Radiation therapy device, medical image processing device, radiation therapy method, and program

Abstract

To provide a radiation therapy device, a medical image processing device, a radiation therapy method, and a program capable of executing positioning of a patient in a short time accurately by accelerating DRR generation processing.SOLUTION: A radiation therapy device includes an acquisition unit, a projection position calculation unit, an element projection image generation unit, and an element projection image synthesis unit. The acquisition unit acquires a condition of an X-ray imaging in a therapy stage and a three-dimensional image of a patient taken before the therapy stage. The projection position calculation unit calculates a projection position when each of pixels included in the three-dimensional image is projected on a two-dimensional X-ray fluoroscopic image generated by X-ray imaging on the basis of the condition of the X-ray imaging. The element projection image generation unit generates an element projection image for each pixel when each of the pixels included in the three-dimensional image is projected on the X-ray fluoroscopic image. The element projection image synthesis unit generates a re-configuration image by synthesizing the element projection image for each pixel on the basis of the projection position.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present invention relate to a radiation therapy apparatus, a medical image processing apparatus, a radiation therapy method, and a program.

Background Art

[0002] Radiation therapy is a treatment method that destroys a diseased part in a patient's body by irradiating the diseased part with radiation. In radiation therapy, it is necessary to accurately align the aiming of the radiation with the diseased part so as not to damage normal tissues. For this reason, before starting the radiation irradiation, the position of the diseased part is specified by an X-ray fluoroscopic image or the like, and the position and angle of a movable treatment table on which the patient is placed are appropriately adjusted to accurately align the diseased part with the radiation irradiation range. Such alignment is performed by collating a digitally reconstructed radiograph (DRR) obtained by virtually reconstructing an X-ray fluoroscopic image from a three-dimensional CT image obtained by performing computed tomography (CT) in advance at the treatment planning stage with an X-ray fluoroscopic image taken at the treatment stage.

[0003] In the above alignment, the amount of patient movement is obtained by solving a six-dimensional (translation three-dimensional, rotation three-dimensional) search problem using the similarity between the X-ray fluoroscopic image taken at the treatment stage and the DRR as an index. Since this search problem cannot be solved analytically, it is generally solved by iterative calculation, and it takes time for the process to achieve high-precision alignment. In particular, since the amount of calculation required for generating the DRR is large and occupies most of the processing time, it is necessary to reduce the number of times of generating the DRR or increase the generation speed in order to achieve high-speed alignment.

[0004] In order to shorten the processing time, a method has been proposed in which the number of DRR generations is reduced by evaluating the similarity between the DRR and the fluoroscopic image only in one direction where the change in the image is large, and alignment is performed at high speed. With this conventional method, it is possible to reduce the number of DRR generations. However, since a ray tracing method that requires a large amount of calculation and time for processing is used for DRR generation, the time required for generating one DRR cannot be shortened, and thus high-speed alignment has still not been achieved.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The problem to be solved by the present invention is to provide a radiotherapy apparatus, a medical image processing apparatus, a radiotherapy method, and a program that can perform patient positioning in a short time and with high accuracy by accelerating the DRR generation process.

Means for Solving the Problems

[0007] The radiotherapy apparatus according to the embodiment includes an acquisition unit, a projection position calculation unit, an elemental projection image generation unit, and an elemental projection image synthesis unit. The acquisition unit acquires the X-ray imaging conditions in the treatment stage and the three-dimensional image of the patient imaged before the treatment stage. The projection position calculation unit calculates the projection position when each pixel included in the three-dimensional image is projected onto the two-dimensional fluoroscopic image generated by X-ray imaging based on the X-ray imaging conditions. The elemental projection image generation unit generates an elemental projection image for each pixel when each pixel included in the three-dimensional image is projected onto the fluoroscopic image. The elemental projection image synthesis unit generates a reconstructed image that virtually reproduces the fluoroscopic image from the three-dimensional image by synthesizing the generated elemental projection images for each pixel based on the calculated projection positions.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0009] Hereinafter, a radiotherapy apparatus, a medical image processing apparatus, a radiotherapy method, and a program according to embodiments will be described with reference to the drawings.

[0010] FIG. 1 is a block diagram showing a schematic configuration of a radiation therapy system including a radiation therapy apparatus according to an embodiment. The radiation therapy system 1 includes, for example, a treatment table 10, two radiation sources 20 (radiation source 20-1 and radiation source 20-2), two radiation detectors 30 (radiation detector 30-1 and radiation detector 30-2), a treatment beam irradiation door 40, and a radiation therapy apparatus 100. The radiation therapy apparatus 100 is an example of a "radiation therapy apparatus" or a "medical image processing apparatus".

[0011] The treatment table 10 is a bed on which a subject (patient) P to be treated by radiation is placed and fixed. The treatment table 10 includes a translation mechanism and a rotation mechanism for changing the direction of a treatment beam irradiated to the fixed patient P. The treatment table 10 can move in three axial directions, that is, six axial directions, by each of the translation mechanism and the rotation mechanism.

[0012] The radiation source 20-1 irradiates radiation r-1 for fluoroscoping the inside of the patient P from a predetermined angle. The radiation source 20-2 irradiates radiation r-2 for fluoroscoping the inside of the patient P from a predetermined angle different from that of the radiation source 20-1. The radiation r-1 and the radiation r-2 are, for example, X-rays. FIG. 1 shows a case where X-ray imaging is performed on the patient P fixed on the treatment table 10 from two directions. In FIG. 1, the illustration of a control unit for controlling the irradiation of the radiation r by the radiation source 20 is omitted. The illustration of a control unit for controlling the irradiation of the radiation r by the radiation source 20 is omitted.

[0013] The radiation detector 30-1 detects the radiation r-1 irradiated from the radiation source 20-1, passing through the inside of the patient P and reaching, and generates an X-ray fluoroscopic image of the inside of the patient P according to the magnitude of the energy of the detected radiation r-1. The radiation detector 30-2 detects the radiation r-2 irradiated from the radiation source 20-2, passing through the inside of the patient P and reaching, and generates an X-ray fluoroscopic image of the inside of the patient P according to the magnitude of the energy of the detected radiation r-2.

[0014] The radiation detector 30 includes a plurality of X-ray detectors arranged in a two-dimensional array. The radiation detector 30 generates a digital image representing the magnitude of the energy of the radiation r that has reached each X-ray detector as a digital value, as an X-ray fluoroscopic image. The radiation detector 30 is, for example, a Flat Panel Detector (FPD). The radiation detectors 30-1 and 30-2 output the generated X-ray fluoroscopic images T1 and T2 to the radiation therapy apparatus 100. In FIG. 1, illustration of a control unit that controls generation of the X-ray fluoroscopic image by the radiation detector 30 is omitted.

[0015] In the radiation therapy system 1, since the positions of the radiation source 20 and the radiation detector 30 are fixed, the imaging direction (relative direction with respect to the fixed coordinate system of the treatment room) of the imaging device constituted by the pair of the radiation source 20 and the radiation detector 30 is fixed. For this reason, when three-dimensional coordinates are defined in the three-dimensional space in which the radiation therapy system 1 is installed, the positions of the radiation source 20 and the radiation detector 30 can be represented by coordinate values of three axes. In the following description, the information on the coordinate values of these three axes is referred to as imaging system geometry information of the imaging device constituted by the pair of the radiation source 20 and the radiation detector 30. The imaging system geometry information includes information such as the position of the radiation source 20, the position and inclination of the radiation detector 30, and the like. By using the imaging system geometry information, the position of the patient P within a predetermined three-dimensional coordinate can be obtained from the position when the radiation irradiated from the radiation source 20 passes through the body of the patient P and reaches the radiation detector 30.

[0016] The imaging system geometric information can be obtained from the installation positions of the radiation source 20 and the radiation detector 30 designed when installing the radiation therapy system 1. Alternatively, the geometric information can also be obtained from the installation positions of the radiation source 20 and the radiation detector 30 measured by a three-dimensional measuring instrument or the like. By obtaining the projection matrix from the imaging system geometric information, the radiation therapy apparatus 100 can calculate at which position (projection position) on the captured two-dimensional fluoroscopic image a patient P in the three-dimensional space is captured (at which position each point in the three-dimensional space is projected on the DRR).

[0017] FIG. 2 is a diagram for explaining a projection matrix used in the projection position calculation process according to the embodiment. The projection matrix P is a matrix representing the correspondence when a point in the three-dimensional space is projected onto a two-dimensional fluoroscopic image. A point X(→) = (X, Y, Z) in the three-dimensional space t and a point u = (u, v) on the two-dimensional fluoroscopic image at the projection destination t are related by the following equation (1) ((→) represents a vector).

[0018]

Equation

[0019] The projection matrix P is represented by the following equations (2) and (3). In equations (2) and (3), the position of the radiation source 20 is L(→) = (l X , l Y , l Z ), t the base vectors of the radiation detector 30 (FPD) are u(→) = (u X , u Y , u) t , v(→) = (v X , v, v Z ), t w(→) = (w X , w Y , w) t , the point obtained by projecting L(→) onto the radiation detector 30 is c(→) = (c u , c v ). tLet the distance from L(→) to c(→) be f, and the pixel pitch of the radiation detector 30 be s u [mm / pixel], s v [mm / pixel].

[0020] [Number]

[0021] [Number]

[0022] Also, in an imaging device that simultaneously captures two fluoroscopic images of the patient P as shown in FIG. 1, a projection matrix is obtained for each set of the radiation source 20 and the radiation detector 30. Thereby, from the positions of affected parts such as lesions and bones in the body of the patient P imaged in the two fluoroscopic images, or the positions of images of markers previously placed in the body of the patient P, coordinate values in predetermined three-dimensional coordinates representing the positions of the affected parts or the markers can be calculated.

[0023] Note that in FIG. 1, the configuration of the radiation therapy system 1 including two sets of the radiation source 20 and the radiation detector 30, that is, two imaging devices, is shown. The radiation therapy system 1 may include three or more imaging devices (three or more sets of the radiation source 20 and the radiation detector 30). Also, the radiation therapy system 1 may include only one imaging device (one set of the radiation source 20 and the radiation detector 30).

[0024] The treatment beam irradiation port 40 irradiates the affected part, which is the target site for treatment in the body of the patient P, with radiation as the treatment beam B. The treatment beam B is, for example, X-rays, γ-rays, electron beams, proton beams, neutron beams, heavy particle beams, etc. The treatment beam B is irradiated linearly from the treatment beam irradiation port 40 to the patient P. Note that in FIG. 1, the configuration of the radiation therapy system 1 including one fixed treatment beam irradiation port 40 is shown, but it is not limited thereto, and the radiation therapy system 1 may include a plurality of treatment beam irradiation ports.

[0025] The radiation therapy device 100 controls the operations of the functions of the radiation therapy system 1. The radiation therapy device 100 includes, for example, an input interface 110, a display unit 120, a storage unit 130, and a control unit 140. Note that each of these functional units may be provided in a distributed manner across a plurality of devices. For example, the function of generating DRRs in the control unit 140 may be realized by a processing device separate from the radiation therapy device 100. This processing device is an example of a "medical image processing device".

[0026] The input interface 110 receives various input operations from the implementers (such as doctors and technicians) of radiation therapy who use the radiation therapy system 1, and outputs a signal indicating the received input operation to the control unit 140. The input interface 110 is, for example, a keyboard, a mouse, a touch panel, or the like.

[0027] The display unit 120 displays information such as CT images, DRRs, fluoroscopic X-ray images, the current position of the patient P, and a suitable position (hereinafter referred to as the "suitable position") determined in advance for performing radiation therapy. The display unit 120 is, for example, a liquid crystal display (LCD). When the input interface 110 is realized by a touch panel, the function of the display unit 120 may be incorporated into the touch panel.

[0028] The memory unit 130 stores various types of information necessary for radiotherapy. The memory unit 130 stores, for example, a three-dimensional image that can penetrate the body of the patient P taken at the treatment planning stage. The three-dimensional image is, for example, three-dimensional image data obtained by imaging the patient P with an imaging device such as a CT device, a cone-beam (CB) CT device, or a magnetic resonance imaging (MRI) device. In the following description, the case where the three-dimensional image is the CT image D1 obtained by imaging the patient P with a CT device will be taken as an example for explanation. In addition, the memory unit 130 stores, for example, treatment plan information D2 such as the irradiation position, irradiation direction, irradiation level, and irradiation times of the radiation beam B for each patient determined at the treatment planning stage, imaging system geometry information D3, and the like. The memory unit 130 is realized by, for example, a RAM (Random Access Memory), a ROM (Read Only Memory), an HDD (Hard Disk Drive), or the like.

[0029] The control unit 140 controls operations for realizing various functions of the radiotherapy system 1. The control unit 140 includes, for example, a first acquisition unit 151, a second acquisition unit 153, a DRR generation unit 155, a positioning unit 157, a couch control unit 159, an irradiation control unit 161, and a display control unit 163.

[0030] The first acquisition unit 151 acquires the CT image D1 of the patient P, the treatment plan information D2 of the patient P, and the imaging system geometry information D3 from the memory unit 130. Note that the first acquisition unit 151 may acquire the CT image D1 or the like based on information input via the input interface 110. In addition, the first acquisition unit 151 may acquire the CT image D1 or the like from a database (such as a file server) connected via a network. Further, the first acquisition unit 151 may acquire the CT image D1 from a storage medium such as a DVD or a CD-ROM via a drive device attached to the radiotherapy apparatus 100. That is, the first acquisition unit 151 acquires the conditions for X-ray imaging in the treatment stage and the three-dimensional image of the patient taken before the treatment stage. The first acquisition unit 151 is an example of an "acquisition unit".

[0031] The second acquisition unit 153 acquires the fluoroscopic X-ray images T1 and T2 input from the radiation detectors 30-1 and 30-2 at the treatment stage.

[0032] The DRR generation unit 155 generates a DRR based on the CT image D1 acquired by the first acquisition unit 151 and the imaging system geometry information D3. FIG. 3A is a diagram showing how a DRR is generated by a conventional ray tracing method. FIG. 3B is a diagram showing how a DRR is generated by the DRR generation unit 155 according to the embodiment.

[0033] As shown in FIG. 3A, in the conventional ray tracing method, the CT image D1 is virtually arranged between the radiation source 20 and the DRR. The luminance value of each pixel of the DRR is obtained by integrating the luminance values of the respective pixels PX of the CT image D1 on the X-ray path connecting the radiation source 20 and that pixel. In this case, sampling is performed at short intervals on the X-ray path, and the luminance values of the CT image D1 are added together. That is, it is necessary to refer to the luminance of the pixels of the CT image D1 through which the X-ray passes and perform the integration process for each pixel of the DRR, resulting in a large amount of calculation. Although a highly accurate DRR can be generated by shortening the sampling interval and increasing the number of samplings, as the number of samplings increases, the processing time increases, so there is a trade-off between the image quality of the DRR and the processing time. In order to generate a DRR with sufficient image quality for positioning, a sampling interval equal to or less than the pixel pitch of the CT image D1 is desirable.

[0034] On the other hand, as shown in FIG. 3B, in the DRR generation process by the DRR generation unit 155, the information on the X-ray path is not used. Instead, based on the information on the projection position of the DRR where each pixel of the CT image D1 is projected and the information on the projected pixel (hereinafter referred to as "element projection image"), the DRR is generated. Since the DRR is a projection of the CT image D1, the DRR generation unit 155 can generate the DRR by superimposing the element projection images of all the pixels of the CT image D1. For example, in the example shown in FIG. 3B, the DRR generation unit 155 generates an element projection image EP1 corresponding to a representative pixel PX1 (hereinafter referred to as "reference pixel") in the CT image D1, and generates element projection images (such as element projection image EP2) corresponding to other pixels by two-dimensionally converting the generated element projection image EP1. Also, when generating the DRR from these element projection images, unlike the case of using ray tracing, the calculation amount depends only on the number of pixels of the CT image D1. Therefore, the processing time for generating the DRR can be shortened.

[0035] FIG. 4 is a functional block diagram showing a schematic configuration of the DRR generation unit 155 according to the embodiment. The DRR generation unit 155 includes, for example, a projection position calculation unit 201, an element projection image generation unit 203, and an element projection image synthesis unit 205.

[0036] The projection position calculation unit 201 calculates the projection position when each pixel of the CT image D1 is projected onto the DRR based on the imaging system geometry information D3. In the CT image D1, information such as three-dimensional position and rotation angle is set based on the treatment plan. The projection position calculation unit 201 uses the following formula (4) to convert the three-dimensional image coordinate system x(→)=(x,y,z) t of the CT image D1 into the room coordinate system X(→)=(X,Y,Z) t The position on the DRR where a point in the room coordinate system is projected can be calculated based on the imaging system geometry information D3. In formula (4), A is a predetermined conversion matrix set based on the imaging system geometry information D3. Further, the projection position calculation unit 201 uses the following formula (5) to convert from the room coordinate system X(→) to the DRR coordinate system u(→)=(u,v) tCalculate it. In Equation (5), P is a projection matrix.

[0037]

Number

[0038]

Number

[0039] That is, the projection position calculation unit 201 calculates the projection position when each pixel included in the three-dimensional image is projected onto the two-dimensional X-ray fluoroscopic image generated by X-ray imaging based on the conditions of X-ray imaging.

[0040] The elemental projection image generation unit 203 generates an elemental projection image when each pixel of the CT image D1 is projected onto the DRR. However, if an accurate elemental projection image is to be generated for all the pixels included in the CT image D1, it takes a long processing time. For this reason, the elemental projection image generation unit 203 first generates an elemental projection image for the reference pixel, and approximates and generates the elemental projection images of other pixels by two-dimensionally converting the generated elemental projection image. That is, the elemental projection image generation unit 203 generates an elemental projection image for each pixel when each pixel included in the three-dimensional image is projected onto the X-ray fluoroscopic image. The elemental projection image generation unit 203 generates an elemental projection image of the reference pixel included in the three-dimensional image, and generates an elemental projection image of a pixel other than the reference image included in the three-dimensional image by performing a two-dimensional conversion process on the generated elemental projection image of the reference pixel.

[0041] The elemental projection image synthesis unit 205 generates a DRR by pasting and synthesizing the elemental projection images generated by the elemental projection image generation unit 203 at the projection positions. Basically, the size of the elemental projection image is one pixel or more, and since a plurality of elemental projection images overlap each pixel of the DRR, the elemental projection image synthesis unit 205 adds the luminance values during synthesis. That is, the elemental projection image synthesis unit 205 generates a reconstructed image that virtually reproduces an X-ray fluoroscopic image from a three-dimensional image by synthesizing the generated elemental projection images for each pixel based on the calculated projection positions. Details of the processing of the projection position calculation unit 201, the elemental projection image generation unit 203, and the elemental projection image synthesis unit 205 will be described later.

[0042] Returning to FIG. 1, the positioning unit 157 collates the DRR generated by the DRR generation unit 155 with the X-ray fluoroscopic images T1 and T2 acquired by the second acquisition unit 153, and determines the position of the patient P suitable for performing radiation therapy. Then, the positioning unit 157 obtains the amount of movement of the treatment table 10 for moving the current position of the patient P fixed to the treatment table 10 to a position suitable for performing radiation therapy. In other words, the positioning unit 157 obtains the amount of movement of the treatment table 10 necessary to irradiate the treatment site with the treatment beam B from the irradiation direction previously determined with respect to the CT image D1 in the planning stage for the current position of the patient P. The positioning unit 157 outputs the obtained amount of movement to the treatment table control unit 159. That is, the positioning unit 157 performs patient positioning based on the generated reconstructed image.

[0043] Based on the information on the amount of movement output by the positioning unit 157, the treatment table control unit 159 controls the translation mechanism and the rotation mechanism provided on the treatment table 10 to change the position and direction of the patient P fixed to the treatment table 10. The treatment table control unit 159 outputs a signal S1 indicating the amount of movement to the treatment table 10. The treatment table control unit 159 controls each of the translation mechanism and the rotation mechanism of the treatment table 10, for example, in three axial directions, that is, in six axial directions.

[0044] The irradiation control unit 161 controls the irradiation of the treatment beam B by the treatment beam irradiation gate 40. Based on the treatment plan information D2 acquired by the first acquisition unit 151 and the fluoroscopic images T1 and T2 acquired in real time at the stage of treatment by the second acquisition unit 153, the irradiation control unit 161 outputs a signal S2 instructing the irradiation timing of the treatment beam B to the treatment beam irradiation gate 40.

[0045] The display control unit 163 controls the display unit 120 to display information such as CT images, DRRs, fluoroscopic images, the current position of the patient P, and the preferred position.

[0046] Among the functions of the control unit 140 of the radiotherapy apparatus 100 described above, some or all of them may be realized by, for example, a hardware processor such as a CPU (Central Processing Unit) and a storage device (a storage device having a non-transitory storage medium) storing a program (software), and various functions are realized when the processor executes the program. Also, some or all of the functions of the control unit 140 of the radiotherapy apparatus 100 described above may be realized by hardware (including a circuit unit; circuitry) such as LSI (Large Scale Integration), ASIC (Application Specific Integrated Circuit), FPGA (Field-Programmable Gate Array), GPU (Graphics Processing Unit), etc., or various functions may be realized by the cooperation of software and hardware. Further, some or all of the functions of the control unit 140 of the radiotherapy apparatus 100 described above may be realized by a dedicated LSI. The program (software) may be stored in the storage unit 130, or may be stored in a removable storage medium (non-transitory storage medium) such as a DVD or a CD-ROM, and may be installed in the storage unit 130 when the storage medium is mounted on the drive device of the radiotherapy system 1. Also, the program (software) may be downloaded in advance from another computer device via a network and installed in the storage unit 130.

[0047] Next, the processing of the radiation therapy system 1 will be described. FIG. 5 is a flowchart showing an example of the processing flow of the radiation therapy system according to the embodiment. In the following description, it is assumed that the CT image D1 of the patient P captured by the CT device and the treatment plan information D2 at the treatment planning stage are stored in advance in the storage unit 130.

[0048] First, the first acquisition unit 151 acquires the CT image D1 of the patient P to be treated from the storage unit 130 (step S101). The first acquisition unit 151 outputs the acquired CT data D1 to the DRR generation unit 155.

[0049] Next, the second acquisition unit 153 acquires the current fluoroscopic X-ray image of the patient P output by the radiation detector 30 (step S103). The second acquisition unit 153 outputs the acquired fluoroscopic X-ray image to the positioning unit 157.

[0050] Next, the DRR generation unit 155 and the positioning unit 157 start the rough search process for the position of the CT image D1 (hereinafter referred to as the "CT position") virtually arranged in the three-dimensional space of the treatment room. In the rough search process for the CT position, the DRR generation unit 155 generates a DRR based on the CT image D1 output by the first acquisition unit 151 (step S105). The DRR generation unit 155 outputs the generated DRR to the positioning unit 157. The details of the DRR generation process by the DRR generation unit 155 will be described later.

[0051] Next, the positioning unit 157 searches for the CT position with the highest similarity between the current DRR and the fluoroscopic X-ray image based on the DRR output by the DRR generation unit 155 and the fluoroscopic X-ray image output by the second acquisition unit 153 (step S107).

[0052] Subsequently, the positioning unit 157 determines whether or not the amount of patient P's positional deviation at the searched CT position is within a predetermined range (step S109). The amount of positional deviation indicates the amount of positional deviation between the CT position of the CT image D1 (the position of patient P in the CT image D1) and the current position of patient P fixed to the treatment table 10.

[0053] If the positioning unit 157 determines that the amount of patient P's positional deviation at the searched CT position is not within the predetermined range, it outputs the information of the searched CT position to the DRR generation unit 155 and returns the process to step S105. As a result, in step S105, the DRR generation unit 155 generates a new DRR based on the information of the CT position output by the positioning unit 157, and in step S107, the positioning unit 157 searches for the CT position with the highest similarity between the new DRR generated by the DRR generation unit 155 and the fluoroscopic image. In this way, the DRR generation unit 155 and the positioning unit 157 cooperate with each other to repeat the rough search process of the CT position until the amount of patient P's positional deviation at the searched CT position is within the predetermined range, that is, until the similarity between the DRR and the fluoroscopic image is higher than the predetermined similarity threshold.

[0054] On the other hand, if it is determined in step S109 that the amount of patient P's positional deviation at the searched CT position is within the predetermined range, the DRR generation unit 155 and the positioning unit 157 start the fine search process of searching more detailedly for the CT position with the least amount of patient P's positional deviation. In the fine search process of the CT position, the DRR generation unit 155 generates a DRR based on the CT position searched in the rough search process (step S111). The DRR generation unit 155 outputs the generated DRR to the positioning unit 157.

[0055] Next, based on the CT position searched in the sparse search process, the positioning unit 157 searches for the final CT position based on the DRR output by the DRR generation unit 155 and the fluoroscopic X-ray image output by the second acquisition unit 153 (step S113). For example, the positioning unit 157 moves the CT position along the rotational and translational directions conforming to the three-dimensional coordinates in the treatment room while searching for the CT position with the least amount of patient P's misalignment, based on the DRR and the fluoroscopic X-ray image with the CT position searched in the sparse search process as a reference. In other words, the positioning unit 157 moves the CT position according to six parameters representing the amount of rotation and translation conforming to the three-dimensional coordinates in the treatment room, and searches for the CT position with the highest similarity between the DRR and the fluoroscopic X-ray image.

[0056] Next, based on the finally searched CT position, the positioning unit 157 calculates the amount of movement (six control parameters) for rotating and translating the treatment table 10 conforming to the three-dimensional coordinates in the treatment room (step S115). The positioning unit 157 outputs the calculated amount of movement to the couch control unit 159.

[0057] Next, the couch control unit 159 moves the treatment table 10 according to the amount of movement output by the positioning unit 157 (step S117). Thereafter, the irradiation control unit 161 controls the treatment beam irradiation door 40 to irradiate the treatment beam B to the affected part of the patient P. Thus, the processing of this flowchart ends.

[0058] Next, the details of the DRR generation process in steps 105 and 111 described above will be described. FIG. 6 is a flowchart showing an example of the flow of the DRR generation process of the DRR generation unit 155 according to the embodiment.

[0059] First, the projection position calculation unit 201 calculates the projection position when each pixel of the CT image D1 is projected onto the DRR based on the imaging system geometry information D3 (step S201). The projection position calculation unit 201 converts the image coordinate system set in the CT image D1 into the room coordinate system, and multiplies the projection matrix based on the imaging system geometry information D3 with respect to the room coordinate system to calculate the DRR coordinate system, which is the position on the DRR.

[0060] Next, the elemental projection image generation unit 203 generates an elemental projection image when each pixel of the CT image D1 is projected onto the DRR (step S203). Each pixel included in the CT image D1, even if having the same shape, will result in a different elemental projection image if its position in the three-dimensional space changes. If calculated precisely, it is necessary to generate accurate elemental projection images for all pixels included in the CT image D1, but the calculation cost is high and the DRR cannot be generated at high speed. Therefore, the elemental projection image generation unit 203 first generates an elemental projection image corresponding to the reference pixel, and approximates the elemental projection images of other pixels than the reference pixel by two-dimensionally converting the generated elemental projection image.

[0061] Next, the elemental projection image synthesis unit 205 generates the DRR by pasting and synthesizing a plurality of elemental projection images generated by the elemental projection image generation unit 203 at the projection positions (step S205).

[0062] FIG. 7 is a diagram showing how the elemental projection image is generated by the DRR generation unit 155 according to the embodiment. The DRR generation unit 155 generates an elemental projection image corresponding to the reference pixel, generates elemental projection images of other pixels by two-dimensionally converting the generated elemental projection image, and generates the DRR by pasting and synthesizing the generated plurality of elemental projection images at the projection positions.

[0063] Specifically, let the image generated by projecting one pixel of the CT image D1 at the position X(→) = (X, Y, Z) in the three-dimensional space onto the DRR plane (radiation detector 30) be the elemental projection image e(u, v). The center position of e(u, v) on the DRR is the coordinate e where X(→) is projected onto the DRR t (→) = (e c (→) = (eu , e v ) t becomes. X(→) and e c (→) satisfies the following relationship of Equation (6).

[0064]

Equation

[0065] In the above Equation (6), P is the projection matrix calculated from the imaging system geometry D3. Consider I(u, v) generated by superimposing e(u, v). The pixels of the CT image D1 are three-dimensionally arranged in the three-dimensional space, and in general, the size of the elemental projection image is mostly larger than one pixel. Therefore, there are generally multiple elemental projection images overlapping the coordinates (u, v) on the DRR. For this reason, I(u, v) is calculated by the following Equation (7).

[0066]

Equation

[0067] In the above Equation (7), E uv is the set of elemental projection images overlapping the coordinates (u, v), w i , h i is the image size of the i-th elemental projection image in E uv , and s eu [mm / pixel], s ev [mm / pixel] is the pixel pitch of the elemental projection image.

[0068] Next, a method for generating e(u, v) will be described. Strictly speaking, it is necessary to generate element projection images for all pixels of the CT image D1. However, this would require the same amount of calculation as when generating a DRR by the conventional ray tracing method. Therefore, the DRR generation unit 155 simplifies the process by two-dimensionally transforming the element projection image corresponding to the reference pixel and approximating the element projection images of other pixels. The reference pixel is, for example, the pixel of the isocenter, which is the part where radiation is intensively irradiated. In the following, the case where the reference pixel is the pixel of the isocenter will be described as an example.

[0069] The luminance value of the element projection image depends (is proportional) on the luminance value V(X, Y, Z) of the CT image D1 used as a basis. Therefore, by multiplying the luminance value of the element projection image of the isocenter pixel by a constant multiple, the luminance values of the element projection images of other pixels can be obtained. That is, the element projection image generation unit 203 calculates the ratio of the luminance value of each other pixel to the luminance value of the isocenter pixel in the CT image D1. Then, the element projection image generation unit 203 can calculate the luminance values of the element projection images of other pixels by multiplying the calculated ratio by the luminance value of the element projection image of the isocenter pixel.

[0070] Also, for the pixels included in the CT image D1, the closer the pixel is to the radiation source 20, the larger the element projection image becomes, and the closer the pixel is to the radiation detector 30 (the farther away from the radiation source 20), the smaller the element projection image becomes. In other words, if the position of another pixel is closer to the radiation source 20 than the position of the isocenter pixel, the element projection image becomes larger, and if the position of another pixel is closer to the radiation detector 30 (DRR) than the position of the isocenter pixel, the element projection image becomes smaller. Considering such a tendency, the size of the element projection image can be calculated geometrically. Therefore, the element projection image generation unit 203 can perform the transformation considering the difference in the positions of each pixel included in the CT image D1 by enlarging or reducing the size of the element projection image.

[0071] The position of the isocenter (X iso , Y iso , Z isoFor the pixel at (0), the reference element projection image e iso (u, v) generated by the ray tracing method is used. For a pixel located at a position (X i , Y i , Z i ) other than the isocenter, if the element projection image of the pixel is approximated by a two-dimensional transformation of e iso (u, v) as e i (u, v), the transformation formula is represented by the following formulas (8), (9), and (10).

[0072]

Number

Number

Number

[0073] In the above formulas (8) to (10), w and h are the sizes of the respective element projection images. α is the ratio of the pixel values of the CT image D1 on which each element projection image is based. Since the pixel values of the CT image D1 cannot approximate the luminance values of the element projection images of other pixels (hereinafter also referred to as "target pixels") to be processed only by resizing the reference element projection image regardless of the pixel position, correction is performed using the ratio of pixel values. λ i and λ iso are calculated by the above formula (6), and β represents the ratio of the depth from the radiation source 20 to the target pixel and the depth from the radiation source 20 to the position of the isocenter. The depth from the radiation source 20 to the target pixel is, for example, the distance W1 between the radiation source 20 and the point obtained by dropping a perpendicular from the position of the target pixel (for example, pixel 1) to the straight line L1 connecting the radiation source 20 and the position of the isocenter (see Fig. 7). The depth from the radiation source 20 to the position of the isocenter is, for example, the straight-line distance W0 from the radiation source 20 to the position of the isocenter (see Fig. 7).

[0074] In the example shown in FIG. 7, first, the element projection image generation unit 203 projects the pixels at the isocenter among the pixels included in the CT image D1 to generate a reference element projection image EP10. Next, the element projection image generation unit 203 generates an element projection image EP11 of pixel 1, which is another pixel among the pixels included in the CT image D1. Here, pixel 1 is located closer to the radiation source 20 than the isocenter. Therefore, the element projection image generation unit 203 generates an element projection image EP11 (an enlarged element projection image) that is larger in size than the reference element projection image EP10 based on the above depth ratio. Further, the element projection image generation unit 203 calculates the luminance value of the element projection image EP11 by multiplying the reference element projection image EP10 by the ratio of the luminance value of pixel 1 to the pixel at the isocenter position.

[0075] Similarly, the element projection image generation unit 203 generates an element projection image EP12 of pixel 2, which is another pixel among the pixels included in the CT image D1. Here, pixel 2 is located closer to the radiation detector 30 than the isocenter. Therefore, the element projection image generation unit 203 generates an element projection image EP12 with the size of the reference element projection image EP10 reduced based on the above depth ratio. Further, the element projection image generation unit 203 calculates the luminance value of the element projection image EP12 by multiplying the reference element projection image EP10 by the ratio of the luminance value of pixel 2 to the pixel at the isocenter position.

[0076] The element projection image generation unit 203 similarly generates element projection images for the remaining pixels included in the CT image D1. The element projection image synthesis unit 205 can generate a DRR as shown in FIG. 8 by pasting and synthesizing the plurality of element projection images generated by the element projection image generation unit 203 at the projection positions.

[0077] That is, the elemental projection image generation unit 203 virtually arranges the three-dimensional image between the radiation source that performs X-ray imaging and the radiation detector. When other pixels are closer to the radiation source than the reference pixel, a conversion process is performed to enlarge the elemental projection image of the reference pixel to generate the elemental projection image of the other pixels. When other pixels are closer to the radiation detector than the reference pixel, a conversion process is performed to reduce the elemental projection image of the reference pixel to generate the elemental projection image of the other pixels. Further, the elemental projection image generation unit 203 calculates the luminance value of the elemental projection image of the other pixels based on the ratio between the luminance value of the reference pixel and the luminance value of the other pixels in the three-dimensional image. The elemental projection image generation unit 203 calculates the luminance value of the elemental projection image of the other pixels by multiplying the luminance value of the elemental projection image of the reference pixel by the ratio of the luminance value of the other pixels to the luminance value of the reference pixel.

[0078] As described above, since strict conversion is impossible with two-dimensional conversion, the approximation error of the elemental projection image increases for pixels that are horizontally farther from the isocenter to the radiation detector 30. In patient positioning, the affected part is located at the isocenter, which is the location where the most accurate positioning is desired. That is, if a DRR is generated with the elemental projection image generated at the pixel at the position of the isocenter as in this embodiment, it is possible to significantly suppress the error near the isocenter.

[0079] FIG. 9 is a diagram showing the experimental results of the positioning process of the radiation therapy apparatus 100 according to the embodiment and the apparatus of the comparative example. In this experiment, a computer having specific processing performance was used, and in each case of generating a DRR using the elemental projection image according to the embodiment and generating a DRR using the conventional ray casting method of the comparative example, a positioning process (coarse search, fine search) was performed from an appropriate initial position to calculate the amount of movement. In FIG. 9, tx, ty, and tz indicate the amounts of movement in the three axial directions in the translation mechanism, and rx, ry, and rz indicate the amounts of movement in the three axial directions in the rotation mechanism. As shown in FIG. 9, it was confirmed that the processing time can be significantly shortened in the case of the process using the elemental projection image according to the embodiment compared to the processing time in the case of adopting the conventional ray casting method of the comparative example.

[0080] According to the embodiments described above, by generating and synthesizing elemental projection images from a three-dimensional image, the generation process of the DRR can be accelerated, and the patient positioning can be performed in a short time with high accuracy.

[0081] In addition, when the CT image D1 is a rectangular parallelepiped three-dimensional image, the DRR generation unit 155 may perform a process of equalizing the CT image D1 (a process of converting the CT image D1 into a cube) and then perform the generation process of the elemental projection image. Since a cube is more likely to produce elemental projection images that are closer when projected from any angle than a rectangular parallelepiped, the variation of the elemental projection images can be suppressed.

[0082] Further, the DRR generation unit 155 may generate a DRR by placing one pixel with a luminance of 1 at a reference position (for example, the position of the isocenter) to obtain a projection image of one pixel. Thereby, the error of the image near the isocenter where a highly accurate DRR is required can be reduced. In this case, the luminance value can be represented by a constant multiple, and the movement in the depth direction can be represented by a scale change. Also, the pixel size of the CT image D1 may be reduced. Thereby, a high-quality DRR can be generated.

[0083] According to at least one of the embodiments described above, an acquisition unit (151) that acquires the X-ray imaging conditions in the treatment stage and the three-dimensional image of the patient imaged before the treatment stage, and based on the X-ray imaging conditions, a projection position calculation unit (201) that calculates the projection position when each pixel included in the three-dimensional image is projected onto the two-dimensional X-ray fluoroscopic image generated by X-ray imaging, an elemental projection image generation unit (203) that generates an elemental projection image for each pixel when each pixel included in the three-dimensional image is projected onto the X-ray fluoroscopic image, and an elemental projection image synthesis unit (205) that generates a reconstructed image (DRR) that virtually reproduces the X-ray fluoroscopic image from the three-dimensional image by synthesizing the generated elemental projection images for each pixel based on the calculated projection positions. By providing these components, the generation process of the DRR can be accelerated, and the patient positioning can be performed in a short time with high accuracy.

[0084] Although some embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, as well as in the invention described in the claims and the equivalent scope thereof.

Explanation of Reference Numerals

[0085] 1…Radiation therapy system, 10…Treatment table, 20, 20-1, 20-2…Radiation source, 30, 30-1, 30-2…Radiation detector, 40…Treatment beam irradiation door, 100…Radiation therapy apparatus, 110…Input interface, 120…Display unit, 130…Storage unit, 140…Control unit, 151…First acquisition unit, 153…Second acquisition unit, 155…DRR generation unit, 157…Positioning unit, 159…Bed control unit, 161…Irradiation control unit, 163…Display control unit, 201…Projection position calculation unit, 203…Element projection image generation unit, 205…Element projection image synthesis unit

Claims

1. An acquisition unit that acquires X-ray imaging conditions in a treatment stage and a three-dimensional image of a patient imaged prior to the treatment stage; A projection position calculation unit that calculates, based on the X-ray imaging conditions, a projection position when each pixel included in the three-dimensional image is projected onto a two-dimensional X-ray fluoroscopic image generated by the X-ray imaging; An element projection image generation unit that generates an element projection image for each pixel when each pixel included in the three-dimensional image is projected onto the X-ray fluoroscopic image; An element projection image synthesis unit that generates a reconstructed image that virtually reproduces the X-ray fluoroscopic image from the three-dimensional image by synthesizing the generated element projection images for each pixel based on the calculated projection positions; Comprising: The element projection image generation unit: Generates an element projection image of a reference pixel included in the three-dimensional image; Generates an element projection image of other pixels other than the reference pixel included in the three-dimensional image by performing a two-dimensional conversion process on the generated element projection image of the reference pixel; A radiation therapy device.

2. Further comprising a positioning unit that positions the patient based on the generated reconstructed image; The radiation therapy device according to claim 1.

3. The reference pixel is a pixel at the position of the isocenter in radiation therapy; The radiation therapy device according to claim 1 or 2.

4. The element projection image generation unit: Virtually arranges the three-dimensional image between a radiation source that performs the X-ray imaging and a radiation detector; When the other pixel is closer to the radiation source than the reference pixel, performs a conversion process of enlarging the element projection image of the reference pixel to generate an element projection image of the other pixel; When the other pixel is closer to the radiation detector than the reference pixel, performs a conversion process of reducing the element projection image of the reference pixel to generate an element projection image of the other pixel; The radiation therapy device according to any one of claims 1 to 3.

5. The element projection image generation unit: Calculates the luminance value of the element projection image of the other pixel based on the ratio between the luminance value of the reference pixel and the luminance value of the other pixel in the three-dimensional image; The radiation therapy device according to any one of claims 1 to 4.

6. The element projection image generation unit: Calculates the luminance value of the element projection image of the other pixel by multiplying the luminance value of the element projection image of the reference pixel by the ratio of the luminance value of the other pixel to the luminance value of the reference pixel; The radiation therapy device according to claim 5.

7. An acquisition unit that acquires X-ray imaging conditions in the treatment stage and a three-dimensional image of a patient imaged before the treatment stage; A projection position calculation unit that calculates, based on the X-ray imaging conditions, the projection position when each pixel included in the three-dimensional image is projected onto a two-dimensional X-ray fluoroscopic image generated by the X-ray imaging; An element projection image generation unit that generates an element projection image for each pixel when each pixel included in the three-dimensional image is projected onto the X-ray fluoroscopic image; An element projection image synthesis unit that generates a reconstructed image that virtually reproduces the X-ray fluoroscopic image from the three-dimensional image by synthesizing the generated element projection images for each pixel based on the calculated projection positions; Comprising: The element projection image generation unit: Generates an element projection image of a reference pixel included in the three-dimensional image; Generates element projection images of other pixels other than the reference pixel included in the three-dimensional image by performing two-dimensional conversion processing on the generated element projection image of the reference pixel; Medical image processing apparatus.

8. A computer: Acquires X-ray imaging conditions in the treatment stage and a three-dimensional image of a patient imaged before the treatment stage; Calculates, based on the X-ray imaging conditions, the projection position when each pixel included in the three-dimensional image is projected onto a two-dimensional X-ray fluoroscopic image generated by the X-ray imaging; Generates an element projection image for each pixel when each pixel included in the three-dimensional image is projected onto the X-ray fluoroscopic image; Generates a reconstructed image that virtually reproduces the X-ray fluoroscopic image from the three-dimensional image by synthesizing the generated element projection images for each pixel based on the calculated projection positions; A radiotherapy method, wherein generating the element projection image includes generating an element projection image of a reference pixel included in the three-dimensional image and generating element projection images of other pixels other than the reference pixel included in the three-dimensional image by performing two-dimensional conversion processing on the generated element projection image of the reference pixel; Radiotherapy method.

9. Causes a computer to: Acquire X-ray imaging conditions in the treatment stage and a three-dimensional image of a patient imaged before the treatment stage; Calculate, based on the X-ray imaging conditions, the projection position when each pixel included in the three-dimensional image is projected onto a two-dimensional X-ray fluoroscopic image generated by the X-ray imaging; Generate an elemental projection image for each pixel when each pixel included in the three-dimensional image is projected onto the fluoroscopic X-ray image. Generate a reconstructed image that virtually reproduces the fluoroscopic X-ray image from the three-dimensional image by synthesizing the generated elemental projection images for each pixel based on the calculated projection positions. A program, Generating the elemental projection images includes generating an elemental projection image of a reference pixel included in the three-dimensional image, and generating elemental projection images of other pixels other than the reference pixel included in the three-dimensional image by performing two-dimensional conversion processing on the generated elemental projection image of the reference pixel. Program.

Images