device 11 creates a treatment plan for patient B based on the three-dimensional fluoroscopic images stored in the data server 10, and stores treatment plan information indicating the treatment plan in the data server 10.

[0027] The X-ray fluoroscopic imaging device 12 controls the FPD 5A and the X-ray tube 6A, and the FPD 5B and the X-ray tube 6B, respectively, to obtain a plurality of fluoroscopic X-ray images of the patient B taken from different angles as fluoroscopic images, and transmits the obtained fluoroscopic X-ray images to the patient positioning device 20. In this embodiment, there are two fluoroscopic X-ray images.

[0028] The bed control device 13 controls the robot arm 8 to adjust the position of the bed 7, thereby adjusting the position of the patient B.

[0029] The patient positioning device 20 performs positioning processing for the patient B based on the three-dimensional fluoroscopic images and treatment plan information stored in the data server 10 and the fluoroscopic X-ray images acquired by the fluoroscopic X-ray imaging device 12.

[0030] The positioning process for patient B is a process for positioning patient B, who is placed on the bed 7, in the same position as the planned position indicated in the treatment plan information before the start of particle beam therapy for patient B. The patient positioning device 20 controls the robot arm 8 via the bed control device 13 to adjust the position and angle of the bed 7, thereby positioning patient B in the same position as the planned position.

[0031] Once the positioning process is complete, particle beam therapy is actually performed on patient B. Specifically, a particle beam accelerated to an energy level suitable for treatment by accelerator 1 is transported to gantry 3 via beam transport device 2. The particle beam is deflected in an appropriate direction by gantry 3, passes through irradiation nozzle 4, and is irradiated onto the affected area of ​​patient B.

[0032] The patient positioning device 20 is described in more detail below.

[0033] As shown in FIG. 1, the patient positioning device 20 includes an image acquisition unit 21, a pseudo-fluoroscopic X-ray image creation unit 22, an ROI drawing unit 23, an image matching unit 24, an image display unit 25, and a control unit 26.

[0034] The image acquisition unit 21 acquires three-dimensional fluoroscopic images from the data server 10 via the communication device 9, and acquires fluoroscopic X-ray images from the fluoroscopic X-ray imaging device 12.

[0035] The pseudo-fluoroscopic X-ray image creating unit 22 is a creating unit that creates a plurality of pseudo-fluoroscopic X-ray images, which are a plurality of pseudo-fluoroscopic images obtained by projecting the 3D fluoroscopic images acquired by the image acquiring unit 21 onto a plurality of planes corresponding to the imaging axes for capturing the fluoroscopic X-ray images. The pseudo-fluoroscopic X-ray image creating unit 22 creates the pseudo-fluoroscopic X-ray images by arranging a 3D image of patient B in a virtual space that is the same as the imaging system that generated the fluoroscopic X-ray images and performing projection processing. The plane corresponding to the imaging axis is, for example, the detection plane of the FPD corresponding to the imaging axis, that is, a plane that is approximately perpendicular to the imaging axis.

[0036] The ROI drawing unit 23 specifies an ROI, which is a region of interest used for positioning a patient in a pseudo-fluoroscopic X-ray image. Specifically, the ROI drawing unit 23 specifies the ROI by displaying a pseudo-fluoroscopic X-ray image and having a user draw an ROI on the pseudo-fluoroscopic X-ray image. The ROI is drawn so as to include a structure to be positioned, such as a bone.

[0037] The image matching unit 24 is a calculation processing unit that calculates the bed movement amount for moving the bed 7 based on the fluoroscopic X-ray image and the pseudo fluoroscopic X-ray image. When an ROI is specified by the ROI drawing unit 23, the image matching unit 24 may calculate the bed movement amount based on the fluoroscopic X-ray image and the pseudo fluoroscopic X-ray image in the ROI. In this embodiment, the bed movement amount includes movement amounts in each of a plurality of translation directions.

[0038] The image display unit 25 is a display unit that displays various information and images, such as a fluoroscopic X-ray image, a pseudo fluoroscopic X-ray image, and an ROI image showing an ROI region.

[0039] The control unit 26 controls the bed control device 13 based on the bed movement amount calculated by the image comparison unit 24 to move the bed 7, thereby adjusting the position of the patient B.

[0040] The patient positioning device 20 having the above functions can be realized by an information processing device capable of various information processing, such as a computer device. The information processing device has, for example, a processing element, a storage medium, and a communication interface, and may further have an input unit such as a mouse and keyboard, and a display unit such as a monitor, as necessary.

[0041] The computing element is, for example, a processor such as a CPU (Central Processing Unit) or an FPGA (Field-Programmable Gate Array). The storage medium is, for example, a magnetic storage medium such as an HDD (Hard Disk Drive), or a semiconductor storage medium such as a RAM (Random Access Memory), a ROM (Read Only Memory), or an SSD (Solid State Drive). Alternatively, a combination of an optical disk such as a DVD (Digital Versatile Disk) and an optical disk drive may be used as the storage medium. Furthermore, other high-value storage media such as magnetic tape media may also be used as the storage medium.

[0042] The storage medium stores programs such as firmware. When the patient positioning device 20 starts operating (for example, when the power is turned on), the processor reads and executes the programs from the storage medium, thereby realizing the various units 21-27 of the patient positioning device 20 and executing a series of overall controls. In addition to the programs, the storage medium also stores data and the like required for each process of the patient positioning device 20.

[0043] The patient positioning device 20 of this embodiment may be configured using so-called cloud computing, in which a plurality of information processing devices are configured to be able to communicate with each other via a communication network.

[0044] The patient positioning process performed by the patient positioning device 20 will now be described in more detail with reference to FIGS.

[0045] FIG. 2 is a flowchart illustrating an example of a patient positioning process.

[0046] It is assumed that patient B is placed in the setup position of the bed 7. The setup position is a position for placing patient B in the same position as the planned position. For example, the position of the body surface of patient B on the bed 7 is measured using an infrared laser installed in the treatment room, and patient B is placed in the setup position of the bed 7 based on that position.

[0047] In the patient positioning process, first, the control unit 26 acquires treatment plan information from the data server 10, and based on the planned placement information included in the treatment plan information, controls the robot arm 8 via the bed control device 13 to move the bed 7 on which patient B is placed so that the placement of patient B becomes the planned placement indicated in the planned placement information (step S100). At this time, the positioning target structure of patient B placed on the bed 7 is included in the X-ray irradiation area formed by the FPDs 5A and 5B and the X-ray tubes 6A and 6B.

[0048] Thereafter, the image acquiring unit 21 acquires a plurality of fluoroscopic X-ray images of the patient B taken from a plurality of different directions via the fluoroscopic X-ray imaging device 12 (step S101). In this embodiment, the image acquiring unit 21 acquires two fluoroscopic X-ray images taken from two directions along two imaging axes.

[0049] The pseudo-fluoroscopic X-ray image creating unit 22 acquires the three-dimensional fluoroscopic image from the data server 10, and creates two pseudo-fluoroscopic X-ray images from the three-dimensional fluoroscopic image according to each of the two imaging axes (step S102).

[0050] The image matching unit 24 calculates, for each imaging axis, the amount of two-dimensional deviation between the fluoroscopic X-ray image and the pseudo fluoroscopic X-ray image corresponding to that imaging axis as the amount of two-dimensional movement on the detection surface of the FPD corresponding to the imaging axis (step S103).

[0051] A known method for calculating the amount of image misalignment is to scan a pseudo fluoroscopic X-ray image horizontally and vertically relative to a fluoroscopic X-ray image to search for the position where the similarity between the images is highest, but this method requires sequential calculation of the similarity, which increases the amount of calculation. Therefore, in this embodiment, a calculation method using POC (Phase-Only Correlation) method, which is known to enable high-speed image matching, will be described.

[0052] The POC method is a method for matching (aligning) images using only the phase component obtained from a two-dimensional discrete Fourier transform of the image, and is characterized by its robustness against disturbances such as changes in image brightness. Furthermore, unlike methods that match based on image feature points such as edges or corners, the POC method can perform accurate alignment even for images that do not have clear features.

[0053] In this embodiment, the image matching unit 24 calculates the two-dimensional movement amount, which is the amount of deviation between the fluoroscopic X-ray image and the pseudo fluoroscopic X-ray image, using a POC function (phase-only correlation function) used as an evaluation index for matching by the POC method.

[0054] Here, the two images that are the subject of the POC calculation method are images f(n1, n2) and g(n1, n2). Images f(n1, n2) and g(n1, n2) are both images of N1 x N2 pixels. n1 and n2 are discrete spatial indexes that indicate pixels, where n1 = -M1, ..., M1, and n2 = -M2, ..., M2. Note that n1 and n2 are integers, and M1 and M2 are positive integers, satisfying N1 = 2M1 + 1 and N1 = 2M1 + 1.

[0055] The two-dimensional Discrete Fourier Transform (DFT) of the images f(n1, n2) and g(n1, n2) is expressed by the following equations (1) and (2).

number

[0056] Furthermore, the normalized cross power spectrum of images f(n1, n2) and g(n1, n2) is expressed by the following equation (3) using the functions F(k1, k2) and G(k1, k2) after Fourier transform.

number

number

[0057] The POC function r(n1, n2) is defined as the two-dimensional inverse discrete Fourier transform (IDFT) of the normalized cross power spectrum by the following equation (4):

number

[0058] The POC function has a sharp peak called a correlation peak when the target images f(n1,n2) and g(n1,n2) are similar to each other. The height of the correlation peak represents the linearity of the phase difference spectrum of images f(n1,n2) and g(n1,n2) with respect to frequency. If the phase difference spectrum is linear with respect to frequency, the height of the correlation peak is 1. The height of the correlation peak is useful as a measure of image similarity and is used in image matching, etc. The coordinates of the correlation peak also represent the relative shift amount of the images. For example, the shift amount of the correlation peak coordinates relative to the origin (n1=0, n2=0) of the images can be used as the shift amount of images f(n1,n2) and g(n1,n2).

[0059] In the two-dimensional DFT, it is assumed that the image wraps around the edges of the target image, resulting in discontinuities that should not actually exist at the image edges. In this embodiment, to reduce these discontinuities, the image matching unit 24 calculates the two-dimensional movement amount using images f(n1, n2) and g(n1, n2) obtained by multiplying the fluoroscopic X-ray image and the pseudo-fluoroscopic X-ray image by a window function. The window function is, for example, a two-dimensional Hanning window w(n1, n2) expressed by Equation (5).

number

[0060] Using the POC method as described above, the image matching unit 24 calculates, for each imaging axis, the amount of two-dimensional shift between the position of the correlation peak of the phase-only correlation function calculated from the fluoroscopic X-ray image and the pseudo fluoroscopic X-ray image and the origin as the amount of two-dimensional movement.

[0061] Returning to the description of Fig. 2, the image matching unit 24 executes a three-dimensional movement amount calculation process to calculate a three-dimensional movement amount as a bed movement amount for moving the bed 7, based on the two-dimensional movement amount of each imaging axis (step S104).

[0062] In the three-dimensional movement amount calculation process, the image matching unit 24 first obtains a corrected axis by correcting the imaging axis based on the two-dimensional movement amount, which is the amount of deviation between the fluoroscopic X-ray image and the pseudo fluoroscopic X-ray image corresponding to each imaging axis. Then, the image matching unit 24 calculates the movement amount from the intersection of each imaging axis to the midpoint of the common perpendicular line of each correction axis as the three-dimensional movement amount, which is the bed movement amount.

[0063] 3 to 5 are diagrams for explaining the three-dimensional movement amount calculation process in more detail. Specifically, FIG. 3 is a diagram for explaining the process of determining the correction axis from the two-dimensional movement amount, FIG. 4 is a diagram for explaining the process of determining the three-dimensional movement amount from the correction axis, and FIG. 5 is an enlarged view of the common perpendicular line shown in FIG. 4. It is assumed that distortion of the fluoroscopic X-ray image due to the arrangement angles of FPDs 5A and 5B, etc., has been removed in advance by distortion correction. Distortion correction may be performed, for example, by an imaging device that captures the fluoroscopic X-ray image, or by patient positioning device 20. Furthermore, even if distortion correction has not been performed, the following three-dimensional movement amount calculation process can be performed.

[0064] As shown in FIG. 3, the center point of the detection surface 5A1 of the FPD 5A is O A , the center point of the detection surface 5B1 of the FPD 5B is O B The imaging axis is the center point O of the detection surface 5A1. A and the X-ray tube 6A, the line L1 connecting the center point O of the detection surface 5B1 B and the X-ray tube 6B.

[0065] The image matching unit 24 sets the intersection of the imaging axes L1 and L2 as the reference position IC (origin of the coordinate system), and sets the correction axes as line l1 connecting the position obtained by moving the reference position IC along the detection surface 5A1 of the FPD 5A by a two-dimensional movement amount corresponding to the imaging axis L1 to the X-ray tube 6A, and line l2 connecting the position obtained by moving the reference position IC along the detection surface 5B1 of the FPD 5B by a two-dimensional movement amount corresponding to the imaging axis L2 to the X-ray tube 6B.

[0066] Here, as shown in FIG. 4, the position of the X-ray tube 6A is A(x a ,y a ,z a), and the position of the matching center point on the detection surface 5A1 of the FPD 5A is B(x b ,y b ,z b ), and the position of the X-ray tube 6B is C(x c ,y c ,z c ), and the position of the matching center point on the detection surface 5B1 of the FPD 5B is D(x d ,y d ,z d The coordinates of each of positions A to D are three-dimensional coordinates in a coordinate system (X, Y, Z) previously set in the treatment room where the gantry 3 and the bed 7 are placed, and the reference position IC is the origin of the coordinate system. The matching center points are the intersections of the correction axes l1 and l2 and the detection surfaces 5A1 and 5B1.

[0067] Ideally, the lines l1 and l2, which are the correction axes, intersect with each other. However, in reality, they may not intersect with each other due to minute errors in the positions of the matched center points that depend on the image resolution, minute misalignments between the FPDs 5A and 5B and the X-ray tubes 6A and 6B and the mechanical arrangement, etc.

[0068] If lines l1 and l2 do not intersect, the image matching unit 24 determines the points on lines l1 and l2 where the distance between lines l1 and l2 is smallest as points P and Q, and calculates the position of the midpoint of line segment l3 connecting points P and Q in three-dimensional coordinates. Line l3 is a common perpendicular line that is perpendicular to both lines l1 and l2, which are twisted relative to each other. Hereinafter, the length of line l3 will be referred to as the common perpendicular line length. Furthermore, points P and Q are the feet of common perpendicular line l3.

[0069] Point P on line l1 and point Q on line l2 can be expressed as vectors using parameters s and t as follows: p=a+su q=c+tv

[0070] Here, p is the position vector of point P (x p ,y p ,z p ), q is the position vector of point Q (x q ,y q ,z q), a is the position vector of point A (x a ,y a ,z a ), c is the position vector of point C (x c ,y c ,z c ), u is the direction vector of line l1, and v is the direction vector of line l2.

[0071] Since line segment PQ is perpendicular to each of direction vectors u and v, the dot product of direction vector w of line segment PQ and direction vectors u and v is zero. In other words, w·u=0, w·v=0. Note that the operator "·" indicates a dot product.

[0072] By solving these two dot products as simultaneous linear equations, the values ​​of the parameters s and t can be found. This gives the coordinates of points P and Q, as well as the length of the common perpendicular line L, which is the length of the line segment PQ, as L = |qp| = (|p| + |q| - 2p q) 1 / 2 ={(x q -x p ) 2 +(y q -y p ) 2 +(z q -z p ) 2} 1 / 2 It is found that:

[0073] Furthermore, the coordinates of the midpoint M of the line segment PQ (x m ,y m ,z m )M(x m ,y m ,z m )=((x q +x p ) / 2,(y q +y p ) / 2,(z q +z p ) / 2) is obtained. As a result, the three-dimensional movement amount is the movement amount from the intersection of each imaging axis to the midpoint M of the line segment PQ, and in this embodiment, since the intersection of each imaging axis is set as the origin, the coordinate value of the midpoint M of the line segment PQ can be calculated as the three-dimensional movement amount, which is the bed movement amount.

[0074] The image matching unit 24 calculates the three-dimensional movement amount and the common perpendicular length according to the above method. When the lines l1 and l2, which are the correction axes, intersect with each other, the image matching unit 24 regards the intersection of the lines l1 and l2 as the midpoint M of the line segment PQ and calculates the three-dimensional movement amount.

[0075] Returning to the explanation of FIG. 3, after calculating the three-dimensional movement amount and the common perpendicular length according to the above method in step S104, the image matching unit 24 determines whether the common perpendicular length is less than a threshold value (e.g., 1 mm) (step S105). The common perpendicular length is ideally zero, that is, lines l1 and l2 intersect with each other. The longer the common perpendicular length, the less consistent the two-dimensional movement amount and three-dimensional movement amount of the pseudo fluoroscopic X-ray image and the fluoroscopic X-ray image are. Alternatively, the image matching unit 24 may determine whether the correlation peak of the POC function is less than a threshold value instead of the common perpendicular length.

[0076] If the common perpendicular length is equal to or greater than the threshold value (step S105: No), the image matching unit 24 changes at least one of the fluoroscopic X-ray image and the pseudo fluoroscopic X-ray image (step S106), and returns to the processing of step S102.

[0077] The image is changed by, for example, performing predetermined image processing on the image to be changed, which is at least one of a fluoroscopic X-ray image and a pseudo-fluoroscopic X-ray image. The predetermined image processing is, for example, a filter process that emphasizes the edges of the image to be changed, or a process that extracts a specific partial image from the image to be changed. The partial image is, for example, an image indicating an ROI, and may be performed by the ROI drawing unit 23. Furthermore, when the processes of steps S103 to S104 are first performed, an image indicating an ROI extracted from the fluoroscopic X-ray image and the pseudo-fluoroscopic X-ray image may be used. In this case, the image may be changed by returning the partial image indicating the ROI to the original fluoroscopic X-ray image and the pseudo-fluoroscopic X-ray image. Furthermore, the image may be changed by acquiring another fluoroscopic X-ray image from the fluoroscopic X-ray imaging device 12 or creating another pseudo-fluoroscopic X-ray image from another three-dimensional fluoroscopic image.

[0078] On the other hand, if the common perpendicular length is less than the threshold value (step S105: Yes), the control unit 26 moves the bed 7 via the bed control device 13 based on the three-dimensional movement amount calculated by the image matching unit 24 (step S107), and ends the patient positioning process. This makes it possible to move the patient from the current position to the position in the treatment plan, and then the actual particle beam irradiation is performed.

[0079] The patient positioning process described above is merely an example and is not limited thereto. For example, after calculating the bed movement amount through the above process, the image matching unit 24 may perform a fine-tuning process to calculate the translation amount and rotation amount of the bed 7 through optimization calculation based on the similarity between each fluoroscopic image and each corrected pseudo fluoroscopic image obtained by correcting the pseudo fluoroscopic X-ray image based on the bed movement amount. In this case, the control unit 26 moves the bed 7 via the bed control device 13 based on the three-dimensional movement amount calculated by the image matching unit 24 and the translation amount and rotation amount calculated in the fine-tuning process. For example, the control unit 26 moves the bed 7 by the three-dimensional movement amount, and then translates and rotates the bed 7 by the translation amount and rotation amount calculated in the fine-tuning process. Note that the translation amount is calculated for each of the multiple movement axes of the bed 7, and the rotation amount is calculated for each of the multiple rotation axes of the bed 7.

[0080] In the fine adjustment process, the image matching unit 24 may perform, for example, the processes described in Patent Documents 1 to 3. Furthermore, the image matching unit 24 may perform a process of calculating, based on the similarity, the amount of movement of the bed 7 in each of a plurality of translation directions along each of a plurality of optimization axes including a plurality of imaging axes and a plurality of rotation directions around a plurality of rotation axes, such that each perspective image and each pseudo perspective image most closely match.

[0081] In addition, in this embodiment, a particle beam therapy system is exemplified as a radiation therapy device, but the radiation therapy device is not limited to a particle beam therapy system, and may be a radiation therapy system using non-particle beams such as X-rays. In this case, the accelerator 1 is, for example, configured as an electron beam accelerator that outputs X-rays.

[0082] As described above, according to this embodiment, the image acquisition unit 21 acquires multiple fluoroscopic X-ray images of a subject. The pseudo-fluoroscopic X-ray image creation unit 22 creates a pseudo-fluoroscopic image for each imaging axis of the fluoroscopic X-ray image by projecting a 3D fluoroscopic image of the subject onto a detection plane corresponding to the imaging axis. The image matching unit 24 determines a correction axis for each imaging axis based on a two-dimensional movement amount, which is the amount of deviation between the fluoroscopic X-ray image and the pseudo-fluoroscopic X-ray image corresponding to that imaging axis, and calculates the movement amount from the intersection of each imaging axis to the midpoint of the common perpendicular line of each correction axis as the bed movement amount. Therefore, patient positioning is possible without performing repeated optimization calculations, thereby further reducing calculation time.

[0083] In this embodiment, the image matching unit 24 determines, for each of the multiple imaging axes, an axis connecting the X-ray tube and a position obtained by moving the intersection of the imaging axes by the two-dimensional movement amount, as a correction axis. In this case, it is possible to calculate an appropriate correction axis according to the deviation between the fluoroscopic X-ray image and the pseudo fluoroscopic X-ray image, thereby enabling more accurate positioning.

[0084] In this embodiment, the image matching unit 24 calculates the two-dimensional movement amount based on the position of the peak of the phase-only correlation function calculated from the fluoroscopic X-ray image and the pseudo fluoroscopic X-ray image. In this case, the two-dimensional movement amount can be calculated without performing sequential calculations such as optimization calculations, and therefore the calculation time can be further reduced.

[0085] In this embodiment, the image matching unit 24 calculates a phase-only correlation function from ROIs set on the fluoroscopic X-ray image and the pseudo fluoroscopic X-ray image, thereby making it possible to more appropriately calculate the two-dimensional movement amount.

[0086] Furthermore, in this embodiment, when the length of the common perpendicular to each correction axis is equal to or greater than a threshold, the image matching unit 24 changes at least one of the fluoroscopic X-ray image and the pseudo fluoroscopic X-ray image and determines the correction axis again. In this case, it becomes possible to determine a correction axis in which the two-dimensional movement amount and three-dimensional movement amount of the pseudo fluoroscopic X-ray image and the fluoroscopic X-ray image are more consistent, thereby enabling more accurate positioning.

[0087] In this embodiment, the image is modified by performing predetermined image processing, which eliminates the need to retake fluoroscopic X-ray images or regenerate pseudo fluoroscopic X-ray images from 3D fluoroscopic images, thereby further reducing calculation time.

[0088] Furthermore, in this embodiment, the image matching unit 24 further calculates the translational and rotational movement amounts of the bed 7 based on the similarity between each corrected pseudo fluoroscopic image, which is obtained by correcting each pseudo fluoroscopic X-ray image based on the bed movement amount, and each fluoroscopic image. In this case, more accurate positioning is possible. Note that even in this case, since each pseudo fluoroscopic image is corrected based on the bed movement amount, it is possible to prevent the patient's position at the start of fine adjustment from moving too far from the planned position, and therefore it is possible to prevent an increase in the number of iterative calculations in the optimization calculation. Therefore, it is possible to further reduce the calculation time.

[0089] The above-described embodiments of the present disclosure are merely illustrative examples of the present disclosure, and are not intended to limit the scope of the present disclosure to these embodiments alone. Those skilled in the art may implement the present disclosure in various other forms without departing from the scope of the present disclosure. [Explanation of symbols]

[0090] A...particle beam therapy system, B...patient, 1...accelerator, 2...beam transport device, 3...gantry, 4...irradiation nozzle, 5A...FPD, 5B...FPD, 6A...X-ray tube, 6B...X-ray tube, 7...bed, 8...robot arm, 9...communication device for patient, 10...data server, 11...treatment planning device, 12...fluoroscopic X-ray imaging device, 13...bed control device, 20...patient positioning device, 21...pseudofluoroscopic X-ray image creation unit, 23...ROI drawing unit, 24...image matching unit, 25...image display unit, 26...control unit

Claims

1. A positioning device for controlling the position of a bed on which a subject is placed, an image acquisition unit that acquires a plurality of perspective images of the subject by detecting light from a light source on a detection surface through the subject for each of a plurality of imaging axes; a generating unit that generates a pseudo perspective image by projecting a three-dimensional perspective image of the subject onto a detection plane corresponding to each of the plurality of imaging axes; a calculation processing unit that calculates, for each of the plurality of imaging axes, a corrected axis obtained by correcting the imaging axis based on a deviation amount in a two-dimensional direction between the perspective image and the pseudo perspective image corresponding to the imaging axis, and calculates a movement amount from an intersection of the plurality of imaging axes to a midpoint of a common perpendicular line of each correction axis as a bed movement amount for moving the bed, The calculation processing unit determines, for each of the plurality of imaging axes, an axis connecting the light source and a position obtained by moving the intersection by the amount of deviation corresponding to the imaging axis, as the correction axis.

2. The positioning device according to claim 1 , wherein the calculation processing unit calculates the amount of deviation based on a peak position of a phase-only correlation function calculated from the perspective image and the pseudo perspective image.

3. The positioning apparatus according to claim 2 , wherein the calculation processing unit calculates the phase-only correlation function from regions of interest set on the perspective images and pseudo perspective images.

4. The positioning device according to claim 1 , wherein the calculation processing unit, when the length of the common perpendicular line is equal to or greater than a threshold, modifies at least one of the perspective image and the pseudo perspective image and determines the correction axis again.

5. The positioning device according to claim 4 , wherein the calculation processing unit performs predetermined image processing on at least one of the perspective image and the pseudo perspective image, thereby changing at least one of the perspective image and the pseudo perspective image.

6. 2. The positioning device according to claim 1, wherein the calculation processing unit further calculates translational and rotational movement amounts of the bed based on a similarity between each of the perspective images and each of the corrected pseudo perspective images obtained by correcting each of the pseudo perspective images based on the bed movement amount.

7. The positioning device according to claim 1 ; a bed control device that moves the bed based on the bed movement amount calculated by the positioning device; and an irradiation device that irradiates radiation onto the subject placed on the moved bed.

8. A positioning method using a positioning device that controls the position of a bed on which a subject is placed, comprising: a plurality of perspective images of the subject are acquired by receiving light from a light source through the subject at a detection surface for each of a plurality of imaging axes; For each of the plurality of imaging axes, a pseudo-perspective image is created by projecting a three-dimensional perspective image of the subject onto a detection plane corresponding to the imaging axis; determining a correction axis obtained by correcting each of the plurality of imaging axes based on a two-dimensional deviation amount between the perspective image and the pseudo perspective image corresponding to the imaging axis, and calculating a movement amount from an intersection of the plurality of imaging axes to a midpoint of a common perpendicular line of each correction axis as a bed movement amount for moving the bed; In the calculation, for each of the plurality of imaging axes, an axis connecting the light source and a position where the intersection point is moved by the amount of deviation corresponding to the imaging axis is obtained as the correction axis.

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