Isocenter calibration quality control method and system for radiotherapy image guidance system

Abstract

The invention discloses an isocenter calibration quality control system and method for a radiotherapy image guidance system, and relates to the technical field of medical image processing, and the method comprises the steps: S1, enabling radiotherapy rays to be imaged on a scintillator through an optical body surface imaging mode, and obtaining the radiation isocenter of a linear accelerator according to the imaging information of the scintillator; s2, calculating a 3D point cloud of the ball array by using an image processing module to obtain a 3D coordinate of the center position of the ball array; and S3, aligning the 3D coordinate of the center position of the ball array with the radiation isocenter of the linear accelerator to realize calibration of a point cloud coordinate system so as to accurately position the patient in a positioning and treatment stage. According to the invention, the isocenter position of the accelerator can be accurately positioned, the isocenter point of the accelerator is mapped to the point cloud three-dimensional space coordinate for coordinate alignment, accurate positioning and calibration of the system are realized, and the system can also be used for positioning verification before radiotherapy.

Description

Technical Field

[0001] The present invention relates to the technical field of medical image processing, and in particular to a method and system for isocentric calibration quality control of a radiotherapy image guidance system. Background Art

[0002] Inaccurate radiotherapy positioning and real-time monitoring will greatly increase the probability of recurrence in radiotherapy patients. Therefore, quality control methods are needed to ensure the accuracy of radiotherapy. Currently, radiotherapy positioning often requires doctors to determine the coordinates of the tumor center on the planning system image, and the operator places the tumor center at the center of the radiotherapy equipment, which is time-consuming and labor-intensive.

[0003] The isocenter of the linear accelerator of the radiotherapy equipment refers to the intersection of the rotation axis of the gantry and the rotation axis of the treatment bed. To confirm the position of the isocenter, the commonly used methods are laser light indicating the isocenter and airborne imaging equipment indicating the isocenter. The laser light isocenter method relies on the mechanical accuracy of the laser light. A small angle deviation of the laser light will cause a large displacement deviation of the crosshair isocenter of the laser light. The airborne imaging equipment indicates the isocenter method by mounting the imaging device on the accelerator gantry and pre-determining the isocenter coordinates displayed in the airborne image. The accuracy of this method depends on the mechanical deviation and loss of the rotation of the source and the imaging plate. The CBCT airborne imaging used in recent years has solved the problem of low quality of traditional airborne imaging, but it still brings additional radiation to the patient, is not suitable for use in each fractionated treatment, and cannot monitor the error within the fraction. In short, the above-mentioned prior art has the following problems: the error of the laser light indicating the isocenter method is large; the mechanical structure deformation caused by the equipment load in the airborne imaging equipment indicating the isocenter method has a greater impact on the isocenter error, and is accompanied by additional radiation.

[0004] Optical surface monitoring technology is a non-radiative positioning technology that uses one or more camera units to map multiple arbitrary points on the patient's body surface, receive reflected light beams, quickly obtain the patient's body surface contour information, and generate high-precision 3D body surface contours. It can also monitor the patient's body surface in real time and dynamically throughout the radiotherapy treatment process to improve the safety level of treatment. Optical surface monitoring technology can not only reduce the positioning error between fractions and monitor the patient's position movement within the fraction, but also achieve respiratory motion management in radiotherapy through gating technology. It has the characteristics of reducing the frequency of CT use and reducing the additional radiation brought by CT. When part of the patient's body surface deviates from the reference position set based on the planned CT, or when the calculated isocenter deviation exceeds the threshold, the treatment beam can be stopped in association. Through the quality control method of linear accelerator isocenter registration, the precise positioning of optical surface technology is achieved, which is used for positioning verification and precise radiotherapy before patient radiotherapy.

[0005] Therefore, how to achieve precise positioning of optical surface technology through central calibration quality control such as linear accelerators, and use it for positioning verification and precise radiotherapy before patient radiotherapy, is an urgent problem that needs to be solved. Summary of the invention

[0006] The purpose of the present invention is to provide an isocenter calibration quality control system and method for a radiotherapy image guidance system, which can accurately locate the isocenter position of an accelerator, and align the coordinates by mapping the isocenter point of the accelerator to the three-dimensional space coordinates of the point cloud, thereby achieving precise positioning and calibration of the system, and can also be used for positioning verification before radiotherapy.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] An isocenter calibration quality control system for a radiotherapy image guidance system comprises a three-dimensional structured light imaging system, a radiotherapy device, and an isocenter calibration quality control device.

[0009] The radiotherapy device is used to emit therapeutic rays to a target area, and the radiotherapy device includes a linear accelerator;

[0010] The three-dimensional structured light imaging system includes a structured light camera, a projection device, and an image processing module; the structured light camera is used to collect the target image of the ball array to obtain the spatial coordinates of the three-dimensional ball array;

[0011] The isocenter calibration quality control device includes a tray, a ball array, a scintillator, and a scintillator bracket fixed on the tray, a level, three threaded sub-knobs, and four ball racks; the ball array includes two identical balls and two identical line balls;

[0012] The tray is engraved with X-axis engraved lines and Y-axis engraved lines;

[0013] The ball rack is connected to the tray and has three heights. Two ball racks of the same height are fixed with scored balls, and the other two ball racks are used to fix two balls. The threaded secondary knob is used to adjust the levelness of the entire device.

[0014] The level is used to detect the level in the X and Y directions, and when adjusting the height of the threaded secondary knob, the position of the bubble inside the level is observed to determine whether the tray is level;

[0015] The Z-axis height lines of the two scribed balls are consistent and on the same horizontal plane as the Z-axis height lines of the scintillator bracket; the intersection of the X-axis lines and Y-axis lines of the tray and the horizontal plane passes through the center position of the outer surface of the scintillator.

[0016] Furthermore, the tray is provided with a plurality of holes for respectively installing the ball stand, the scintillator bracket, and the level;

[0017] One end of the ball rack seat is used to fix the ball rack, and the other end is fixed to the tray;

[0018] The scintillator bracket is generally in a 45° inclined plane, a scintillator placement groove is provided on the 45° inclined plane, and a Z-axis height engraved line is provided on the side;

[0019] The ball has a hole, the axis of which passes through the center of the ball, and is used for inserting a ball holder into the hole to fix the ball.

[0020] Furthermore, the scintillator support is also provided with a scintillator dust cover and a scintillator pressure cover; the diameter of the scintillator dust cover is slightly larger than the diameter of the scintillator, and is used to prevent the surface of the scintillator from being contaminated;

[0021] The scintillator pressing cover is used to fix the scintillator on the scintillator bracket so that the scintillator fits with the scintillator bracket and is placed at an angle of 45°.

[0022] Furthermore, the scintillator is a circular cerium-doped lutetium yttrium silicate (LYSO:CE) crystal with a diameter of 50 mm and a thickness of 1 mm.

[0023] The present invention also provides an isocenter calibration quality control method for a radiotherapy image guidance system, which is applied to the isocenter calibration quality control system for a radiotherapy image guidance system, and comprises the following steps:

[0024] S1, using optical body surface imaging to image the radiotherapy rays on the scintillator, and obtaining the linear accelerator radiation isocenter based on the imaging information of the scintillator;

[0025] S2, using the image processing module to calculate the 3D point cloud of the ball array and obtain the 3D coordinates of the center position of the ball array;

[0026] S3, aligning the 3D coordinates of the center position of the ball array with the linear accelerator radiation isocenter to achieve calibration of the point cloud coordinate system for accurate positioning of the patient during the placement and treatment stages; or calculating the difference between the 3D coordinates of the center position of the ball array and the linear accelerator radiation isocenter to check and correct the system error.

[0027] Furthermore, the S1, through optical body surface imaging, based on scintillator imaging, obtains the linear accelerator radiation isocenter, specifically including:

[0028] By rotating the linear accelerator rack, the structured light imaging of the radiotherapy rays on the scintillator at different angles is captured, and multiple structured light images at each angle are superimposed to the boundary to extract the boundary position of the radiotherapy rays;

[0029] The centerline position of each radiotherapy ray is calculated multiple times according to the boundary position, the centerline straight line equation is fitted, and the minimum circle that makes all center lines pass through the circle or is tangent to it is calculated. The center of the minimum circle is the linear accelerator isocenter, and its radius is the radiation isocenter error range.

[0030] Furthermore, the step S2 uses an image processing module to calculate the 3D point cloud of the ball array to obtain the 3D coordinates of the center position of the ball array, which specifically includes:

[0031] The isocenter calibration quality control device is placed near the isocenter of the accelerator by aligning the scribed lines on the device surface with the laser lines: the scribed lines are the horizontal and vertical scribed lines on the base and the height scribed lines on the ball array, so that the center position of the isocenter calibration device is preliminarily aligned with the isocenter of the accelerator;

[0032] The target image of the ball array is captured by a structured light camera, and the point cloud data of the ball array is obtained by using the four-step phase shift method and the three-frequency heterodyne method;

[0033] Using the point cloud processing algorithm, the sampling points of each spherical target are identified and the 3D coordinates of the center position of the spherical array are calculated; the calculated point cloud center is matched with the calibration sphere center.

[0034] Furthermore, the method further comprises:

[0035] Calibrate the structured light camera:

[0036] Let the three-dimensional point P in the object coordinate system = [X, Y, Z] T , after rotation, translation, perspective projection, and pixel sampling, it becomes a two-dimensional point U = [u, v] in the pixel coordinate system T , the process is expressed as:

[0037] U=K[R|t]P

[0038]

[0039] Among them, K is the internal parameter matrix f x is the focal length in the x direction, f y is the focal length in the y direction, c x and c y are the x and y coordinates of the center of the camera plate in the pixel coordinate system; R is the rotation matrix r ij is the relevant value of rotation, i = 1, 2, 3, j = 1, 2, 3, t is the translation vector t i is the translation value in the x, y, and z directions, i=1, 2, 3;

[0040] After calibration, three-dimensional reconstruction is achieved through three-dimensional image analysis and calculation to obtain a three-dimensional image.

[0041] Furthermore, the method further comprises:

[0042] Perform parameter measurements on the ball array:

[0043] Using fringe projection technology, sinusoidal fringes are generated by computer programming, and the sinusoidal fringes are projected onto the object to be measured through a projection device. Using the phase shift method, multiple phase shift images are projected to mark a unique position, and the unique position refers to a unique phase corresponding to each pixel; in the phase shift process, fringe images under different phase shift amounts are collected to obtain a fringe image group;

[0044] Phase unwrapping and point cloud solution are performed on the pixel data of the fringe pattern group to obtain the surface information of the ball array. According to the calculated coordinates of the center of the ball array, the coordinate system of the point cloud is aligned with the center of the ball, and finally the physical center position of the scintillator corresponding to the ball array is found.

[0045] The light intensity formula of the sinusoidal stripes is as follows:

[0046] I(x,y)=a(x,y)+b(x,y)cos[φ(x,y)+φ i ]

[0047] In the formula, a(x, y) is the ambient light intensity, that is, the reflected light of the object to be measured; b(x, y) is the modulated light intensity; φ(x, y) is the initial phase information of the wavefront of the object to be measured; φ i is the displacement; (x, y) is the coordinate of the pixel point in the fringe pattern.

[0048] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects: the isocenter calibration quality control system and method for radiotherapy image guidance system provided by the present invention obtains the isocenter information of the linear accelerator radiation based on the imaging of the scintillator by means of optical body surface imaging. The 3D coordinates of the center position of the spherical array are obtained through the 3D point cloud of the spherical array calculated by the structured light camera, and then the 3D coordinates of the center of the spherical array are aligned with the isocenter of the accelerator solved to the point cloud system, so as to achieve accurate positioning of the patient before treatment and accurate positioning of the patient during treatment, thereby achieving accurate radiotherapy for the affected part to reduce the frequency of CT use and reduce the additional radiation brought by CT. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0050] Figure 1 is a structural diagram of an isocenter calibration quality control device in an embodiment of the present invention;

[0051] Figure 2 It is a front view of the isocenter calibration quality control device according to an embodiment of the present invention;

[0052] Figure 3 A top view of the isocenter calibration quality control device according to an embodiment of the present invention;

[0053] Figure 4 A top view of a tray according to an embodiment of the present invention;

[0054] Figure 5 A three-dimensional diagram of a scintillator support according to an embodiment of the present invention;

[0055] Figure 6-Figure 11 The effect diagram corresponding to different combinations of radiotherapy ray angles;

[0056] Fig.12 is the luminous intensity of the scintillator of the embodiment of the present invention;

[0057] Fig.13 A target ray image obtained by an embodiment of the present invention;

[0058] Fig.14 The target ray image subjected to binarization processing according to an embodiment of the present invention;

[0059] Fig.15 The final target ray image is obtained after superposition according to the embodiment of the present invention;

[0060] Fig.16 The calculation result of the center line and the effect diagram of the swing circle of the embodiment of the present invention;

[0061] Explanation of the reference numerals in the accompanying drawings: 1. ball; 2. marked ball; 3. ball rack; 4. ball rack seat; 5. tray; 6. threaded sub-knob; 7. scintillator dust cover; 8. scintillator bracket; 9. level; 10. scintillator pressure cover; 11. scintillator; 201. Z-axis height markings of the marked ball; 501. X-axis markings of the tray; 502. Y-axis markings of the tray; 801. Z-axis height markings of the scintillator bracket; 802. scintillator placement groove. DETAILED DESCRIPTION

[0062] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0063] The purpose of the present invention is to provide an isocenter calibration quality control system and method for a radiotherapy image guidance system, which can accurately locate the isocenter position of an accelerator, and align the coordinates by mapping the isocenter point of the accelerator to the three-dimensional space coordinates of the point cloud, thereby achieving precise positioning and calibration of the system, and can also be used for positioning verification before radiotherapy.

[0064] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0065] like Figure 1-Figure 5 As shown, an isocenter calibration quality control system for a radiotherapy image guidance system provided by an embodiment of the present invention comprises: a three-dimensional structured light imaging system, a radiotherapy device, and an isocenter calibration quality control device.

[0066] The radiotherapy device is used to emit therapeutic rays to a target area, and the radiotherapy device includes a linear accelerator;

[0067] The three-dimensional structured light imaging system includes a structured light camera, a projection device, and an image processing module. The imaging system obtains a structured light image by projecting active structural information, such as sinusoidal stripes, onto the surface of the object being measured, and photographing the surface being measured with a single or multiple cameras. After the camera calibration is completed, three-dimensional reconstruction is achieved through three-dimensional image analysis and calculation; the structured light camera is used to collect the target image of the ball array to obtain the spatial coordinates of the three-dimensional ball array;

[0068] The isocenter calibration quality control device comprises a tray 5, two identical balls 1, two identical scribed balls 2, a scintillator 11, and a scintillator support 8 fixed on the tray 5, a level 9, three threaded sub-knobs 6, and four ball racks 3; the ball array comprises two identical balls 1, and two identical scribed balls 2;

[0069] The tray 5 is engraved with an X-axis engraved line 501 and a Y-axis engraved line 502. Figure 4 As shown;

[0070] The ball rack 3 is connected to the tray 5, and the ball rack 3 has three heights, two of which are fixed with scored balls, and the other two are used to fix two balls without scored lines; the threaded auxiliary knob is used to adjust the levelness of the entire device;

[0071] The level meter 9 is used to detect the level in the X and Y directions, and when adjusting the height of the threaded secondary knob, the position of the bubble inside the level meter 9 is observed to determine whether the tray is level;

[0072] The Z-axis height lines of the two scribed balls are consistent and on the same horizontal plane as the Z-axis height lines of the scintillator bracket; the intersection of the X-axis lines and Y-axis lines of the tray and the horizontal plane passes through the center position of the outer surface of the scintillator.

[0073] In this embodiment, the tray 5 is provided with a plurality of holes for respectively installing four ball holders 4, a threaded auxiliary knob 6, a scintillator bracket 8, and a level 9;

[0074] One end of the ball rack seat is used to fix the ball rack, and the other end is fixed to the tray;

[0075] The scintillator bracket is generally in a 45° inclined plane, a scintillator placement groove is provided on the 45° inclined plane, and a Z-axis height engraved line is provided on the side;

[0076] The ball 1 has a hole, the axis of which passes through the center of the ball, for inserting a ball holder 3 into the hole to fix the ball 1 .

[0077] In this embodiment, the scintillator bracket is also provided with a scintillator dust cover, the diameter of which is slightly larger than the diameter of the scintillator, which is opened when the scintillator is in use and closed when the scintillator is not in use, so as to prevent the surface of the scintillator from being contaminated;

[0078] The scintillator support is also provided with a scintillator pressure cover for fixing the scintillator on the scintillator support so that the scintillator fits the scintillator support and is placed at an angle of 45°.

[0079] The specific features of the engraved ball are as follows: based on the features of the ball, the features of engraved lines processed on the outer contour surface are added, the perpendicularity of the engraved lines to the axis of the hole must be guaranteed, and the whole set of devices includes 2 identical engraved balls.

[0080] In this embodiment, the scintillator is a circular cerium-doped lutetium yttrium silicate (LYSO:CE) crystal with a diameter of 50 mm and a thickness of 1 mm; scintillators of different thicknesses and shapes may also be used. LYSO crystal refers to a scintillating crystal composed of lutetium yttrium silicate, which is widely used in various fields, especially in medical imaging and high-energy physics. LYSO crystal has excellent scintillation performance, including high light yield, fast decay time and good energy resolution. The light-emitting principle of the scintillator is:

[0081] When high-energy rays such as X-rays pass through the scintillator, they interact with each other to form high-energy electrons and generate corresponding holes in the valence band. Due to the instability of high-energy electrons and holes, a large number of secondary electrons and holes are generated through radiation and non-radiation relaxation processes, which are further relaxed by thermalization to generate electron-hole pairs with energy close to the band gap width. Due to the relaxation of the lattice, the electron-hole pairs continue to migrate and eventually migrate to the luminescence center and transfer their own energy to the center. The luminescence center in the excited state emits fluorescence after deexcitation.

[0082] In a further embodiment, a hole is processed on the ball 1 for inserting the ball holder into the hole and fixing it with glue. Processing is required to ensure that the axis of the hole passes through the center of the ball.

[0083] In a further embodiment, the tray 5 is made of a material with high strength and good stability, such as carbon fiber.

[0084] In a further embodiment, the ball, the ball rack and the ball rack seat are processed into one piece by CNC machining, and the line ball, the ball rack and the ball rack seat are processed into one piece and then fixed to the tray.

[0085] In other embodiments, a sphere with a larger diameter may be used, and the ball rack and ball rack seat may be eliminated so that the sphere is directly fixed to the tray.

[0086] Example 2

[0087] The embodiment of the present invention provides an isocenter calibration quality control method for a radiotherapy image guidance system, which is applied to the isocenter calibration quality control system for a radiotherapy image guidance system described in Example 1, and includes the following steps:

[0088] S1, using optical body surface imaging to image the radiotherapy rays on the scintillator, and obtaining the linear accelerator radiation isocenter based on the imaging information of the scintillator;

[0089] S2, using the image processing module to calculate the 3D point cloud of the ball array and obtain the 3D coordinates of the center position of the ball array;

[0090] S3, aligning the 3D coordinates of the center position of the ball array with the linear accelerator radiation isocenter to achieve calibration of the point cloud coordinate system for accurate positioning of the patient during the placement and treatment stages; or calculating the difference between the 3D coordinates of the center position of the ball array and the linear accelerator radiation isocenter to check and correct the system error.

[0091] In this embodiment, the S1 obtains the linear accelerator radiation isocenter by optical body surface imaging based on scintillator imaging, which specifically includes:

[0092] This process uses the Starshot method to capture the imaging of radiotherapy rays on the scintillator at different angles by rotating the linear accelerator frame, and superimposes multiple images at each angle until the boundary is sufficiently uniform and clear, extracts the boundary of the ray, calculates the centerline position of each ray multiple times based on the boundary position, fits the centerline straight line equation, and calculates the minimum circle that makes all center lines pass through the inside of the circle or are tangent to it, which is called the wobble circle, and the center of the circle is the accelerator isocenter.

[0093] In this embodiment, the S2, using the image processing module to calculate the 3D point cloud of the ball array to obtain the 3D coordinates of the center position of the ball array, specifically includes:

[0094] The isocenter calibration quality control device is placed near the isocenter of the accelerator by aligning the scribed lines on the surface of the device with the laser lines, wherein the scribed lines are the horizontal and vertical scribed lines on the base and the height scribed lines on the ball array, so that the center position of the isocenter calibration device is preliminarily aligned with the isocenter of the accelerator;

[0095] The target image of the ball array is captured by a structured light camera, and the point cloud data of the ball array is obtained by using the four-step phase shift method and the three-frequency heterodyne method;

[0096] Using a point cloud processing algorithm (which can be done by fitting a sphere using the least squares method), the sampling points of each spherical target are identified, and the 3D coordinates of the center position of the spherical array are calculated; then, the calculated point cloud center is matched with the calibration sphere center (here, the center of each sphere obtained through the point cloud is combined with the positional relationship between the spheres of the spherical array device measured in advance with high precision to match the isocenter of the device with the smallest error, which is used to obtain the precise coordinate information of the device).

[0097] In this embodiment, the method further includes: calibrating the structured light camera, specifically as follows:

[0098] Let the three-dimensional point P in the object coordinate system = [X, Y, Z] T , after rotation, translation, perspective projection, and pixel sampling, it becomes a two-dimensional point U = [u, v] in the pixel coordinate system T , the process is expressed as:

[0099] U=K[R|t]P

[0100]

[0101] Among them, K is the internal parameter matrix f x is the focal length in the x direction, f y is the focal length in the y direction, c x and c yare the x and y coordinates of the center of the camera plate in the pixel coordinate system; R is the rotation matrix r ij is the relevant value of rotation, i = 1, 2, 3, j = 1, 2, 3, t is the translation vector t i is the translation value in the x, y, and z directions, i=1, 2, 3;

[0102] After calibration, three-dimensional reconstruction is achieved through three-dimensional image analysis and calculation to obtain a three-dimensional image.

[0103] In this embodiment, the method further includes: performing parameter measurement of the ball array, specifically as follows:

[0104] Since the contour of a spherical object changes little at different viewing angles, it is conducive to automatic detection. The device is placed close to the center of the accelerator by aligning the engraved lines on the device surface with the laser lines. The target image of the spherical array is captured by a structured light camera. The point cloud data of the spherical array is obtained using the four-step phase shift method and the three-frequency heterodyne method. The sampling point of each spherical target is identified using the point cloud processing algorithm, and its center position is calculated. The calculated point cloud center is matched with the center of the calibration ball.

[0105] Using fringe projection technology, sinusoidal fringes are generated through computer programming, and the sinusoidal fringes are projected onto the object to be measured through a projection device. Using the phase shift method, multiple phase shift images are projected to mark the unique position, and the unique position is the unique phase corresponding to each pixel. In the phase shift process, fringe images under different phase shift amounts are collected, and the pixel data of the fringe image group is phase-unwrapped and point cloud solved to obtain the surface information of the ball array (the point cloud information of each ball surface), and the coordinate system of the point cloud is aligned with the ball center according to the calculated ball array ball center coordinates, and finally the physical center position of the scintillator corresponding to the ball array is found.

[0106] It is compared with the isocenter of the linear accelerator obtained by the Starshot method, and the difference between the two is calculated for the verification and correction of system errors.

[0107] The light intensity formula of the sinusoidal stripes is as follows:

[0108] I(x,y)=a(x,y)+b(x,y)cos[φ(x,y)+φ i ]

[0109] Where a(x, y) is the ambient light intensity, i.e., the reflected light of the object to be measured; b(x, y) is the modulated light intensity; φ(x, y) is the initial phase information of the wavefront of the object to be measured; φ i is the displacement; (x, y) is the coordinate of the pixel point in the fringe pattern;

[0110] The four-step term shift method is used to obtain the phase, which is calculated as follows:

[0111] I1=a+bcosφ

[0112]

[0113] According to the modulated phase, the main phase value is solved by the inverse tangent function:

[0114]

[0115] The principal value is distributed between [0, 2π), φ(x, y) is the folding phase, and its corresponding unfolding phase is:

[0116] φ(x,y)=φ(x,y)+2kπ(k=0,1...n)

[0117] k is the fringe order, and phase unwrapping is to determine the true phase distribution of each (x, y) point. It is necessary to use the multi-frequency heterodyne method to perform image superposition on multiple sinusoidal gratings of different frequencies, and obtain the absolute phase of each frequency by solving the superimposed folded phase. Calculate the phase difference, convert the high-frequency phase into a low-frequency phase, so that the phase difference signal covers the entire field of view, and then obtain the absolute phase distribution of the entire image based on the phase difference.

[0118] The values ​​used are n, n-1, The three groups of frequencies correspond to grating fringe pitches p1, p2, and p3, and the corresponding phase principal values ​​are φ1, φ2, and φ3, respectively, and the corresponding phase differences are:

[0119]

[0120] After superposition, the pitch is p 12 The stacked grid:

[0121]

[0122] Right now Similarly 23 It is a stacked gate formed by the superposition of p2 and p3. 123 Yes 12 and p 23 By superposition, we can get Then come out When p 123 When the resolution is slightly larger than the projector, the grating p 123 It just covers the entire field of view, that is, what is finally synthesized on the image is a cycle.

[0123] Perform phase expansion on the superimposed phase, where floor represents rounding down:

[0124]

[0125] in,

[0126]

[0127] in,

[0128]

[0129] in,

[0130]

[0131] in,

[0132]

[0133] in,

[0134] In this embodiment, the scintillator imaging results are as follows:

[0135] The highest intensity of scintillator light is around 400-450nm. Fig.12 As shown:

[0136] Adjust the width of the linear accelerator radiation according to the width supported by the multi-leaf collimator (MLC) to ensure that the radiation is symmetrical with the center line, adjust the placement of the scintillator bracket and the height of the treatment bed to ensure that the laser lines in all directions are aligned with the scintillator bracket. The camera is facing the scintillator and the focus is completed. When collecting data, follow the steps of starting collection, starting radiation (the radiation time is guaranteed to be more than 2s), stopping radiation, and stopping collection.

[0137] The acquired image is subjected to noise processing. The noise that needs to be processed mainly includes: quantum noise generated by x-rays, random noise generated by camera exposure and gain, and environmental noise in the corresponding band of the filter.

[0138] Among them, quantum noise and random noise are processed by median filtering. To prevent noise from affecting the edge sharpness of the ray after image superposition, since the brightness of quantum noise is usually high, denoising is considered frame by frame or after accumulating a certain number of frames. Random noise has low brightness and random position. The gray value after superposition will hardly affect the edge sharpness of the ray and is processed together with quantum noise. The background noise of the filter is mainly guaranteed by the bandpass of the scintillator, the device of the scintillator bracket and the cleanliness of the scintillator itself.

[0139] In this embodiment, the image processing process is as follows:

[0140] Depending on the number of superimposed images, the ray edge is sharp enough, the brightness inside the ray is overexposed, and the noise is within an acceptable range. If the brightness is not enough, you can use data processing to increase the brightness until you are satisfied. Keep 255 pixels, and then use a circular mask to remove the residual brightness at the scintillator boundary to obtain the target ray image, such as Fig.13 After filtering and noise reduction, binarization is performed, as shown in Fig.14 shown.

[0141] After that, the binary images from multiple angles are superimposed. Here, floating-point data is used to ensure that the superimposed images are not overexposed. The resulting images are as follows: Fig.15 shown.

[0142] Finally, the centerline position of each ray is calculated by extracting the ray boundary, and the smallest circle that is tangent to or intersects each centerline is calculated, which is called a wobble circle. The center of the circle is the accelerator isocenter, and the radius of the circle is the size of the radiation isocenter (here we only take the method of superimposing first and then calculating the centerline as an example. Similarly, you can also calculate the centerline first and then superimpose multiple lines). Use the open source library pylinac to assist in the calculation, such as Fig.16 As shown, the left picture is the calculation result of the center line after the ray images are superimposed, and the right picture is the calculation of the wobble circle after the center line intersection area is enlarged. The coordinates are the coordinate values ​​of the pixel points (the horizontal coordinate is arranged from large to small, and the vertical coordinate is arranged from small to large). Finally, the calculated isocenter point is brought into the point cloud system for system coordinate correction.

[0143] In this embodiment, the camera takes pictures at a distance of 1.7m from the scintillator, and the actual physical size of a single pixel is 0.36mm. Using this data to calculate the actual distance error, we get:

[0144] The actual physical size of the graphic = number of pixels * the actual physical size of a single pixel

[0145] The three ray data formed by different angles are divided into one group, and the calculation results of multiple groups of data are verified to verify the consistency of errors and results. The experimental data are shown in Table 1:

[0146] Table 1 Experimental data

[0147]

[0148]

[0149] In the above data, the minimum circle radius obtained by Starshot is at most 0.2 pixels, the actual physical size is 0.072mm, and the floating range of the center pixel coordinates of several sets of data is concentrated in the range of (74.5±0.1.68.4±0.2). The results have small errors and good consistency.

[0150] In summary, the isocenter calibration quality control system and method for the radiotherapy image guidance system provided by the present invention detects the spatial coordinates of the three-dimensional spherical array based on a structured light camera, and uses a scintillator to perform Starshot to obtain the isocenter of the linear accelerator, and maps the isocenter point of the accelerator to the three-dimensional spatial coordinates of the point cloud for coordinate alignment to achieve precise positioning of the system. This technology is not only used for positioning verification before radiotherapy, but also can detect the deviation between the target and the isocenter of the accelerator in real time during radiotherapy. At the same time, the Starshot method of transmitting rays through a rotating frame can more accurately locate the isocenter position of the ray, and the floating range of multiple measurements is very small, with good consistency.

[0151] The remaining technical features in this embodiment can be flexibly selected by those skilled in the art according to actual conditions to meet different specific practical needs. However, it is obvious to those skilled in the art that it is not necessary to adopt these specific details to implement the present invention. In other examples, in order to avoid confusing the present invention, the well-known components, structures or parts are not specifically described, which are all within the technical protection scope defined by the technical solution claimed for protection in the claims of the present invention.

[0152] Modifications and changes made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the scope of protection of the claims attached to the present invention. In the above description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is obvious to those of ordinary skill in the art that these specific details are not necessary to practice the present invention. In other examples, in order to avoid confusing the present invention, well-known technologies, such as specific construction details, operating conditions and other technical conditions, are not specifically described.

[0153] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. An isocenter calibration quality control system for a radiotherapy image-guided system, characterized in that: Including 3D structured light imaging system, radiotherapy equipment, isocenter calibration quality control device, The radiotherapy device is used to emit therapeutic rays to a target area, and the radiotherapy device includes a linear accelerator; The three-dimensional structured light imaging system includes a structured light camera, a projection device, and an image processing module; the structured light camera is used to collect the target image of the ball array to obtain the spatial coordinates of the three-dimensional ball array; The isocenter calibration quality control device includes a tray, a ball array, a scintillator, and a scintillator bracket fixed on the tray, a level, three threaded sub-knobs, and four ball racks; the ball array includes two identical balls and two identical line balls; The tray is engraved with X-axis engraved lines and Y-axis engraved lines; The ball rack is connected to the tray and has three heights. Two ball racks of the same height are fixed with scored balls, and the other two ball racks are used to fix two balls. The threaded secondary knob is used to adjust the levelness of the entire device. The level is used to detect the level in the X and Y directions, and when adjusting the height of the threaded secondary knob, the position of the bubble inside the level is observed to determine whether the tray is level; The Z-axis height lines of the two scribed balls are consistent and on the same horizontal plane as the Z-axis height lines of the scintillator bracket; the intersection of the X-axis and Y-axis lines of the tray and the horizontal plane passes through the center position of the outer surface of the scintillator.

2. The isocenter calibration quality control system for a radiotherapy image-guided system according to claim 1, characterized in that: The tray is provided with a plurality of holes for respectively installing a ball stand, a scintillator bracket, and a level; One end of the ball rack seat is used to fix the ball rack, and the other end is fixed to the tray; The scintillator bracket is generally in a 45° inclined plane, a scintillator placement groove is provided on the 45° inclined plane, and a Z-axis height engraved line is provided on the side; The ball has a hole, the axis of which passes through the center of the ball, and is used for inserting a ball holder into the hole to fix the ball.

3. The isocenter calibration quality control system for a radiotherapy image-guided system according to claim 1, characterized in that: The scintillator bracket is also provided with a scintillator dust cover and a scintillator pressure cover; the diameter of the scintillator dust cover is slightly larger than the diameter of the scintillator, and is used to prevent the surface of the scintillator from being contaminated; The scintillator pressing cover is used to fix the scintillator on the scintillator bracket so that the scintillator fits with the scintillator bracket and is placed at an angle of 45°.

4. The isocenter calibration quality control system for a radiotherapy image-guided system according to claim 1, characterized in that: The scintillator is a round cerium-doped yttrium lutetium silicate crystal with a diameter of 50 mm and a thickness of 1 mm.

5. A method for isocenter calibration quality control for a radiotherapy image guidance system, applied to the isocenter calibration quality control system for a radiotherapy image guidance system according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1, using optical body surface imaging to image the radiotherapy rays on the scintillator, and obtaining the linear accelerator radiation isocenter based on the imaging information of the scintillator; S2, using the image processing module to calculate the 3D point cloud of the ball array and obtain the 3D coordinates of the center position of the ball array; S3, aligning the 3D coordinates of the center position of the ball array with the linear accelerator radiation isocenter to achieve calibration of the point cloud coordinate system for accurate positioning of the patient during the placement and treatment stages; or calculating the difference between the 3D coordinates of the center position of the ball array and the linear accelerator radiation isocenter to check and correct the system error.

6. The isocenter calibration quality control method for a radiotherapy image-guided system according to claim 5, characterized in that: The S1, obtaining the linear accelerator radiation isocenter by optical body surface imaging based on scintillator imaging, specifically includes: By rotating the linear accelerator rack, the structured light imaging of the radiotherapy rays on the scintillator at different angles is captured, and multiple structured light images at each angle are superimposed to the boundary to extract the boundary position of the radiotherapy rays; The centerline position of each radiotherapy ray is calculated multiple times according to the boundary position, the centerline straight line equation is fitted, and the minimum circle that makes all center lines pass through the circle or is tangent to it is calculated. The center of the minimum circle is the linear accelerator isocenter, and its radius is the radiation isocenter error range.

7. The isocenter calibration quality control method for a radiotherapy image-guided system according to claim 5, characterized in that: The S2, using the image processing module to calculate the 3D point cloud of the ball array to obtain the 3D coordinates of the center position of the ball array, specifically includes: The isocenter calibration quality control device is placed near the isocenter of the accelerator by aligning the engraved lines on the device surface with the laser lines: the engraved lines on the device surface are the horizontal and vertical engraved lines on the base and the height engraved lines on the ball array, so that the center position of the isocenter calibration device is preliminarily aligned with the isocenter of the accelerator; The target image of the ball array is captured by a structured light camera, and the point cloud data of the ball array is obtained by using the four-step phase shift method and the three-frequency heterodyne method; Using the point cloud processing algorithm, the sampling points of each ball target are identified, the 3D coordinates of the center position of the ball array are calculated, and the calculated point cloud center is matched with the center of each ball.

8. The isocenter calibration quality control method for a radiotherapy image-guided system according to claim 5, characterized in that: The method further comprises: Calibrate the structured light camera: Let the three-dimensional point P in the object coordinate system = [X, Y, Z] T , after rotation, translation, perspective projection, and pixel sampling, it becomes a two-dimensional point U = [u, v] in the pixel coordinate system T , the process is expressed as: U=K[R|t]P Among them, K is the internal parameter matrix f x is the focal length in the x direction, f y is the focal length in the y direction, c x and c y are the x and y coordinates of the center of the camera plate in the pixel coordinate system; R is the rotation matrix r ij is the relevant value of rotation, i = 1, 2, 3, j = 1, 2, 3, t is the translation vector t i is the translation value in the x, y, and z directions, i=1, 2, 3; After calibration, three-dimensional reconstruction is achieved through three-dimensional image analysis and calculation to obtain a three-dimensional image.

9. The isocenter calibration quality control method for a radiotherapy image-guided system according to claim 5, characterized in that: The method further comprises: Perform parameter measurements on the ball array: Using fringe projection technology, sinusoidal fringes are generated by computer programming, and the sinusoidal fringes are projected onto the object to be measured through a projection device. Using the phase shift method, multiple phase shift images are projected to mark a unique position, and the unique position is a unique phase corresponding to each pixel; in the phase shift process, fringe images under different phase shift amounts are collected to obtain a fringe image group; Phase unwrapping and point cloud solution are performed on the pixel data of the fringe pattern group to obtain the surface information of the ball array. According to the calculated coordinates of the center of the ball array, the coordinate system of the point cloud is aligned with the center of the ball, and finally the physical center position of the scintillator corresponding to the ball array is found. The light intensity formula of the sinusoidal stripes is as follows: I(x,y)=a(x,y)+b(x,y)cos[φ(x,y)+φ i ] Where a(x, y) is the ambient light intensity, i.e., the reflected light of the object to be measured; b(x, y) is the modulated light intensity; φ(x, y) is the initial phase information of the wavefront of the object to be measured; φ i is the displacement; (x, y) is the coordinate of the pixel point in the fringe pattern.

Images