JP2000197710A - Medical treatment planning system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extract the movement of an intercorporeal organ including a portion of a target lesion by providing a static image extracting means making a calculation value of an area of a portion showing the movement of organ almost zero (0), and a medical treatment planning means to determine a stationary period essential for respiratory gate intermission control and dosimetry distribution based on a static image. SOLUTION: An image-image computation is carried out at a time series image- image by an image-image computation means 16 and a subtraction image showing movement of intercoporeal organ including a portion of target lesion is outputted. Then, an area of the portion showing the movement in the subtraction image is computed by a static image extraction means 17, and a time variation in the organ is catched. when the area takes a value of almost zero (0), an original image used for forming the subtraction image is outputted as an image during the time when the movement of organ stops. By the use of the image obtained in this way, a medical treatment planning means 18 performs a medical treatment planning. In the planning, it is possible to perform extraction of target lesion during the stationary period essential for respiratory gate intermission control and dosimetry distribution and/or the like of lesion at the stationary position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiotherapy system for performing radiotherapy on the basis of image diagnostic information of a lesion of a subject.

[0002]

2. Description of the Related Art In radiation therapy, it is important to irradiate only a lesion with an electron beam and a radiation beam while suppressing exposure of normal tissues around the lesion. In particular, it is important that the respiratory movement of the treatment target can accurately irradiate only the lesion that moves with the respiration.
In that sense, it is significant to use the respiratory-gated irradiation method.

[0003] Here, the respiratory-gated irradiation method is a method of irradiating a lesion with the above-mentioned beam in synchronization with the rest period of the lesion moving by respiratory movement. For the period during which the lesion is stationary, see "Study on respiratory phase-synchronized irradiation."
(Kiyoshi Ohara, 6 others: Journal of the Japan Society of Medical Radiology, 47th
Vol. 3, No. 3, pp. 488-496, 1987), and the lesion is located at a fixed position during end-expiration (when exhaling) of about 2 seconds out of about 5 seconds in one cycle of breathing. .

As for the setting of a synchronizing (control) signal for irradiating in synchronization with the rest period of a lesion, see "Development of respiratory-gated irradiation and its clinical evaluation" (Hiroshi Tsuji, et al .: Video Information Medical: Vol.No.19: P1071-107
7: 1993), and confirming that the synchronization (control) signal is correctly synchronized with the actual respiratory phase by using the aiming / confirmation system of the irradiation field by the X-ray fluoroscope, This is a method of performing irradiation after setting.

[0005] Further, for a method of accurately determining the rest period of a lesion, see "Radiation Therapy System" (Japanese Patent Application No. 9-15 / 1997).
No. 4288), for any organ including the lesion, it is possible to grasp the period during which the lesion moving with respiration is stationary for a certain period, and to quantitatively and automatically determine the period during which irradiation can be performed based on that period. This is a method of performing radiation treatment in synchronization with the quantified period.

According to such a respiratory-gated irradiation method, more ideal radiation treatment can be performed as compared with a general irradiation method in which an irradiation field is set to be wide so as to include the entire moving range of a lesion.

[0007]

In order to accurately determine the quiescent period of a lesion, it is important to extract the motion of internal organs including the lesion based on a plurality of image data arranged in time series. It is an issue.

"Radiation therapy system" (Japanese Patent Application No. 9-15)
No. 4288), the subtraction is performed between the images arranged in time series, and the area of the black part and the white part indicating the part where the lesion is moving is calculated from the image based on the gradation range specified in advance. Is determined as a still period, including a time-series period including an image having a substantially zero value.

However, this method has a problem that it is difficult to capture the motion of the soft tissue because the result of specifically capturing the motion near the boundary between the human body and the space such as the body surface is obtained. That is, as described later (description of FIGS. 4C and 4D), the CT value of the fat of the human body on the body surface and the CT value of the space
The difference from the value is a large value of 900, while the difference of the CT value between the soft tissues of the human body is a small value of 80. In the image, the larger the difference between the CT values is emphasized than the smaller. Is displayed. Therefore, the movement between fat and space is emphasized and displayed on the image, and the movement between soft tissues is weakly displayed on the image. is there.

This will be described with reference to FIGS. First, the CT value will be described with reference to FIG. The CT value of the CT image is such that the CT value of water = 0 and the CT value of air
The value is determined based on the value = -1000. For this criterion, the CT value of the human body is the CT value of the bone = 150-100.
0, CT value of soft tissue = 0-80, CT value of fat = -1
A value such as 00 is obtained. Image display is performed using the difference between the CT values. This image display method will be described with reference to FIGS. If a scan line 20 having a center in the horizontal direction of the image is taken like the CT image in FIG. 2A, the profile of the CT value is as shown in FIG. The vertical axis is the CT value. 30 is fat and the upper limit is-
100 indicates that it has a value less than that. 31 is a bone part whose CT value is 150-1.
Since it is 000, the profile is displayed in a vertically extended form. 32 is an air layer of soft tissue (internal organ),
Since the CT value has a large value of -1000, the profile has a vertically elongated shape like the bone 31. Reference numeral 33 denotes a soft tissue having a CT value of 80 as an upper limit and a value lower than the upper limit. In the image display, the CT value is not displayed using the entire range of -1000 to 1000, which is the entire range of the CT value, but the level and width of the CT value in the range to be displayed as shown in FIG. Is set such that, for example, the CT value level = 0 and the CT value width = ± 150, and the gradation 40 obtained by dividing the range between the minimum value and the maximum value of the CT value into 512 is applied to FIG. A CT image as shown in (b) is obtained. 3, the same parts as those in FIG. 2 are indicated by the same symbols.

Next, subtraction of a CT image will be described with reference to FIGS. CT image A of FIG.
And the subtraction of the CT image B will be described with reference to the profile of FIG. When the scan line 20 is taken for each image in FIG. 4A as shown in the figure, the profile data indicating the change in the CT value is shown in FIG.
(B). The CT image A in FIG. 4A and the profile A in FIG. 4B are the same as the CT image and profile in FIG. 2, respectively. Therefore, the same parts are indicated by the same symbols. Hereinafter, it is similarly described in each drawing. In contrast to the CT image A shown in FIG. 4A, the CT image B moves the soft tissue 60 (visceral organ) due to the breathing of the patient, and the portion 61 of the soft tissue 60 which is hidden in the image A becomes the portion 61 in the image B. Appears like '. In addition, fat also swells due to the movement of the abdomen due to breathing. As a result, FIG.
As shown in (b), in the profile B of the CT image B, the width W ′ of the fat 30 is wider than the width W of the fat 30 in the profile B, and the profile 70 of the soft tissue (visceral) 61 ′ has the CT value. = 0 to 80.

FIG. 4 (c) shows the result of the subtraction of profiles A and B, showing the absolute value of the difference between the CT values, which makes it easier to grasp the amount of change due to exercise. 80 is the difference between the absolute values of the fat on the left, 80 '
Is the absolute value difference of the fat part on the right. Numeral 81 indicates a difference between absolute values of CT values in the soft tissue. Looking at this profile, it can be seen that fat (CT value = −900) is much larger than the difference (80) in CT value (0 to 80) between soft tissues. This is because the CT value of soft tissue and fat changes around ± 100, while the CT value of air is -1000.
This is because the absolute value takes a very large value. Thus, in the subtraction image, the C of the body tissue itself is
Irrespective of the T value, there is a feature that the larger the difference between the CT values at the boundary with air or the like, the more the portion is enhanced. As shown in FIG. 4 (c), the level and width of the CT value are arbitrarily set to the result of the subtraction, as shown in FIG. A CT image as shown in FIG. 4D is obtained. In this image, the moving parts 90, 9 between fat and space
0 ′ will be displayed in an emphasized manner as compared with the moving part 91 between the soft tissues.

Further, since the difference between the CT values obtained by the subtraction is determined irrespective of the original organ, the standard for setting the level and width of the CT value is not clear. For this reason, when the level and the width of the CT value are set as shown in FIG. 5A, the change between the soft tissues with a small difference in the CT value cannot be captured as shown in FIG. 5B. Can also occur. That is, as shown in FIG. 4D, if the soft tissue is in the range of 0 to 512 gradations, the image becomes white emphasized like the moving part 91, but as shown in FIG.
If the difference 81 in the CT value of the soft tissue is outside the range of 0-512 gradations, the image will not be white and the movement of the soft tissue will not be recognized.

Lesions to be treated by the respiratory-gated irradiation method include:
It is included in soft tissue, which is an organ in the body, and it is necessary to extract the motion of this organ. When extracting the motion waveform of the organ from the subtraction image,
It is necessary to specify a certain gradation range in advance (Japanese Patent Laid-Open No. 9-1
No. 54288), as in the case of the above-described subtraction image display, depending on the setting of the gradation range, there may be a case where it is not possible to capture a change between soft tissue tissues having a small difference in CT value.

An object of the present invention is to provide a treatment planning system capable of extracting the motion of an organ in a body including a focus of interest.

[0016]

SUMMARY OF THE INVENTION An object of the present invention is to provide an X-ray CT apparatus for obtaining an image which captures a time change of the movement of an organ moving with respiration, and an organ in the body including a focus of interest from a captured image. Adjusting means for adjusting the level and width of the CT value so as to capture the image, converting means for converting image information described by the CT value into image information described by gradation based on the adjustment result, and recording the converted image. Recording means for calculating the movement of the organ from the recorded image, and means for calculating between the images which are continuous in time to extract the movement of the organ, and calculating the area of the portion representing the movement of the organ from this calculation result, Is almost 0
This can be achieved by a treatment planning system including a still image extraction unit that extracts an original image serving as a value, and a treatment planning unit that determines a stationary period necessary for respiratory-gated intermittent irradiation and calculates a dose distribution based on the still image. .

The converting means comprises a tone changing means for converting the image information into image information described in an arbitrary width from two to multiple tones, and further comprises the inter-image calculating means. Is characterized by comprising means for calculating the exclusive OR of the gradation between the images for the two-gradation image information.

[0018]

Embodiments of the present invention will be described below. The system configuration of the treatment planning system consists of an X-ray CT apparatus that performs image diagnosis to grasp the position of the lesion, and how to perform treatment by irradiating based on information of image information obtained by the image diagnosis. And a treatment planning device for planning.

The X-ray CT apparatus has a function of obtaining image data of a lesion by using a dynamic scan or a spiral scan. The treatment planning device has an image gradation adjustment function,
It has an image calculation function such as subtraction, an area calculation function, and a still area extraction function of a lesion.

Next, the operation will be described with reference to FIGS. The X-ray CT apparatus 10 is used to obtain information on lesions. Image information collection (step 1) by the X-ray CT apparatus 10 is started. In this image information collection, a plurality of time-continuous images indicating a time change of the movement of the organ are collected.

An arbitrary one of a plurality of images obtained by the X-ray CT apparatus 10 is displayed on the display device by the display means 11 (step 2). Next, the level and width of the CT value of this image are adjusted by the adjusting means 11 (step 3), and the region of interest is clearly displayed on the display device.
This operation can be performed while viewing the image on the display device,
The result of adjusting the CT value can be confirmed. FIG. 6A shows profiles C and D of images displayed on the display device at different time points, and focusing on the range from fat 30 to soft tissue 33, the display range is -120 to 100 in CT value. The CT value is adjusted by the adjusting means 12 so as to fall within the range of. Specifically, in profiles C and D, CT value =
The CT value is instructed such that the lower side is -120 and the upper side is -120 with respect to the reference line of 0, and the range of the CT value is -120.
Adjust so as to be ~ 100. In this case, the level of the CT value = −10 and the width = ± 110, and particularly the adjustment is made so that the soft tissue portion 70 of the profile D falls within this range. In this way, the level and width of the CT value are adjusted for all of the plurality of images that are continuous in time, and if the adjustment result is OK (step 4), the level and width of the CT value at this time are changed. The data is recorded on the recording device by the first recording means 13 (step 5). In the above-described example, the level -10 and the width ± 110 of the CT value of the images of the profiles C and D are recorded in the recording device. Next, based on the levels and widths of the CT values of all the images read from the recording apparatus, the image information described by the CT values is converted by the conversion means 14 into image information described by 512 divided gradations ( Step 6). FIG. 6B shows a range of −10 to 100 of the CT value level −10 and width ± 110 specified in FIG.
This figure shows a result of conversion into image information described by the gradation 40 divided into two. The profiles C ′ and D ′ are obtained by displaying the fat 30 and the soft tissue 33 in 511 gradations 40 particularly in the CT value range of −120 to 100.
The frames indicating gradations 0 to 511 in FIG. 6A are for explanation for converting the profiles C and D into the profiles C ′ and D ′ in FIG. 6B, respectively. FIG. 6B shows that the profiles C and D are converted into the range indicated by the frame of FIG. 6A, instead of being converted into 511 gradations at the stage of FIG.

The converted image converted as described above is converted to a CT image.
Separately from the original image described by the value, the image is stored in the second recording device by the second recording means 15 as an image described by the gradation (step 7).

On the converted image described in this gradation, the inter-image operation means 16 performs an inter-image operation such as subtraction between two images which are continuous in time (step 8). FIG. 6C shows the absolute value of the subtraction of the profile C ′ and the profile D ′ in FIG. 6B. Here, the reason for taking the absolute value for the subtraction is to capture the amount of change due to exercise. By performing the subtraction on the image information described in the gradation as described above, unlike the result in which the fat movement is enhanced when the subtraction is performed between the CT values illustrated in FIG. In (c), the movements of fat and soft tissue are extracted at almost the same level. As a result, the motion of the attention site can be extracted. That is, as a result of subtraction, 0-5
The absolute value of the 11-tone difference is a tone difference 140 between the fat and air at the target site and a tone difference 141 between the soft tissue at the target site, as in the case of the target site.

When the level and width of the CT value of the image are adjusted (step 3), as shown in profiles E and F shown in FIG. Paying attention to only the display range, the CT value is -90.
CT value level = 5, width =
With the adjustment of ± 95, only the movement of the soft tissue can be extracted as the gradation difference 160 between the soft tissues as in the subtraction result shown in FIG. 7B.

Further, when adjusting the level and width of the CT value of the image (step 3), as shown in FIG.
CT value level = 40 and width = ± so that T value is 40
By adjusting the value to 0, a binarized profile G and profile H as shown in FIG. 8B are obtained. By taking the absolute value of the subtraction between these profiles, only the change due to the movement of the soft tissue can be extracted as the difference 190 of the gradation of the soft tissue as shown in FIG. In the operation between the binarized images,
Taking the absolute value of the subtraction is the same as performing an exclusive OR.

By performing the inter-image calculation (step 8) by the inter-image calculation means 16 between the time-continuous images as described above, a subtraction image showing the motion of the organ in the body including the focus of interest is obtained. Output (step 9).

Next, the still image extracting means 17 calculates the area of the portion showing the motion in the subtraction image (step 10), and captures the time variation of the motion of the organ. That is, when the area is large, the change in organ motion is large, and when the area is small, the change in organ motion is small. Then, when the area takes a substantially zero value (step 11), the original image for which the subtraction image is created is output as an image during a period in which the motion of the organ is stationary (step 12). This image is an original image described by CT values.

Using the original image obtained as described above, a treatment plan is made by the treatment planning means 18 (step 1).
3). In the treatment plan, it is possible to extract a rest period of a lesion, which is essential for intermittent respiratory irradiation, and calculate a dose distribution at a rest position of the lesion.

[0029]

According to the present invention, for any organ including a lesion, the range in which the lesion moving with respiration stops for a certain period can be grasped, and the range that can be irradiated is quantitatively determined based on the range. And because it can be set automatically, radiotherapy with good operability is possible, and because the irradiation range is accurate,
A safe treatment that minimizes exposure to normal tissues around the lesion can be achieved.

[Brief description of the drawings]

FIG. 1 is a flowchart of a treatment planning system according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a CT value and a profile of a human body.

FIG. 3 is an explanatory diagram showing a CT image obtained by designating the level and width of a CT value to be displayed and the level and width of a CT value;

FIG. 4 is a CT showing two images to be subtracted.
FIG. 3 is an explanatory diagram showing an image, a profile, and a subtraction image obtained by the subtraction.

FIG. 5 is an explanatory diagram showing a profile and a subtraction image obtained by the subtraction.

FIG. 6 is an explanatory diagram showing a level and a width of a CT value for converting image information from a CT value to a gradation, a profile, and a subtraction result according to the present invention.

FIG. 7 is an explanatory diagram showing a profile obtained by converting image information into gradation and a subtraction result according to the present invention.

FIG. 8 is an explanatory diagram showing a level and width of a CT value for converting image information from a CT value to two gradations, a profile, and a subtraction result according to the present invention.

[Explanation of symbols]

 Reference Signs List 30 fat 31 bone 32 air layer 33,60 soft tissue 61,61 'soft tissue part 70 61' profile 90,90 ', 91 moving part

Claims (1)

[Claims] 1. An X-ray CT apparatus for obtaining an image capturing a temporal change of the movement of an organ moving with breathing, and a CT value level for capturing an internal organ including a focus of interest from a captured image. Adjusting means for adjusting the width and width of the image, converting means for converting the image information described by the CT value into image information described by the gradation based on the adjustment result, recording means for recording the converted image, and recording means for recording the converted image. An inter-image calculation means for calculating between time-continuous images in order to extract the motion of the organ from the image, and calculating the area of a portion representing the motion of the organ from the calculation result and obtaining an original image having a value substantially equal to 0 A treatment planning system comprising: a still image extracting unit for extracting a still image; and a treatment planning unit for determining a stationary period necessary for respiratory-gated intermittent irradiation and calculating a dose distribution based on the still image.