JP2010104452A - Multileaf collimator and radiotherapy apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiotherapy apparatus for simplifying and downsizing a leaf detecting mechanism and improving leaf detection accuracy in radiotherapy. <P>SOLUTION: A position detecting mechanism 40 changes light of a laser beam or the like from a light emitting element 41 to a linear light beam through a cylindrical lens (columnar lens) 42 and irradiates the entire end face of a leaf block 27. The reflected light of the laser beam with which the entire end face of the leaf block 27 is irradiated is received by the imaging element 43 of a CCD or a CMOS or the like through an optical lens. The pixel of the imaging element 43 is smaller than a leaf width, an end face position is described on the imaging element 43 as in (c) in the figure, a pattern image is analyzed by image processing, and the displacement of the leaf block 27, that is the absolute position, is calculated. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a radiotherapy apparatus that is used for the treatment of diseases such as malignant tumors, for example, and a multi-division aperture (multi-leaf collimator) that limits a radiation irradiation range (hereinafter referred to as a radiation irradiation field) to a subject. The present invention relates to detection of the position of a diaphragm (leaf).

  In the radiation therapy apparatus, from the viewpoint of radiation protection, a diaphragm device made of a material that does not transmit radiation, such as tungsten, is provided so as to irradiate the treatment area of the subject in a limited manner. Since this diaphragm device is required to form an irradiation field approximated to the shape of the treatment site more finely without causing a penumbra, it is arranged so as to overlap along the radiation irradiation direction. And the second diaphragm.

  The first diaphragm provided on the side close to the radiation source is formed as a pair of single units arranged so as to face each other with the radiation irradiation axis in between, and the pair of single units approach and separate from each other. To be driven. For example, the pair of simplexes are driven so as to approach and separate from each other along a track surface on a concentric circle including the radiation source. On the other hand, the second diaphragm provided on the side farther from the radiation source is a pair of diaphragms arranged to face each other with the radiation irradiation axis in a direction perpendicular to the moving direction of the first diaphragm. Formed as a body element (block). Each diaphragm element of the second diaphragm is closely arranged with a plurality of leaves that move exceptionally so as to approach and separate from each other along a circular orbit on a concentric circle including the radiation source. It has become a thing.

  The second diaphragm is called a multi-leaf collimator, and is composed of, for example, a pair of blocks that are aggregated by closely adjoining several tens of leaves. In the second diaphragm, each leaf is driven by a moving device provided for each leaf so as to be movable along the track surface. Accordingly, the first diaphragm made of a single element facing each other is moved so as to approach and separate from each other in the X direction, and each leaf of the second diaphragm made of a collection of opposed leaves is individually moved in the Y direction. Irradiation field having an irregular shape approximated to the shape of the treatment site is formed by combining the movements so as to approach and separate from each other. Note that the first diaphragm and the second diaphragm may be collectively referred to as a multi-leaf collimator.

  It is preferable that the shape error of the affected area and the irradiation field be within about 1 mm in the vicinity of the affected area. For that purpose, the positional deviation of the leaf block must be suppressed to about 0.3 mm. This is based on the ratio of the distance from the radiation source to the multi-leaf collimator installation surface and the affected part position. Therefore, the position detection error due to backlash greatly affects the therapeutic effect.

Therefore, in the leaf position detection method, a position detection mechanism such as an encoder or a potentiometer is added to a drive motor speed reducer as a moving device attached to each leaf. For this reason, the moving device is complicated and large. In addition, a technique for detecting a leaf position by an image sensor is known in order to improve a detection accuracy decrease due to a gear (see, for example, Patent Document 1).
JP 2007-202805 A

  However, in the radiotherapy system described in Patent Document 1, in order to detect the leaf position for each leaf, it is necessary to arrange a detection element for each leaf. In other words, if the number of leaves is increased, the same number of detection elements as the number of leaves is required, so that there is enough space in the limited space to provide detection for the number of leaves. There was a problem that was difficult.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a radiotherapy apparatus in which the leaf detection mechanism is simplified and miniaturized and the leaf detection accuracy is improved in radiotherapy. And

  In order to achieve the above object, an invention according to claim 1 of the present invention is a multi-leaf collimator for narrowing a radiation irradiation field to a predetermined shape, a plurality of leaf blocks movable in the irradiation field direction, and the plurality of leaf blocks. And at least one position detecting means for detecting the displacement of the leaf block based on the end face shape of the leaf block.

  In order to achieve the above object, an invention according to claim 4 of the present invention includes a radiation source for irradiating radiation, a bed on which a subject is placed, and the radiation source and a previous bed. A multi-leaf collimator that narrows an irradiation field of radiation radiated from the radiation source into a predetermined shape, and the multi-leaf collimator includes a plurality of leaf blocks movable in the irradiation field direction, and the plurality of leaf blocks. And at least one position detecting means for detecting the displacement of the leaf block from the end face shape.

  According to the present invention, it is possible to provide a radiotherapy apparatus in which a leaf detection mechanism is simplified and miniaturized in radiotherapy and leaf detection accuracy is improved.

Hereinafter, embodiments of a radiation therapy system according to the present invention will be described in detail with reference to FIGS. 1 to 9. In these drawings, the same portions are denoted by the same reference numerals.

FIG. 1 is an external view showing a configuration example of a radiotherapy apparatus according to the present invention. First, with reference to FIG. 1, the schematic structure of the radiotherapy apparatus 1 of this Embodiment is demonstrated.

The radiotherapy apparatus 1 can be broadly classified as follows: a radiation irradiation apparatus 10 that irradiates a subject with radiation from a radiation source; a treatment table 20 on which the subject P is placed to position a radiation irradiation site; and radiation irradiation. The apparatus 10 and the treatment table 20, and the controller 30 that organically controls each device constituting the radiotherapy apparatus 1 are configured.

The radiation irradiation apparatus 10 includes a fixed base 11 installed on a floor, a rotary base 12 that is instructed to be rotatable by the fixed base 11, and an irradiation head that is provided at a distal end portion that extends laterally from one end of the rotary base 12. 13 and an aperture device 14 incorporated in the irradiation head 13. The rotary mount 12 can rotate about 360 degrees around the horizontal rotation center axis H of the fixed mount 11, and the diaphragm device 14 also rotates around the irradiation axis I of the radiation irradiated from the irradiation head 13. It is possible. The intersection of the rotation center axis H of the rotating gantry 12 and the radiation irradiation axis I is referred to as an isocenter IC. Further, the rotary mount 12 is configured so as to be able to rotate not only in fixed irradiation of radiation but also in other various irradiation modes such as rotation irradiation, pendulum irradiation, and intermittent irradiation.

On the other hand, the treatment table 20 is installed on the floor so as to be rotatable in a predetermined angle range in the direction of arrow G along an arc centered on the isocenter IC. A top plate 22 for placing the subject P supported by the upper mechanism 21 is provided on the treatment table 20. The child upper mechanism 21 includes a mechanism for moving the top plate 22 in the front-rear direction indicated by arrow e and in the left-right direction indicated by arrow f.

The upper mechanism 21 is supported by the lifting mechanism 23. The elevating mechanism 23 is constituted by, for example, a link mechanism, and elevates and lowers the upper mechanism 21 and the top plate 22 by a predetermined range by itself elevating in the vertical direction indicated by the arrow d. Further, the elevating mechanism 23 is supported by the lower mechanism 24. The lower mechanism 24 includes a mechanism that rotates the elevating mechanism 23 in the direction indicated by the arrow F around a position that is a distance L from the isocenter IC. Therefore, together with the lifting mechanism 23, the upper mechanism 21 and the top plate 22 can rotate by a predetermined angle in the direction of arrow F.

Note that the setting of the radiation field by the aperture device 14 in which the subject P is positioned during the treatment is performed by operating the operation unit provided in the control device 30 by the medical staff D such as a doctor.

  By the way, when performing radiotherapy, it is important to irradiate only a treatment site such as a malignant tumor with radiation intensively so as not to damage normal tissues. The diaphragm device 14 regulates the radiation irradiation position so that the normal tissue is not irradiated with radiation as much as possible, and the diaphragm device 14 is incorporated in the irradiation head 13 so as to be rotatable around the radiation irradiation axis I. Yes.

  FIG. 2 is a diagram showing a basic structure of the radiation therapy apparatus 1. As shown in FIG. 2, the irradiation head 13 includes a radiation source 25, a diaphragm block 26, and a multi-leaf collimator 27 arranged in the direction toward the top plate 22.

  The radiation source 25 includes an electron accelerator, a counter-electron beam target, and the like, and generates radiation by accelerating electrons with the electron accelerator and colliding with the counter-electron beam target. The generated radiation is a photon beam (x-ray, γ-ray, etc.), electron beam, heavy particle beam (proton, helium, carbon, neon, π-meson beam, neutron beam, etc.).

  The diaphragm block 26 and the multi-leaf collimator 27 are installed in the radiation radiation range, narrow the radiation radiation range, and define an irradiation field F that matches the affected part shape. The aperture block 26 includes a pair of blocks facing each other with the radiation axis interposed therebetween. The material of the block pair is made of a material that absorbs radiation, such as tungsten. The block pair approaches or moves away from each other to narrow the radiation irradiation range.

  FIG. 3 is a perspective view showing the multi-leaf collimator 27. The multi-leaf collimator 27 includes leaf blocks 27A and 27B that face each other across the radiation axis. A plurality of pairs of leaf blocks 27 </ b> A and 27 </ b> B are arranged side by side close to or in contact with the side surface direction.

  Each leaf block 27A and 27B is provided with a moving mechanism 28, respectively. The moving mechanism 28 displaces each leaf block 27A or 27B to be moved with the same arc trajectory centered on the radiation source 25 as the moving direction. By this moving mechanism 28, the pair of leaf blocks 27A and 27B move toward or away from each other, and the irradiation field F is narrowed to an appropriate shape. The radiation radiated to places other than the irradiation field F is absorbed by the leaf blocks 27 </ b> A and 27 </ b> B, and only the radiation passing through the irradiation field F passes through the multi-leaf collimator 27.

  Each leaf block 27A and each leaf block 27B is provided with at least one position detection mechanism 40, respectively. The position detection mechanism 40 detects the displacement of the leaf block 27A or 27B to be detected. In other words, the displacement is a vector including the moving direction and the moving amount.

  The displacement detection result by the position detection mechanism 40 is fed back to the movement mechanism 28. The multi-leaf collimator 27 is displaced to a desired position of each of the leaf blocks 27A and 27B by the feedback of the mutation detection result, and defines an irradiation field F that matches the shape of the affected part.

  FIG. 4 is a perspective view showing details of the position detection mechanism 40. 4A is a top view of the position detection mechanism 40, and FIG. 4B is a side view thereof. The position detection mechanism 40 irradiates the entire end face of the leaf block 27 by changing light such as laser light from the light emitting element 41 through a cylindrical lens (cylindrical lens) 42 into a linear selection. The cylindrical lens 42 is a lens having at least one surface shaped like a part of a cylinder, and generates astigmatism that extends a point of light to a line. It is also widely used to correct astigmatism.

  The reflected light of the laser light applied to the entire end face of the leaf block 27 is received by the image sensor 43 such as a CCD or CMOS through an optical lens. The pixel of the image sensor 43 is smaller than the leaf width, the end face position is depicted on the image sensor 43 as shown in FIG. 4C, the pattern image is analyzed by image processing, the displacement of the leaf block 27, That is, the absolute position is calculated.

  FIG. 5 is a block diagram showing the position detection mechanism 40 in detail. The position detection mechanism 40 includes an image recognition unit 44, a comparison unit 45, and a conversion unit 47.

  The image recognition unit 44 is electrically connected to the image sensor 43 and receives a pattern image acquired by the image sensor 43. The image recognition unit 44 recognizes the arrangement position of the pattern image. Note that the leaf block 27 performs only two-dimensional movement in the direction of narrowing the irradiation field F.

  The comparison unit 45 acquires the shift of the pattern image by comparing the arrangement positions of two pattern images that are different over time. The comparison unit 45 and the image recognition unit 44 are electrically connected, and arrangement position information is input from the image recognition unit 44 to the comparison unit 45.

  The comparison unit 45 includes an arrangement position storage unit 46 that includes a storage circuit. The arrangement position storage unit 46 stores arrangement position information about the pattern image acquired last time. The comparison unit 45 reads the previous arrangement position information stored in the arrangement position storage unit 46, and obtains deviation information by subtracting it from the arrangement position information newly output from the image recognition unit 44. The deviation information indicates the deviation of the arrangement position, and includes information on the deviation direction and the deviation amount.

  In the difference processing, the arrangement position information newly input from the image recognition unit 44 and the previous arrangement position information are differentiated to acquire the remaining coordinate range. The distribution of the remaining coordinate range indicates the shift amount, and the difference between the value of the coordinate range indicated by the previously acquired arrangement position information and the value of the remaining coordinate range indicates the shift direction. If the value of the remaining coordinate range is smaller, it indicates that the pixel has moved in the direction of the pixel having the young value of the column coordinate. The value of the coordinate range is, for example, the midpoint coordinate of each point in the coordinate range. The comparison unit 45 creates deviation information including the deviation amount and the deviation direction, and outputs the deviation information to the conversion unit 47.

  The conversion unit 47 is electrically connected to the comparison unit 45 and receives deviation information. The conversion unit 47 has a conversion formula for converting the shift information indicating the displacement in pixel units into the actual displacement amount of the leaf block 27. The input deviation information is converted into an actual displacement of the leaf block 27 by a conversion formula.

  The displacement of the leaf block 27 detected by the position detection mechanism 40 is input to a position counter unit (not shown) provided in the radiation therapy apparatus 1. The position counter unit is configured to include storage means such as a semiconductor memory, and the displacement detected by the position detection mechanism 40 is accumulated, so that the accumulated displacement value indicates the position of the leaf block 27.

  6 to 9 are schematic views showing the positional relationship between the light emitting element 41 and the imaging element 43. FIG.

FIG. 6 is a schematic diagram regarding installation of the position detection mechanism 40 when the leaf block 27 has a tapered cross section and a side surface of which has an arch shape with a short circumference. In the case of FIG. 6, a position detection mechanism is provided at the upper part of the end face for each end face of the paired leaf block 27, and the light beam linearly passed from the light emitting element 41 through the cylindrical lens 42 The block 27 group is irradiated, and the image sensor 43 receives the irradiated light beam through the lens.

  FIG. 7 is a schematic diagram showing a positional relationship including a position detection mechanism 40 including a reflection mechanism such as a mirror, in the case where the leaf block 27 has the same shape as in FIG. In the case of FIG. 7, one position detection mechanism is provided on the side surface side rather than the upper part of the leaf block 27 group with respect to the end surface of the paired leaf block 27, and linearly passes from the light emitting element 41 through the cylindrical lens. The reflected light beam is reflected by the mirror 50A and then irradiated to the leaf block 27 group. The irradiated light beam reflected by the leaf block 27 group is reflected by the mirror 50B and received by the image sensor 43 through the lens. Although two mirror arrangements in FIG. 7 are used, the number of mirrors may be reduced to one by providing the light emitting element 41 and the cylindrical lens 42 or the imaging element 43 at the upper part of the leaf block 27.

  Note that the position of the leaf block 27 can be detected by using the space more effectively through the mirror.

  FIG. 8 is a schematic diagram showing the positional relationship between the position detection mechanism 40 and the leaf block 27 when the leaf block 27 has a parallel shape. In the case of FIG. 8, since the leaf blocks 27 are parallel, the end face of the group of leaf blocks 27 is the side surface of the leaf block 27. Therefore, the position detection mechanism 40 is provided on the side surface of the leaf block 27. The configuration of the position detection mechanism 40 is the same as that in FIG.

  FIG. 9 is a schematic diagram showing the positional relationship between the position detection mechanism 40 and the leaf block 27 when the leaf block 27 has a parallel shape as in FIG. 8 and the leaf block 27 includes a light receiving projection 51. is there. In the case of FIG. 9, the position of the position detection mechanism 40 can be freely designed by providing the leaf block 27 with the protrusion 51 to receive light. The configuration of the position detection mechanism 40 is the same as that in FIG.

  As described above, in the embodiment of the present invention, a plurality of leaf positions can be measured collectively by detecting the position of the leaf block 27 using linear laser light. Therefore, the position detection mechanism 40 can be downsized compared to the conventional one, and the installation location can be designed freely.

In addition, since the leaf position is directly detected, the detection accuracy is improved, leading to an improvement in the accuracy of forming an irradiation field, and even when treatment is performed, since no extra exposure is applied, the irradiation can be performed safely.

Note that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention.

It is an external view which shows the structural example of the radiotherapy apparatus which concerns on this invention. It is a figure which shows the basic structure of the radiotherapy apparatus which concerns on this invention. It is a perspective view which shows the multileaf collimator which concerns on this invention. It is a perspective view which shows the detail of the position detection mechanism which concerns on this invention. It is a block diagram which shows the position detection mechanism concerning this invention in detail. It is the schematic which shows an example of the positional relationship of the light emitting element which concerns on this invention, and an image pick-up element. It is the schematic which shows an example of the positional relationship of the light emitting element which concerns on this invention, and an image pick-up element. It is the schematic which shows an example of the positional relationship of the light emitting element which concerns on this invention, and an image pick-up element. It is the schematic which shows an example of the positional relationship of the light emitting element which concerns on this invention, and an image pick-up element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Radiation therapy apparatus 13 Irradiation head 14 Diaphragm apparatus 25 Radiation source 26 Diaphragm block 27, 27A, 27B Multi-leaf collimator 28 Movement mechanism 40 Position detection mechanism 41 Light emitting element 42 Cylindrical lens 43 Imaging element 44 Image recognition part 45 Comparison part 46 Arrangement position Storage unit 47 Conversion unit

Claims (7)

A multi-leaf collimator that narrows the radiation field to a predetermined shape,
A plurality of leaf blocks movable in the irradiation field direction;
At least one position detecting means for detecting the displacement of the leaf block from the end face shape of the plurality of leaf blocks;
A multi-leaf collimator comprising: The position detecting means includes
A light emitting element for irradiating the plurality of leaf blocks with light;
A lens that changes light emitted from the light emitting element into a linear light;
An image sensor that receives a light beam on a line passing through the lens and obtains a pattern image of a leaf block in the previous period;
The multi-leaf collimator according to claim 1, wherein a displacement of the leaf block is acquired from the pattern image. The position detecting means includes
Recognition means for recognizing the arrangement position of the pattern image;
Comparing means for acquiring the displacement of the pattern image by comparing the arrangement position of the pattern image acquired in advance with the arrangement position of the pattern image acquired this time;
The multi-leaf collimator according to claim 2, wherein the displacement of the previous leaf block is obtained by the shift. A radiation source that emits radiation;
A bed on which the subject is placed;
A multi-leaf collimator that is interposed between the radiation source and the bed, and squeezes the irradiation field of the radiation emitted from the radiation source into a predetermined shape,
The multi-leaf collimator is
A plurality of leaf blocks movable in the irradiation field direction;
At least one position detecting means for detecting the displacement of the leaf block from the end face shape of the plurality of leaf blocks;
A radiation therapy apparatus comprising: The position detecting means includes
A light emitting element for irradiating the plurality of leaf blocks with light;
A lens that changes light emitted from the light emitting element into a linear light;
An image sensor that receives a light beam on a line passing through the lens and obtains a pattern image of a leaf block in the previous period;
The radiotherapy apparatus according to claim 4, wherein a displacement of the leaf block is acquired from the pattern image. The position detecting means includes
Recognizing means for recognizing the arrangement position of the pattern image;
Obtaining the position of the leaf block according to the arrangement position of the pattern image;
The radiotherapy apparatus according to claim 5. The position detecting means includes
Recognition means for recognizing the arrangement position of the pattern image;
Comparing means for acquiring the displacement of the pattern image by comparing the arrangement position of the pattern image acquired in advance with the arrangement position of the pattern image acquired this time;
With
The radiotherapy apparatus according to claim 4, wherein the displacement of the leaf block is acquired by the shift.

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