JP5247565B2 - Multi-leaf collimator observation device and radiotherapy device - Google Patents

Description

  The present invention observes a multi-leaf collimator that defines a radiation irradiation field in radiation therapy for treating a tumor or the like by irradiating an affected area with radiation such as X-rays or particle beams (hereinafter, collectively referred to as radiation). The present invention relates to an observation device and a radiotherapy device using the same.

  In a radiotherapy apparatus, particularly a radiotherapy apparatus using a particle beam for irradiation, the influence of irradiation on a normal site around an affected area is large. For this reason, it is necessary to minimize the irradiation amount to the normal tissue around the affected area, and to irradiate the radiation with the optimum energy distribution (irradiation field and irradiation amount).

  A multi-leaf collimator (also referred to as a multi-leaf collimator) for narrowing the irradiation field so as to substantially match the shape of the affected part is installed in the irradiation nozzle of the radiotherapy apparatus. This multi-leaf collimator is configured by combining a plurality of metal plates called leaves, and each leaf can be moved and positioned in the longitudinal direction independently by an individual motor.

  In a typical multi-leaf collimator, a pair of left and right movable leaves are arranged for each line, and a leaf opening located between the left leaf group and the right leaf group can be changed to a desired shape. Therefore, by accurately controlling the edge position of each leaf, the irradiation field of the treatment beam can be matched with various affected part shapes.

  Further, the entire multi-leaf collimator is held so as to be rotatable about the irradiation axis of the treatment beam, thereby enabling the rotation angle of the leaf opening to be controlled, and the adaptability to the shape of the affected part is enhanced.

  Usually, the leaf opening shape is calculated and set at the time of treatment planning so as to correspond to the shape of the affected part. However, if a failure occurs in the motor that drives each leaf or the encoder for position detection, there is a possibility that the shape does not match the treatment plan. Therefore, for safety, it is necessary to confirm whether or not the leaf opening shape can be set to a shape as planned for treatment when irradiating with radiation.

  As a method for confirming the shape of the leaf opening in advance, the leaf opening is irradiated with visible light from the inside of the irradiation nozzle and projected onto the surface in the vicinity of the affected area before the start of irradiation, and the projected image and the treatment plan shape are compared with the eyes of the operator It is generally done.

  However, for simple comparison and confirmation by visual inspection, it is difficult to detect a minute shape difference. In addition, it is very difficult to perform comparison and collation by using such a method in the case of layered body irradiation or multi-portion irradiation in which irradiation is continuously performed with different collimator shapes.

  In Patent Document 1 below, a magnetic encoder is connected to a motor shaft for leaf movement, a pulse signal is output at a predetermined rate and phase according to the amount of rotation of the motor, and the number of pulses is counted so that each leaf is counted. A method for detecting the position has been proposed.

  Patent Document 2 below proposes a method of detecting a leaf opening shape by providing a reflector that strongly reflects illumination light from the illumination means at the tip of each leaf and imaging the position of the reflector with a camera. ing.

Japanese National Patent Publication No. 11-507253 Japanese Patent No. 2644007

  The leaf is usually made of metal in consideration of low friction between the leaves and radiation durability. When the leaf opening is imaged using illumination light, since the leaf material is metal, some specular reflection may occur depending on the irradiation angle, and a clear image may not be obtained.

  In the method proposed in Patent Document 1, a magnetic encoder is installed on a motor shaft for leaf movement and the leaf position is detected. Therefore, a magnetic encoder for position detection is newly added. Since this is a change in the basic part of the multi-leaf collimator, it can be applied to a newly developed product, but it is difficult to apply to a multi-leaf collimator that is already in operation. Furthermore, since final confirmation by visual inspection is not assumed, it is difficult to avoid in advance human error such as a mistake in the treatment plan, or a failure of a device such as a magnetic encoder.

  In addition, in the method proposed in Patent Document 2, each leaf is provided with a reflector or a pattern image to check the leaf position. Therefore, it is necessary to attach the reflector to each leaf, resulting in a burden of installation. Becomes higher. In addition, similarly to the specular reflection of the leaf surface, the fluctuation of the reflected light intensity due to the leaf angle is large, so there is a concern about instability of detection.

  An object of the present invention is to provide a multi-leaf collimator observation apparatus and a radiotherapy apparatus that can easily and accurately confirm the shape of a leaf opening of a multi-leaf collimator.

In order to achieve the above object, the present invention is to observe a multi-leaf collimator that has a plurality of movable leaves, is rotatably held around a radiation irradiation axis, and defines a radiation field of radiation from a radiation source. An observation device,
An imaging unit provided on the radiation source side of the multi-leaf collimator, for imaging the leaf opening shape of the multi-leaf collimator;
A rotation angle detector for detecting the rotation angle around the irradiation axis of the multi-leaf collimator;
A data processing unit for storing, calculating and displaying data,
The data processing unit, based on the rotation angle detected by the rotation angle detection unit, coordinate conversion means for converting the leaf opening shape of the treatment plan data stored in advance,
A visual collating means for displaying the reference leaf aperture shape subjected to coordinate conversion and the actual leaf aperture shape captured by the imaging unit for visual verification;
And image processing collating means for collating the reference leaf opening shape and the actual leaf opening shape by image processing.

According to the present invention, the reference leaf opening shape obtained from the treatment plan data and the actual leaf opening shape obtained by imaging are displayed for visual verification, thereby preventing erroneous irradiation due to human error or equipment failure. It can be prevented in advance.
Further, by comparing the actual leaf opening shape and the reference leaf opening shape by image processing, the identity between the affected part shape and the irradiation field can be easily and accurately confirmed.

It is a schematic block diagram which shows Embodiment 1 of this invention. It is a perspective view which shows an example of a multi-leaf collimator. It is a schematic block diagram which shows Embodiment 2 of this invention.

Embodiment 1 FIG.
FIG. 1 is a schematic configuration diagram showing Embodiment 1 of the present invention. The radiation therapy apparatus includes a radiation irradiation apparatus 1 having a radiation source that generates radiation, a treatment table TB for fixing the patient 2, and the like. The radiation irradiation apparatus 1 is fixed to an irradiation head HD mounted on a three-dimensional positioning mechanism (not shown), and is configured to be able to irradiate a treatment beam BM from a desired direction toward an affected area of the patient 2. The treatment table TB is also mounted on another three-dimensional positioning mechanism (not shown), and is configured so that the position and posture of the patient 2 can be adjusted. A multi-leaf collimator 3 is provided on the beam emission side of the irradiation head HD to define the irradiation field of the radiation from the radiation source and reduce the irradiation amount to the site other than the affected part.

  FIG. 2 is a perspective view showing an example of the multi-leaf collimator 3. The multi-leaf collimator 3 is configured by laminating a plurality of leaves 31 formed of a metal plate in the Y direction. Each leaf 31 can be independently moved in the X direction by an individual motor. Typically, a pair of left and right leaves 31 is arranged for each X line. A leaf opening 32 is formed between the left leaf group and the right leaf group, and its shape is determined by the inner edge of each leaf 31.

  Such a multi-leaf collimator 3 is installed on the irradiation head HD of FIG. 1 via a rotation mechanism (not shown), and is held rotatably around the axis of the treatment beam BM. Therefore, the leaf opening 32 can be arbitrarily controlled with respect to the two-dimensional shape along the XY plane and the rotation angle around the Z axis, and thereby, the irradiation field of the treatment beam BM irradiated along the Z direction can be variously affected. Can match the shape.

  In the treatment plan, which is the pre-stage of radiotherapy, a patient's lesion is imaged using a tomographic imaging device such as X-ray CT (Computed Tomography), and the tumor is determined based on the diagnosis result of the obtained 3D CT data. The position and shape of the affected area are specified, and treatment plan data such as a region to be irradiated with radiation, an irradiation direction, and an irradiation dose are determined. Based on such treatment plan data, the shape of the leaf opening 32 is set for each patient.

  Referring to FIG. 1, the multi-leaf collimator observation device according to the present embodiment includes an imaging unit 4, a rotation angle detection unit 5, a data processing unit DP, and the like.

  The imaging unit 4 includes, for example, a solid-state imaging device having a plurality of pixels arranged two-dimensionally, and is provided on the radiation source side of the multi-leaf collimator 3 and inside or outside the irradiation head HD. It has a function of imaging 32 shapes. The imaging unit 4 may be installed in a direction inclined with respect to the axis of the beam BM, and can be converted into an image captured from the axial direction of the beam BM by considering the inclination angle. The obtained collimator image 41 includes an actual leaf opening shape and is transferred to the data processing unit DP.

  The imaging unit 4 may be a digital output camera that allows easy image processing, or may be configured to use an analog output camera together with a digital capture device. Moreover, although the case where the single imaging part 4 was provided is illustrated in FIG. 1, you may provide several imaging part 4 so that it can image from several directions. In order to irradiate the illumination light for imaging toward the leaf opening 32, a single or a plurality of illumination light sources are provided.

  When radiotherapy is performed, the imaging unit 4 is exposed to intense radiation for a long period of time, so that there is a high possibility that the imaging pixel will fail, and as a result, the image quality is extremely deteriorated. In general, a defective pixel due to radiation exposure often has a state in which a pixel value is always saturated. As a countermeasure, the difference between the value of the failed pixel and the value of several pixels adjacent to the failed pixel (for example, the adjacent 8 pixels) is taken, and when the difference exceeds a certain threshold, the intermediate value or the average value is used. It is preferable to correct the defective pixel by interpolation.

  Also, radiation exposure often results in isolated and damaged pixels, and in the case of a color camera, a specific color component of RGB protrudes. Therefore, in the case of a color camera, it is possible to restore a natural image by correcting only the protruding color components so as to be the same as the hue of the surrounding pixels.

  As a result, even if a pixel failure occurs to some extent, it is possible to maintain a good image quality at the time of visual observation and facilitate collation. Such a defective pixel correction unit may be provided in the signal processing unit of the imaging unit 4 or may be provided in the data processing unit DP.

  Next, the rotation angle detection unit 5 is provided in the irradiation head HD and has a function of detecting a rotation angle around the Z axis of the multi-leaf collimator 3. The rotation angle detection unit 5 may be configured by a device that actually measures the rotation angle of the multi-leaf collimator 3 with respect to the irradiation head HD, for example, a rotary encoder, or a control of a motor that rotationally drives the multi-leaf collimator 3. A configuration for acquiring a rotation angle setting value for the apparatus may be used.

  The data processing unit DP includes a computer, a display, a mass storage, and the like, and has a function of storing, calculating, and displaying various data according to predetermined software. The data processing unit DP includes three-dimensional CT data used in the treatment plan, the treatment plan data such as the position and shape of the tumor affected part, the irradiation region, the irradiation direction, the irradiation dose, and the shape of the leaf opening 32 according to the diagnosis result. Is stored in advance.

  The rotation angle detected by the rotation angle detector 5 is sent to the coordinate conversion means 6. The coordinate conversion means 6 is configured by software or the like, and based on the rotation angle detected by the rotation angle detection unit 5, the coordinate conversion unit 6 converts the leaf opening shape of the treatment plan data stored in advance and is imaged by the imaging unit 4. Match the coordinate system of the actual leaf opening shape. The leaf opening shape thus obtained is used as a reference leaf opening shape for verification.

  The collimator image 41 from the imaging unit 4 and the reference leaf opening shape whose coordinates are converted by the coordinate conversion means 6 are sent to the visual verification means 7. The visual verification means 7 is configured by software or the like, and displays the reference leaf opening shape and the actual leaf opening shape included in the collimator image 41 on the display, and is used for the operator's visual verification.

  The visual collating unit 7 preferably includes an image overlap unit that displays the reference leaf opening shape and the actual leaf opening shape in an overlapping manner, thereby supporting the operator's visual collating operation. The image overlap means is composed of software or the like, and not only simply superimposes the contour line of the reference leaf opening shape but also flickers freely by the operator's operation or at regular intervals so as to facilitate visual verification. It may flicker. Further, not only the outline portion but also the leaf opening shape inside may be displayed in a superimposed state.

  The collimator image 41 from the imaging unit 4 and the reference leaf opening shape whose coordinates have been converted by the coordinate conversion means 6 are also sent to the image processing collation means 8. The image processing collation means 8 is configured by software or the like, and collates the reference leaf opening shape and the actual leaf opening shape by image processing. The collation by image processing is a method of performing collation by extracting the position of each leaf end in the collimator image 41 by image processing, or by overlapping the position of each leaf calculated at the time of treatment planning on the collimator image 41 by a predetermined conversion. There is a method of displaying and collating, and it is also possible to use existing image processing software.

  For example, the image processing collating unit 8 may detect an edge portion of the actual leaf opening shape, extract a contour line, and collate the obtained contour line and the reference leaf opening shape by image processing. Such contour extraction can reduce the amount of calculation required for image processing collation and improve processing speed.

  As a method for extracting the contour line, the gradation is binarized using the gradation difference between the inside and the outside of the leaf opening 32, thereby detecting the inner part of the opening and then detecting the contour as a boundary line. Also good. Further, by performing stereo imaging using the parallax of the two imaging units 4 and extracting only the image corresponding to the upper plane of each leaf 31, the leaf portion excluding the leaf opening 32 can be detected. May be extracted.

  In this way, by using the visual verification means 7 to display the reference leaf opening shape and the actual leaf opening shape for visual verification, erroneous irradiation due to human error or equipment failure can be prevented in advance. Can do.

  In addition, by using the image processing collation unit 8 to collate the actual leaf opening shape and the reference leaf opening shape by image processing, the identity of the affected part shape and the irradiation field can be easily and accurately confirmed.

  Next, the procedure of radiation irradiation using the radiotherapy apparatus according to the present embodiment will be described. When the patient is irradiated with radiation, the irradiation field to the affected area (tumor) is determined in advance by a doctor. The determined irradiation field is stored as treatment plan data in an irradiation control device (not shown) and the data processing unit DP. The irradiation control device is for controlling the radiation irradiation device 1, the multi-leaf collimator 3, the three-dimensional positioning mechanism of the irradiation head HD, the three-dimensional positioning mechanism of the treatment table TB, and the like.

  Based on the treatment plan data stored in the irradiation control device, the leaf opening shape and the multi-leaf collimator rotation angle of the multi-leaf collimator 3 are set to values calculated at the time of the treatment plan.

  Next, the collimator image 41 obtained by the imaging unit 4 is visually collated by the visual collating unit 8, and it is checked whether the actual leaf opening shape is different from the reference leaf opening shape which is the treatment plan shape after the coordinate conversion. The If it is determined that the two match, the data processing unit DP outputs an irradiation permission signal to the irradiation control device, whereas if it is determined that they are different, an output stop signal is output.

  Independent of this visual collation, the image processing collation means 8 collates the reference leaf opening shape (or its outline) and the actual leaf opening shape by image processing. If the two coincide with each other within a preset error range, the data processing unit DP outputs an irradiation permission signal to the irradiation control device. On the other hand, if they do not match, the data processing unit DP outputs an irradiation stop signal.

  Therefore, only when both the visual verification and the image processing verification are normal, it is determined that the setting of the multi-leaf collimator 3 is satisfactory, and the treatment beam BM can be irradiated. As a result, erroneous irradiation due to human error or equipment failure can be reliably prevented.

  As described above, in the present embodiment, both visual verification and automatic verification by image processing are used. When performing a high-accuracy check visually as in the past, the operator is subjected to a heavy load and requires a considerable amount of collation time.In this embodiment, since the image processing collation is in charge of high-precision collation, the operator It is possible to focus on the difference in the entire pattern, and an efficient radiotherapy operation is possible.

  In addition, when image processing collation is used, it is possible to easily and accurately confirm the identity between the affected part shape and the irradiation field. Therefore, the unnecessary dose irradiated to normal tissues other than the affected part, the number of irradiations necessary for treatment, the number of patient compensators necessary for each irradiation gate, and the like can be reduced.

Embodiment 2. FIG.
FIG. 3 is a schematic configuration diagram showing Embodiment 2 of the present invention. In the present embodiment, the pattern projection unit 9 is installed inside or outside the irradiation head HD shown in FIG. The pattern projection unit 9 includes a display screen and a projection zoom optical system, and has a function of displaying a pattern image transmitted from the data processing unit DP on the display screen and projecting the optical pattern onto the multi-leaf collimator 3. . The pattern projection unit 9 is preferably mounted on a three-dimensional positioning mechanism (not shown) so that the projection position, projection direction, and projection magnification can be adjusted.

  As shown in FIG. 3, the pattern projection unit 9 preferably projects an optical pattern 91 corresponding to the reference leaf opening shape obtained by coordinate conversion of the leaf opening shape of the treatment plan data. At this time, the projection position, the projection direction, and the projection magnification are adjusted so that the optical pattern 91 and the shape of the leaf opening 32 of the multi-leaf collimator 3 substantially coincide. When the actual shape of the leaf opening 32 is different from the optical pattern 91, the optical pattern 91 is partially missing or expanded. Thereby, the identity of the actual shape of the leaf opening 32 and the reference leaf opening shape can be easily confirmed by the operator's visual observation.

  The optical pattern 91 may be arbitrarily moved up and down and left and right or periodically moved so that the collation between the projected optical pattern 91 and the edge of the leaf opening 32 is easy to see. In addition, it is preferable to set the contour of the optical pattern 91 to be projected slightly larger than the leaf opening 32, which facilitates collation near the edge. .

  Further, the image pickup unit 4 picks up the optical pattern 91 projected on the leaf opening 32 and transmits it to the data processing unit DP, and the image processing collation means 8 collates the picked optical pattern and the reference leaf opening shape by image processing. It is also possible to do. At this time, when the optical pattern 91 is projected only inside the leaf opening 32, the projected portion is not visible. Therefore, by taking an image while shifting the optical pattern 91 from the normal projection position, how much the actual leaf position is changed. Information can be obtained.

  Furthermore, in order to perform quick observation, it is preferable to use two types of projection patterns, that is, an optical pattern 91 in which the shape of the reference leaf opening is slightly reduced and an optical pattern 91 in which the shape is slightly enlarged. If the leaf position is normal at this time, when the enlarged pattern is projected, the entire contour line can be observed, whereas when the reduced pattern is projected, the entire contour line becomes invisible, so pattern matching can be performed in a short time. Complete.

Embodiment 3 FIG.
When the multi-leaf collimator 3 is used for a long time, the origin position of each leaf 31 may be slightly shifted. As a countermeasure, in the present embodiment, the data processing unit DP shown in FIG. 1 includes leaf origin position correcting means for correcting the origin position of each leaf 31. The origin position correcting means is constituted by software or the like, and when the collation by the image processing collating means 8 is not normal, the origin position for calculating the deviation amount between the actual leaf opening shape and the reference leaf opening shape and eliminating the deviation amount The correction data is transmitted to the irradiation control device. The irradiation control device updates the origin position of the motor control circuit that controls each leaf position based on the origin correction data, and as a result, the actual leaf opening shape matches the reference leaf opening shape. Such origin position correction always enables highly accurate collation.

1 radiation irradiation device, 2 patient, 3 multi-leaf collimator, 31 leaf,
32 leaf opening, 4 imaging unit, 41 collimator image,
5 rotation angle detector, 6 coordinate conversion means, 7 visual verification means,
8 image processing collation means, 9 pattern projection unit, 91 optical pattern,
BM treatment beam, DP data processing unit, HD irradiation head, TB treatment table.

Claims (9)

An observation device for observing a multi-leaf collimator having a plurality of movable leaves, rotatably held around a radiation irradiation axis, and defining a radiation field of radiation from a radiation source,
An imaging unit provided on the radiation source side of the multi-leaf collimator, for imaging the leaf opening shape of the multi-leaf collimator;
A rotation angle detector for detecting the rotation angle around the irradiation axis of the multi-leaf collimator;
A data processing unit for storing, calculating and displaying data,
The data processing unit, based on the rotation angle detected by the rotation angle detection unit, coordinate conversion means for converting the leaf opening shape of the treatment plan data stored in advance,
A visual collating means for displaying the reference leaf aperture shape subjected to coordinate conversion and the actual leaf aperture shape captured by the imaging unit for visual verification;
An image processing collating means for collating the reference leaf opening shape and the actual leaf opening shape by image processing. The image processing collating unit further includes a contour extracting unit that extracts a contour of the actual leaf opening shape,
The multi-leaf collimator observation apparatus according to claim 1, wherein the image processing collating unit collates the extracted contour of the actual leaf opening shape and the reference leaf opening shape by image processing. The imaging unit has a plurality of pixels arranged two-dimensionally,
The multi-leaf collimator observation apparatus according to claim 1, wherein the imaging unit or the data processing unit includes a defective pixel correcting unit for correcting the defective pixel.   The multi-leaf collimator observation apparatus according to claim 1, wherein the visual collating unit includes an image overlap unit that displays the reference leaf opening shape and the actual leaf opening shape in an overlapping manner.   The multi-leaf collimator observation apparatus according to claim 1, further comprising a pattern projecting unit for projecting a predetermined optical pattern onto the multi-leaf collimator.   The multi-leaf collimator observation apparatus according to claim 5, wherein the pattern projection unit projects an optical pattern corresponding to the shape of the reference leaf opening. The imaging unit images the optical pattern projected by the pattern projection unit,
The multi-leaf collimator observation apparatus according to claim 6, wherein the image processing collating unit collates the captured optical pattern and the reference leaf opening shape by image processing.   2. The multi-leaf collimator observation apparatus according to claim 1, wherein the data processing unit includes leaf origin position correcting means for correcting the origin position of each leaf. The multi-leaf collimator observation device according to any one of claims 1 to 8,
A radiation therapy apparatus comprising: a radiation source that generates radiation toward an affected area.

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