A method for calibrating the isocenter position of intensity modulated radiotherapy equipment

Abstract

A method for calibrating the isocenter position of an intensity-modulated radiotherapy device utilizes an infrared binocular imaging device to capture a coordinate point group of infrared markers at different rotation angles. The rotation axes of the accelerator and treatment bed are obtained using a coplanar optimal circle fitting method. The common perpendicular between the two rotation axes is obtained based on their spatial positions. The calibrated isocenter position is obtained using an approximation correction fitting method. The effective field of view of the infrared binocular imaging device for capturing the coordinates of the infrared marker points is expanded. For infrared marker coordinates that are not within any lattice, an edge field of view correction method is used to locate the lattice to which they belong, thereby obtaining the true spatial coordinates of the infrared marker points. This invention solves the problem that most infrared marker points captured by the infrared binocular imaging device are located at the edge of the imaging device's field of view, thereby enabling accurate recording of the coordinates of the infrared marker point group. It also solves the problem that the two rotation axes obtained from the coordinate point group data do not intersect, making it impossible to accurately determine the isocenter position.

Description

Technical Field

[0001] The present invention belongs to the field of medical equipment, relates to the measurement and calibration of medical equipment, and is a method for calibrating the center position of intensity modulated radiotherapy equipment. Background Art

[0002] As radiotherapy is a primary approach to cancer treatment, its role in tumor treatment is becoming increasingly prominent. The effectiveness of radiotherapy depends on the accuracy of the radiation, which has a crucial impact on treatment outcomes. Low-accuracy radiotherapy can negatively impact normal physiological tissues and organs. However, precisely targeted isocenter radiotherapy can simultaneously treat tumor tissue and protect normal tissues and organs, placing even higher demands on the targeting accuracy of radiotherapy.

[0003] An intensity-modulated radiotherapy device includes a rotatable accelerator, a rotatable treatment couch, infrared markers, and an infrared binocular imaging device for collecting the spatial coordinates of the infrared markers. The isocenter position for intensity-modulated radiotherapy is the intersection of the accelerator's rotation axis and the treatment couch's rotation axis. Infrared markers are placed on the accelerator and treatment couch, and the accelerator and treatment couch are rotated at different angles around the rotation axis. The infrared binocular imaging device collects the coordinates of the infrared marker groups at different rotation angles. The spatial positions of the two rotation axes are then calculated based on the coordinate point groups. Existing methods for determining isocenter coordinates typically use a circular fitting method to obtain the two rotation axes, then take the midpoint of the common perpendicular line between the two rotation axes as the isocenter coordinate. However, due to the inability to guarantee the validity and accuracy of the collected infrared marker coordinates, as well as mechanical and computational errors, it is difficult to meet the high precision requirements of clinical radiotherapy. Summary of the Invention

[0004] The problem to be solved by the present invention is that the existing method for correcting and determining the isocenter coordinates of intensity modulated radiotherapy equipment is not accurate enough and cannot meet the usage requirements. The present invention provides a method for calibrating the isocenter position of intensity modulated radiotherapy to accurately locate the coordinate position of the isocenter of radiotherapy.

[0005] The technical solution of the present invention is: a method for calibrating the isocenter position of an intensity modulated radiotherapy device, characterized in that the intensity modulated radiotherapy device includes: a rotatable accelerator, a rotatable treatment couch, an infrared marker, and an infrared binocular imaging device for collecting spatial coordinates of the infrared marker. The infrared marker is fixed to the accelerator and the treatment couch, the accelerator and the treatment couch are rotated, and the infrared binocular imaging device is used to capture coordinate point groups of the infrared marker at different rotation angles. Based on the collected coordinate point groups of the infrared marker, the rotation axes of the accelerator and the treatment couch are obtained using a coplanar optimal circle fitting method. Based on the spatial positions of the two rotation axes, a common perpendicular between them is obtained. The calibrated isocenter position is obtained using an approximation correction fitting method. When capturing the coordinate points of the infrared marker, the effective field of view of the infrared binocular imaging device for capturing the coordinates of the infrared marker is expanded, and the field of view of the imaging device is divided into lattices to obtain the lattices to which the infrared marker belongs and the real-space coordinates. For infrared marker coordinates that are within the field of view of the imaging device but not within any lattice, the lattice to which they belong is found using an edge field correction method to obtain the real-space coordinates of the infrared marker.

[0006] The benefits of the present invention are: the present invention uses an infrared binocular imaging device to locate infrared marker points. For the visual positioning solution, it solves the problem that most of the infrared marker points captured by the infrared binocular imaging device are at the edge of the imaging device's field of view, thereby being able to accurately record the coordinates of the infrared marker point group. Then it solves the problem that the two rotation axes obtained through the coordinate point group data do not intersect and thus the isocenter position cannot be accurately determined, thereby accurately reflecting the three-dimensional coordinates of the intensity modulated radiotherapy isocenter, and the measurement error is kept within 0.1mm. The operation is simple, which is conducive to achieving precise radiotherapy positioning. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is a principle flow chart of the present invention.

[0008] Figure 2 This is a schematic diagram of the correction of edge infrared marking points in the present invention.

[0009] Figure 3 Schematic diagram of the correction of eight-point deformed lattice coordinates in the present invention.

[0010] Figure 4 Schematic diagram of an application scenario of an embodiment of the present invention.

[0011] Figure 5 This is a simulation diagram based on real collected data according to an embodiment of the present invention.

[0012] Figure 6 This is a schematic diagram of the principle of the offset-corrected isocenter determination method of the present invention. DETAILED DESCRIPTION

[0013] The purpose of the present invention is to provide a method for calibrating the center position of intensity modulated radiotherapy, accurately positioning the center coordinate position of radiotherapy, and maximally protecting normal physiological tissues and organs while achieving high-precision tumor treatment.

[0014] The technical solution of the present invention is mainly divided into two parts: the first part is to build an infrared binocular imaging device for collecting the coordinates of infrared marker points. The positioning accuracy of this imaging device is within 0.1mm, and the spatial coordinates of the infrared marker points are obtained through two lattice transformations. The infrared marker points located at the edge of the imaging device's field of view are captured and the primary positioning spatial coordinates are calculated. The coordinates obtained from the primary positioning calculation are then corrected to obtain the lattice where they are actually located. The secondary positioning three-dimensional coordinates of the infrared marker points are calculated using a lattice correction algorithm. The recorded eight-point distorted coordinates of the lattice, the ideal coordinates, and the calculated infrared marker coordinates are linearly transformed to obtain the three-dimensional coordinates of the precisely positioned infrared marker points. After correction, the accuracy of the infrared binocular imaging device can reach 0.05mm. The second part is to rotate the accelerator and treatment bed at different angles to obtain a series of infrared marker point coordinate groups. The spatial position of the rotation axis and the rotation center of the accelerator and treatment bed are then calculated using the optimal circle fitting method in the same plane. The preliminary spatial positions of the accelerator and treatment table rotation axes and their relationship are calculated. Generally, they are not intersecting, making it impossible to determine the isocenter coordinates. The ideal isocenter is the intersection of the two axes, with a 90° angle between them. Based on the positional relationship between the two axes and the length of the common perpendicular between them, a quadratic approximation is used to correct and fit the new accelerator and treatment table rotation axes so that they intersect at a constant point. This intersection is the precise coordinate of the isocenter.

[0015] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific examples.

[0016] Figure 1 This is a flow chart of a method for calibrating the center position of intensity modulated radiotherapy of the present invention. The specific implementation method is as shown in the flow chart.

[0017] The present invention uses an infrared binocular imaging device to collect the three-dimensional coordinates of infrared markers placed on the accelerator and treatment bed. The principle of this imaging device is to use two infrared lenses to collect the two-dimensional coordinates of the infrared markers in two two-dimensional images, and then calculate the three-dimensional coordinates of the infrared markers based on the basic matrix. The specific formula is as follows:

[0018]

[0019] Among them, x, y, z are the three-dimensional coordinates of the infrared marker point obtained by preliminary calculation, the 4*4 matrix is ​​the basic matrix, x l ,y lis the two-dimensional pixel coordinate of the infrared marker point collected by the left camera, x r ,y r The two-dimensional pixel coordinates collected by the right camera.

[0020] The infrared marker's x, y, and z coordinates calculated using the basic matrix are the primary coordinates. Secondary positioning is then achieved by using spatial region segmentation to approximate the camera lens. The imaging device's field of view is divided into square lattices, and the secondary positioning coordinates of the infrared marker are obtained using the lattice matrix. Since the infrared marker on the accelerator is generally located at the edge of the imaging device's field of view during rotation, it may deviate from the imaging device's field of view after the basic matrix transformation.

[0021] refer to Figure 2 , corresponding to a situation where a coordinate deviates from the imaging device's field of view, indicating that the infrared marker's initial positioning coordinates do not belong to any cell. The present invention expands the effective field of view, searches for the cell to which the coordinate belongs, and determines whether the coordinate is within the imaging device's field of view. If so, the cell ID of the cell is displayed; if not, -1 is displayed. Coordinates displayed as -1 are corrected by translating the marker point into the imaging device's field of view by a distance equal to the length of one cell.

[0022] At this point, the infrared marker has been moved into the field of view of the imaging device. The three-dimensional coordinates of the infrared marker are calculated based on the current lattice matrix. The calculation formula is as follows:

[0023] R=M*U

[0024] Where R is a 4*1 matrix, R(0), R(1), and R(2) are the calculated three-dimensional coordinates of the infrared marker points, M is a 4*4 lattice matrix, and U is a 4*1 matrix, where U(0), U(1), and U(2) are the three-dimensional coordinates of one positioning, and U(3) is equal to 1.

[0025] However, the lattice obtained by translation is not necessarily the lattice where the infrared marker point is actually located. Therefore, it is necessary to traverse several surrounding lattices again. The principle of traversal is to traverse several lattices adjacent to the initially obtained lattice, and the one with the smallest error is used as the basis.

[0026] Lens distortion and other reasons can cause the imaging device lattice to be a distorted lattice, which deviates from the actual ideal lattice. Figure 3 , the eight-point linear transformation method is used to calculate the coordinates of the infrared marker point in the ideal lattice. The calculation formula is:

[0027]

[0028]

[0029] Q i =P i +R i -P i '

[0030] Among them, P i is the center point of the calculated ideal lattice in the x, y, and z directions, P ij is the coordinate of the ideal corner point of the jth lattice, i is 0 for x-coordinate, i is 1 for y-coordinate, i is 2 for z-coordinate, P i ' is the center point of the calculated distorted lattice, P ij ' is the coordinate of the jth lattice distortion corner point, Q i represents the coordinates of the infrared marker point in the ideal lattice, R i Indicates the secondary positioning coordinates of the infrared marker point.

[0031] refer to Figure 4 , rotate the accelerator and treatment bed at arbitrary angles, and use an infrared binocular imaging device to obtain the three-dimensional coordinates of the infrared markers on the accelerator and treatment bed, respectively. The accelerator rotates N times, and the treatment bed rotates M times. The coordinate data sets of the two sets of infrared markers are recorded as:

[0032]

[0033]

[0034] Where A and T represent the three-dimensional coordinate sets of infrared markers obtained as the accelerator and treatment bed rotate, respectively. n represents the nth rotation of the accelerator, and m represents the mth rotation of the treatment bed.

[0035] Solve the rotation axis of the accelerator and the treatment bed separately. Taking the accelerator as an example, theoretically all discrete points are on a plane, that is, all points on A are in a plane equation. The equation and matrix form are as follows:

[0036] ax+by+cz-1=0

[0037] Al=L1

[0038] Where A is a 3*n matrix formed by the three-dimensional coordinate set of the infrared marker points, l is the plane normal vector, which is also the spatial position of the rotation axis, and L1 is a 3*1 matrix with all values ​​1. The normal vector l can be obtained by solving the following formula:

[0039] l=(A T A) -1 A T L1

[0040] After obtaining the spatial positions of the two rotation axes according to this method, refer to Figure 5 It is found that they do not intersect at this time and the specific coordinates of the isocenter cannot be determined. The isocenter determination method with offset correction is used to obtain the isocenter coordinates. For the specific process, refer to Figure 6 As shown in the figure, after obtaining the two rotation axes and finding their common perpendiculars, the isocenter is determined at intervals of 0.05 mm starting from one of the perpendicular feet. Two intersecting axes are then formed based on the two center points of the original accelerator and treatment bed rotation. The angle between the two axes is calculated. At the same time, the rotation radius data set of the accelerator and treatment bed is calculated based on the coordinates of the isocenter at this time, the coordinate set of the infrared marker points on the accelerator or treatment bed, and the coordinates of the center points of the accelerator and treatment bed:

[0041]

[0042]

[0043] Among them, E and F represent the calculated rotation radius point sets of the accelerator and the treatment bed respectively, and E rn The accelerator rotation radius is calculated by recalculating the infrared marker point obtained by the accelerator's nth rotation, F rm The rotation radius of the treatment bed is calculated by recalculating the infrared marker points obtained from the mth rotation of the treatment bed. Then, the radius point set is compared with the radius obtained by fitting to obtain the sum of the errors. The formula is as follows:

[0044]

[0045] Among them, R A ,R T The rotation radii corresponding to the rotation axes of the accelerator and the treatment bed are obtained by using the optimal circle fitting method in the same plane, and Δr is the sum of the cumulative radius errors.

[0046] In order to ensure that the angle between the two rotation axes is close to 90° and to minimize the cumulative radius error, the approximate minimum error formula proposed in the present invention is used for determination, which is as follows:

[0047] s=λ|∠l A Pl T -90|+μΔr

[0048] Among them, λ∈(0,1), μ∈(0,1), and λ+μ=1, ∠l A Pl T To set the angle between the two rotation axes after the isocenter P, s is the calculated result. When s is less than 0.5, the isocenter is a reasonable calibration isocenter. The present invention sets the λ value to 0.8 and the μ value to 0.2.

[0049] It should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each implementation method can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0050] The series of detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent implementation methods or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for calibrating the center position of an intensity modulated radiotherapy device, characterized by Intensity Modulation The radiotherapy apparatus includes: a rotatable accelerator, a rotatable treatment bed, an infrared marker, and an infrared binocular imaging device for collecting spatial coordinates of the infrared marker. The infrared marker is fixed to the accelerator and the treatment bed, and the accelerator and the treatment bed are rotated. The infrared binocular imaging device is used to capture coordinate point groups of the infrared marker at different rotation angles. The rotation axes of the accelerator and the treatment bed are obtained based on the collected coordinate point groups of the infrared marker using a coplanar optimal circle fitting method. The common perpendicular line between the two rotation axes is obtained based on the spatial positions of the two rotation axes. The isocenter is determined starting from one of the perpendicular feet and at intervals of 0.05 mm. Two intersecting axes are then formed based on the two center points of the original rotation of the accelerator and the treatment bed, and the angle between the two axes is calculated. The rotation radius data set of the accelerator and the treatment bed is calculated based on the coordinates of the isocenter at this time, the coordinate set of the infrared marker on the accelerator or the treatment bed, and the coordinates of the center points of the accelerator and the treatment bed. Among them, the optimal isocenter coordinates are obtained by using the approximation correction fitting method with the isocenter on the common perpendicular line of the two rotation axes as the reference. The formula for determining whether it is optimal is as follows: in, , ,and , To set the isocenter The next two rotation axes 、 The angle of the accelerator rotation times, the treatment bed rotates Second-rate, For the accelerator The accelerator rotation radius is recalculated by the infrared marker obtained by the rotation. For treatment bed The rotation radius of the treatment bed is recalculated by the infrared marking points obtained by the rotation. , The rotation radii corresponding to the rotation axes of the accelerator and the treatment bed are obtained by using the optimal circle fitting method in the same plane. s is the calculated result. When s is less than 0.5, the isocenter is the optimized calibration isocenter. When capturing the coordinates of the infrared marker points, the effective field of view of the infrared binocular imaging device to capture the coordinates of the infrared marker points is expanded, and the field of view of the imaging device is divided into lattices to obtain the lattices and real-space coordinates of the infrared marker points. For the coordinates of the infrared marker points that are in the field of view of the imaging device but not in any lattice, the edge field of view correction method is used to find the lattice to which they belong to obtain the real-space coordinates of the infrared marker points.

2. The method for calibrating the center position of an intensity modulated radiotherapy device according to claim 1, wherein The infrared binocular imaging device collects the two-dimensional coordinates of the infrared marker points in the two-dimensional images through two infrared lenses, and then calculates the three-dimensional coordinates of the infrared marker points based on the basic matrix. The specific formula is as follows: in, is the three-dimensional coordinate of the infrared marker point obtained by preliminary calculation, is the two-dimensional pixel coordinate of the infrared marker point collected by the left camera, is the two-dimensional pixel coordinates collected by the right lens, let The first coordinate is obtained, and then the spatial region segmentation is used to approximate the camera lens to achieve secondary positioning. The field of view of the infrared binocular imaging device is divided into pieces of lattice, and then the secondary positioning coordinates of the infrared marker point are obtained through the lattice matrix.

3. The method for calibrating the center position of an intensity modulated radiotherapy device according to claim 2, wherein the method is characterized in that Determine whether the primary coordinates of the infrared marker point are within the field of view of the infrared binocular imaging device. If so, the cellId of the lattice where it is located is displayed. If not, -1 is displayed. For the coordinates displayed as -1, edge field correction is performed. The infrared marker point is moved to the inside of the field of view of the imaging device by translation. The moving distance is the length of a lattice. Then, the three-dimensional coordinates of the infrared marker point are calculated based on the current lattice matrix. The calculation formula is as follows: in for The matrix, is the calculated three-dimensional coordinate of the infrared marker point, that is, the secondary positioning coordinate, yes The lattice matrix, for The matrix of is a coordinate, Equal to 1.

4. The method for calibrating the center position of an intensity modulated radiotherapy device according to claim 3, wherein When translating the infrared marker point, traverse several surrounding lattices. The principle of traversal is to traverse several lattices adjacent to the lattice obtained by the initial translation, and finally take the secondary positioning coordinate with the smallest error with the primary coordinate as the standard.

5. A method for calibrating the center position of an intensity modulated radiotherapy device according to claim 2 or 3, characterized in that After the infrared marker coordinates and the lattice to which they belong are captured using an infrared binocular imaging device, the coordinates of the eight lattice corner points of the lattice and the ideal eight lattice corner points are calculated to eliminate the influence of lens distortion. The coordinates of the infrared marker in the ideal lattice are obtained by linearly transforming the distorted lattice to the ideal lattice. The calculation formula is: in, is the calculated ideal lattice The center point of three directions, For the The coordinates of the ideal corner points of the lattice, 0 means coordinate, 1 means coordinate, 2 means coordinate, is the center point of the calculated distorted lattice, For the The coordinates of the lattice distortion corners, represents the coordinates of the infrared marker point in the ideal lattice, Indicates the secondary positioning coordinates of the infrared marker point.

6. The method for calibrating the isocenter position of an intensity modulated radiotherapy device according to claim 1, wherein Set the λ value to 0.8 and the μ value to 0.2.

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