JP6482827B2 - Irradiation position detector - Google Patents

Description

  The present invention relates to an irradiation position detection apparatus that detects an irradiation position of radiation.

  The beam irradiation device used for radiation therapy is mounted on, for example, a gantry with a rotation function, and can perform beam irradiation while moving relative to the patient lying on the couch (changing the gantry angle). It has become. The couch can also set an angle (couch angle) with respect to the normal of the surface formed by the movement locus of the irradiation apparatus. In addition, there is a robot arm with a beam irradiation device installed at the tip of the robot arm, and the radiation therapy device has specifications that allow beam irradiation from the 4π direction.

  As a result, the irradiation position of the beam is controlled so that the beam is not applied to normal cells in the vicinity thereof while accurately irradiating the target cancer cell or the like with the beam. In recent years, technology has been developed to focus the beam more closely on the target cells, improving the reproducibility of the irradiation position and guaranteeing and managing the quality (Quality Assurance / Quality control; QA / QC). It is becoming important to do.

  At the clinical site, the irradiation position (isocenter) of the beam is set by a wall surface laser or an image guidance device. When evaluating whether the irradiation position of the beam is a desired position of the therapist, the following operations are conventionally performed.

  That is, the evaluator places the radiation film in a plane that is perpendicular to the moving direction of the beam irradiation position (parallel to the surface formed by the movement locus of the irradiation apparatus) and passes through the isocenter (scheduled irradiation point of the beam). Then, the evaluator controls the beam irradiation device to change the irradiation position along the moving direction (for example, changing the angle by 30 degrees with respect to the axis), and the beam is applied to the radiation film. Irradiate.

  As a result of this irradiation, the pattern obtained by developing the radiation film shows a trace of the beam passing radially in a plurality of directions. The evaluator draws a straight line along the center of the trajectory of each beam and checks whether or not the intersection of the trajectories of each beam is within a predetermined radius (for example, a radius of 1 mm) from the point corresponding to the isocenter.

  Here, if it is within a predetermined radius, it is determined that the beam can be irradiated with sufficient accuracy. If it is not within the predetermined range, it is determined that adjustment of the beam irradiation apparatus is necessary (so-called star shot method). And Winston-Lutz test).

inet: Masashi Tani, “Winston-Lutz test with EPID and ImageJ”, [online], [October 8, 2014 search], Internet <URL: http://katarou-kai.kenkyuukai.jp/images/sys % 5Cinformation% 5C20140319104309-7D462E3CA60F6A6126A93682A37FAC7E15A65F3151A6392254C260781778DC6E.pdf>

  However, the conventional method requires time for developing the film, and it takes time to determine accuracy. In addition, the above method can only verify the accuracy in the in-plane direction of the film. However, in recent years, there is an irradiation apparatus that can irradiate the film surface (that is, the cross section of the patient) obliquely, and its application is limited. It was. Furthermore, digitalization is also progressing in the medical field, and there is a problem that development type films are difficult to use. There is also a method that uses a detector (Electric Portal Imaging Device: EPID, etc.) installed in the radiation therapy device without using a film, but detection is performed at each irradiation position by rotating the detector together with the radiation therapy device. The detector also moved, and there was a problem with the installation accuracy of the detector. In addition, the beam position at the isocenter position cannot be directly observed, and there is a problem that the metal sphere installed on the isocenter can be viewed only at a position about several tens of centimeters away from the isocenter position.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an irradiation position detection apparatus capable of detecting the irradiation position of a beam irradiation apparatus simply and quickly.

  Non-Patent Document 1 discloses a technique for performing a Winston-Lutz test by detecting a shadow of a tungsten sphere at the time of beam irradiation using an EPID for visualizing the beam intensity and a test tool using a tungsten sphere. ing.

  The present invention for solving the problems of the conventional example described above is a detection device that detects the irradiation position of a beam by an irradiation device that can irradiate the irradiation object on the couch from a plurality of different irradiation angles. A scintillator having a rotationally symmetric shape with respect to a predetermined central axis and having light transmittance, the scintillator being arranged on the couch and receiving a beam irradiated by the irradiation device from a side surface; and An image capturing unit that captures an image including at least the scintillator within an angle of view of the scintillator from the plane side or the bottom surface side, and an image captured by the image capturing unit when the irradiation device emits a beam, Detection means for detecting a beam passage path in the scintillator from the acquired image and detecting a beam irradiation position based on the detected beam passage path; In which it was decided to include the.

  According to the present invention, the beam irradiation position of the irradiation apparatus can be detected easily and quickly by using the image data of the scintillation light.

It is the schematic showing the structural example of the irradiation position detection apparatus which concerns on embodiment of this invention. It is a functional block diagram showing the example of the irradiation position detection apparatus which concerns on embodiment of this invention. It is explanatory drawing showing the example of the image data which the irradiation position detection apparatus concerning embodiment of this invention obtains. It is the schematic showing an example of the detection body of the irradiation position detection apparatus which concerns on embodiment of this invention. It is the side surface, bottom face, and sectional drawing showing an example of the hat member of the irradiation position detection apparatus which concerns on embodiment of this invention. It is the schematic showing an example of an effect | action of the detection body of the irradiation position detection apparatus which concerns on embodiment of this invention. It is explanatory drawing showing the example of the image data obtained by the irradiation position detection apparatus which concerns on embodiment of this invention, and its processing example. It is explanatory drawing showing the example of another image data obtained by the irradiation position detection apparatus concerning embodiment of this invention, and its processing example. It is explanatory drawing showing the example of the image data obtained by the irradiation position detection apparatus which concerns on one Example of this invention. It is explanatory drawing showing the image processing example by the irradiation position detection apparatus which concerns on one Example of this invention. It is explanatory drawing showing the example of another image data obtained by the irradiation position detection apparatus which concerns on one Example of this invention. It is explanatory drawing showing the example which compared the image data obtained by the irradiation position detection apparatus which concerns on one Example of this invention. It is explanatory drawing showing the example of another image data obtained by the irradiation position detection apparatus which concerns on one Example of this invention. It is explanatory drawing showing another example of image processing by the irradiation position detection apparatus which concerns on one Example of this invention.

  Embodiments of the present invention will be described with reference to the drawings. The irradiation position detection apparatus 1 according to the embodiment of the present invention detects an irradiation position of a beam by an irradiation apparatus that can irradiate a beam on a couch from a plurality of different irradiation angles.

[Basic configuration]
Specifically, the irradiation position detection apparatus 1 includes a detection body 10 and an image processing apparatus 20 as illustrated in FIG. Here, the detection body 10 has a rotationally symmetric shape with respect to a predetermined central axis C, and includes a scintillator 11 having optical transparency. The image processing apparatus 20 includes an imaging unit 21 and an image processing control unit 22. The image processing control unit 22 can be realized by a general computer, and includes a control unit 25, a storage unit 26, an operation unit 27, a display unit 28, and an interface unit 29. Note that the sizes and arrangement positions of the scintillator 11 and the imaging unit 21 shown in the drawings used in the present embodiment do not indicate actual sizes or arrangement conditions, and their scales are not shown in the drawing or for convenience. It has been changed for explanation.

  As illustrated in FIG. 1, the scintillator 11 of the detection body 10 is a plastic scintillator having optical transparency and a cylindrical shape. The scintillator 11 does not necessarily have a cylindrical shape, but has a shape that is rotationally symmetric with respect to a predetermined central axis C, such as a regular polygonal column shape, or a hollow shape such as a cylindrical shape or a cylindrical shape of a regular polygon. Any shape having a plane 111 and a bottom surface 112 with C as a normal line (in the case of a cylindrical body, these planes 111 and bottom surface 112 may be virtual) may be used. The evaluator of the irradiation apparatus fixes the scintillator 11 of the detection body 10 on the couch in a state where the central axis C is matched with the isocenter. In order to fix the scintillator 11, for example, a holding body that holds the scintillator 11 so as not to roll may be used. However, since such a holding body can be appropriately selected, detailed description (and illustration) thereof is omitted.

  In the following description, the longitudinal direction of the couch (the direction perpendicular to the plane formed by the rotation trajectory of the beam irradiation device) is taken as the Z axis, the vertical upper direction is the Y axis, and the couch width direction axis orthogonal to these axes is X Axis. The scintillator 11 is arranged so that the center axis C described above coincides with the Z-axis direction.

  The imaging unit 21 of the image processing apparatus 20 is a camera or the like having an imaging element such as a CCD (Charge Coupled Device) or a CMOS, for example, and receives image data to obtain image data obtained by imaging an image in a set imaging direction. Generate and output. In the present embodiment, the imaging unit 21 is disposed on the plane side or the bottom surface side of the scintillator 11 of the detection body 10 and the optical axis thereof is aligned with the central axis C. That is, the imaging direction of the imaging unit 21 is the normal direction (Z-axis direction) of the plane or bottom surface of the scintillator 11. Further, at least the scintillator 11 is included in the range (view angle) captured by the imaging unit 21.

  The control unit 25 of the image processing control unit 22 is a program control device such as a CPU, and operates according to a program stored in the storage unit 26. In the present embodiment, the control unit 25 acquires image data obtained by the imaging unit 21 when the irradiation device irradiates a beam, and detects a beam passage path in the scintillator 11 from the acquired image data. To do. And this control part 25 performs the process which detects the irradiation position of a beam based on the said detected beam passage path | route. Details of the processing of the control unit 25 will be described later.

  The storage unit 26 is a memory device or the like, and holds a program executed by the control unit 25. The program may be provided by being stored in a computer-readable non-transitory recording medium and copied in the storage unit 26. The storage unit 26 also operates as a work memory of the control unit 25 and stores image data and the like.

  The operation unit 27 is a keyboard, a mouse, or the like, and accepts a user's instruction operation and outputs information representing the contents of the accepted instruction operation to the control unit 25. The display unit 28 is a display or the like, and displays and outputs an image in accordance with an instruction input from the control unit 25.

  The interface unit 29 is a USB (Universal Serial Bus) interface or the like, is connected to the imaging unit 21, and outputs image data output by the imaging unit 21 to the control unit 25. Further, the interface unit 29 outputs an instruction output by the control unit 25 to the imaging unit 21.

  Here, the contents of the processing by the control unit 25 will be described. The control unit 25 functionally executes a program stored in the storage unit 26 to functionally include an image data receiving unit 31, a scintillation light detection unit 32, and a beam passage path as illustrated in FIG. A detection unit 33, a detection result generation unit 34, and an output unit 35 are included.

  The image data receiving unit 31 receives image data output from the imaging unit 21 via the interface unit 29. The scintillation light detection unit 32 detects scintillation light from the image data received by the image data receiving unit 31. Specifically, in the present embodiment, image data having a main light source as scintillation light can be obtained by preventing ambient light from entering the imaging unit 21 such as turning off the indoor lamp during imaging.

  The scintillation light detection unit 32 extracts a pixel group having a luminance higher than a predetermined threshold from the image data to thereby form a linear pixel group on the scintillation light trajectory, and an outline of the scintillator 11 illuminated with the scintillation light. Are extracted and labeled as pixel groups P and Q, respectively (FIG. 3A). Here, the scintillation light detection unit 32 sets a pixel group arranged in a straight line in the image data as a pixel group P on the beam passage path. In addition, the scintillation light detection unit 32 defines pixel groups arranged in a plane or bottom surface shape of the scintillator 11 (in this example, a circular shape because the rotation axis is a rotational body having a rotational axis as a symmetry axis) as a pixel group Q. To do. These pixel groups are detected by a known process such as Hough transform.

  The beam passage path detector 33 detects a beam passage path in the scintillator 11 based on the pixels detected as the pixel group P on the scintillation light locus by the scintillation light detector 32 from the image data. Specifically, the pixels labeled as the pixel group P on the locus of the scintillation light are generally arranged on a straight line having a width w as illustrated in FIG. Therefore, the beam passage path detection unit 33 generates information specifying the virtual line segment L passing through the center in the width direction of the straight line having the width w as information representing the beam passage path. As an example, the information specifying the virtual line segment L can be expressed as a straight line expression in the (ξ, η) coordinate system representing the pixel arrangement of the image data.

  Further, the beam passage path detection unit 33 finds the center (center axis C) c of the scintillator 11 from the pixel group Q representing the outline of the scintillator 11 illuminated with the scintillation light extracted from the image data. For the detection of the center c, for example, a widely known process such as a method of obtaining an intersection of a rectangular diagonal line circumscribing the pixel group Q can be used, and detailed description thereof is omitted here.

  The detection result generation unit 34 detects whether or not the virtual line segment L representing the trajectory of the scintillation light detected by the beam passage path detection unit 33 passes through the center c of the scintillator 11. Specifically, the detection result generation unit 34 determines the distance from the center c of the detected scintillator 11 to the imaginary line segment L (the perpendicular line when F is the foot of the perpendicular line from the center c to the imaginary line segment L). The length cF) is obtained and output. Since this calculation is widely known, a detailed description thereof is omitted here. The output unit 35 outputs the information generated by the detection result generation unit 34 to the display unit 28.

  The irradiation position detection apparatus 1 according to an example of the present embodiment has the above-described configuration and operates as follows. In an example of the present embodiment, a beam irradiation position (isocenter) is set by a wall surface laser or an image guidance device, and the central axis C of the scintillator 11 of the detection body 10 is placed on the couch in a state where the center axis C coincides with this isocenter. Fix it.

  Further, the imaging unit 21 of the image processing device 20 is arranged on the bottom surface side of the scintillator 11, and the optical axis thereof is made to coincide with the central axis C of the scintillator 11. The position and zoom are set so that the scintillator 11 is included in the imaging range (view angle) of the imaging unit 21.

  The evaluator irradiates the detection body 10 with the beam while controlling the beam irradiation device and changing the irradiation position along the moving direction (for example, changing the angle by 30 degrees with respect to the axis). The imaging unit 21 of the image processing apparatus 20 outputs image data obtained by imaging when the beam is irradiated to the control unit 25.

  The control unit 25 of the image processing apparatus 20 receives the image data. And the control part 25 extracts the pixel which represents the outline of the scintillator 11 illuminated with the scintillation light by the pixel group P on the locus of the scintillation light by extracting pixels whose luminance is higher than a predetermined threshold from the received image data. Group Q is extracted. Further, the control unit 25 specifies information (image) that specifies a virtual line segment L representing the beam passage path as a line segment passing through the center in the width direction from the pixel group P arranged on the line segment of the width w extracted here. A straight line expression in the (ξ, η) coordinate system representing the pixel arrangement of data is obtained by calculation.

  Specifically, when the center in the width direction of the pixel group P includes pixels (ξ1, η1) and (ξ2, η2) at different positions, the formula of the virtual line segment L is η = (η2−η1) X (ξ−ξ1) / (ξ2−ξ1) + η1 The image processing apparatus 20 also uses the center c (center of the scintillator 11 using a widely known process such as a method of obtaining an intersection of rectangular diagonal lines circumscribing the group from the pixel group Q representing the outline of the scintillator 11. Find the point when viewing the axis C from the direction of the axis).

  The image processing apparatus 20 then sets the distance r from the center c (position corresponding to the isocenter) of the found scintillator 11 to the imaginary line segment L (the leg of the perpendicular line from the center c to the imaginary line segment L as F). The length of the perpendicular to the time cF) and output it.

  Thus, in the irradiation position detection apparatus 1 of the present embodiment, the evaluator irradiates the scintillator 11 that is the detection body 10 while controlling the beam irradiation apparatus and changing the irradiation position along the moving direction. Every time, the image data obtained by imaging at the time of irradiation is analyzed, and the deviation amount r of the beam passage path from the center c (set to the isocenter) of the scintillator 11 is output. The evaluator determines whether or not the beam irradiation apparatus needs to be adjusted by checking whether or not the deviation amount r is within a predetermined range (for example, 1 mm).

[Use of reflectors]
In the basic configuration of the present embodiment, when the beam passage path is deviated within the XY plane (within the (ξ, η) coordinate system representing the pixel arrangement), the deviation amount r can be detected. Become. However, when the scintillator 11 has a cylindrical shape, it is difficult to detect the shift amount in the Z-axis direction. Similarly, although the beam should enter the Z axis vertically, the beam passage path is inclined with respect to the desired angle, but it is difficult to detect when the beam intersects the central axis C. Therefore, in another example of the embodiment of the present invention, the detection body 10 includes a scintillator 11 and a hat member 12 as illustrated in FIG. Here, the scintillator 11 has a rotationally symmetric shape (a cylindrical shape as an example) with respect to a predetermined center axis C, and has light transmittance. In FIG. 4, the outline of the scintillator 11 that may not actually be visible with visible light through the hat member 12 is indicated by a one-dot chain line.

  Here, the hat member 12 has a rotationally symmetric shape with respect to a predetermined center axis γ, and the center axis γ coincides with an axis (center axis C) passing through the center of the plane of the scintillator 11 and the center of the bottom surface. To be aligned. The hat member 12 is a cylindrical member formed so that its diameter increases toward one side (hereinafter referred to as the bottom surface side) (as it goes in the direction along the central axis γ), Further, the inner surface facing the scintillator 11 is mirror-finished so as to reflect the scintillation light emitted by the scintillator 11.

  Specifically, as shown in FIGS. 5A to 5C, the hat member 12 has a truncated conical shape as illustrated in a side view, a bottom view (viewed from the larger diameter side), and a cross-sectional view, respectively. The main body 120 that is a cylindrical body, a mirror-finished layer 121 disposed on the inner surface side of the main body 120, and a scintillator holding body 122 are configured. Here, the mirror-finished layer 121 is formed by vacuum-depositing aluminum on the inner surface of the main body 120. Further, in an example of the present embodiment, the end portion of the main body 120 on the smaller diameter side is extended into a cylindrical shape having the diameter (120p in FIG. 5A), and the scintillator holding body 122 is formed inside thereof. A clamp (which may be a general pipe clamp) is provided.

  In this example of the present embodiment, the scintillator 11 is sandwiched and fixed to a clamp as the scintillator holding body 122 of the hat member 12. At this time, the center axis C of the scintillator 11 and the center axis γ of the hat member 12 are aligned and fixed. The scintillator holding body 122 is not limited to the one described here, and the scintillator 11 can be fixed to the hat member 12 with its central axis C and the central axis γ of the hat member 12 being matched. It does not ask about the shape or the like, and may be anything. The hat member 12 is formed of a material that transmits an irradiated beam, such as acrylic resin.

  In this example of the present embodiment, the imaging unit 21 of the image processing device 20 is disposed on the bottom surface side (the larger diameter side) of the hat member 12 of the detection body 10, and the optical axis thereof is the central axis C (the central axis γ). ) To match. Therefore, the imaging direction is the normal direction of the bottom surface of the hat member 12. In addition, the range (field angle) captured by the imaging unit 21 includes at least the inner surfaces (mirror-finished portions) of the scintillator 11 and the hat member 12. Also in this example, since the detection body 10 is fixed on the couch, a holding body that holds the detection body 10 so as not to roll may be used. However, since such a holding body can be selected as appropriate, a detailed description (and illustration) thereof is possible. Is omitted.

  In this example of the present embodiment, the control unit 25 of the image processing apparatus 20 has the same functional configuration as illustrated in FIG. 2, but the operations of the beam passage path detection unit 33 and the detection result generation unit 34. Is a little different. Therefore, in the following description, the beam passage path detection unit and the detection result generation unit are indicated as a beam passage path detection unit 33 ′ and a detection result generation unit 34 ′ with different signs for distinction. That is, in this example of the present embodiment, the image data receiving unit 31 of the control unit 25 receives the image data output from the imaging unit 21 via the interface unit 29. The scintillation light detection unit 32 detects scintillation light from the image data received by the image data receiving unit 31. Specifically, in the present embodiment, image data having a main light source as scintillation light can be obtained by preventing ambient light from entering the imaging unit 21 such as turning off the indoor lamp during imaging.

  In the present embodiment, the pixel group R by the scintillation light reflected by the mirror-finished inner surface of the hat member 12 is an image in which the scintillation light emitted from each part on the linear path inside the scintillator 11 is reflected by the conical mirror surface. It represents. Specifically, as in the previous example, the longitudinal direction of the couch (the direction perpendicular to the plane formed by the rotation trajectory of the beam irradiation device) is the Z axis, the upper vertical direction is the Y axis, and the couch width direction is orthogonal to these axes. The scintillator 11 is arranged so that the center axis C described above coincides with the Z-axis direction. In the following example, the position of the apex of the conical shape formed by the hat member 12 (here, since the hat member 12 is a truncated conical shape, there is no actual apex, but it should be the apex when the side surface is extended) Position) is the origin (0, 0, 0).

  Here, as schematically shown in FIG. 6, the light emission point at the position where the beam is incident on the scintillator 11 is pi (pix, piy, piz), and the light emission point at the position where the beam is emitted from the scintillator 11 is po (pox). , Poy, poz), the radius of the bottom surface of the scintillator 11 is rsc, and when the hat member 12 is broken at a plane including the central axis γ, the angle formed by the pair of conical buses is 90 degrees.

  At this time, the image pickup unit 21 has two points Ri_1 (pix × piz / rsc, pix × piz / rsc) which are on the extension of the perpendicular line extending from the light emitting point pi to the central axis C and intersect the inner surface of the hat member 12. , Piz), Ri_2 (−pix × (2rsc + piz) / rsc, −piy × (2rsc + piz) / rsc, pix), each of which is an extension of a perpendicular line extending from the light emitting point po to the central axis C. Two points Ro_1 (pox × poz / rsc, poy × poz / rsc, poz), Ro_2 (−pox × (2rsc + poz) / rsc, −poy × (2rsc + poz) / rsc, poz) intersecting the inner surface of the member 12 are respectively obtained. A pair of semicircular arc-shaped reflected lights as end points arrive. Since the image pickup surface of the image pickup unit 21 is an XY plane, the image data picked up and output by the image pickup unit 21 starts from the coordinates corresponding to (pix × piz / rsc, piy × piz / rsc) (pox). A pixel group R1 having a semicircular arc shape whose end point is a coordinate corresponding to × poz / rsc, poy × poz / rsc) and higher brightness than the surroundings, and (−pix × (2rsc + piz) / rsc, −piy × (2rsc + piz) ) / Rsc), starting from the coordinates corresponding to (−pox × (2rsc + poz) / rsc, −poy × (2rsc + poz) / rsc), and having a luminance higher than the surroundings. The pixel group R2 is included (FIG. 3B). Note that the pixel groups R1 and R2 may be included in the image data as one annular pixel group R having higher luminance than the periphery, with their ends overlapping depending on the beam passage path. In addition, both ends (pixels corresponding to the start point and the end point) of the pixel groups R1 and R2 have relatively high luminance among the pixels included in the pixel group R1 or R2.

  Accordingly, the scintillation light detection unit 32 extracts a pixel group P on the trajectory of the scintillation light by the beam passing through the inside of the scintillator 11 by extracting pixels whose luminance is higher than a predetermined threshold value from the received image data. (FIG. 3B). Here, the extraction method of the pixel group P can be performed in the same manner as already described, and thus the repeated description is omitted. The scintillation light detection unit 32 labels the pixel group P included in this pixel group.

  The beam passage path detector 33 'passes the beam in the scintillator 11 based on the pixels detected by the scintillation light detector 32 from the image data and labeled as pixels included in the pixel group P on the locus of the scintillation light. Detect the route. Specifically, the pixels labeled as the pixel group P on the locus of the scintillation light are generally arranged on a straight line having a width w as in the case illustrated in FIG. Therefore, the beam passage path detection unit 33 ′ generates information specifying the virtual line segment L passing through the center in the width direction of the straight line having the width w as information representing the beam passage path. Also in this example, the information specifying the virtual line segment L can be expressed as a straight line expression in the coordinate system representing the pixel arrangement of the image data. The beam passage path detector 33 ′ acquires the coordinates of both ends of the virtual line segment L as (ξi, ηi) and (ξo, ηo), respectively.

  The beam passage path detection unit 33 ′ also generates corrected image data obtained by removing the pixel group P from the image data received from the imaging unit 21. Then, the beam passage path detection unit 33 ′ sets the luminance threshold Lmin to a predetermined initial value, and extracts pixels that exceed the luminance threshold Lmin among the pixels included in the corrected image data (significant pixel extraction processing). ). The beam passage path detection unit 33 ′ selects the extracted pixel as a significant pixel, selects one of the unlabeled significant pixels as a target pixel, issues a label unique to the pixel, and performs labeling. If there are significant pixels in any of the eight neighboring pixels of the selected target pixel, the beam passage path detection unit 33 ′ performs labeling on each of the significant pixels with the same label as the target pixel. Hereinafter, while each of the significant pixels is sequentially selected as a target pixel, it is determined whether or not a significant pixel is included in the eight neighboring pixels, and a labeling process is performed.

  In this way, the beam passage path detection unit 33 ′ performs labeling specific to the region in the region where the significant pixels are continuous (hereinafter referred to as a high-luminance continuous region) (continuous region detection). processing). The beam passage path detection unit 33 ′ obtains a circumscribed rectangle for each pixel (that is, for each high-luminance continuous region) that has been labeled differently. The beam passage path detection unit 33 ′ excludes circumscribed rectangles having an area smaller than a predetermined area from the obtained circumscribed rectangles, and checks the number of obtained circumscribed rectangles (detected high luminance continuous regions). If the number of circumscribed rectangles obtained here is not 2 or 4, the beam passage path detection unit 33 ′ increments the luminance threshold Lmin by a predetermined increment value, and returns to the significant pixel extraction process to perform the process. to continue.

  If the number of circumscribed rectangles obtained is 2 or 4, the beam passage path detection unit 33 ′ obtains the center coordinates of the circumscribed rectangle. In the following, the values of the central coordinates are (ξ1, η1), (ξ2, η2).

  When there are four central coordinates obtained here, the beam passage path detection unit 33 ′ includes a pair of central coordinates including one of them, for example, (ξ1, η1), that is, (ξ1, η1). And (ξ2, η2), (ξ1, η1) and (ξ3, η3), (ξ1, η1) and (ξ4, η4), and a line passing through the two central coordinates contained in each of these sets Formulas for the minutes L1, L2, and L3 are obtained. The beam passage path detection unit 33 ′ then determines the distances to the obtained line segments L1, L2, and L3, the one end side coordinates (ξi, ηi) of the virtual line segment L, and the other end coordinates (ξo, ηo). (Distances d1_1, d1_2 for L1, distances d2_1, d2_2, etc. for L2). Then, of the obtained distances d1_1, d1_2,..., D3_2, the one having the shortest distance is selected. Here, for example, it is assumed that the distance d1_1 from the line segment L1 (the line segment connecting (ξ1, η1) and (ξ2, η2)) to the one end side coordinate (ξi, ηi) of the virtual line segment L is the shortest ( Even with this assumption, generality is not lost. The beam passage path detection unit 33 ′ uses the line segment L1 as a connecting line that connects reflected light of the same scintillator light.

  The beam passage path detection unit 33 ′ obtains an expression of a line segment L1 ′ that is another connection line that passes through the pair of central coordinates (ξ3, η3) and (ξ4, η4) through which the connection line L1 does not pass. Further, intersection coordinates (ξc, ηc) of these line segments L1 and L1 ′ are obtained. Then, the beam passage path detection unit 33 ′ sets the intersection coordinates (ξc, ηc) as a position corresponding to a point (center point c) on the center axis C of the scintillator 11 (FIG. 7). Note that the beam passage path detection unit 33 ′ generates an error (of the detection body 10) when the distance between the line segment L 1 ′ and the other end side coordinates (ξo, ηo) of the virtual line segment L is larger than a predetermined threshold value. There is a possibility that the arrangement etc. may be wrong).

  In this example, the beam passage path detection unit 33 ′ is a reflected image of the scintillation light that appears at a position on the beam incident side with respect to the central axis C when the beam enters the scintillator 11 (the above-described central coordinates (ξ1, η1 ) And a reflected image of scintillation light appearing at a point-symmetrical position with respect to the central axis C with respect to the position (corresponding to the pixel at the above-mentioned central coordinates (ξ2, η2)) , A pair of scintillation light images (corresponding to pixels at one end side coordinates (ξi, ηi) of the virtual line segment L) appearing on the side surface of the scintillator 11 and the beam emitted from the scintillator Sometimes, with respect to the central axis C, a reflected image of scintillation light appearing at the position on the beam emission side (e.g., corresponding to the pixel at the above-mentioned central coordinates (ξ3, η3)), and the central axis C with respect to the position And a scintillation light reflection image (e.g., corresponding to the pixel at the above-mentioned central coordinates (ξ4, η4)) and a scintillation light image when the beam appears on the side surface of the scintillator 11 ( The central axis C is detected on the basis of each image included in at least one of the sets of the pair of the virtual line segment L (corresponding to a pixel at one end side coordinate (ξo, ηo)).

  The detection result generation unit 34 ′ determines whether or not the virtual line segment L representing the trajectory of the scintillation light detected by the beam passage path detection unit 33 ′ passes the coordinates (ξc, ηc) of the center point c of the scintillator 11. To detect. Specifically, the detection result generation unit 34 ′ is a distance from the center point c of the detected scintillator 11 to the virtual line segment L (when F is a foot of a perpendicular line dropped from the center c to the virtual line segment L). The perpendicular length CF) Δxy is obtained and output. Since this calculation is widely known, a detailed description thereof is omitted here.

  When the beam passage path detection unit 33 ′ obtains two connection lines L1 and L1 ′, the detection result generation unit 34 ′ determines the coordinates of the center point c of the scintillator 11 (for each of the connection lines L1 and L1 ′). The radii r1 and r2 of the circle passing through the center coordinates through which each connecting line passes are obtained with ξc, ηc) as the center.

  In addition, the detection result generation unit 34 ′ is configured so that when the beam passage path detection unit 33 ′ does not obtain two connection lines L 1 and L 1 ′ (when two high-luminance continuous regions are found), each detection result generation unit 34 ′ The midpoint of the center coordinates (ξ1, η1) and (ξ2, η2) of the circumscribed rectangle of the luminance continuous area is set as the coordinates (ξc, ηc) of the center point c of the scintillator 11. Then, as illustrated in FIG. 8, the detection result generation unit 34 ′ is a position where the line segment connecting these central coordinates (ξ1, η1) and (ξ2, η2) intersects the circumscribed rectangle of the high luminance continuous region. The distances between each of the two high-luminance continuous areas P1 and P2 and the center point c are r1 and r2, respectively. At this time, Δxy = 0.

として求める。ここで｜＊｜は、＊の絶対値を表す。また、ｒscは、シンチレータ１１の半径である。 Then, the detection result generation unit 34 ′ calculates the beam shift angle ΔθZ with respect to the direction perpendicular to the Z axis,

Asking. Here, | * | represents the absolute value of *. Rsc is the radius of the scintillator 11.

  The detection result generation unit 34 ′ outputs the average (arithmetic average) rav, ΔθZ, and Δxy of the r1 and r2. The output unit 35 displays and outputs the information output from the detection result generation unit 34 ′ on the display unit 28.

  Thereby, the irradiation position detection apparatus 1 according to this example of the present embodiment operates as follows. Here, it is assumed that the scintillator 11 has a cylindrical shape, and when the hat member 12 is broken along a plane including the central axis γ, the angle formed by the pair of conical buses is 90 degrees. Further, the irradiation position (isocenter) of the beam is set by a wall surface laser or an image guiding device, and a point on the central axis C of the scintillator 11 of the detection body 10 (a point where the value of the Z axis is z) is defined as this isocenter. Fix it on the couch in a state that matches.

  Further, the imaging unit 21 of the image processing device 20 is arranged on the bottom surface side of the scintillator 11, and the optical axis thereof is made to coincide with the central axis C of the scintillator 11. Further, the position and zoom are set so that the imaging range (view angle) of the imaging unit 21 includes the mirror-finished portions inside the scintillator 11 and the hat member 12.

  The evaluator irradiates the detection body 10 with the beam while controlling the beam irradiation device and changing the irradiation position along the moving direction (for example, changing the angle by 30 degrees with respect to the axis). The imaging unit 21 of the image processing apparatus 20 outputs image data obtained by imaging when the beam is irradiated to the control unit 25.

  The control unit 25 finds a pixel (P) on the locus of the scintillation light by extracting pixels having a luminance higher than a predetermined threshold value and arranged in a straight line from the image data. Further, the control unit 25 obtains information (linear equation in the coordinate system representing the pixel arrangement of the image data) for specifying the virtual line segment L representing the beam passage path by calculation.

  In addition, the control unit 25 increases the luminance threshold for pixels other than the pixel (P) until there are two or four regions in which significant pixels are continuous (high luminance continuous region). Then, when there are four continuous regions, the center point c is an intersection of two line segments connecting a pair of corresponding regions (high brightness portions caused by the same scintillation light). The distance Δxy between c and the virtual line segment L, and the distances r1 and r2 to the high brightness continuous region through which the center point c and the two line segments pass, are calculated, and the average rav is calculated. ) ΔΔZ is obtained from the equation (1), and these values are output.

  The evaluator examines the deviation amount of the beam passage path from the center c (set to the isocenter) of the scintillator 11 based on these values. That is, when the beam passage path is deviated in the XY plane with respect to the isocenter, the amount Δxy (Δxy = 0 when there is no deviation) may be referred to. Further, if the Z-axis direction is deviated in parallel to the XY plane, the value of rav deviates from the predetermined value (iso-center Z-axis coordinate value), so this value rav may be referred to. .

  Further, when the beam passage path is inclined with respect to the direction perpendicular to the Z axis, the Z coordinate of the incident point of the beam on the scintillator 11 and the emission regardless of whether or not it intersects the central axis C. Since the Z coordinate of the point is different, a significant difference appears between r1 and r2, and the amount of inclination ΔθZ is obtained. That is, the evaluator can examine the inclination of the beam passage path with respect to the direction perpendicular to the Z axis by this ΔθZ.

  The evaluator adjusts the beam irradiation apparatus by checking whether the deviation amount Δxy and the deviation amount in the Z-axis direction are within a predetermined range (for example, 1 mm) and whether ΔθZ is a desired angle. It is determined whether or not is necessary.

[Example using high-intensity part and end point of scintillation light trajectory]
Here, the image processing apparatus 20 has the coordinates of the reflected image of the scintillation light appearing at the beam incident side position with respect to the central axis C, and the scintillation light appearing at a point-symmetrical position with respect to the central axis C with respect to the position. Although both the coordinates of the reflected image are used, the present embodiment is not limited to this.

  That is, when four high-luminance continuous regions are obtained, the image processing apparatus 20 sequentially sets any one of the center coordinates as the attention center coordinates, and the distance (pixel) between the attention center coordinates and each end point coordinate of the virtual line segment L. The Euclidean distance on the (ξ, η) coordinate system of the array may be calculated. Here, with respect to the center coordinates (ξ1, η1), the distance to the one end side coordinates (ξi, ηi) of the virtual line segment L is d1_i, and the distance to the other end side coordinates (ξo, ηo) of the virtual line segment L is d1_o. Then, dj_i and dj_o (j = 1, 2, 3, 4) are obtained for each center coordinate.

  The image processing apparatus 20 selects the shortest of these dj_i and dj_o (j = 1, 2, 3, 4), and selects the center coordinates related to the selected distance. Here, it is assumed that the central coordinates (ξ1, η1) are selected without losing generality. The reflection image caused by the same scintillation light as the central coordinate is the central coordinate related to the second shortest of the above dj_i, dj_o (j = 1, 2, 3, 4) (here, generality is lost). The center coordinates (ξ2, η2) are selected), the image processing apparatus 20 does not use the center coordinates related to the second shortest distance, and the center coordinates and virtual lines related to the shortest distance. The expression of the line segment L1 connecting the coordinates of the end points of the minute L is obtained.

  Further, the image processing apparatus 20 selects the third shortest from these dj_i, dj_o (j = 1, 2, 3, 4), and the center coordinates and the coordinates of the end points of the virtual line segment L related to the selected distance. The equation of the line segment L1 ′ connecting is obtained. The image processing apparatus 20 obtains the center point c from the intersection of these line segments L1 and L1 ′.

  This process includes a reflected image of scintillation light that appears at a position on the beam incident side with respect to the central axis when the beam enters the scintillator 11, and a scintillation that appears at a point-symmetrical position with respect to the central axis C with respect to the position. Among the reflected light images, a set of a reflected image on the side close to the image of the scintillation light at the time of beam incidence appearing on the side surface of the scintillator 11 and an image of the scintillation light at the time of beam incidence appearing on the side surface of the scintillator 11; Further, when the beam exits from the scintillator 11, the reflected image of the scintillation light that appears at the position on the beam exit side with respect to the central axis C, and the scintillation that appears at a point-symmetrical position with respect to the central axis C with respect to the position. Of the reflected image of light, a reflected image on the side close to the image of the scintillation light at the time of beam emission appearing on the side surface of the scintillator Corresponding to the use of set of the image of the scintillation light upon beam emission appearing on the sides of the scintillator.

  Hereinafter, the image processing apparatus 20 performs the same processing as the previous example, and the amount of deviation Δxy, rav, and the deviation angle of the beam with respect to the direction perpendicular to the Z axis when the beam passage path is displaced in the XY plane with respect to the isocenter. Obtain ΔθZ and display it.

[Example by image recognition]
In addition, here, the image processing apparatus 20 changes the brightness threshold so that when the beam enters or exits the scintillator 11, the image processing apparatus 20 is on the beam incident side or the exit side with respect to the central axis C of the scintillator 11. A reflection image of scintillation light that appears at a position and a reflection image of scintillation light that appears at a point-symmetrical position with respect to the central axis C with respect to the position have been found. However, the present embodiment is not limited to this.

  In an example of the present embodiment, the image processing apparatus 20 obtains a pair of semicircular arcs (actually part of a spiral shape but approximates a semicircle from image data received from the imaging unit 21. Or a single arc-shaped high-intensity part (a part having a relatively higher luminance than the surrounding area) is obtained by image recognition, and each end point (four points in total) of these semi-arc-shaped parts is found, and each position (ξ1 , Η1), (ξ2, η2)... May be used to determine the straight lines L1, L1 ′, and the center point c may be determined from their intersection.

  When an arc-shaped high-luminance portion is found, the image processing apparatus 20 finds two points on the diameter of the arc that have higher luminance among the high-luminance portions (ξ1, η1). , (Ξ2, η2), and the center point c may be obtained from the average of the positions of the two points.

  Hereinafter, the image processing apparatus 20 performs the same processing as when the luminance threshold value is changed, and the deviation amounts Δxy, rav, and the direction perpendicular to the Z axis when the beam passage path is deviated in the XY plane with respect to the isocenter. The beam shift angle ΔθZ is obtained and displayed.

[Cooling the imaging unit]
In the examples so far, the imaging unit 21 may reduce noise that may be included in the image data by cooling the imaging element.

  An operation example of the irradiation position detection apparatus 1 according to the embodiment of the present invention will be described. FIG. 9 shows an example of image data obtained when a beam passing through the isocenter is irradiated while changing the angle by 5 degrees from a direction perpendicular to the Z axis (here, parallel to the Y axis). is there.

  As illustrated in FIG. 9, in this example, as the angle with respect to the Y-axis increases, the range of high-brightness pixels increases. Therefore, it is understood that the deviation angle ΔθZ of the beam with respect to the direction perpendicular to the Z axis can be evaluated by the equation (1) using the radius r1 of the circle inscribed in the high luminance pixel range and the radius r2 of the circumscribed circle. Is done.

  Further, in the image shown in FIG. 9, the image obtained by extracting the pixels having the brightness higher than the predetermined brightness threshold for those having an angle with respect to the Y axis of 0 degree and 35 degrees is shown in FIG. , (B). In both FIGS. 10A and 10B, only two high-luminance pixel regions are detected (except for the pixel group P corresponding to the virtual line segment L). Therefore, it is determined that the line segment connecting the center of the region of the high-brightness pixel passes through the center point c. That is, the shift amount Δxy in the XY plane is evaluated as “0” (passing through the isocenter).

  FIG. 11 shows a case where a beam passing through a position shifted by 5 mm in the Z-axis direction from the isocenter is irradiated while changing the angle by 5 degrees from a direction perpendicular to the Z-axis (here, parallel to the Y-axis). An example of the obtained image data is shown.

  The image data obtained when the beam passing through a position shifted by 5 mm in the negative direction of the Z-axis from the isocenter (side closer to the imaging position) and the beam passing through the isocenter illustrated in FIG. FIG. 12 shows a comparison of image data obtained in the case of irradiation with a comparison of the case where the angle with respect to the Y axis is 0 degrees.

  As illustrated in FIG. 12, the high-luminance pixel region in the image data obtained when the beam passing through a position shifted by 5 mm in the negative direction of the Z-axis from the isocenter (side closer to the imaging position) is irradiated. The center position (inverted brightness is shown as black with higher brightness) is centered than the center position of the high brightness pixel area (shown as white with higher brightness) in the image data obtained when the beam passing through the isocenter is irradiated. The position is farther from the point c (that is, rav is larger). Therefore, the evaluator can evaluate the amount of deviation in the Z-axis direction by evaluating the size of rav.

  FIG. 13 shows a case where a beam passing through a position displaced by 5 mm in the X-axis direction from the isocenter is irradiated while changing the angle by 5 degrees from a direction perpendicular to the Z-axis (here, parallel to the Y-axis). An example of the obtained image data is shown. FIG. 14 shows an image obtained by extracting pixels having a luminance higher than a predetermined luminance threshold for the image shown in FIG. 13 having an angle with respect to the Y axis of 35 degrees.

  As understood from FIGS. 13 and 14, four high-luminance pixel regions are detected in this example (except for pixels corresponding to the virtual line segment L). As the angle of the beam with respect to the Y axis increases, the difference between the radius r1 of the inscribed circle and the radius r2 of the circumscribed circle in the high-luminance pixel region increases. From this, it is understood that the deviation angle ΔθZ of the beam with respect to the direction perpendicular to the Z axis can be evaluated by the equation (1).

  Also, the distance Δxy (see FIG. 14) between the center point c obtained from the intersection of the line segments connecting the high brightness pixel areas corresponding to the common scintillation light and the virtual line segment L (see FIG. 14), the beam in the XY plane The amount of deviation can be evaluated.

DESCRIPTION OF SYMBOLS 1 Irradiation position detection apparatus, 10 detection body, 11 scintillator, 12 hat member, 20 image processing apparatus, 21 imaging part, 22 image processing control part, 25 control part, 26 memory | storage part, 27 operation part, 28 display part, 29 interface Unit, 31 image data receiving unit, 32 scintillation light detection unit, 33, 33 ′ beam passage path detection unit, 34, 34 ′ detection result generation unit, 35 output unit, 111 plane, 112 bottom surface, 120 main body, 121 mirror finish layer 122 A scintillator holder.

Claims (4)

A detection device that detects an irradiation position of a beam by an irradiation device that can irradiate a beam from a plurality of different irradiation angles with respect to an irradiation target on the couch,
A scintillator having a rotationally symmetric shape with respect to a predetermined central axis and having light transmittance, the scintillator disposed on the couch and receiving a beam irradiated by the irradiation device from a side surface;
Imaging means for capturing an image including at least the scintillator within the angle of view from the plane side or the bottom surface side of the scintillator;
An image captured by the imaging unit is acquired when the irradiation device irradiates a beam, a beam passage path in the scintillator is detected from the acquired image, and beam irradiation is performed based on the detected beam passage path. Detecting means for detecting the position;
Only including,
A side that has a rotationally symmetric shape with respect to a predetermined center axis, and that the center axis is aligned with an axis passing through the center of the plane of the scintillator and the center of the bottom surface, and is imaged by the imaging means A cylindrical member whose diameter increases, and further has a mirror-finished hat member whose inner surface facing the scintillator side reflects scintillation light,
The hat member is arranged on the couch together with the scintillator,
The imaging means captures an image including the scintillator and the inner surface of the hat member at an angle of view;
The detection unit acquires an image captured by the imaging unit when the irradiation device irradiates a beam, detects a beam passage path in the scintillator from the acquired image, and detects the detected beam passage path. An irradiation position detection device for detecting the irradiation position of a beam based on the above. The irradiation position detection device according to claim 1 ,
The detection means is a reflected image of the inner surface of the hat member,
At least one of a reflected image of scintillation light that appears at a position on the beam incident side when the beam is incident on the scintillator, a point symmetric with respect to the central axis with respect to the position, and a side surface of the scintillator A pair with the image of the scintillation light at the time of beam incidence appearing in
At least one of the reflected image of the scintillation light that appears at a position on the beam emission side when the beam exits from the scintillator, a point-symmetrical position with respect to the central axis with respect to the position, and on a side surface of the scintillator A pair with the image of the scintillation light when the beam appears in
The irradiation position detection apparatus which detects the said center axis based on the image contained in and further detects the shift | offset | difference of the path | route which passes along the said center axis | shaft, and the said beam passage path | route. The irradiation position detection device according to claim 1 ,
The detection means is a reflected image of the inner surface of the hat member,
A reflected image of scintillation light that appears at a position on the beam incident side when the beam is incident on the scintillator, and a point-symmetrical position with respect to the central axis with respect to the position;
A reflected image of scintillation light that appears at a position on the beam exit side when the beam exits from the scintillator and a point-symmetric position with respect to the central axis with respect to the position;
The irradiation position detection apparatus which detects the said center axis based on this, and further detects the shift | offset | difference of the path | route which passes along the said center axis | shaft, and the said beam passage path | route. The irradiation position detection device according to claim 1 ,
The detection means is a reflected image of the inner surface of the hat member,
Appears on the side surface of the scintillator among the reflected images of the scintillation light that appears at the position on the beam incident side when the beam is incident on the scintillator and a position that is point-symmetric with respect to the central axis with respect to the position. A set of a reflected image on the side close to the image of the scintillation light at the time of beam incidence and an image of the scintillation light at the time of beam incidence appearing on the side surface of the scintillator, and
Of the reflected image of the scintillation light that appears at a position on the beam exit side when the beam exits from the scintillator and a position symmetric with respect to the central axis with respect to the position, the beam appears on the side surface of the scintillator. A set of a reflected image on the side close to the image of the scintillation light at the time of beam emission and an image of the scintillation light at the time of beam emission that appears on the side surface of the scintillator,
An irradiation position detection device that detects the central axis based on an image included in at least one of the sets and further detects a deviation between a path passing through the central axis and the beam passage path.

Images