JP2017104398A - X-ray imaging apparatus, subject positioning apparatus, and subject positioning method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray imaging apparatus, a subject positioning apparatus, and a subject positioning method capable of performing X-ray imaging under an appropriate X-ray condition according to the body thickness of the subject.SOLUTION: A control unit 40 includes an image processing part 41 for creating an X-ray image, a DRR creation part 42 for acquiring a DRR from X-ray CT volume data, a body thickness calculation part 43 for calculating the body thickness of a subject based on the X-ray CT volume data, ax X-ray condition determination part 44 for determining an X-ray condition at the time of positioning the subject, a positional deviation amount calculation part 45 for calculating an amount of positional deviation of the subject by comparing the DRR and the X-ray image, and a subject moving part 46 for creating a signal for moving a medical examination table on which the subject is placed, based on the amount of positional deviation calculated by the positional deviation amount calculation part 45. The control unit 40 is connected to the medical examination table moving mechanism 30 for moving the medical examination table based on the signal for moving the medical examination table created by the subject moving part 46.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an X-ray imaging apparatus, a subject positioning apparatus, and a subject positioning method.

  In radiation therapy in which radiation such as X-rays, electron beams, and particle beams is irradiated to an affected area such as cancer, it is necessary to accurately irradiate the affected area with radiation. When performing radiotherapy using a radiotherapy apparatus, a treatment plan is formulated prior to treatment. When performing radiotherapy, it is necessary to perform positioning so that the position of the patient coincides with that at the time of treatment planning. When performing such positioning, a comparison between DRR and an X-ray image is performed (see Patent Document 1).

  When creating a DRR (Digital Reconstructed Radiography) that is a virtual perspective projection using three-dimensional image data collected by an X-ray CT apparatus, an X-ray imaging system of the X-ray imaging apparatus is created on a computer. Reproduce the geometry. That is, on the computer, a geometry that is a geometric arrangement of the X-ray tube and the X-ray detector is virtually reproduced with the CT image interposed therebetween. Then, the line integral of the CT value in the CT data voxel on the line segment connecting the virtual X-ray tube to the virtual X-ray detector is obtained. Thereafter, the X-ray attenuation is calculated by converting the line integral of the CT value into the line integral of the line attenuation coefficient, and based on this, the relative X-ray dose reaching each pixel is calculated. Then, by normalizing the relative X-ray dose, the pixel value of each pixel is calculated to obtain the DRR.

  On the other hand, when creating an X-ray image, X-ray imaging is performed with the geometrical arrangement of the X-ray imaging system in the X-ray imaging apparatus composed of an X-ray tube and an X-ray detector matched with that at the time of DRR creation. To do. Then, by comparing the X-ray image obtained in this way with the DRR, the amount of displacement of the subject is calculated, and the examination table on which the subject is placed based on the calculated amount of displacement The subject is positioned by moving the.

JP 2013-99431 A

  When X-ray imaging is performed in order to obtain the above-described X-ray image, it is necessary to set X-ray conditions such as the magnitude of the tube voltage for the X-ray tube. The X-ray conditions at this time are set so that appropriate X-ray imaging can be performed even on a subject having a large body thickness, which is the distance that the X-ray passes through the subject. For this reason, there is a problem that a subject having a small body thickness is photographed under a high dose of X-rays even though X-ray imaging can be performed with a smaller amount of X-ray.

  The present invention has been made to solve the above-described problem, and an X-ray imaging apparatus capable of performing X-ray imaging under an appropriate X-ray condition according to the body thickness of the subject, An object of the present invention is to provide a positioning device and a method for positioning a subject.

  The first invention is obtained by reproducing the geometric arrangement of an X-ray imaging system on a computer and virtually performing perspective projection on X-ray CT volume data obtained by X-ray CT imaging of a subject. The subject is positioned by comparing the obtained DRR with an X-ray image obtained by detecting an X-ray irradiated from the X-ray tube and passing through the subject with an X-ray detector. In the X-ray imaging apparatus, based on the X-ray CT volume data, a body thickness calculation unit that calculates a body thickness that is a distance that X-rays pass through the subject, and the body thickness calculation unit calculates the body thickness And an X-ray condition determining unit that determines an X-ray condition for the X-ray tube at the time of positioning of the subject based on a body thickness of an imaging region of the subject.

  According to a second aspect of the present invention, there is provided a body thickness calculator that calculates the length of an imaging region of a subject based on X-ray CT volume data obtained by X-ray CT imaging of the subject, and the body thickness calculator An X-ray condition determining unit that determines an X-ray condition irradiated from the X-ray tube at the time of X-ray imaging based on the body thickness of the imaging region of the subject calculated by the above.

  A third invention includes an X-ray tube and an X-ray detector, and X-ray images are taken by detecting X-rays emitted from the X-ray tube and passing through the subject by the X-ray detector. The X-ray imaging system and the geometric arrangement of the X-ray imaging system are reproduced on a computer, and the perspective projection is virtually performed on the X-ray CT volume data obtained by X-ray CT imaging of the subject. A DRR creation unit that obtains a DRR, a body thickness calculation unit that calculates a body thickness that is a distance that an X-ray passes through the subject based on the X-ray CT volume data, and a body thickness calculation unit An X-ray condition determining unit that determines an X-ray condition for the X-ray tube at the time of positioning of the subject based on the calculated body thickness of the imaging region of the subject and the DRR creating unit DRR and X determined by the X-ray condition determining unit By comparing the X-ray image captured by the X-ray imaging system under conditions, the position shift amount calculation unit that calculates the position shift amount of the subject, and the position calculated by the position shift amount calculation unit And a subject moving unit that creates a signal for moving the examination table on which the subject is placed based on the amount of deviation.

  The fourth invention reproduces the geometric arrangement of the X-ray imaging system on a computer, and virtually performs perspective projection on X-ray CT volume data obtained by X-ray CT imaging of the subject. A DRR creation step of obtaining a body thickness, a body thickness calculation step of calculating a body thickness that is a distance that X-rays pass through the subject based on the X-ray CT volume data, and the body thickness calculation step Based on the body thickness of the imaging region of the subject, an X-ray condition determining step for determining an X-ray condition for the X-ray tube, and X-rays from the X-ray tube according to the X-ray condition determined in the X-ray condition determining step In the X-ray image creation step of obtaining an X-ray image by irradiating and detecting the X-rays passing through the subject with an X-ray detector, the DRR obtained in the DRR creation step, and the X-ray image creation step By comparing the obtained X-ray image, A positional deviation amount calculating step for calculating the positional deviation amount of the person, and moving the examination table on which the subject is placed based on the positional deviation amount calculated in the positional deviation amount calculating step. And a positioning step for performing positioning.

  According to the first to fourth inventions, since the X-ray condition is determined based on the body thickness calculated using the X-ray CT volume data used for creating the DRR, it corresponds to the body thickness of the subject. X-ray imaging can be performed under appropriate X-ray conditions. For this reason, it is possible to prevent the subject from being irradiated with an X-ray with an excessive dose.

1 is a perspective view showing an X-ray imaging apparatus according to the present invention together with a radiation irradiation apparatus 90. FIG. It is a perspective view which shows the examination table 31 with the examination table moving mechanism 30. FIG. It is a block diagram which shows the control system of the X-ray imaging apparatus which concerns on this invention. It is a flowchart which shows the subject's positioning operation | movement by the X-ray imaging apparatus which concerns on this invention. It is explanatory drawing which shows the determination method of the length of the area | region of the subject. It is explanatory drawing which shows the method of determining a tube voltage from the length of the area | region of the subject M.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing an X-ray imaging apparatus according to the present invention together with a radiation irradiation apparatus 90. The X-ray imaging apparatus and the radiation irradiation apparatus 90 constitute a radiotherapy apparatus.

  The radiation irradiating apparatus 90 irradiates the subject M on the examination table 31 also called a couch, and can swing with respect to a base 91 installed on the floor of the treatment room. An installed gantry 92 and a head 93 that emits a treatment beam disposed in the gantry 92 are provided. According to this radiation irradiation apparatus 90, the irradiation direction of the treatment beam irradiated from the head 93 can be changed by the gantry 92 swinging with respect to the base 91. For this reason, it becomes possible to irradiate a treatment beam from various directions to the affected part such as a tumor in the subject M.

  The X-ray imaging apparatus used together with this radiotherapy apparatus performs X-ray imaging for positioning the subject M, which will be described later, and also performs moving body tracking for specifying the position of the affected part of the subject M. X-ray fluoroscopy is performed.

  That is, at the time of radiotherapy using the radiation irradiation apparatus 90 described above, it is necessary to accurately irradiate the affected area that moves with the body movement of the subject M. For this reason, a marker is installed near the affected part of the subject M. The marker embedded in the body of the subject M is continuously X-rayed and the three-dimensional position information of the marker is calculated to detect the marker with high accuracy, so-called moving body tracking is performed. It has a configuration. Note that marker-less tracking that uses an image instead of a marker at a specific site such as a tumor in the subject M may be employed instead of placing a marker near the affected area in the subject M.

  The X-ray fluoroscopic apparatus includes a first X-ray tube 11a, a second X-ray tube 11b, a third X-ray tube 11c, a fourth X-ray tube 11d, a first flat panel detector 21a, a second flat panel detector 21b, and a third flat panel. A detector 21c and a fourth flat panel detector 21d. The X-rays irradiated from the first X-ray tube 11a pass through the subject M on the examination table 31, and are then detected by the first flat panel detector 21a. The first X-ray tube 11a and the first flat panel detector 21a constitute a first X-ray imaging system. X-rays emitted from the second X-ray tube 11b pass through the subject M on the examination table 31, and are then detected by the second flat panel detector 21b. The second X-ray tube 11b and the second flat panel detector 21b constitute a second X-ray imaging system. The X-rays irradiated from the third X-ray tube 11c pass through the subject M on the examination table 31, and are then detected by the third flat panel detector 21c. The third X-ray tube 11c and the third flat panel detector 21c constitute a third X-ray imaging system. The X-rays irradiated from the fourth X-ray tube 11d are detected by the fourth flat panel detector 21d after passing through the subject M on the examination table 31. The fourth X-ray tube 11d and the fourth flat panel detector 21d constitute a fourth X-ray imaging system.

  When performing X-ray imaging for positioning the subject M and X-ray fluoroscopy for tracking a moving object, the first X-ray imaging system, the second X-ray imaging system, the third X-ray imaging system, Two of the 4 X-ray imaging systems are selected and used.

  FIG. 2 is a perspective view showing the examination table 31 together with the examination table moving mechanism 30.

  The examination table 31 on which the subject M is placed is supported in a cantilever manner by the examination table moving mechanism 30 having an arm structure. The examination table 31 is supported by the examination table moving mechanism 30 so as to be movable in the six axis directions of the X, Y, and Z directions and its rotation direction, and by moving the subject M via the examination table 31. Then, positioning of the subject M is executed.

  FIG. 3 is a block diagram showing a control system of the X-ray imaging apparatus according to the present invention. In FIG. 3, only a control system necessary for executing determination of an X-ray condition and positioning of the subject M, which will be described later, is illustrated.

  This X-ray fluoroscopic apparatus is equipped with a CPU that performs logical operations, a ROM that stores operation programs necessary for controlling the apparatus, a RAM that temporarily stores data during control, and the like, and controls the entire apparatus. The unit 40 is provided. The control unit 40 generates an X-ray image based on the X-rays detected by the first flat panel detector 21a, the second flat panel detector 21b, the third flat panel detector 21c, and the fourth flat panel detector 21d. 41, a DRR creation unit 42 that obtains a DRR from X-ray CT volume data, a body thickness calculation unit 43 that calculates the body thickness of the subject M based on the X-ray CT volume data, and the positioning of the subject M By comparing the X-ray condition determination unit 44 for determining the X-ray conditions for the first X-ray tube 11a, the second X-ray tube 11b, the third X-ray tube 11c, and the fourth X-ray tube 11d in FIG. A displacement amount calculation unit 45 for calculating the displacement amount of the subject M, and the subject M is mounted based on the displacement amount calculated by the displacement amount calculation unit 45. And a subject moving unit 46 that creates a signal for moving the placed examination table 31.

  The control unit 40 is connected to the examination table moving mechanism 30 that moves the examination table 31 based on a signal for moving the examination table 31 created by the subject moving unit 46. Although not shown in FIG. 3, the control unit 40 includes a first X-ray tube 11a, a second X-ray tube 11b, a third X-ray tube 11c, a fourth X-ray tube 11d, and a first flat panel detector 21a. The second flat panel detector 21b, the third flat panel detector 21c, and the fourth flat panel detector 21d are also connected.

  The control unit 40 further includes an X-ray CT imaging apparatus 47 that performs X-ray CT imaging of the subject M via the in-hospital network 100 that is in-hospital communication of the subject management system in the hospital, and the subject M A treatment planning device 48 that creates a treatment plan and a patient data storage unit 49 that stores various data about the subject M are connected. Here, based on the X-ray CT image of the subject M imaged by the X-ray CT imaging device 47, the treatment planning device 48 determines from what direction the radiation of how much energy is applied to the affected part such as a tumor. A treatment plan for the subject M is created by scheduling the number of times of irradiation.

  Next, after determining the X-ray conditions for the first X-ray tube 11a, the second X-ray tube 11b, the third X-ray tube 11c, and the fourth X-ray tube 11d using the X-ray imaging apparatus having the above-described configuration. An operation when positioning the subject M will be described. FIG. 4 is a flowchart showing the positioning operation of the subject M by the X-ray imaging apparatus according to the present invention.

  When positioning the subject M, first, a DDR is created by the DRR creation unit 42 shown in FIG. 3 (step S1). When creating this DRR, the first X-ray tube 11a, the second X-ray tube 11b, and the third X-ray tube are virtually inserted on the computer with the X-ray CT volume data obtained by the X-ray CT imaging apparatus 47 at the time of creating the treatment plan. A geometry that is a geometric arrangement of the tube 11c, the fourth X-ray tube 11d, the first flat panel detector 21a, the second flat panel detector 21b, the third flat panel detector 21c, and the fourth flat panel detector 21d is reproduced. Then, the line integral of the X-ray CT value in the CT data voxel on the line segment connecting the virtual X-ray tube and the virtual flat panel detector is obtained. Then, X-ray attenuation is calculated by converting the line integral of the X-ray CT value into a line integral of the linear attenuation coefficient, and based on this, the relative X-ray dose reaching each pixel is calculated. Thereafter, by normalizing the relative X-ray dose, the pixel value of each pixel is calculated to obtain the DRR.

  This DRR is the one when the subject M is placed at the correct position when the treatment plan is created by the treatment plan device 48 shown in FIG. This DRR is created corresponding to two X-ray imaging systems of the first X-ray imaging system, the second X-ray imaging system, the third X-ray imaging system, and the fourth X-ray imaging system described above.

  Next, based on the CT data on the line segment connecting the virtual X-ray tube to the virtual flat panel detector, the body thickness calculation unit 43 shown in FIG. The length of the area is calculated (step S2). In this case, it is determined that the length of the region where the CT data value is a certain value or more is the length of the region of the subject M.

  FIG. 5 is an explanatory diagram showing a method of determining the length of the area of the subject M.

  As shown in this figure, the X-ray CT volume data 50 obtained by X-ray CT imaging of the subject M is on the line segment connecting the virtual flat panel detector 21 to the virtual X-ray tube 11. The CT data value at is obtained. In the X-ray CT volume data 50, the length L of the region where the CT data value is a certain value or more is determined to be the length L that the X-ray passes through the subject M. Note that the length L of the subject M may be, for example, the length of the optical axis portion of the X-ray from the virtual X-ray tube 11 to the virtual flat panel detector 21, or the virtual length The average value of the length of the region where the X-ray from the typical X-ray tube 11 to the virtual flat panel detector 21 passes through the subject M may be used.

  Then, the body thickness calculation unit 43 calculates the body thickness of the subject M from the length of the area of the subject M (step S3), and the X-ray condition determination unit 44 shown in FIG. X-ray conditions are determined from the body thickness of the examiner M (step S4).

  FIG. 6 is an explanatory diagram showing a method of determining the tube voltage that is the X-ray condition from the length of the region of the subject M.

  As shown in this figure, the relationship between the length of the area of the subject M, the body thickness of the subject M, and the appropriate tube voltage when X-raying the subject M is experimentally determined in advance. And is stored as a graph. Therefore, as shown by the broken arrow in this figure, the body thickness of the subject M is obtained from the length of the area of the subject M, and the subject M is obtained from the body pressure of the obtained subject M. It is possible to obtain an appropriate tube voltage when X-rays are taken. That is, as shown in this figure, when the length of the area of the subject M is large, it is determined that the body thickness of the subject M is large, and the tube voltage is set large. Conversely, if the length of the area of the subject M is small, it is determined that the body thickness of the subject M is small, and the tube voltage is set small.

  In this embodiment, a tube voltage that is a voltage applied to the first X-ray tube 11a, the second X-ray tube 11b, the third X-ray tube 11c, and the fourth X-ray tube 11d during X-ray imaging is used as the X-ray condition. However, not only the tube voltage but also the tube current or the tube current time product may be determined as the X-ray condition instead of the tube voltage. For example, in the embodiment shown in FIG. 6, when the body thickness of the subject M is large, the tube current and the tube current time product may be increased instead of increasing the tube voltage.

  If the X-ray condition is determined, X-ray imaging is executed under this X-ray condition (step S5). Then, by this X-ray imaging, an X-ray image is created in the image processing unit 41 shown in FIG. 3 (step S6). In addition, this X-ray image corresponds to two X-ray imaging systems like DRR among the above-mentioned first X-ray imaging system, second X-ray imaging system, third X-ray imaging system, and fourth X-ray imaging system. Is created.

  Next, the positional deviation amount of the subject M is calculated by comparing the DRR and the X-ray images in the two X-ray imaging systems by the positional deviation amount calculation unit 45 shown in FIG. 3 (step S7). Calculation is performed (step S8). That is, by comparing the DRR when the subject M is placed at the correct position during the treatment plan and the X-ray image actually obtained by X-raying the subject M, the subject M's Calculate the amount of displacement.

  Thereafter, a signal for moving the examination table 31 on which the subject M is placed is created by the subject moving unit 46 based on the obtained positional deviation amount. 2 and 3 is used to move the examination table 31 in the X, Y, Z directions and the six axial directions of the rotation direction to move the subject M via the examination table 31. Is moved (step S9), thereby positioning the subject M.

  In addition, after the positioning operation | movement of the subject M shown in FIG. 4 is completed, the radiation treatment by the radiation irradiation apparatus 90 is performed. At this time, moving object tracking is executed by the X-ray imaging apparatus described above. When the moving body tracking for detecting the position of the marker by X-ray fluoroscopy is executed by this X-ray radiographing device, X-ray fluoroscopy is selected from the first imaging system, the second imaging system, the third imaging system, and the fourth imaging system. Two imaging systems to be used are selected, and moving body tracking by X-ray fluoroscopy is performed using these imaging systems.

  In the embodiment described above, X-ray conditions for X-ray imaging for performing positioning of the subject M are determined based on the body thickness of the subject M calculated based on the X-ray CT volume data. However, the present invention may be applied not only to X-ray imaging at the time of positioning but also to determination of X-ray conditions at other X-ray imaging.

11a 1st X-ray tube 11b 2nd X-ray tube 11c 3rd X-ray tube 11d 4th X-ray tube 21a 1st flat panel detector 21b 2nd flat panel detector 21c 3rd flat panel detector 21d 4th flat panel detector 30 Examination table moving mechanism 31 Examination table 40 Control unit 41 Image processing unit 42 DRR creation unit 43 Body thickness calculation unit 44 X-ray condition determination unit 45 Position shift amount calculation unit 46 Subject movement unit 47 X-ray CT apparatus 50 X-ray CT volume data 90 Radiation irradiation Device M Subject

Claims (4)

DRR obtained by reproducing the geometrical arrangement of the X-ray imaging system on a computer and virtually performing perspective projection on X-ray CT volume data obtained by X-ray CT imaging of the subject; In the X-ray imaging apparatus for positioning the subject by comparing with the X-ray image obtained by detecting the X-ray irradiated from the X-ray tube and passing through the subject with an X-ray detector,
Based on the X-ray CT volume data, a body thickness calculator that calculates a body thickness that is the distance that the X-ray passes through the subject;
An X-ray condition determining unit that determines an X-ray condition for the X-ray tube at the time of positioning of the subject based on the body thickness of the imaging region of the subject calculated by the body thickness calculating unit;
An X-ray imaging apparatus comprising: A body thickness calculator that calculates the length of the imaging region of the subject based on the X-ray CT volume data obtained by X-ray CT imaging of the subject;
An X-ray condition determining unit that determines an X-ray condition irradiated from an X-ray tube during X-ray imaging based on the body thickness of the imaging region of the subject calculated by the body thickness calculating unit;
An X-ray imaging apparatus comprising: An X-ray imaging system comprising an X-ray tube and an X-ray detector, wherein an X-ray image is obtained by detecting X-rays irradiated from the X-ray tube and passing through the subject by the X-ray detector; ,
DRR creation that reproduces the geometrical arrangement of the X-ray imaging system on a computer and obtains DRR by virtually performing perspective projection on X-ray CT volume data obtained by X-ray CT imaging of the subject And
Based on the X-ray CT volume data, a body thickness calculator that calculates a body thickness that is the distance that the X-ray passes through the subject;
An X-ray condition determining unit that determines an X-ray condition for the X-ray tube at the time of positioning of the subject based on the body thickness of the imaging region of the subject calculated by the body thickness calculating unit;
By comparing the DRR created by the DRR creation unit and the X-ray image taken by the X-ray imaging system under the X-ray condition determined by the X-ray condition determination unit, the position of the subject A positional deviation amount calculation unit for calculating the deviation amount;
A subject moving unit that creates a signal for moving the examination table on which the subject is placed, based on the amount of misregistration calculated by the misregistration amount calculating unit;
A positioning apparatus for a subject characterized by comprising: A DRR creation step of obtaining a DRR by reproducing a geometric arrangement of an X-ray imaging system on a computer and performing a virtual perspective projection on X-ray CT volume data obtained by X-ray CT imaging of a subject; ,
Based on the X-ray CT volume data, a body thickness calculating step for calculating a body thickness that is a distance that the X-ray passes through the subject;
An X-ray condition determining step for determining an X-ray condition for the X-ray tube based on the body thickness of the imaging region of the subject calculated in the body thickness calculating step;
An X-ray image is obtained by irradiating an X-ray from an X-ray tube under the X-ray condition determined in the X-ray condition determining step and detecting an X-ray that has passed through the subject with an X-ray detector. Creation process,
A displacement amount calculation step of calculating the displacement amount of the subject by comparing the DRR obtained in the DRR creation step and the X-ray image obtained in the X-ray image creation step;
A positioning step for positioning the subject by moving a medical examination table on which the subject is placed based on the positional deviation amount calculated in the positional deviation amount calculating step;
A method for positioning a subject characterized by comprising:

Images