JP2010187991A - Bed positioning system, radiotherapy system and bed positioning method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bed positioning system enhancing the positioning precision of a bed using simple X-ray image data in radiotherapy. <P>SOLUTION: Radiotherapy equipment 102 includes an irradiation head 105 and an X-ray generator 106 provided to a rotary gantry 103, and the bed positioning system 301 has the X-ray source 308 and an X-ray image receiver 309 provided in opposed relation to the rotary gantry 103 so as to hold a top plate and forming X-ray data having at least two kinds of mutually different energy distributions formed by the X-ray source 308 and the X-ray image receiver 309. The image processing arithmetic device of an imaging operation table 306 forms an image emphasizing bone tissue necessary for positioning by the subtraction processing between a plurality of the X-ray images formed on the basis of the X-ray data having the different energy distributions and a positioning device 305 uses the image data along with tomographic image data used in a medical treatment plan to perform the positioning of the bed 107. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a bed positioning system, a radiotherapy system, and a bed positioning method, and in particular, is used for radiotherapy in which various types of radiation such as X-rays or proton beams are irradiated to a patient to be treated. The present invention relates to a bed positioning system, a radiation therapy system, and a bed positioning method.

  In recent years, radiation therapy aiming at necrosis of cancer cells by irradiating various types of radiation has been widely performed. As the radiation used, not only the most widely used X-rays but also treatments using particle beams such as proton beams are performed.

  One important process of radiation therapy is bed positioning. The bed positioning process is described below. First, an engineer (or doctor) generally uses a digitally reconstructed radiograph (DRR) image information output from a treatment planning apparatus, and a treatment bed (hereinafter referred to as an X-ray imaging apparatus) before irradiation. The simple X-ray image information obtained by imaging the patient lying on the bed is compared. Based on this comparison, a deviation amount between the position of the irradiation target (cancer affected part) determined in the treatment plan and the position of the irradiation target of the patient lying on the current bed is calculated. The amount of movement of the bed is obtained using the calculated shift amount so that the two types of images match. The bed positioning is completed by moving the bed based on the amount of movement. Such a bed positioning process is described in Patent Document 1, for example. Japanese Patent Application Laid-Open No. 2004-26883 describes obtaining the amount of bed movement by pattern matching between DRR image information and simple X-ray image information.

  On the other hand, there is a method called energy subtraction as a technique for obtaining an image obtained by extracting a specific portion of a subject from simple X-ray image information. This method uses a difference depending on the energy of the X-ray absorption rate, and a specific portion of the subject can be extracted by taking a difference between images captured by X-rays having different energies. There are Non-Patent Document 1 and Patent Document 3 as conventional techniques for disclosing this method. Non-Patent Document 1 describes using a soft tissue image obtained by subtracting the spine, ribs, and the like in a chest X-ray image generated by an energy subtraction method. Further, Patent Document 3 generates an image that selectively emphasizes a temporally changing portion of a subject using two soft tissue images respectively generated by an energy subtraction method based on simple X-ray image information at different imaging times. It is described to do.

JP 2000-510023 JP Japanese Patent No. 3748433 JP-A-8-336517

Masao Kiguchi, et al. “Evaluation of detectability of diffuse lung disease by dual energy subtraction method using flat panel detector, Journal of Japanese Society of Radiological Technology, Vol. 63, No. 12, pp. 1362-1369, 2007.

Frederik Maes, et al., “Multimodality image registration by maximization of mutual information”, IEEE Trans. Med. Image., Vol. 16, No. 2, pp. 187-197, 1997.

  The DRR image information is an image simulating a simple X-ray image and is generated from a CT image for treatment planning taken at the time of treatment planning. The creation of a DRR image is generally performed using a method applying a ray tracing method based on a CT value in the body obtained from a CT image having information on the three-dimensional structure in the body. Note that in bed positioning, image information captured using an X-ray simulator or the like may be used as reference image information instead of DRR image information.

  On the other hand, a simple X-ray image taken at the time of radiation irradiation is a projected image by X-rays and mainly shows a clear structure such as a bone. For this reason, as described in Patent Document 1, in the bed positioning using simple X-ray image information, it is assumed that the positional relationship between the affected area of cancer, that is, the soft tissue and the bone does not change greatly, and positioning is performed with the structure of the skeleton. Often. However, since a simple X-ray image has only projection, that is, only integrated value information of a linear attenuation coefficient, for example, parts such as a chest, a soft tissue such as a bone, a lung, and an air portion in the lung that have greatly different X-ray absorption rates. In the case of a mixture of bones, the contrast due to the bone becomes less dominant than the contrast due to other substances. As a result, it may be difficult to clearly recognize the boundary between the bone region and other regions. In this case, when positioning the bed, the operator has to determine the position while estimating the structure of the skeleton, and the positioning accuracy of the bed may deteriorate. Even in the method of directly comparing the DRR image information and the simple X-ray image information by the pattern matching described in Patent Document 2 to obtain the movement amount of the bed, in order to increase the accuracy of the pattern matching and increase the positioning accuracy of the bed, the simple X It is preferable that the outline of the bone is clear in the line image.

  If CT images are used, it is possible to relatively easily grasp the three-dimensional position information of bones and organs. Therefore, in order to increase positioning accuracy, a CT image may be taken instead of a simple X-ray image before radiation irradiation. By directly comparing this image with the CT image for treatment planning, positioning including the position of the internal organ can be performed. However, this technique has a problem that the photographing time is extended and the troublesomeness for photographing is increased.

  As a technique for dramatically increasing the amount of image information of a simple X-ray image, there is an energy subtraction method as described in Non-Patent Document 1 and Patent Document 3. In the energy subtraction method, it is possible to separate information on bone tissue and soft tissue by taking a difference between images captured by X-rays of different energies, and it is possible to emphasize or make it inconspicuous. However, Non-Patent Document 1 and Patent Document 3 aim to generate a soft tissue image obtained by subtracting the spine, ribs, etc. by the energy subtraction method, and improve the diagnostic accuracy and efficiency, and this technique is used in radiotherapy. No mention is made of using it for positioning the bed.

  As described above, in the positioning using the conventional DRR image and the simple X-ray image, when the outline of the bone is not clear in the simple X-ray image, comparison at the time of positioning is difficult, and sufficient accuracy may not be ensured.

  An object of the present invention is to provide a bed positioning system, a radiation therapy system, and a bed positioning method capable of improving the positioning accuracy of a bed using simple X-ray image information in radiotherapy.

  In order to achieve the above object, the present invention has an X-ray source device and an X-ray detection device that enters X-rays emitted from the X-ray source device and transmitted through an irradiation target, An X-ray imaging apparatus that generates X-ray information having at least two different energy distributions, an image information generation apparatus that generates a plurality of corresponding first X-ray image information based on the X-ray information, and the plurality of second An image processing apparatus that creates second X-ray image information by subtraction processing between 1 X-ray image information, and a bed movement amount calculation apparatus that calculates a bed movement amount based on the second X-ray image information and tomographic image information used for a treatment plan And a bed control device that controls a bed driving device that supports the irradiation object based on the bed movement amount.

  By using the second X-ray image information created by the subtraction process for the calculation of the bed movement amount, it becomes easy to compare with the tomographic image information for the treatment plan referred to for the movement amount calculation, and the positioning accuracy of the bed is improved. be able to.

  For X-ray information having at least two different energy distributions in the X-ray imaging apparatus, an X-ray detection apparatus having an ability to discriminate X-ray energy is used, or a plurality of kinds of information having a plurality of different representative energies are used. It can be generated by using an X-ray source device capable of emitting X-rays.

  As the second X-ray image information created by the subtraction process, it is preferable to create image information that emphasizes the bone tissue, and thereby the irradiation target (affected part) of the irradiation target (patient) in the second X-ray image information and tomographic image information. It is easy to compare both images for calculating the amount of positional deviation, and the bed positioning accuracy can be further improved by calculating the amount of bed movement based on the amount of positional deviation.

  Further, as the second X-ray image information created by the subtraction process, when creating image information that emphasizes the bone tissue, the bed movement amount calculating device emphasizes the bone tissue also on the side of the tomographic image information used for the treatment plan. It is preferable that image information to be created is created, whereby the outline of the bone tissue in the tomographic image based on the tomographic image information becomes clear, the comparison between the two images becomes easier, and the bed positioning accuracy can be further improved.

  In order for the image processing apparatus to generate the second X-ray image information by the subtraction process, a line attenuation coefficient of the imaging region is required. As this linear attenuation coefficient, a representative value may be prepared in advance, and it may be used. Preferably, the linear attenuation coefficient is calculated from tomographic image information used for the treatment plan, and the linear attenuation coefficient is used. Thereby, the image quality of the second X-ray image obtained by the subtraction process is improved, and the bed positioning accuracy can be further improved.

  According to the present invention, in radiotherapy, it is possible to improve the positioning accuracy of the bed using simple X-ray image information regardless of the skill of the operator.

BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram of the X-ray treatment system provided with the bed positioning system which is 1st Example (Example 1) of this invention, and this bed positioning system. It is a front view of the treatment apparatus in the X-ray treatment system shown in FIG. It is a figure which shows the structure of the other subsystem (treatment plan apparatus and data server) contained in the bed positioning system and X-ray treatment system in the X-ray treatment system shown in FIG. It is a block diagram which shows the detail of the X-ray imaging system in the bed positioning system shown in FIG. It is a block diagram which shows the detail of the X-ray receiver in the X-ray imaging system shown in FIG.3 and FIG.4. It is a block diagram which shows the detail of the positioning device in the bed positioning system shown in FIG. It is a flowchart which shows the procedure of the bed positioning method performed with the bed positioning system in Example 1. FIG. It is a flowchart which shows the procedure of the bed positioning method performed with the bed positioning system in the modification which modified a part of Example 1. FIG. It is a flowchart which shows the procedure of the bed positioning method performed with the bed positioning system in the other modification which corrected a part of Example 1. FIG. It is a flowchart which shows the process sequence which produces | generates the energy subtraction image in the bed positioning system which is 2nd Example (Example 2) of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

A bed positioning system according to a first embodiment (Example 1) of the present invention and an X-ray treatment system including the bed positioning system will be described with reference to the drawings. First, before describing the bed positioning system, the overall configuration and treatment apparatus of a radiation therapy system including the bed positioning system will be described with reference to FIGS. In this embodiment, the present invention is applied to an X-ray treatment system using X-rays as radiation. In addition, although an application to an X-ray therapy system is described in the present embodiment, the present invention can also be applied to a positioning system in a particle beam therapy system using a proton beam or a carbon beam.
<Overall configuration of X-ray treatment system and treatment apparatus>
As shown in FIGS. 1 to 3, the X-ray treatment system 101 includes a treatment apparatus 102 and a bed positioning system 301. The treatment apparatus 102 includes a rotating gantry 103, a support 104, an irradiation head (also referred to as an irradiation nozzle or an irradiation apparatus) 105, a therapeutic X-ray generator 106, and a bed 107. The rotating gantry 103 is rotatably attached to a column 104 installed on the floor surface. The rotating gantry 103 has an arm part 110 extending in the direction of the rotation center axis 123 and is driven by a first rotation mechanism (not shown) attached to the support column 104 to rotate around the rotation center axis 123.

  The bed 107 includes a treatment table 109 and a top plate 108 installed at the upper end of the treatment table 109. The treatment table 109 is installed on a turntable (not shown) having a second rotation mechanism (not shown) installed on the floor surface. The top plate 108 is elongated in one direction. The treatment table 109 includes three driving devices (not shown) that move the top board 108 in three directions. The top plate 108 moves 120 in the horizontal direction (referred to as the Y-axis direction) along the rotation center axis 123 by the first driving device. The top plate 108 is moved 122 in the horizontal direction (referred to as the X direction) orthogonal to the rotation center axis 123 by the second driving device. The top plate 108 moves 121 in the height direction (vertical direction) (referred to as the Z direction) by the third driving device. The top plate 108 rotates about the bed rotation shaft 125 by driving the second rotation mechanism. Furthermore, although not shown, the treatment table 109 moves the top plate 108 around the rotation center axis 123 (rolls), and raises and lowers (pitches) the tip of the top plate 108. A fifth drive device is provided. The fourth and fifth driving devices are used for fine adjustment of the positioning of the bed 107, that is, the top plate 108. A state in which the axis extending in the longitudinal direction of the top plate 108 is parallel to the rotation center shaft 123 in the horizontal direction and the vertical direction (the state of the top plate 108 shown in FIGS. 1 and 2) around the bed rotation axis 123. The rotation angle of the bed 107 is defined as zero degrees.

The irradiation head 105 is installed at a portion extending in the horizontal direction of the rotating gantry 103, that is, at a distal end portion of the arm portion 110 so as to face the top plate 108. The arm unit 110 rotates around the top plate 108 as the rotating gantry 103 rotates. An X-ray generator 106 is installed in the arm part 110. The irradiation head 107 irradiates X-rays incident from the X-ray generator 106 toward an irradiation target (for example, an affected part of cancer existing in a patient). Since the direction of the irradiation head 105 in the circumferential direction is changed by the rotation of the rotating gantry 103, X-rays can be irradiated from any direction within a range of 360 degrees around the rotation center axis 123 to the irradiation target. An intersection of the irradiation center line 124 and the rotation center axis 123 that passes through the axis of the irradiation head 105 and is the direction in which X-rays are irradiated is referred to as an irradiation center point (isocenter) 126.
<Bed positioning system>
The configuration of the bed positioning system 301 for realizing the present invention will be further described with reference to FIGS. The bed positioning system 301 includes an X-ray imaging system 304 and a positioning device 305, which are connected to a treatment planning device 302 and a data server 303 through a network as shown in FIG.

  In the bed positioning system 301, the X-ray imaging system 304 includes an imaging console 306, an imaging control device 307, an X-ray source (X-ray source device) 308, and an X-ray receiver (X-ray injector) 309. An apparatus 307, an X-ray source (X-ray source apparatus) 308, and an X-ray image receiver (X-ray injector) 309 constitute an X-ray imaging apparatus 315. The X-ray source 308 and the X-ray receiver 309 are attached to the rotating gantry 103 so as to face each other with the top plate 108 interposed therebetween (see FIG. 2).

  The X-ray source 308 emits X-rays having a single representative energy, and the X-rays having a single representative energy have a single continuous energy distribution peaking at the representative energy. . The X-ray receiver 309 has the ability (function) to discriminate energy, and thereby generates X-ray information having at least two different energy distributions as X-ray information.

  FIG. 5 is a diagram showing details of the X-ray receiver 309. In FIG. 5, a large number of semiconductor radiation detectors 601 are arranged on a substrate 602, and the lower part of the semiconductor radiation detector 601 is pixelated in a grid pattern. For example, one pixel is the region illustrated by pixel 602. When the semiconductor radiation detector 601 has N pixels per one and the X-ray receiver 309 has M semiconductor radiation detectors 601, the total number of pixels (= total number of pixels) is N × M. . FIG. 5 is an enlarged view of one semiconductor radiation detector 601. A bias voltage is uniformly applied to the upper portion of the semiconductor radiation detector 601 (not shown), and an electric field is generated inside the semiconductor radiation detector 601. In this state, when the X-ray 608 is incident and the photoelectric effect is generated, carriers (electrons and holes) are generated, and the carriers are detected as currents in the pixels corresponding to the positions. X-rays are a type of electromagnetic wave, but can be regarded as photons having a certain energy in terms of quantum theory. Since the amount of carriers is proportional to the energy of one photon of X-rays, the energy of X-rays can be known by measuring the amount of carriers, that is, the amount of charge. Specifically, the charge from each pixel is read by the charge amplifier 604, and a pulse train having a wave height proportional to the amount of charge is generated by the waveform shaping amplifier 605. The pulse train is sorted by the wave height discrimination circuit 606 according to two levels. These pulse signals are input to the pulse processing circuit 607, and digital signal processing according to the X-ray incident position and X-ray energy is performed. That is, the incident amount of high energy X-rays and the incident amount of low energy X-rays can be obtained independently. Simple X-ray image information is obtained by converting the incident amount obtained for each pixel 602 into pixel information, whereby data for energy subtraction can be obtained.

  Also, as a method for energy discrimination, apart from the method using a semiconductor radiation detector, by inserting a copper plate or the like having an appropriate thickness between two imaging plates, the X and the like detected by the front and rear plates can be detected. There is also a method of making a difference in line energy.

  As shown in FIG. 4, the imaging console 306 includes an image processing arithmetic device 401, a communication device 402, a memory 403, and a storage device 404. The image processing arithmetic device 401 has two pieces of corresponding simple X-ray image information (first X-ray image information) based on the X-ray information of the incident amount of high energy X-rays and the incident amount of low energy X-rays acquired by the X-ray receiver 309 described above. Line image information) and new X-ray image information (second X-ray image information) are generated by subtraction processing between the two simple X-ray image information (described later). That is, the image processing arithmetic device 401 creates two pieces of simple X-ray image information (first X-ray image information) and new X-ray image information (second X-ray image information) by subtraction processing. It also functions as an image processing device. The image processing arithmetic device 401 has only the function of an image information creation device that creates two simple X-ray image information (first X-ray image information), and new X-ray image information (second X-ray image information) is obtained by subtraction processing. The function of the image processing apparatus for creating a) may be provided to another arithmetic device.

The positioning device 305 of the bed positioning system 301 includes a bed control device 310 and a movement amount calculation device 311. The movement amount calculation device 311 includes a movement amount calculation device 501, a communication device 502, and a memory 503 as shown in FIG. And a storage device 504. The movement amount calculation device 311 calculates a target bed movement amount (target value) based on the movement command input from the imaging console 306, and outputs it to the bed control device 310. Further, the movement amount calculation device 311 inputs DRR image information and X-ray image information (second X-ray image information generated by subtraction processing) from the imaging console 306, and calculates the bed movement amount based on these image information. And output to the bed control device 310. The calculation of the amount of bed movement can use a known technique described in Patent Document 1, Patent Document 2, and the like. For example, the DRR image information and the X-ray image information are compared, and based on this comparison, the displacement amount of the irradiation target position of the patient is calculated, and the two types of images are matched using the calculated displacement amount. Determine the amount of movement. The bed control device 310 sends a drive control command based on the bed movement amount input from the movement amount calculation device 311 to the drive devices (first, second and third drive devices and second rotation mechanism) of the treatment device 102 described above. Output and control the drive.
<Flow of treatment>
Next, the flow of treatment from the treatment plan to irradiation with radiation will be described with reference to FIGS. 7, 8 and 9. FIG. 7 is a flowchart showing the processing contents performed in each of the X-ray imaging system 304, the positioning device 305, and the treatment planning device 302 in this embodiment in association with each other.
<Draft treatment plan>
First, a treatment plan is prepared for treatment. For this purpose, a CT image for treatment planning is taken using a CT apparatus (not shown). Thereafter, the engineer (or doctor) uses the treatment planning apparatus 302 to set the position and size of the irradiation target of the patient, the irradiation direction, and the like based on the CT image for treatment planning. The result of the treatment plan and the CT image information for treatment are stored in the data server 303 through the network (step 701). In addition, the treatment planning apparatus 302 generates DRR image information from the treatment plan CT image information for positioning, and the DRR image information is also stored in the data server 303 through the network (step 702).
<Positioning of bed>
Before irradiating treatment radiation to the irradiation target based on the treatment plan, it is necessary to match the irradiation target in the patient lying on the top board 108 with the irradiation center point 126. For this reason, positioning of the bed 107, that is, the top plate 108 is performed. The bed positioning method of the present embodiment using the bed positioning system 301 will be described below.
<Coarse positioning of the bed>
First, the bed is moved (step 703). The irradiation target that irradiates X-rays is an affected area of cancer (hereinafter referred to as an affected area) present in a patient that is an irradiation target. After the patient lies on the top panel 108, the top panel 108 is moved so that the affected area is positioned near the irradiation center point 126. This movement of the top panel 108 is calculated by inputting a movement command input by the engineer (or doctor) from the input device of the imaging console 306 to the movement amount calculation device 311 to calculate the target bed movement amount. This is performed by outputting to the bed control device 310. The bed control device 310 outputs drive control commands to the first, second, and third drive devices based on the amount of movement, and drives these drive devices. As a result, movements 120, 121, 122 with respect to the top plate 108 are performed, and the target target reaches near the irradiation center point 126. When the bed control device 310 drives the second rotation mechanism based on the movement command, the top panel 108 turns by a predetermined angle around the bed rotation shaft 125. The top plate 108 is moved near the irradiation center point 126 of the target target using an optical device such as a laser marker as a mark. In some cases, the top plate 108 is moved by using a marker such as a sticker and a crosshair attached to (or drawn on) the surface of the patient without using an optical device.
<X-ray imaging>
Next, X-ray imaging of the irradiation target is executed (step 704). The X-ray imaging for positioning is usually performed from two directions perpendicular to the vertical direction and the horizontal direction. For example, one sheet is irradiated from a direction parallel to the irradiation center line 124 of FIG. 1, and the other sheet is rotated 90 degrees with the gantry 103, and is orthogonal to the rotation center axis 123 and the irradiation center line 124 in FIG. Shoot along the direction (ie, direction 122). A gantry control device (not shown) drives the first rotation mechanism so as to correspond to each imaging angle. The imaging control device 307 sets the X-ray from the X-ray source 308 based on the imaging command input from the imaging console 306 by the engineer (or doctor) after the rotation angle of the rotating gantry 103 is set to a preset imaging angle. Is emitted to irradiate the irradiation target. X-rays transmitted through the affected area of the patient are detected by each semiconductor radiation detector 601 (see FIG. 5) of the X-ray receiver 309 facing the X-ray source 308. When shooting is completed in one direction, the gantry control device drives the first rotation mechanism until the next imaging angle is reached, and then shooting is performed in the same manner.

As a result of imaging, an incident amount of X-rays having different energy in each direction can be obtained for each pixel of the detector 601 in accordance with the principle of the X-ray receiver 309 described above. These pieces of information obtained by the X-ray receiver 309 are developed on the memory 403 of the imaging console 306 via the communication device 402, and the image processing arithmetic device 401 converts them into image data. This image data is stored in the storage device 404 as simple X-ray image information (first X-ray image information) (step 705). Normally, two images corresponding to two types of energy regions are obtained for one imaging direction. If the energy region is further divided, it is possible to obtain three or more images.
<Generation of energy subtraction images>
An energy subtraction image is formed for each imaging direction from the plurality of images thus obtained.

  Here, the principle for generating an energy subtraction image will be described.

A simple X-ray image is an image of the amount of X-rays that pass through while reaching the detector from the radiation source in the body. The absorption rate of X-rays changes depending on not only the transmitting substance and its length but also energy. Generally, in the region below MeV, the absorption rate decreases as the energy increases. For example, when transmitting through a homogeneous material, if the thickness of the material to be transmitted is z, the intensity of the incident X-ray is I ₀ , and the intensity of the transmitted X-ray is I, the relationship between I and I ₀ is (Equation 1) It is represented by

  This μ is called a linear attenuation coefficient.

By using the difference between the energy dependence of the linear attenuation coefficient for the soft tissue image and the bone tissue image, an image in which each target is emphasized can be obtained. As the simplest example, let us consider a case in which the body is composed of only two types of bone tissue and soft tissue, and the linear attenuation coefficients for the two energies of each tissue are all known. The linear attenuation coefficients for two types of energy 1 and energy 2 are μ _b1 and μ _{b2 for} bone tissue and μ _s1 and μ _{s2 for} soft tissue. The intensity of the transmitted X-ray is expressed by (Equation 1). If the intensity of the incident X-ray is I ₀ and the intensity of the transmitted X-ray reaching the detector is I ₁ and I ₂ for energy 1 and energy 2, these are expressed by (Equation 2) and (Equation 3). The

Here, x and y represent transmission lengths of bone tissue and soft tissue, respectively. A new image is obtained by performing weighted subtraction processing on the image captured with these two energies. For example, by subtracting (Equation 2) to (Equation 3) times (μ _s1 / μ _s2 ), the bone penetration length x can be obtained. This process is represented by (Formula 4).

In this specification, the image created by the subtraction process is called an energy subtraction image or simply a subtraction image. The obtained image quality of the energy subtraction image changes depending on the coefficient at the time of subtraction. In order to obtain an image having a desired image quality, μ _b1 , μ _b2 , μ _s1 , and μ _s2 need to be known. A typical value may be prepared in advance, but in practice, the optimum value varies depending on the region to be imaged and the patient.

Based on the above principle, the image processing arithmetic device 401 generates a subtraction image from two images captured in a certain direction, and stores it in the storage device 404 (step 706). First, the image processing arithmetic device 401 reads two pieces of image information stored in the storage device 404 and develops them in the memory 403 within the imaging console 306. Subsequently, the image processing arithmetic unit 401 determines a weighting coefficient for subtraction. The image quality of the generated image is determined by the coefficient used in this subtraction. When it is desired to generate a bone tissue image, a process like (Equation 4) may be performed. As is clear from (Equation 4), in order to obtain an appropriate coefficient, the bone attenuation factor in the high energy region, the low energy region, and the linear attenuation coefficient of other tissues are required. Usually, an image in which the bone tissue is emphasized is desirable for positioning at the position of the bone tissue, and a value suitable for the image is stored in the storage device 404 of the imaging console 306 in advance. The image processing arithmetic unit 401 reads this value to generate a subtraction image. The image processing arithmetic unit 401 performs subtraction processing using this coefficient for each pixel from the two images, generates a new image, and stores it in the storage device 404.
<Calculation of linear attenuation coefficient>
Although the subtraction image can be generated by the above operation, the image quality of the subtraction image depends on the coefficient when subtracting the two images. In the first place, the generation of the subtraction image is a technique for visualizing the transmission length on the assumption that only the linear attenuation coefficient is known while the value on the right side is unknown in (Expression 2) and (Expression 3). A known linear attenuation coefficient value, that is, a coefficient value for obtaining a subtraction image is originally different for each patient or imaging region. This is due to variations in the density of bone tissue and soft tissue among patients. In general, only representative values need be prepared in advance, and in this embodiment, the values are stored in the storage device 404. However, since the positioning apparatus of the present invention can use the information of the CT image for treatment planning separately from the X-ray image captured at the time of positioning, the coefficient necessary for generating the subtraction image can be calculated therefrom. . In this case, the coefficients do not need to be the same over the entire image, and can be set for each pixel when the subtraction image is generated. The method will be described below.

  The CT image for treatment planning holds the CT value in the patient. The CT value is a value obtained by standardizing the X-ray linear attenuation coefficient so that the linear attenuation coefficient of water becomes 0. Although there is a deviation due to calibration for each apparatus, the linear attenuation coefficient at the X-ray energy at the time of CT imaging You may think that it corresponds to. On the other hand, the values necessary for generating the subtraction image are on the X-ray transmission path corresponding to each pixel of the X-ray image (referred to as positioning X-ray image) captured by the X-ray imaging system 309 as shown in (Equation 4). The linear attenuation coefficient at. In order to derive a linear attenuation coefficient corresponding to the positioning X-ray image from the treatment planning CT image, it is assumed that the exact positional relationship between the treatment planning CT image and the positioning X-ray image is known. Actually, there is a deviation of about several millimeters between the two before the final positioning, but this apparatus assumes that the affected center position of the CT image for treatment planning coincides with the irradiation center point 126. A linear attenuation coefficient obtained by weighting and averaging the transmission length along the transmission path corresponding to each pixel of the positioning X-ray image is obtained separately for the bone tissue and the soft tissue. If there is a deviation of the position assumed from the actual position, the line attenuation coefficient of the tissue in the vicinity of the tissue for which the true line attenuation coefficient is to be obtained is obtained. There is no problem because the difference in attenuation coefficient value can be almost ignored. On the other hand, the transmission length, which is another unknown in (Expression 2) and (Expression 3), cannot be correctly determined from the CT image for treatment planning if there is a positional deviation of several millimeters. This is because the transmission length for each tissue may vary greatly even if the position changes slightly. As a result, based on the information on the linear attenuation coefficient extracted from the CT image for treatment planning, an image in which the transmission length is visualized by the subtraction process is obtained.

  However, there are two points to note. One is that the X-ray energy when capturing a CT image for treatment planning is different from the X-ray energy when capturing a positioning X-ray image. In order to accurately calculate the linear attenuation coefficient at another energy from the linear attenuation coefficient at one energy, the atomic number of the substance to be transmitted must be assumed. The other is an error caused by handling a CT value at a certain representative monochromatic energy, although the spectrum of X-rays for imaging CT is broad. In consideration of these errors, a table is prepared in advance that correlates the CT value of the CT image for treatment planning with the linear attenuation coefficient of bone tissue and soft tissue at the representative X-ray energy emitted from the X-ray source 308. Will do.

  As described above, the line attenuation coefficient corresponding to each pixel of the positioning X-ray image is obtained from the CT value of the treatment planning CT image. Subsequently, a coefficient for each pixel necessary for subtraction is calculated from this information.

FIG. 8 is a flowchart of processing in a modified example in which a part of the bed positioning method in the first embodiment is corrected based on such an idea. First, the image processing arithmetic unit 401 acquires a patient treatment plan and a treatment plan CT image from the data server 303 connected to the network (step 801). Subsequently, the CT value of the CT image for treatment planning is converted into a linear attenuation coefficient corresponding to the X-ray for imaging the positioning X-ray image using a table. Next, for each pixel of the positioning X-ray image, the linear attenuation coefficient is weighted and averaged by the transmission length for the bone tissue and soft tissue on the line connecting the pixel center position and the radiation source. As a result, the linear attenuation coefficient corresponding to each pixel is obtained as μ _b1 , μ _s1 , μ _b2 , and μ _{s2 in} (Equation 2) and (Equation 3) (step 802). In FIG. 8, the calculation of the linear attenuation coefficient is performed after the X-ray image is captured. However, since the linear attenuation coefficient can be calculated even before the X-ray image, the coefficient can be calculated in advance.
<Acquisition of DRR image information and X-ray image information for calculating bed movement amount>
Finally, the amount of bed movement is calculated. In calculating the bed movement amount, the movement amount calculation device 311 reads DRR image information and X-ray image information from the data server 303 and the storage device 404 in the imaging console 306, respectively, and stores them in the storage device 504 (step 707). ). As described above, the X-ray image information is generated by the image processing arithmetic device 401 and then stored in the storage device 404 in the imaging console 306, and is acquired through the network. The DRR image information is generated by the treatment planning apparatus 302 based on the treatment planning CT image and stored in the data server 303. In both the X-ray image information and the DRR image information, there are two or more pieces of image information corresponding to the imaging direction. The movement amount calculation device 311 acquires all of the image information from the network through the communication device.
<Create a new DRR image>
As described above, the DRR image information generated by the treatment planning apparatus can be used as it is, but the movement amount calculation apparatus 311 can also create a new DRR image as necessary. As described above, the CT image can relatively easily grasp the three-dimensional position information of the bone tissue or organ. For example, a bone tissue can be distinguished by having a higher CT value than other tissues. If this information is used, for example, an image in which the position of the bone tissue is identified and emphasized, or an image in which the bone is removed and the internal organs are easily seen can be obtained. FIG. 9 is a flowchart of a process in another modified example in which a part of the bed positioning method in the first embodiment is corrected based on such an idea. In this embodiment, since the bone tissue image is generated from the information for each energy of the X-ray image, the DRR image in which the bone tissue is emphasized so as to match the X-ray image is set. The movement amount calculation device 501 of the movement amount calculation apparatus 311 acquires CT image information for treatment planning from the data server 303 via the network (step 902). Next, the movement amount calculation device 501 creates DRR image information in which the bone tissue is emphasized (step 903). Information on the positions of the X-ray source 308 and the X-ray receiver 309 necessary for creating the DRR image is held in the data server 303. Therefore, the movement amount calculation device 311 also appropriately stores these information from the network. get.
<Calculation of bed movement>
Subsequently, the movement amount calculation device 501 of the movement amount calculation apparatus 311 uses the DRR image information created based on the X-ray image information and the treatment plan CT image information, that is, the movement amount of the bed 108. (Target value) is calculated (step 708). The movement amount calculation device 501 compares the created DRR image information and the X-ray image, calculates the positional deviation amount of the irradiation target (affected part) of the irradiation target (patient) in both images, and based on this positional deviation amount. To calculate the amount of bed movement. Since there are a plurality of images taken from a plurality of directions, the corresponding images are compared with each other. The comparison between the DRR image information and the X-ray image information is performed by an operator specifying feature points in both images as described in Patent Document 1, for example, and the movement amount (target value). Ask for. Further, the movement amount may be calculated by pattern matching as described in Patent Document 2, or the mutual information maximization method may be used as described in Non-Patent Document 2. The mutual information maximization method is a method for obtaining the similarity between two images.
<Bed movement>
The movement amount calculation device 501 of the movement amount calculation device 311 outputs the bed movement amount calculated as described above to the bed control device 310. The bed control device 310 outputs a drive control command to the first, second and third drive devices and the second rotation mechanism of the treatment device 102 based on the amount of bed movement, and drives them (step 709). Thereby, movement 120, 121, 122 with respect to the top plate 108 and rotation around the axis 125 are performed, and the top plate 108 is positioned so that the target target is located at the irradiation center point 126 (step 710).
<Radiation of therapeutic X-ray>
After the positioning of the bed is completed, the gantry control device, based on the X-ray generation device 106 and the first rotation mechanism drive commands input from the gantry console (not shown), One rotation mechanism is driven. The rotation gantry 103 is rotated by driving the first rotation mechanism, and the arm unit 110 is swung around the patient lying on the top board 108. Based on a control command from the gantry control device, the X-ray generation device 106 irradiates the patient's affected area with X-rays having a predetermined energy when the rotation angles are set. In this manner, X-rays are irradiated to the affected area of cancer.
<Effect of the first embodiment>
According to the present embodiment configured as described above, by using the subtraction image information (second X-ray image information) for calculating the bed movement amount, the DRR image information (for treatment planning) that is referred to for the movement amount calculation. Comparison with tomographic image information), and the positioning accuracy of the bed can be improved regardless of the skill of the operator.

  In addition, according to the present embodiment, image information that emphasizes bone tissue is created as the subtraction image information (second X-ray image information), so that the irradiation target in the subtraction image information and the DRR image information (tomographic image information) It is easy to compare both images for calculating the positional deviation amount of the irradiation target (affected part) of the (patient), and the bed movement accuracy is calculated based on the positional deviation amount, thereby further improving the positioning accuracy of the bed. be able to.

  In addition, when creating image information that emphasizes bone tissue as subtraction image information, it is preferable to create image information that emphasizes bone tissue even on the DRR image information side in the movement amount calculation device 311. The outline of the bone tissue becomes clear, the comparison between both images becomes easier, and the bed positioning accuracy can be further improved.

  Further, a linear attenuation coefficient for creating subtraction image information is calculated from CT image information (specifically, its CT value) which is tomographic image information used in the treatment plan, and the subtraction processing is performed using the linear attenuation coefficient. As a result, the image quality of the subtraction image is improved, and the bed positioning accuracy can be further improved.

  A bed positioning system that is a second embodiment (embodiment 2) of the present invention will be described. The hardware configuration of the bed positioning system of the present embodiment is the same as the hardware configuration of the bed positioning system of the first embodiment, but the apparatus performance of the X-ray imaging system 304 is different. In the X-ray imaging system 304 of the first embodiment, the X-ray imaging device 315 has an ability to discriminate energy from an X-ray source 308 that emits X-rays having a single energy distribution having a single representative energy. In the X-ray imaging system 304 of this embodiment, a plurality of types of X having a plurality of different energy distributions having a plurality of different representative energies are used in the X-ray imaging system 304 of the present embodiment. Instead, the X-ray receiver 309 does not require energy discrimination.

  The X-ray source 308 used in this embodiment can change the representative energy of X-rays to be irradiated by changing the X-ray tube voltage for accelerating electrons for generating X-rays. The X-ray tube voltage can be changed by changing the setting by the imaging control device 307 of the X-ray imaging device 315.

  The X-ray receiver 309 used in this embodiment is a flat panel detector (FPD) having a plurality of semiconductor detectors (not shown). The detector only needs to be able to record only the amount of incident X-rays. Any of an FPD having a scintillator and a plurality of photodiodes, an image intensifier, and a CCD can be used for the X-ray receiver 5.

  By using the X-ray source 308 and the X-ray receiver 309 as described above, a simple X-ray image is captured with X-rays having the first representative energy, and then X-rays having the second representative energy are used. If another new simple X-ray image is picked up, two simple X-ray images of X-rays having different energies can be obtained as in the first embodiment.

  FIG. 10 is a flowchart showing the generation process of the subtraction image information in this embodiment.

  The imaging control device 307 of the X-ray imaging device 315 stores a program for generating subtraction image information in advance, and the imaging control device 307 operates as follows based on the program. First, the X-ray tube voltage of the X-ray source 308 is set so as to generate X-ray energy having a relatively low representative energy (step 401), and an X-ray image based on the X-ray energy is taken (step 402). Subsequently, the imaging control device 307 of the X-ray imaging device 315 sets the X-ray tube voltage of the X-ray source 308 so as to generate X-ray energy having a relatively high representative energy based on the program (step 403). Then, an X-ray image with the X-ray energy is taken (step 404). The image processing arithmetic device 401 of the X-ray imaging system 304 uses the X-ray information to generate two types of X-ray image information of low energy and high energy (Steps 405 and 406), and the two types of X-rays. Image information of energy subtraction is generated using the image information (step 407). Subsequent processing may be performed in the same manner as in the first embodiment.

  The image obtained by this embodiment is equivalent to that of the first embodiment, and the same effect as that of the first embodiment can be obtained.

DESCRIPTION OF SYMBOLS 101 ... X-ray treatment system 102 ... Treatment apparatus 103 ... Rotary gantry 104 ... Strut 105 ... Irradiation head 106 ... X-ray generator 107 ... Bed 108 ... Top plate 109 ... Treatment table 110 ... Arm part 301 ... Bed positioning system 302 ... Treatment Planning device 303 ... Data server 304 ... X-ray imaging system 305 ... Positioning device 306 ... Imaging console 307 ... Imaging control device 308 ... X-ray source 309 ... X-ray receiver 310 ... Bed control device 311 ... Movement amount calculation device 315 ... X-ray imaging device 401 ... image processing arithmetic devices 402 and 502 ... communication devices 403 and 503 ... memory 404 and 504 ... storage device 601 ... semiconductor radiation detector 602 ... pixel 603 ... substrate 604 ... charge amplifier 605 ... waveform shaping amplifier 606 ... Wave height discrimination circuit 607 ... Pulse processing circuit 608 ... X-ray

Claims (18)

An X-ray source device and an X-ray detection device that enters X-rays emitted from the X-ray source device and transmitted through an irradiation target, and having at least two different energy distributions as X-ray information An X-ray imaging device for generating information;
An image information creation device for creating a plurality of corresponding first X-ray image information based on the X-ray information;
An image processing apparatus that creates second X-ray image information by subtraction processing between the plurality of first X-ray image information;
A bed movement amount calculation device for calculating a bed movement amount based on the second X-ray image information and the tomographic image information used for the treatment plan;
A bed positioning system comprising: a bed control device that controls a drive device for a bed that supports the irradiation object based on the amount of bed movement.   The X-ray detection device has an ability to discriminate X-ray energy, discriminates X-rays transmitted through the irradiation object based on the discrimination ability, and has at least two different energy distributions from each other. The bed positioning system according to claim 1, wherein the information is generated.   The X-ray source device can emit a plurality of types of X-rays having a plurality of different representative energies, and the X-ray detection device has a plurality of at least two different representative energies emitted from the X-ray source device. The bed positioning system according to claim 1, wherein X-ray information is generated by inputting X-rays of different types and having at least two different energy distributions.   The bed according to claim 1, wherein the image processing apparatus creates image information that emphasizes bone tissue as the second X-ray image information created by subtraction processing between the plurality of first X-ray image information. Positioning system.   The image processing device creates image information that emphasizes bone tissue as the second X-ray image information created by subtraction processing between the plurality of first X-ray image information, and the bed movement amount calculation device also The bed positioning system according to claim 1, wherein image information that emphasizes bone tissue is created as tomographic image information used in a treatment plan.   The bed positioning system according to claim 1, wherein the image processing device calculates a linear attenuation coefficient used in subtraction processing between the plurality of first X-ray image information from tomographic image information used in the treatment plan. . A treatment apparatus having an irradiation apparatus for irradiating an irradiation object with therapeutic radiation and a bed driving apparatus for supporting the irradiation object;
A bed positioning system that moves the bed to position the irradiation target at the irradiation position of the therapeutic radiation emitted from the irradiation device;
The bed positioning system includes:
An X-ray source device and an X-ray detection device that enters X-rays emitted from the X-ray source device and transmitted through an irradiation target, and having at least two different energy distributions as X-ray information An X-ray imaging device for generating information;
An image information creation device for creating a plurality of corresponding first X-ray image information based on the X-ray information;
An image processing apparatus that creates second X-ray image information by subtraction processing between the plurality of first X-ray image information;
A bed movement amount calculation device for calculating a bed movement amount based on the second X-ray image information and the tomographic image information used for the treatment plan;
A radiation therapy system comprising: a bed control device that controls a drive device for a bed that supports the irradiation target based on the amount of bed movement.   The X-ray detection device has an ability to discriminate X-ray energy, discriminates X-rays transmitted through the irradiation object based on the discrimination ability, and has at least two different energy distributions from each other. The radiation therapy system according to claim 7, wherein the information is generated.   The X-ray source device can emit a plurality of types of X-rays having a plurality of different representative energies, and the X-ray detection device has a plurality of at least two different representative energies emitted from the X-ray source device. 8. The radiotherapy system according to claim 7, wherein X-ray information having at least two types of energy distributions different from each other is generated by entering different types of X-rays.   The radiation according to claim 7, wherein the image processing device creates image information that emphasizes bone tissue as the second X-ray image information created by subtraction processing between the plurality of first X-ray image information. Treatment system.   The image processing device creates image information that emphasizes bone tissue as the second X-ray image information created by subtraction processing between the plurality of first X-ray image information, and the bed movement amount calculation device also The radiotherapy system according to claim 7, wherein image information that emphasizes a bone tissue is created as tomographic image information used in a treatment plan.   The radiotherapy system according to claim 7, wherein the image processing device calculates a linear attenuation coefficient used in a subtraction process between the plurality of first X-ray image information from tomographic image information used in the treatment plan. . X-rays emitted from the X-ray source device and transmitted through the irradiation target are incident on the X-ray detection device, and X-ray information is generated as X-ray information having at least two different energy distributions.
A plurality of corresponding first X-ray image information is created based on the X-ray information,
Creating second X-ray image information by subtraction processing between the plurality of first X-ray image information;
A bed movement amount is calculated based on the second X-ray image information and the tomographic image information used for the treatment plan,
A bed positioning method, wherein a bed driving device that supports the irradiation target is controlled based on the bed movement amount.   As the X-ray detection device, an X-ray detection device having the ability to discriminate X-ray energy is used, and X-rays transmitted through the irradiation object are discriminated based on the discrimination capability of the X-ray detection device, and the mutual 14. The bed positioning method according to claim 13, wherein X-ray information having at least two different energy distributions is generated.   As the X-ray source device, an X-ray source device capable of emitting a plurality of types of X-rays having a plurality of different representative energies is used, and the X-ray detection device is at least two different ones emitted from the X-ray source device. 14. The bed positioning method according to claim 13, wherein a plurality of types of X-rays having representative energy are incident, and X-ray information having at least two different energy distributions is generated.   The bed positioning method according to claim 13, wherein image information that emphasizes bone tissue is created as the second X-ray image information created by subtraction processing between the plurality of first X-ray image information.   Image information that emphasizes bone tissue is created as the second X-ray image information created by subtraction processing between the plurality of first X-ray image information, and bone tissue is emphasized as tomographic image information used for the treatment plan The bed positioning method according to claim 13, wherein image information is created.   The bed positioning method according to claim 13, wherein a linear attenuation coefficient used in a subtraction process between the plurality of first X-ray image information is calculated from tomographic image information used for the treatment plan.

Images