JP6883800B2 - DRR image creation device - Google Patents

Description

The present invention relates to a DRR image creating apparatus, and particularly includes an X-ray tube and an X-ray detector for positioning a subject when irradiating the subject with a treatment beam to perform radiotherapy. The present invention relates to a DRR image creating device for creating a DRR image used for comparison with an X-ray image taken by an X-ray imaging system.

A DRR (Digital Reconstructed Radiography) image, which is a virtual perspective projection using three-dimensional image data collected by an X-ray CT apparatus, is used, for example, for positioning a subject. That is, in a treatment device that irradiates a subject with a treatment beam to perform radiotherapy, the DRR image is used to calculate the displacement of the X-ray image when the subject is positioned. Further, after positioning the subject, it is confirmed by interpretation by a doctor or the like whether the positional deviation between the DRR image and the X-ray image is within the permissible range.

When creating this DRR image, the geometry, which is the geometric arrangement of the X-ray tube and the X-ray detector, is virtually reproduced on the computer with the CT image in between. Then, the line integral of the CT value in the CT data voxel on the line segment connecting the virtual X-ray detector from the virtual X-ray tube is obtained. After that, the line integral of the CT value is converted into the line integral of the line attenuation coefficient to calculate the X-ray attenuation, 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 a DRR image (see Patent Document 1).

Japanese Unexamined Patent Publication No. 2013-99431

When creating a DRR image, multiple calculation points are set on the line segment connecting each pixel of the virtual X-ray detector from the virtual X-ray tube, and the CT value in the CT data voxel corresponding to this calculation point is set. We are looking for the line segment of. At this time, since the resolution of the CT data is inferior to that of the X-ray image, the CT value at each calculation point is calculated by performing an interpolation calculation from the CT value in the CT data voxels around the calculation point. ing.

Due to this interpolation calculation, there arises a problem that the outline of the DRR image is blurred. Further, since the contour of the CT data itself is also blurred, there arises a problem that the contour of the DRR image is blurred. In order to deal with such a problem, it is conceivable to weight the CT value corresponding to the bone part, which is important for positioning, to emphasize the bone part, but such a method improves the contrast of the DRR image. Although it can be made, it is impossible to eliminate the blurring of the edge portion.

Therefore, in the DRR image, for example, it becomes difficult to clearly recognize the contours of the bone and soft tissues. Therefore, it becomes difficult to recognize the positional deviation with high accuracy by comparing the DRR image and the X-ray image. Further, even when a doctor or the like determines by interpretation whether the positional deviation between the DRR image and the X-ray image is within the permissible range, it takes a long time to interpret the image. In such a case, there arises a problem that the positioning accuracy of the subject is lowered. In addition to causing pain to the subject, there arises a problem that the throughput of radiotherapy using an expensive radiotherapy device is reduced.

The present invention has been made to solve the above problems, and by sharpening the region between the bone and soft tissues of the DRR image, positioning of the DRR image and the X-ray image can be performed with high accuracy and ease. It is an object of the present invention to provide a DRR image creating apparatus capable of executing the above.

The first invention is to perform radiotherapy for a subject by reproducing the geometrical arrangement of an X-ray imaging system on a computer and virtually performing fluoroscopic projection on CT image data collected in advance. It is a DRR image creation device that creates a DRR image used for comparison with an X-ray image when positioning a subject when performing the procedure, and corresponds to the CT value corresponding to the bone part and the soft tissue in the CT image data. An image processing unit is provided that performs conversion processing on a region having a CT value between the CT value and the CT value so that the CT value becomes a CT value close to the CT value of the bone or the CT value of the soft tissue. The image processing unit has a CT value equal to or higher than a preset CT value for a region having a CT value between a CT value corresponding to a bone portion and a CT value corresponding to a soft tissue in the CT image data. The conversion process is performed so that the CT value of the region is close to the CT value of the bone, and the CT value of the region is smaller than the preset CT value of the soft tissue. A conversion process that obtains a CT value that is close to the CT value is executed.

The second invention is to perform radiotherapy for a subject by reproducing the geometrical arrangement of an X-ray imaging system on a computer and virtually performing fluoroscopic projection on CT image data collected in advance. A DRR image creation device that creates a DRR image used for comparison with an X-ray image when positioning a subject when performing An image processing unit is provided that performs conversion processing on a region having a CT value between the CT value and the CT value so that the CT value becomes a CT value close to the CT value of the bone or the CT value of the soft tissue. The image processing unit has a CT value between the CT value corresponding to the bone and the CT value corresponding to the soft tissue in the CT image data, and the CT value is the CT value of the bone or the soft tissue. Multiply by a weighting coefficient such that the CT value is close to the CT value of the tissue.

The third invention is to perform radiotherapy for a subject by reproducing the geometrical arrangement of an X-ray imaging system on a computer and virtually performing fluoroscopic projection on CT image data collected in advance. It is a DRR image creation device that creates a DRR image used for comparison with an X-ray image when positioning a subject when performing the above, and corresponds to the geometrical arrangement of the X-ray imaging system reproduced on the computer. A plurality of calculation points are set on the line segment, and the CT value of the calculation point is calculated by performing interpolation based on the CT value around the calculation point, and the calculated value is the bone in the CT image data. So that the CT value is close to the CT value of the bone or the CT value of the soft tissue for the calculation point having the CT value between the CT value corresponding to the part and the CT value corresponding to the soft tissue. It is characterized by including an image processing unit that executes conversion processing and creates a DRR image by accumulating the CT values of the calculation points located on the line segment using the CT values of each calculation point after conversion. To do.

In the fourth invention, the image processing unit sets a plurality of calculation points on a line segment corresponding to the geometric arrangement of the X-ray imaging system reproduced on the computer, and the CT value around the calculation points. The CT value of the calculation point is calculated by performing interpolation based on the above, and the calculated value is a CT value between the CT value corresponding to the bone part and the CT value corresponding to the soft tissue in the CT image data. Multiply the calculated points that have a weighting coefficient so that the CT value is a CT value that is close to the CT value of the bone or the CT value of the soft tissue, and use the CT value of each calculated point after weighting. A DRR image is created by accumulating the CT values of the calculation points located on the line segment.

According to the first and second inventions, it is possible to sharpen the region between the bone and soft tissues of the DRR image by performing a conversion process (for example, a weighting process) on the CT image data. Therefore, positioning of the DRR image and the X-ray image can be performed with high accuracy and easily. At this time, since the conversion process (for example, the weighting process) is executed in advance on the CT image data, the DRR image can be quickly created.

According to the third and fourth inventions, the region between the bone and the soft tissue of the DRR image is sharpened by executing the conversion process (for example, the weighting process) together with the interpolation calculation of the CT value of the calculation point. This makes it possible to easily perform positioning of the DRR image and the X-ray image with high accuracy.

It is a perspective view which shows the X-ray fluoroscopy apparatus provided with the DRR image creating apparatus as the DRR creating apparatus which concerns on this invention together with the radiation irradiation apparatus 90. It is a block diagram which shows the main control system of the X-ray fluoroscope. It is a flowchart which shows the DRR image creation operation. It is explanatory drawing which shows typically the state which creates the DRR image by virtual fluoroscopic photography. It is explanatory drawing which shows typically the form which performs the weighting process. It is a flowchart which shows the DRR image creation operation which concerns on 2nd Embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing an X-ray fluoroscopic device including a DRR image creating unit as a DRR creating device according to the present invention together with a radiation irradiating device 90. A radiation therapy device is configured by these X-ray fluoroscopes and a radiation irradiation device 90.

The radiation irradiation device 90 irradiates the subject on the examination table 29, which is also called a couch, and is oscillatingly installed on the base 91 installed on the floor of the treatment room. The gantry 92 is provided with a head 93 that emits a treatment beam disposed on the gantry 92. According to the radiation irradiation device 90, the irradiation direction of the treatment beam emitted from the head 93 can be changed by swinging the gantry 92 with respect to the base 91. Therefore, it is possible to irradiate the affected part such as a tumor in the subject with a treatment beam from various directions.

The X-ray fluoroscope used together with the radiation irradiation device 90 performs X-ray fluoroscopy for positioning the subject. That is, by comparing the X-ray fluoroscopy image obtained by the X-ray fluoroscopy device with the DRR image created from the CT image, the subject is positioned (the examination table 29 on which the subject is placed is treated. To move to the same appropriate position as at the time) is executed.

This X-ray fluoroscope 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 (collectively referred to as "X-ray tube 11"), and a first X-ray tube. It includes a flat panel detector 21a, a second flat panel detector 21b, a third flat panel detector 21c, and a fourth flat panel detector 21d (collectively referred to as "flat panel detector 21"). The X-rays emitted from the first X-ray tube 11a pass through the subject on the examination table 29 and then are detected by the first flat panel detector 21a. The first X-ray tube 11a and the first flat panel detector 21a form a first X-ray imaging system. The X-rays emitted from the second X-ray tube 11b pass through the subject on the examination table 29 and then are detected by the second flat panel detector 21b. The second X-ray tube 11b and the second flat panel detector 21b form a second X-ray imaging system. The X-rays emitted from the third X-ray tube 11c pass through the subject on the examination table 29 and then are detected by the third flat panel detector 21c. The third X-ray tube 11c and the third flat panel detector 21c form a third X-ray imaging system. The X-rays emitted from the 4th X-ray tube 11d pass through the subject on the examination table 29 and then are detected by the 4th flat panel detector 21d. The 4th X-ray tube 11d and the 4th flat panel detector 21d constitute a 4th X-ray imaging system.

When performing X-ray imaging for positioning the subject, two X-ray imaging systems out 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. Is selected and used.

FIG. 2 is a block diagram showing a main control system of the X-ray fluoroscope.

This fluoroscopy device includes a CPU that executes logical operations, a ROM that stores operation programs necessary for controlling the device, a RAM that temporarily stores data and the like during control, and controls that control the entire device. A unit 30 is provided. The control unit 30 includes the above-mentioned first X-ray tube 11a, second X-ray tube 11b, third X-ray tube 11c and fourth X-ray tube 11d, a first flat panel detector 21a, a second flat panel detector 21b, and a third flat. It is connected to the panel detector 21c and the fourth flat panel detector 21d. Further, the control unit 30 is connected to the examination table moving mechanism 28. The control unit 30 includes a DRR image creation unit 31 as a DRR image creation device according to the present invention.

Further, the control unit 30 is connected to the above-mentioned radiation irradiation device 90 and the treatment planning device 99. The control unit 30 and the treatment planning device 99 may be connected via the radiological information system (RIS), which is an in-hospital communication of the subject management system in the hospital. Here, the treatment planning device 99 is for creating a treatment plan prior to performing radiation therapy. In this treatment planning device, the three-dimensional CT image data of the subject M photographed by the CT imaging device is stored. Then, a treatment plan for the subject M is created based on the three-dimensional CT image data and other data of the subject M.

The DRR image creation unit 31 in the control unit 30 functions as a DDR image creation device according to the present invention, and includes an image processing unit 32 that executes various image processing. The image processing unit 32 executes weighting processing on a region having a CT value between the CT value corresponding to the bone and the CT value corresponding to the soft tissue in the CT image data acquired from the treatment planning device 99. A plurality of calculation points are set on the weighting unit 33 and the line segment corresponding to the geometric arrangement of the X-ray imaging system reproduced on the computer, and interpolation is performed based on the CT values around the calculation points. This includes a CT value calculation unit 34 that calculates the CT value of the calculation point, and a CT value accumulation unit 35 that creates a DRR image by accumulating the calculated CT values of the calculation points located on the line segment.

Next, a DRR image creation operation for creating a DRR image by the DRR image creation unit 31 in the control unit 30 will be described. FIG. 3 is a flowchart showing a DRR image creation operation. Further, FIG. 4 is an explanatory diagram schematically showing a state in which a DRR image is created by virtual fluoroscopy.

When creating the DRR image, the control unit 30 acquires the CT image data 100 from the treatment planning device 99 (step S11). The CT image data 100 is three-dimensional voxel data which is a set of a plurality of two-dimensional CT image data. The CT image data 100 has, for example, a structure in which about 200 two-dimensional images of 512 × 512 pixels are stacked in a direction crossing the subject M (a direction along the line segment L1 or L2 shown in FIG. 4). Have. The CT image data 100 is created by the treatment planning device 99 based on the data obtained from the CT device (not shown) at the time of creating the treatment plan.

Next, with respect to the CT image data 100, the weighting unit 33 shown in FIG. 2 has a CT value between the CT value corresponding to the bone portion and the CT value corresponding to the soft tissue in the CT image data 100. A weighting process for multiplying the region by a weighting coefficient is executed (step S12).

FIG. 5 is an explanatory diagram schematically showing a mode in which the weighting process is performed.

In this figure, there is an intermediate region having an intermediate CT value indicated by hatching between a region having a CT value corresponding to a bone portion and a region having a CT value corresponding to a soft tissue. In the CT image, the CT value of the region corresponding to the bone portion is, for example, about 1000 to 1500 HU (Hounsfield Unit), and the CT value of the region corresponding to the soft tissue is, for example, about 0 to 200 HU. On the other hand, the CT value of the intermediate region shown with hatching in FIG. 5 is about 200 to 1000 HU.

As a first form of the weighting process, as shown in FIG. 5A, the CT value of the hatched intermediate region in this figure is close to the CT value of the bone. Multiply the weighting factor so that it becomes a value. More specifically, as a weighted count, the CT value in the intermediate region is multiplied by a coefficient of, for example, about 2.5 to 5. As a result, the CT value of the hatched intermediate region in FIG. 5 becomes a value close to the CT value of the bone portion. This makes it possible to sharpen the edge between the bone and soft tissues of the DRR image.

Further, as a second form of the weighting process, as shown in FIG. 5A, the CT value of the hatched intermediate region in this figure is close to the CT value of the soft tissue. Multiply the weighting coefficient so that the CT value is obtained. More specifically, as a weighted count, the CT value in the intermediate region is multiplied by a coefficient of, for example, about 0.2 to 0.4. As a result, the CT value of the hatched intermediate region in FIG. 5 becomes a value close to the CT value of the soft tissue. This makes it possible to sharpen the edge between the bone and soft tissues of the DRR image.

Further, as a third form of the weighting process, as shown in FIG. 5 (b), with respect to the hatched intermediate region in this figure, the region whose CT value is equal to or higher than the preset CT value is the region. Multiply by a weighting coefficient so that the CT value is a CT value that is close to the CT value of the bone, and for a region where the CT value is smaller than the preset CT value, the CT value is the CT value of the soft tissue. Multiply by a weighting coefficient that gives an approximate CT value. More specifically, for an intermediate region having a CT value of 500 HU or more, for example, a coefficient of about 2.5 to 5 is multiplied, and for an intermediate region having a CT value smaller than 500 HU, for example. Is, for example, multiplied by a coefficient of about 0.2 to 0.4. As a result, among the hatched intermediate regions in FIG. 5B, the CT value of the intermediate region on the bone side is close to the CT value of the bone, and the CT value of the intermediate region on the soft tissue side is the soft tissue. The value is close to the CT value of the tissue. This makes it possible to sharpen the edge between the bone and soft tissues of the DRR image.

When the above weighting process is completed, a DRR image is created by virtually performing a perspective projection on the CT image data 100. At this time, the three-dimensional CT image data 100 is arranged on the computer. Then, the geometry, which is the geometric arrangement of the X-ray imaging system, is reproduced on the computer. In this embodiment, the X-ray tube 11 and the flat panel detector 21 shown in FIG. 1 are arranged on both sides of the CT image data 100. The arrangement of the CT image data 100 and the X-ray tube 11 or the flat panel detector 21 is such that the subject M, the X-ray tube 11, and the flat panel detector 21 when performing fluoroscopy with the X-ray fluoroscope shown in FIG. It has the same geometry as the arrangement of. Here, the geometry means the geometrical arrangement relationship between the object to be photographed and the X-ray tube and the flat panel detector.

In this state, the CT value calculation unit 34 shown in FIG. 2 sets a large number of line segments L connecting the X-ray tube 11 and each pixel of the flat panel detector 21 via each pixel of the CT image data 100. In FIG. 4, two line segments L1 and L2 are shown for convenience of explanation. Then, a plurality of calculation points are set on the line segment L (step S13). This calculation point is set every 1 mm on the line segment L, for example. Then, the CT value calculation unit 34 shown in FIG. 2 calculates the CT value of each calculation point (step S14). At the time of calculating the CT value, interpolation using the CT value in the CT data voxels around the calculation point is executed.

Next, the CT value accumulating unit 35 shown in FIG. 2 accumulates the CT values of each calculation point on the line segment L (step S15). This cumulative value is converted into a line integral of the line attenuation coefficient, and the X-ray attenuation is calculated to create a DRR image.

The created DRR image is used to calculate the misalignment of the X-ray image when positioning the subject M. Based on this amount of misalignment, the examination table 29 is moved by the examination table moving mechanism 28 shown in FIG. 2, and the subject M is positioned. Further, after positioning the subject M, it is confirmed by interpretation by a doctor or the like whether the positional deviation between the DRR image and the X-ray image is within the permissible range. At this time, since the DRR image is created in which the region between the bone and the soft tissue is sharpened, it is possible to accurately position the DRR image and the X-ray image. In addition, the interpretation by a doctor or the like becomes easy.

Next, another embodiment of the DRR image creation operation for creating a DRR image by the DRR image creation unit 31 in the control unit 30 will be described. FIG. 6 is a flowchart showing a DRR image creation operation according to the second embodiment.

In the first embodiment described above, a DRR image is created by performing a weighting process on the CT image data 100 and then virtually performing a perspective projection on the weighted CT image data. .. On the other hand, in the second embodiment, when the CT value is calculated using interpolation, the weighting unit 33 shown in FIG. 2 executes the weighting process.

In the second embodiment, as in the first embodiment, the control unit 30 first acquires the CT image data 100 from the treatment planning device 99 (step S21). Then, as shown in FIG. 4, a perspective projection is virtually performed on the CT image data 100. That is, the CT value calculation unit 34 shown in FIG. 2 sets a large number of line segments L connecting the X-ray tube 11 and the flat panel detector 21 via each pixel of the CT image data 100. Then, a plurality of calculation points are set on the line segment L (step S22). This calculation point is set every 1 mm on the line segment L, for example, as in the first embodiment.

Then, the CT value calculation unit 34 shown in FIG. 2 calculates the CT value of each calculation point (step S23). At the time of calculating the CT value, interpolation using the CT value in the CT data voxels around the calculation point is executed. At the time of calculating the CT value, the weighting unit 33 shown in FIG. 2 executes the weighting process (step S24). In this weighting process, as in the first embodiment, the weighting coefficient is multiplied by the region having the CT value between the CT value corresponding to the bone part and the CT value corresponding to the soft tissue in the CT image data 100. It is a step and is performed by any of the three forms described above.

Then, the CT value accumulating unit 35 shown in FIG. 2 accumulates the CT values of each calculation point on the line segment L (step S25). This cumulative value is converted into a line integral of the line attenuation coefficient, and the X-ray attenuation is calculated to create a DRR image.

Also in this second embodiment, since the DRR image is created in which the region between the bone and the soft tissue is sharpened, the DRR image and the X-ray image can be positioned with high accuracy. In addition, it becomes easy for a doctor or the like to interpret the image.

In each of the above-described embodiments, the process of multiplying the weighting coefficient is performed, but instead of this, a predetermined function or LUT (Look Up Table) is used to correspond to the bone portion in the CT image data. For a region having a CT value between the CT value and the CT value corresponding to the soft tissue, the CT value is processed so that the CT value is close to the CT value of the bone or the CT value of the soft tissue. You can also. These are collectively defined as a process of converting the CT value into a CT value that is close to the CT value of the bone or the CT value of the soft tissue. The DRR image creation unit 31 as the DRR image creation device according to the present invention is arranged in the control unit of the X-ray fluoroscopy device, but the DRR image creation device is configured as a single device separated from the X-ray fluoroscopy device. You may.

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 Control unit 31 DRR image Creation unit 32 Image processing unit 33 Weighting unit 34 CT value calculation unit 35 CT value accumulation unit 90 Irradiation device 99 Treatment planning device 100 CT image data

Claims (5)

By performing virtually perspective projection with respect to the CT image data previously collected by reproducing the geometry of the X-ray imaging system on the computer, a DRR image creation device for creating D RR image,
The CT value is the CT value of the bone or the CT value of the soft tissue with respect to the intermediate region which is the region having the CT value between the CT value corresponding to the bone and the CT value corresponding to the soft tissue in the CT image data. It is equipped with an image processing unit that executes conversion processing so that the CT value is close to the CT value.
The image processing unit executes conversion processing so that the CT value of the intermediate region is equal to or higher than the preset CT value and the CT value is close to the CT value of the bone. A DRR image creation device that executes a conversion process in which the CT value is a CT value that is close to the CT value of the soft tissue in a region where the CT value is smaller than the preset CT value. By performing virtually perspective projection with respect to the CT image data previously collected by reproducing the geometry of the X-ray imaging system on the computer, a DRR image creation device for creating D RR image,
The CT value is the CT value of the bone or the CT value of the soft tissue with respect to the intermediate region which is the region having the CT value between the CT value corresponding to the bone and the CT value corresponding to the soft tissue in the CT image data. It is equipped with an image processing unit that executes conversion processing so that the CT value is close to the CT value.
The image processing unit is a DRR image creating device that multiplies the intermediate region by a weighting coefficient such that the CT value is a CT value that is close to the CT value of the bone or the CT value of the soft tissue. By performing virtually perspective projection with respect to the CT image data previously collected by reproducing the geometry of the X-ray imaging system on the computer, a DRR image creation device for creating D RR image,
A plurality of calculation points are set on the line segment corresponding to the geometrical arrangement of the X-ray imaging system reproduced on the computer, and the calculation points are interpolated based on the CT values around the calculation points. The CT value is calculated, and the calculated value is the intermediate calculation point which is a calculation point having a CT value between the CT value corresponding to the bone part and the CT value corresponding to the soft tissue in the CT image data. The conversion process is executed so that the CT value becomes a CT value close to the CT value of the bone or the CT value of the soft tissue, and the calculation point located on the line segment is used using the CT value of each calculation point after conversion. A DRR image creating apparatus including an image processing unit that creates a DRR image by accumulating CT values of. In the DRR image creating apparatus according to claim 3,
Wherein the image processing section, by multiplying the weighting pickled coefficient over the previous SL intermediate calculation point, the CT value CT value of the intermediate calculation point is approximate to the CT value of CT values or soft tissue of the bone portion A DRR image creation device that performs conversion processing. In the DRR image creating apparatus according to any one of claims 1 to 4.
A DRR image creating apparatus in which a CT value close to the CT value of the soft tissue is a value larger than zero.

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