JP5279637B2 - Bed positioning system and bed positioning method - Google Patents

Description

  The present invention relates to a bed positioning system and a bed positioning method, and more particularly to a bed positioning system suitable for use in radiotherapy in which various types of radiation such as X-rays or proton beams are irradiated to a diseased part. 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, treatment using not only the most widely used X-ray but also a particle beam including a proton beam is performed.

  One important process of radiation therapy is bed positioning, which is performed immediately prior to radiation therapy. The bed positioning process is described in Patent Document 1, for example. That is, first, an engineer (or doctor) generally uses digital reconstructed radiograph (DRR) image information output from a treatment planning apparatus and a treatment bed (XR imaging apparatus before irradiation) using an X-ray imaging apparatus. Hereinafter, simple X-ray image information obtained by imaging with 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. It is known from Patent Document 2 that the amount of bed movement is obtained by pattern matching between DRR image information and X-ray image information.

  The DRR image information is an image simulating an X-ray image and is generated from a CT image for treatment planning taken at the time of treatment planning. The creation of the DRR image is generally performed using a method applying the ray tracing method based on the CT value in the body obtained from the CT image having information on the three-dimensional structure in the body. In the process of positioning by comparing the DRR image information and the X-ray image DRR image captured at the time of treatment, the X-ray image captured from two orthogonal directions and the DRR image generated to correspond to the X-ray image are normally captured. Is used. That is, although the projection images from two directions are compared with each other, it may be difficult to grasp the positional relationship between the three-dimensional images only from the information of the two orthogonal projection images. Specifically, it becomes difficult to determine the amount of rotation about the axis orthogonal to both of the two imaging directions of the projected image by positioning using the projected image. For example, the head or the like is a part having a relatively large degree of freedom of movement due to the neck joint, and it is particularly difficult to align the position only from the projection image. On the other hand, the head has many important parts to avoid radiation, and more careful positioning is required. Therefore, in order to perform positioning with sufficient accuracy from only the DRR image and the positioning X-ray image. There was a problem of requiring a lot of time.

  As a method for solving this problem, a method of acquiring a CT image even at the time of positioning is known (for example, see Non-Patent Document 1). In this method, the CT image for treatment planning is directly compared with the CT image for positioning imaged at the time of treatment to perform positioning. Since the positioning is between the three-dimensional image information, the movement amount is determined more easily than when the projection image is used. Further, in positioning the DRR image and the X-ray image, positioning of bones is mainly performed, but the method of comparing CT images has an advantage that positioning including the position of an internal organ can be performed.

  However, while a method of acquiring a CT image at the time of positioning has many advantages, an image captured at the time of positioning must be reconstructed at the time of positioning. Reconstruction of a CT image has much more image information to be handled than a simple X-ray image, and requires a longer time for creation. Further, in order to correctly reconstruct a three-dimensional CT image from a projection image, correction for suppressing various artifacts is essential. Typical factors that cause artifacts include the partial volume effect and beam hardening (see, for example, Non-Patent Document 2). In the partial volume effect, one pixel or voxel is the minimum unit for image reconstruction. Therefore, when different substances exist in the voxel, the CT value is expressed as an average value, and beam hardening is X This is a phenomenon in which the linearity between the absorptance and the transmission length is lost due to the change in the quality of X-rays depending on the distance of the substance through which the rays pass. In the reconstruction considering the correction for these, the time required for the reconstruction further increases.

  Among these, various correction processes have been conventionally performed for beam hardening. A typical correction method is a method in which a correction function for projection data measured for each channel of a detector is determined in advance so that a reconstructed image of a homogeneous water phantom is correctly uniform (for example, patent document). 3). This correction generally functions without any problem when the substance to be imaged is close to water. However, in a part where there is a lot of material that is greatly different from water, for example, a head with many bones, correction of this method often causes linear or strip-like artifacts. In order to remove this artifact, the ratio of the transmission length between the bone and other tissues is calculated for each detector channel from the reconstructed image, and the coefficient used for correction is adjusted according to that value. A method is known (see, for example, Patent Document 4).

JP 2000-510023 JP Japanese Patent No. 3748433 Japanese Patent No. 3204701 Japanese Patent No. 3223195

Noriya Yokohama et al., “Outline and examination of patient positioning system using CT-treatment common bed in proton therapy”, Journal of Japanese Society of Radiological Technology, Vol. 59, No. 11, pages 1432 to 1436, 2003.

Thorsten M. Buzug “Computed Tomography From Photon Statistics to Modern Cone-Beam CT”, Springer (2008)

  Here, although the method described in Patent Document 4 can efficiently remove artifacts due to beam hardening, there is a problem that the calculation speed becomes slow because it is necessary to perform the calculation for reconstructing the CT image twice. . Increased calculation time during positioning places a burden on the patient. That is, the time required for the radiation treatment itself varies depending on the size of the affected part, the number of irradiations, etc., but is generally 1 or 2 minutes, but generally 10 or more minutes are required for the bed positioning performed immediately before that. Cost. Since the patient is restrained by the bed so that the position of the affected part does not shift during bed positioning and radiotherapy, the burden on the patient is large. In addition, an increase in calculation time during positioning also affects the number of people that can be treated throughout the year by the treatment facility.

  An object of the present invention is to provide a bed positioning system and a bed positioning method that can reduce the time required for radiation therapy.

(1) In order to achieve the above object, the present invention provides an X-ray source apparatus that irradiates X-rays, an X-ray detection apparatus that acquires first X-ray information corresponding to the X-rays, and a treatment plan. The tomographic image information calculating means for obtaining the second tomographic image information by separating the first tomographic image information to be used into a region having a predetermined threshold value or more and other regions, and the second tomographic image information from the second tomographic image information. A transmission length calculating means for obtaining a transmission length at the time of obtaining the first X-ray information; a correction coefficient calculating means for deriving a beam hardening correction coefficient of the X-ray from the transmission length; and correcting the first X-ray information. X-ray information calculating means for generating second X-ray information corrected by a coefficient, reconstructing means for reconstructing third tomographic image information from the second X-ray information, and the first tomographic image base to obtain a bed movement amount based on the information and the third tomographic image information And de movement amount calculating device, is obtained by so and a couch controller for controlling the bed driving unit which supports the irradiation target based on the couch movement amount obtained by said bed movement amount calculating device.
With this configuration, the time required for radiation therapy can be shortened.

  (2) In the above (1), preferably, an input for instructing to start execution of the correction coefficient calculation process so as to calculate the correction coefficient before the end of the X-ray imaging process of the irradiation target by the X-ray detection apparatus. Means are provided.

(3) Moreover, in order to achieve the said objective, this invention acquires 1st X-ray information from the X-ray irradiated toward the irradiation object from X-ray source apparatus, and is used for a treatment plan. The tomographic image information is separated into a region equal to or greater than a predetermined threshold and other regions to generate second tomographic image information, and when the first X-ray information is acquired from the second tomographic image information A transmission length is obtained, a beam hardening correction coefficient of the X-ray is derived from the transmission length, the first X-ray information is corrected from the correction coefficient to generate second X-ray information, and the second X-ray information is generated. generating a third tomographic image information by reconstructing the X-ray information, it calculates a bed movement amount based on the first tomographic image information and the third tomographic image information, the couch movement amount Based on the above, the bed driving device for supporting the irradiation object is controlled. It is.
With this method, the time required for radiation therapy can be shortened.

  (4) In the above (3), preferably, the correction coefficient is calculated before the end of the X-ray imaging processing of the irradiation target by the X-ray detection apparatus.

  According to the present invention, the time required for radiation therapy can be shortened.

It is a front view of the X-ray treatment system which is a radiotherapy system to which the bed positioning system by one Embodiment of this invention is applied. 1 is a side view of an X-ray treatment system to which a bed positioning system according to an embodiment of the present invention is applied. 1 is a system configuration diagram of an X-ray treatment system to which a bed positioning system according to an embodiment of the present invention is applied. 1 is a system configuration diagram of an X-ray imaging system used in an X-ray therapy system to which a bed positioning system according to an embodiment of the present invention is applied. It is a system configuration figure of a positioning device used for a bed positioning system by one embodiment of the present invention. It is a block diagram which shows the structure of the image processing arithmetic unit used for the bed positioning system by one Embodiment of this invention. It is a flowchart which shows the content of the positioning method in the bed positioning system by one Embodiment of this invention. It is explanatory drawing of the positioning method in the bed positioning system by one Embodiment of this invention. It is explanatory drawing of the positioning method in the bed positioning system by one Embodiment of this invention. It is explanatory drawing of the positioning method in the bed positioning system by one Embodiment of this invention.

Hereinafter, the configuration and operation of a bed positioning system according to an embodiment of the present invention will be described with reference to FIGS.
First, the configuration of an X-ray treatment system, which is a radiation treatment system, to which the bed positioning system according to the present embodiment is applied will be described with reference to FIGS. In addition, although this embodiment describes application to an X-ray therapy system, the present invention can also be applied as a positioning system corresponding to a particle beam therapy system using a proton beam or a carbon beam.

  FIG. 1 is a front view of an X-ray therapy system that is a radiation therapy system to which a bed positioning system according to an embodiment of the present invention is applied. FIG. 2 is a side view of an X-ray treatment system to which a bed positioning system according to an embodiment of the present invention is applied. FIG. 3 is a system configuration diagram of an X-ray therapy system to which a bed positioning system according to an embodiment of the present invention is applied. FIG. 4 is a system configuration diagram of an X-ray imaging system used in an X-ray therapy system to which a bed positioning system according to an embodiment of the present invention is applied. FIG. 5 is a system configuration diagram of a positioning device used in a bed positioning system according to an embodiment of the present invention.

  As shown in FIG. 1, the X-ray treatment system 101 includes a treatment apparatus 102 and a bed positioning system 301. The bed positioning system 301 includes an X-ray imaging system 304 and a positioning device 305.

  The treatment apparatus 102 includes a rotating gantry 103, a support column 104, an irradiation head (irradiation nozzle, irradiation apparatus) 105, an X-ray generation apparatus 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. A bed positioning system 301 including an X-ray imaging system 304 and a positioning device 305 is connected to a treatment planning device 302 and a data server 303 through a network as shown in FIG.

  Next, the configuration of the treatment apparatus 102 will be described with reference to FIGS. 1 and 2. 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 is moved in the horizontal direction (Y-axis direction) along the rotation center axis 123 by the first driving device. The top plate 108 is moved in the horizontal direction (X direction) orthogonal to the rotation center axis 123 by the second driving device. The top plate 108 is moved in the height direction (vertical direction) (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.

  Here, the configuration of the bed positioning system 301 according to the present embodiment will be described with reference to FIGS. 3 and 4.

  As shown in FIG. 4, the X-ray imaging system 304 of the bed positioning system 301 includes an X-ray source (X-ray source device) 308, an X-ray receiver (X-ray injector) 309, and an imaging control device 307. As shown in FIG. 2, 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. The X-ray receiver 309 includes a plurality of semiconductor radiation detectors (not shown) (hereinafter referred to as semiconductor detectors) that are radiation detectors. A scintillator may be used as the radiation detector. The X-ray receiver 309 used in this example is a flat panel detector (FPD) having a plurality of semiconductor detectors. 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 309.

  As shown in FIG. 4, the X-ray source 308 and the X-ray receiver 309 are connected to the imaging control device 307. The imaging control device 307 is connected to the imaging console 306 through the communication device 402. The imaging console 306 includes an image processing arithmetic device 401, a communication device 402, a memory 403, a storage device 404, and input means 405. The input unit 405 includes an input interface such as a keyboard and a mouse, and a display device (not shown) such as a display. With these, the operator can instruct an operation on the imaging console 306.

  As shown in FIG. 3, the positioning device 305 includes a bed control device 310 and a movement amount calculation device 311. As illustrated in FIG. 5, the movement amount calculation device 311 includes a movement amount calculation device 501, a communication device 502, a memory 503, and a storage device 504. The movement amount calculation device 311 calculates the movement amount of the bed for positioning by comparing the CT image for positioning obtained by the X-ray imaging system 304 and the CT image for treatment planning, and bed control is performed based on the result. The device 310 moves the bed and the positioning is complete.

  Next, the flow of treatment from the start of the treatment plan to irradiation with radiation will be described with reference to FIGS.

  FIG. 6 is a block diagram showing a configuration of an image processing arithmetic device used in the bed positioning system according to the embodiment of the present invention. FIG. 7 is a flowchart showing the contents of the positioning method in the bed positioning system according to the embodiment of the present invention. 8-10 is explanatory drawing of the positioning method in the bed positioning system by one Embodiment of this invention.

  As shown in FIG. 6, the image processing arithmetic unit 401 includes a tomographic image information calculation unit 401A, a transmission length calculation unit 401B, a correction coefficient calculation unit 401C, an X-ray information generation unit 401D, and a reconstruction unit 104E. I have.

  The tomographic image information calculation unit 401A extracts the first tomographic image information used for the treatment plan as a prescribed value, and obtains the second tomographic image information. The transmission length calculation unit 401B obtains the transmission length when acquiring the first X-ray information acquired at the time of positioning from the second tomographic image information. The correction coefficient calculation means 401C derives the X-ray beam hardening correction coefficient from the transmission length. The X-ray information generation unit 401D corrects the first X-ray information from the correction coefficient, and generates second X-ray information. The reconstruction unit 104E reconstructs the second tomographic image information from the second X-ray information.

  The detailed operation of each means will be described later with reference to FIG.

  First, a treatment plan is prepared for treatment. First, the patient takes a CT image for treatment planning using a CT apparatus (not shown). The imaged therapeutic CT image is stored in the data server 303. Subsequently, the technician (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 is also stored in the data server 303 through the network.

  After the treatment plan is made, the actual treatment is performed. Before the irradiation target is irradiated with the therapeutic radiation based on the treatment plan, the irradiation target in the patient lying on the top board 108 and the irradiation center point 126 must be matched. For this reason, positioning of the bed 107, that is, the top plate 108 is performed.

  Here, the contents of the bed positioning method according to the present embodiment will be described with reference to FIG.

  As a feature of the bed positioning method according to the present embodiment shown in FIG. 7, firstly, as shown in step S20 of FIG. 7, a CT image for treatment planning is taken and corrected as shown in steps S30 to S90. The point is to calculate the coefficient.

  In the method described in Patent Document 4, it is necessary to perform the calculation for CT image reconstruction twice. However, in the method of the present embodiment described above, the CT image for treatment planning captured in step S20 in FIG. Since the calculation for the configuration has been completed, it is only necessary to perform the reconstruction once at the time of obtaining the imaging X-ray information in step S130 of FIG.

  In general, computation for CT image reconstruction takes 1 or 2 minutes, so that the time required for bed positioning can be reduced by 1 or 2 minutes by performing reconstruction at once.

  Secondly, the correction coefficient calculation process in steps S20 to S90 is executed in parallel with the process for X-ray imaging of the irradiation target in steps S110 to S130 in FIG. In other words, the correction coefficient is calculated before the end of the X-ray imaging process of the irradiation target.

  When positioning is performed using the method described in Patent Document 4, with reference to FIG. 7, after the processing in steps S <b> 110 to S <b> 130, using the X-ray information acquired in step S <b> 130, steps S <b> 30 to S <b> 130 are performed. The process of S90 is executed, and thereafter it is executed sequentially, such as the process of steps S140 to S160. Here, the process of steps S110 to S130 requires several minutes, the process of steps S30 to S90 requires several minutes, and the process of steps S140 to S160 requires several minutes. When the entire process is executed sequentially as described in Patent Document 4, it takes ten or more minutes for bed positioning. On the other hand, the time required for bed positioning can be reduced to about 10 minutes by calculating the correction coefficient before the end of the X-ray imaging processing of the irradiation target. Therefore, the burden on the patient can be reduced.

  Hereinafter, the details of the bed positioning process according to the present embodiment will be described with reference to steps S10 to 160 in FIG.

  When positioning is started, in step S10, the operator inputs the patient ID from the input means 405 in FIG.

  The image processing arithmetic unit 401 of the imaging console 306 in FIG. 4 uses the input of the patient ID as a trigger, and the CT image for treatment planning stored in the data server 303 shown in FIG. Copy to 304 (step S20). Specifically, the tomographic image information calculation unit 401A illustrated in FIG. 6 captures a CT image for treatment planning. In step S10, the patient ID is input, and in step S20, the CT image for treatment planning is captured by using the input of the patient ID as a trigger. The calculation of the correction coefficient may be instructed. In other words, an input means for instructing the start of execution of the correction coefficient calculation process may be provided.

  The treatment planning CT image is stored in the storage device 404 in the imaging console 306. The X-ray imaging system creates beam hardening correction data to be used when reconstructing the positioning CT using the therapeutic CT image thus stored.

  Here, beam hardening correction will be described. Usually, in the process of reconstructing CT image information, a plurality of correction processes for suppressing the occurrence of artifacts are essential, and beam hardening correction is a typical correction item. Here, the case of monochromatic X-rays (that is, having a single wavelength) is assumed. The intensity Is after the incident X-ray having the intensity I0 is transmitted through the homogeneous material having the thickness L is expressed by Expression (1).

Here, μ is a coefficient peculiar to a substance and is called an attenuation coefficient.

  If the projection data p defined by the equation (2) is calculated from the incident X-ray intensity I0 and the transmitted X-ray intensity Is of the equation (1), it can be seen that the projection data p is proportional to the transmission length L. .

  Here, FIG. 8 is a graph showing the state of Equation (2). As indicated by a straight line 701, the projection data p is proportional to the transmission length L for monochromatic X-rays. However, incident X-rays emitted from a normal X-ray source are not monochromatic and have a certain width in the energy spectrum. This is called continuous X-ray. The intensity for each energy E of the incident X-ray is represented as I0 (E). In this case, the intensity Ic (L) of the X-ray that has passed through the substance having the thickness L must be integrated with respect to energy as in the expression (3), unlike the expression (1) in the case of monochromatic X-rays. The attenuation coefficient μ also changes depending on the energy.

  Here, Emax represents the maximum energy among the components of incident X-rays.

  In Expression (3), even if the value of the projection data p corresponding to the continuous X-ray corresponding to Expression (2) is calculated, this value is not completely proportional to the transmission length L. Specifically, the projection data p and the transmission length L have a relationship as shown by a curve 702 in FIG. That is, the intensity of X-rays transmitted through a substance having a transmission length L differs between an ideal monochromatic X-ray and a continuous X-ray. As defined in Equation (1) and Equation (3), when the transmitted X-ray intensity is Is (L) and Ic (L), respectively, the ratio thereof, BH (L) is defined by Equation (4).

This is called the degree of cure.

  If this value is known, the measured transmission X intensity can be converted into an ideal monochromatic X-ray, and projection data p proportional to the transmission length L can be obtained.

  The above is a case where a homogeneous substance is transmitted, but the human body is composed of various substances. The magnitude of the attenuation coefficient μ depends on the substance, and varies greatly between bone and other soft tissues. Therefore, Equation (3) and Equation (4) should be expressed separately for bone and soft tissue. When the bone penetration length is Lb and the soft tissue penetration length is Ls, the equations (1), (3), and (4) are expressed by the following equations (5), (6), and (7), respectively. ).

  Here, μb and μs are attenuation coefficients of bone and soft tissue, respectively. BH is an incident X-ray intensity distribution I 0 (E), and depends on attenuation coefficients μb and μs and transmission lengths Lb and Ls. The typical values of the incident X-ray intensity distribution I0 (E) and attenuation coefficients μb and μs can be known in advance. However, normally, since the values of the transmission lengths Lb and Ls are not known in advance, in order to perform beam hardening correction by this method, the correction coefficient BH is obtained after reconfiguration as in Patent Document 4. The method is taken.

  In the positioning device of the present embodiment, a CT image for treatment planning can be used to obtain the transmission lengths Lb and Ls. That is, in FIG. 7, the CT image for treatment plan read from the data server 303 is separated into a bone region and other regions based on the CT value by the tomographic image information calculation unit 401A of the image processing arithmetic device 401 ( Step S30). Since the CT value of bone is greatly different from other tissues, if a certain threshold value is set, the CT value can be easily separated into a region having a higher CT value and a region having a lower CT value. This threshold value may be set in advance or may be designated by the operator every time.

  FIG. 9 shows a state of separation by the threshold value. The image processing apparatus 401 develops the treatment plan CT image 801 stored in the storage device 404 on the memory 403. Subsequently, the CT image 801 for treatment planning is separated into a bone portion 801a and a soft tissue portion 801b. The set threshold value is read, and a CT image obtained by extracting only pixels having a CT value equal to or greater than the threshold value from the CT image 801 is generated as a bone CT image 802, and a CT image obtained by extracting only pixels smaller than the threshold value is generated as a soft tissue CT image 803. And stored in the storage device 404. As a result, two images of a bone CT image 802 and a soft tissue CT image 803 are obtained.

  Subsequently, the transmission length is calculated from the two CT images. First, the image processing arithmetic unit 401 reads the previously generated bone CT image 802 from the storage device 404 and develops it on the memory 403, and then assumes that the CT image 802 is at a target position during positioning. Although the patient position at the stage before positioning using the image does not completely match the target position, it may be considered that the patient position matches within the range of several mm by the operation of step S110 described later.

  The CT image for positioning is taken from a plurality of angles by rotating the rotating gantry 103 by the X-ray source 308 and the X-ray receiver 309. Position information such as these angles and the distance between the X-ray source 308 and the X-ray receiver 309 is held in the storage device 404 of the imaging console 306.

  As shown in FIG. 10A, first, the transmission length calculation unit 401B of the image processing arithmetic unit 401 reads these values and sets the angle of the rotating gantry. Thereafter, one channel 901 is selected from the position of the virtual X-ray source 308 and a plurality of detector channels of the X-ray receiver 309 (step S40). The positions of the X-ray source 308 and the selected channel 901 are connected by a straight line, and the CT values of the bone CT image 802 are integrated along this path 902. By dividing the integrated CT value by the representative bone CT value, the bone penetration length Lb along the X-ray path 902 reaching the channel 901 is obtained (step S50). This representative CT value may be prepared in advance or may be designated by the operator every time.

  After the transmission length for one channel is obtained, the same operation is performed for the other channels (step S60). Although the transmission length may be calculated for each channel position of the detector as described above, after calculating the transmission length for a plurality of arbitrary points on the X-ray receiver 309, You may obtain | require the transmission length corresponding to a certain channel by interpolating from the value of the transmission length in the point which performed the periphery calculation. After the calculation of the transmission length in all detector channels is completed, the angle of the virtual rotating gantry is moved to the next imaging angle, and the same operation is performed (step S70). In this way, the transmission length Lb is obtained for every channel and every angle. These values are stored in the storage device 404 as a table. The same operation is performed on the soft tissue CT image 803, and a table holding the value of Ls is obtained (see FIG. 10B).

  According to the equation (5), a coefficient necessary for beam hardening correction and a degree of hardening BH are obtained from the transmission lengths Lb and Ls of the bone and soft tissue obtained for each angle of the rotating gantry and the channel of the detector. . Therefore, the correction coefficient calculation unit 401C converts the transmission lengths Lb and Ls to the curing degree BH using a conversion table based on the actual measurement stored in the storage device 404 (step S80). In addition, an appropriate approximate expression may be prepared instead of the table. Since the degree of cure BH also depends on the energy spectrum I0 (E) of incident X-rays, a conversion table is required for each channel when the energy spectrum I0 (E) differs for each detector position, that is, for each channel. become. Alternatively, only one conversion table may be prepared, and a correction table for correcting the conversion table may be prepared for each channel position.

  The conversion from the transmission lengths Lb and Ls to the curing degree BH may be performed at once after all the transmission lengths are calculated as shown in FIG. 6, or the transmission lengths Lb and Ls are calculated for each channel. However, it may be converted every time. The obtained curing degree BH value is stored in the storage device 404 as a curing degree table together with the corresponding gantry angle and detector channel information as well as the transmission length (step S90).

  The operation for calculating the table of the degree of cure BH described above is executed by the image processing arithmetic unit 401 of the imaging console 306, and in parallel with this, the operator moves the bed (step S110). 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. The movement of the top plate 108 is performed when the bed control device 310 inputs a movement command from an input device (not shown). The bed control device 310 outputs a drive control command based on the movement command input from the imaging console 306 to the first, second, and third drive devices, and drives these drive devices. As a result, movements 120, 121, and 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 or a crosshair attached to (or drawn on) the surface of the patient without using an optical device.

  The operator performs X-ray imaging of the irradiation target (step S120). A gantry control device (not shown) drives the first rotation mechanism based on a rotation command input from a gantry console (not shown). The rotating gantry 103 rotates around the rotation center axis 123. When the rotation gantry 103 is rotating and the rotation angle of the rotation gantry 103 reaches each preset imaging angle, the imaging control apparatus 307 applies X-rays from the X-ray source 308 to the irradiation target in a pulsed manner. Irradiate. X-rays transmitted through the affected area of the patient are detected at each imaging angle set by each semiconductor detector of the X-ray receiver 309 facing the X-ray source 308. A plurality of set shooting angles (or shooting intervals) are stored in advance in the storage device 404 by an operator input from an input device (not shown) of the imaging console 306. The image processing arithmetic unit 401 transmits information on the shooting angles to the imaging control device 307 via the communication device 402. The imaging control device 307 holds information on each imaging angle (or imaging interval), and controls the operation of the X-ray source 308 and imaging conditions such as the X-ray tube voltage and current of the X-ray source 308. The imaging control device 307 includes a communication device for communicating with the imaging console 306. The detected X-ray detection signal is input to the imaging console 306. The X-ray detection signal output from each semiconductor detector of the X-ray receiver 309 is a voltage signal and is A / D converted in the X-ray receiver 309 to become a digital signal (hereinafter referred to as X-ray data). . X-ray data (X-ray information) is transmitted to the communication device 402 via the imaging control device 307 and input to the image processing arithmetic device 401 (step S130).

  The input X-ray data is stored in the storage device 404. If necessary, the image processing arithmetic unit 401 performs preprocessing such as noise removal on the X-ray data. Subsequently, the X-ray information generation unit 401D of the image processing arithmetic unit 401 confirms that a hardening degree table for beam hardening correction has been created, and if it has been created, reads it into the memory 403. . The value for each detector included in the X-ray data is the transmitted X-ray intensity corresponding to Equation (4). The degree of cure corresponding to the obtained gantry angle information and the position of the detector channel is extracted from the read table and multiplied by the value. By this operation, the linearity deviation as shown in FIG. 7 due to continuous X-rays is corrected, and the occurrence of artifacts can be suppressed. This operation is performed for all channels at all gantry angles (step S140). This operation may be performed after completion of imaging for all set gantry angles. However, if a curing degree table has been created in advance, the time can be further shortened by sequentially performing correction while imaging.

  After the hardening correction is performed, other corrections are performed if necessary. When all the corrected X-ray data have been prepared, the reconstruction unit 104E reconstructs the positioning CT image (step S150). The post-correction reconstruction method is the same as that for normal CT image reconstruction. For example, a back projection method as described in Non-Patent Document 2 is used. The created CT image for positioning is stored in the storage device 404.

  When the creation of the positioning CT image is completed, positioning by the positioning device 305 is performed according to an instruction from the operator. The movement amount calculation device 501 acquires a CT image for treatment planning from the data server 303 and a CT image for positioning from the X-ray imaging system 304 via the communication device 502 and the network. A program for calculating the movement amount is read from the storage device 504 to the memory 503, and the bed movement amount is calculated from these two CT images.

  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), The one-rotation mechanism is driven (step S160). 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 way, the affected area of cancer is irradiated with X-rays.

  As described above, according to the present embodiment, the time required for radiation therapy can be shortened. In other words, the beam hardening correction required when reconstructing the CT image for positioning is calculated before imaging using the CT image for treatment planning, thereby reducing the time required for reconstructing the CT image for positioning and Can be reduced.

  In addition, by calculating the correction coefficient before the end of the X-ray imaging process of the irradiation target, the time required for bed positioning can be shortened, and the burden on the patient can be reduced.

The correction coefficient calculation process only needs to be performed at the end of the X-ray imaging process of the irradiation target. For example, the correction coefficient calculation process is executed immediately after the CT image for treatment planning is acquired by the treatment planning apparatus 302. It is a good thing.

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 401 ... Image processing arithmetic unit 401A ... Tomographic image information calculation means 401B ... Transmission length calculation means 401C ... Correction coefficient calculation means 401D ... X-ray information generation means 401E ... Reconstruction means 402, 502 ... Communication devices 403, 503 ... Memory 404, 504 ... Storage device

Claims (4)

An X-ray source device for irradiating X-rays;
An X-ray detection device for acquiring first X-ray information corresponding to the X-ray;
A first tomographic image information used in the treatment plan, tomographic image information calculating means for separating the first tomographic image information into a region equal to or greater than a predetermined threshold and other regions, and obtaining second tomographic image information;
A transmission length calculation means for obtaining a transmission length at the time of obtaining the first X-ray information from the second tomographic image information;
Correction coefficient calculation means for deriving the X-ray beam hardening correction coefficient from the transmission length;
X-ray information calculation means for correcting the first X-ray information with the correction coefficient to generate second X-ray information;
Reconstructing means for reconstructing third tomographic image information from the second X-ray information;
A bed movement amount calculation device for obtaining a bed movement amount based on the first tomographic image information and the third tomographic image information;
A bed positioning system comprising: a bed control device that controls a drive device for a bed that supports an irradiation object based on a bed movement amount obtained by the bed movement amount calculation device. The bed positioning system according to claim 1, wherein
A bed positioning system comprising input means for instructing to start execution of a correction coefficient calculation process so as to calculate a correction coefficient before the end of the X-ray imaging process of the irradiation target by the X-ray detection apparatus. Obtaining first X-ray information from the X-rays irradiated from the X-ray source device toward the irradiation target;
Separating the first tomographic image information used for the treatment plan into a region having a predetermined threshold value or more and a region other than that, and generating second tomographic image information;
Obtaining a transmission length at the time of obtaining the first X-ray information from the second tomographic image information;
Deriving the X-ray beam hardening correction coefficient from the transmission length,
Correcting the first X-ray information from the correction coefficient to generate second X-ray information;
Reconstructing the second X-ray information to generate third tomographic image information;
A bed movement amount is calculated based on the first tomographic image information and the third tomographic image information,
A bed positioning method, wherein a bed driving device that supports the irradiation target is controlled based on the bed movement amount. The bed positioning method according to claim 3, wherein
A bed positioning method, wherein a correction coefficient is calculated before completion of X-ray imaging processing of an irradiation target by the X-ray detection apparatus.

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