Blade structure of multi-blade collimator for radiotherapy, collimator and method

Abstract

The invention belongs to the technical field of radiotherapy equipment. The invention provides a blade structure of a multi-blade collimator for radiotherapy, the collimator and a method, the blade structure comprises a plurality of first blades, a plurality of second blades and a plurality of third blades, the thickness of the first blades is smaller than that of the second blades, and the thickness of the second blades is smaller than that of the third blades; the first blades are located in the central area, the third blades are located in the peripheral area, and the second blades are located in the middle area between the central area and the peripheral area. The high-density multi-level blade design is adopted, the resolution ratio is remarkably improved, the cross coupling control strategy and high-precision servo driving are combined, high-precision blade position control and synchronous control are achieved, and the overall field contour precision is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of radiotherapy equipment, and in particular to a leaf structure of a multi-leaf collimator used for radiotherapy, a collimator and a method. Background Art

[0002] The statements in this section merely provide background art related to the present invention and do not necessarily constitute prior art.

[0003] Multi-leaf collimator is a key component in radiotherapy equipment. Its function is to dynamically modulate the shape and intensity distribution of the radiation beam by controlling the position and movement of the narrow leaves in the collimator to match the shape and size of the tumor target, thereby achieving precise conformal irradiation of the tumor while maximizing the protection of the surrounding normal tissue.

[0004] However, existing multi-leaf collimators still have deficiencies in leaf position control accuracy, trajectory tracking performance, and resolution, making it difficult to meet the increasingly precise requirements of radiotherapy. Specifically, (1) the leaf position control accuracy is not high enough, making it difficult to achieve precise matching of tumor boundaries, affecting the conformal treatment effect; (2) the motion control of multiple leaves lacks synchronization, and the accuracy of the collimator field contour needs to be improved; (3) the mechanical performance of the leaf drive and transmission system is not ideal, resulting in positioning errors, fragmentation, and missed shots; (4) for small-sized tumors, especially lesions with a diameter of less than 10 mm, it is difficult to achieve fine conformity, mainly due to the leaf width (i.e., resolution). Summary of the invention

[0005] In order to address the deficiencies of the prior art, the present invention provides a leaf structure, a collimator and a method for a multi-leaf collimator for radiotherapy, which adopts a high-density multi-level leaf design to significantly improve the resolution, and combines a cross-coupling control strategy and a high-precision servo drive to achieve high-precision leaf position control and synchronous control, thereby improving the overall field contour accuracy.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a leaf structure of a multi-leaf collimator for radiotherapy.

[0008] A leaf structure of a multi-leaf collimator for radiotherapy, comprising: a plurality of first leaves, a plurality of second leaves, and a plurality of third leaves, wherein the thickness of the first leaves is smaller than that of the second leaves, and the thickness of the second leaves is smaller than that of the third leaves;

[0009] The first blades are all located in the central area, the third blades are located in the peripheral area, and the second blades are located in the middle area between the central area and the peripheral area.

[0010] As a further limitation of the first aspect of the present invention, the thickness of the first blade is 5 mm, the thickness of the second blade is 7.5 mm, and the thickness of the third blade is 10 mm.

[0011] As a further limitation of the first aspect of the present invention, the first blades include 60 blades, the second blades include 40 blades, and the third blades include 20 blades.

[0012] As a further limitation of the first aspect of the present invention, the cross-sections of the first blade, the second blade and the third blade are all designed in an inverted trapezoidal shape, with the two side surfaces parallel to the direction of the rays, the upper and lower surfaces inclined to the center line of the beam, and adjacent blades reduce leakage by overlapping inverted trapezoidal steps. The front end face of the blade is curved to ensure that the edge of the ray is always tangent to the end face during movement.

[0013] As an optional aspect of the first aspect of the present invention, each blade corresponds to a motor, and the blades are arranged in pairs, including 60 pairs of blades. The 60 pairs of blades are divided into 15 groups, each group includes 4 pairs of blades, and each group uses a control circuit consisting of a main control chip, two drive chips and their peripheral circuits to control the motor, and the control circuits of the 15 groups are the same.

[0014] As a further limitation of the first aspect of the present invention, the motor is a vane motor with a built-in incremental rotary encoder.

[0015] As a further limitation of the first aspect of the present invention, the rotation of the motor is converted into the horizontal displacement of the blade through the action of the screw, and the pulse equivalent of the blade displacement is: Every time the rotary encoder generates a feedback pulse, the displacement of the blade is L;

[0016] Among them, a is the pitch of the driving screw, the speed ratio of the motor reduction box is 4:1, and the number of pulses fed back by the built-in incremental rotary encoder of the motor is 12 per rotation.

[0017] In a second aspect, the present invention provides a method for controlling a leaf structure of a multi-leaf collimator for radiotherapy.

[0018] A method for controlling the leaf structure of a multi-leaf collimator for radiotherapy, using the multi-leaf collimator for radiotherapy according to the first aspect of the present invention, comprises the following process:

[0019] The single blade position controller controls the blade drive mechanism according to the blade tracking error, and the errors between each controlled blade and the adjacent blades are input into the cross-coupling controller for synchronization error calculation;

[0020] The synchronization error is superimposed on the output of each controlled single blade position controller for controlling the blade drive mechanism.

[0021] As a further limitation of the second aspect of the present invention, the control model of the cross-coupling controller is:

[0022]

[0023] Among them, K P , K D and K e They are the proportional gain, differential gain and compensation gain for position control respectively, E=e+αε, M is the positive definite inertia matrix, C is the Coriolis force vector, α is the diagonal positive definite matrix, E is the control gain of the coupled position error, e is the synchronization error vector, x is the comprehensive error of the output, and T is the synchronization transfer matrix.

[0024] As a further limitation of the second aspect of the present invention, the synchronization error vector e=[e1, e2, …, e n ] T , where n is the number of blades, e1 represents the tracking error of the first blade, e2 represents the tracking error of the first blade, and e n Represents the tracking error of the first blade.

[0025] In a third aspect, the present invention provides a multi-leaf collimator for radiotherapy, comprising the leaf structure of the multi-leaf collimator for radiotherapy according to the first aspect of the present invention.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The present invention can more accurately control the shape and direction of the radiation beam through the high-density multi-level leaf design, thereby improving the spatial resolution, which means that radiotherapy can more accurately target the tumor, reduce damage to surrounding healthy tissues, and make the treatment more accurate; this design is particularly effective for small tumor lesions; since the location of small tumors is usually more concealed, traditional radiation therapy may not be able to accurately target them, but the collimator with a high-density multi-level leaf design can significantly improve the conformal performance, ensuring that the radiation beam accurately covers the small tumor area, thereby improving the success rate of treatment.

[0028] 2. The innovative application of the cross-coupling control strategy enables the coupling relationship between multiple leaves to be effectively managed, thereby improving the overall contour accuracy. Through cross-coupling control, the movement of each leaf can be better coordinated, the position error between the leaves can be reduced, and the overall accuracy of the collimator can be ensured; combined with adaptive PID control, the system can respond more quickly to changes in the external environment and dynamically adjust the control parameters according to actual conditions, thereby improving the dynamic performance of the multi-leaf collimator and enabling it to operate stably in complex treatment scenarios.

[0029] 3. The present invention introduces high-performance linear servo motors and high-precision grating scale feedback, combined with sophisticated control algorithms, to greatly improve the blade positioning accuracy, while also improving the blade response speed and stability; modular hardware and software design makes the system more flexible and reliable, and modular design simplifies the system structure, making the interaction between the various components clearer and easier to test, maintain and expand; in addition, modular design is also conducive to rapid iterative optimization and functional expansion of the product; each module of the system can be updated and improved independently without affecting the stability of the overall system, thereby making the product more competitive and sustainable.

[0030] 4. The collimator and control method of the present invention can significantly improve the efficiency of radiotherapy. By improving spatial resolution, reducing contour errors, and accelerating leaf positioning speed, the radiotherapy time can be effectively shortened and the treatment cycle can be reduced; at the same time, since the treatment process is more accurate and efficient, the number of treatments for patients can be reduced, thereby reducing the physical and psychological burden on patients. Therefore, the present invention has good clinical application prospects and is expected to bring significant improvements and progress to the field of radiotherapy.

[0031] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0033] Figure 1 Schematic diagram of blade arrangement provided by the present invention Figure 1 ;

[0034] Figure 2 Schematic diagram of blade arrangement provided by the present invention Figure 2 ;

[0035] Figure 3 A schematic diagram of the blade structure provided by the present invention;

[0036] Figure 4 A schematic diagram of blade driving provided by the present invention;

[0037] Figure 5 A schematic diagram of the cross-coupling control method provided by the present invention. DETAILED DESCRIPTION

[0038] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0039] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0040] The present invention uses 120 blades of three specifications, with thicknesses of 5 mm (first blade, 60 blades in the central area), 7.5 mm (second blade, 40 blades in the middle area) and 10 mm (third blade, 20 blades in the outer area), which significantly improves the overall resolution and meets the needs of fine shaping of small tumors.

[0041] like Figure 1 and Figure 2 As shown in the figure, the third blade on the periphery is mainly responsible for adjusting the dose distribution over a larger range. The 10mm third blade is relatively thick, so it can more effectively reduce the intensity of the beam and is suitable for areas that require a wider dose distribution, such as large tumors or the edge of the treatment area. The third blade on the periphery acts like a speed bump, allowing the beam to be more evenly distributed when it reaches the edge of the treatment area, avoiding excessive doses while protecting surrounding normal tissues.

[0042] The second blade in the middle area is in the middle of the dose distribution adjustment, neither the outermost layer needs to cover too wide a range nor the innermost layer needs to be very precise. Therefore, the 7.5mm second blade provides a balance at this level, which can adjust the dose distribution without excessively absorbing the beam. These blades can be used for medium-sized tumors or areas that require medium-precision dose distribution. Due to their moderate thickness, they can ensure uniform dose distribution without excessive dose leakage to surrounding tissues.

[0043] The first leaf in the central area is located in the treatment area that requires the highest precision, such as small tumors or areas that require very precise dose distribution. Therefore, thinner leaves are needed to achieve more delicate dose adjustment. The 5mm first leaf can more accurately control the intensity distribution of the beam, so that the dose can be distributed more concentratedly in the tumor area while minimizing damage to surrounding normal tissue.

[0044] Blades of different thicknesses will encounter other problems when arranged, such as drive and blade movement coordination. In terms of drive, for thinner 5mm blades, when using the same drive motor, 5mm thick blades use thinner drive screws to drive the blades; the friction between blades is also worth considering. When processing blades, high-hardness, smoothly polished tungsten alloys are used as blades, which can effectively reduce the impact of friction on blade coordination. In terms of blade coordination, the controller integrates a cross-coupling control strategy. The basic idea is to introduce the influence of other axes into the control of the current controlled axis to achieve synchronous coordination. It not only considers the position tracking error of a single actuator in traditional asynchronous control, but also includes the position and speed synchronization errors between axes.

[0045] like Figure 3 As shown in the figure, the blade cross section adopts an inverted trapezoidal design, with the two side surfaces parallel to the direction of the ray, and the upper and lower surfaces inclined to the center line of the beam. Adjacent blades are overlapped by inverted trapezoidal steps to reduce leakage. At the same time, a special curved blade front end is used to ensure that the edge of the ray is always tangent to the end face during movement, reducing the penumbra of the radiation field.

[0046] In order to make each blade move independently and flexibly with low friction, adjacent blades should not be too close together, but too loose a contact may easily cause radiation leakage. To resolve this contradiction, the blade cross section is designed as a combination of two upper and lower trapezoids with a concave and convex shape in the middle. When arranged, the concave and convex shapes can overlap, and the characteristic of the straight-line propagation of rays is used to obtain a good anti-leakage effect.

[0047] like Figure 4 As shown in the figure, a high-performance linear servo motor is used to directly drive the blades, and a built-in high-precision grating ruler is used to detect and feedback the blade position. The motion control uses an adaptive PID algorithm, combined with high-resolution PWM speed regulation, to achieve high-precision control of the blade position and speed. In order to ensure the accuracy of blade motion, a magnetic scale is used in the MLC box to detect whether the motor drives the blade to the specified position.

[0048] Since the present invention needs to control 120 motors, it consumes more chip resources. In order to improve the consistency and stability of control, as well as improve fault diagnosis and fault tolerance capabilities, group control is adopted for the control of the blades.

[0049] In order to facilitate the control of 60 pairs of blades, we grouped the blades into groups of 4, for a total of 15 groups. Each group uses a control circuit consisting of a main control chip, two driver chips and their peripheral circuits to control the motor. The 15 groups of control circuits are the same, which makes the circuit design simpler and more convenient for fault finding and repair. The 15 groups of control circuits work together through the same control chip and communicate with the host computer through the 485 chip.

[0050] This improves the consistency and stability of control by grouping the blades and using the same control circuit design, so that the control method and parameters of each group of blades are consistent. This helps to ensure that the performance of each blade group is relatively consistent during mass production or equipment debugging, and reduce control instability factors caused by circuit differences; 15 groups of control circuits work together through the same control chip, which means that the actions of each blade group can be coordinated through a centralized control mechanism. During radiotherapy, different blade groups need to work together according to the treatment plan to achieve precise modulation of the radiation beam.

[0051] In terms of improving fault diagnosis and fault tolerance, when a system fault occurs, group control makes fault finding easier and can also improve the system's fault tolerance to a certain extent. Even if the control circuit of a blade group fails, the blades of other groups can still continue to work, but it may affect the overall treatment accuracy and effect.

[0052] This project uses a vane motor with a built-in incremental rotary encoder. The incremental encoder directly uses the principle of photoelectric conversion to output three sets of square wave pulses A, B and Z phases; the phase difference between the two sets of pulses AB is 90°, so the direction of rotation can be easily determined, and the Z phase has one pulse per rotation, which is used for reference point positioning.

[0053] The rotation of the DC motor is converted into the horizontal displacement of the grating blades through the action of the lead screw. Given that the motor drives the driving lead screw to rotate one circle, the lead screw pushes the DMLC blade to produce a horizontal displacement of one pitch. The driving lead screw pitch is a, the motor reduction box speed ratio is 4:1, and the motor built-in incremental rotary encoder has 12 pulses fed back per revolution. The pulse equivalent of the blade displacement is:

[0054]

[0055] That is, every time the rotary encoder generates a feedback pulse, the displacement of the blade is L.

[0056] The cross-coupling control strategy is introduced to introduce the position deviation information of adjacent leaves into the motion control compensation of the current leaf, suppress the relative position error between adjacent leaves, and comprehensively improve the overall contour accuracy of the multi-leaf collimator. The leaves of the multi-leaf collimator are arranged in pairs, and each leaf is controlled by an independent motor to control its movement speed and position. However, the current multi-leaf collimator leaf position accuracy control is only implemented for a single leaf, ignoring the coupling relationship between the leaves and the impact of the position error of a single leaf on the overall leaf end face. Therefore, it is necessary to adopt an appropriate multi-leaf synchronization control strategy to compensate for the synchronization position error of multiple leaves.

[0057] like Figure 5As shown in the figure, in order to achieve the coordinated control of multiple leaves of the multi-leaf collimator, this software uses a cross-coupling control strategy. In view of the influence of the position error of adjacent leaves, it is used as the input of the cross-coupling controller. The output of the cross-coupling controller will be introduced into the position drive mechanism of the currently controlled leaf, and act on the position drive mechanism together with the leaf desired position setting value, in order to achieve the goal of multi-leaf coordinated control.

[0058] More specifically, the single-blade position controller controls the drive mechanism of the motor corresponding to the blade according to the current position of the blade and the control result feedback. The adjacent blade position error inputs are simultaneously input into the cross-coupling controller for synchronization error calculation. The synchronization errors are superimposed on the output of the single-blade position controller of the manual-controlled blade for controlling the blade.

[0059] Cross-coupling control is a control strategy that uses a cross-coupling operator to calculate the contour error and uses it as the input of the control law; then, the output control signal is distributed to other motors through the coupling operator to ensure the motion synchronization of each motor, thereby reducing the contour error of the system. The basic idea of ​​cross-coupling control is to introduce the influence of other axes into the control of the currently controlled axis to achieve the effect of synchronous coordination. This control method not only takes into account the position tracking error of a single actuator in traditional asynchronous control, but also includes the position and speed synchronization errors between axes.

[0060] Specifically, in this implementation, the multi-leaf collimator is regarded as a multi-axis multi-motor motion control system, and its control system model can be shown as follows:

[0061]

[0062] Among them, τ is the n×1 dimensional control input vector, x is the n×1 dimensional coordinate vector, M is the positive definite inertia matrix, and C is the Coriolis force vector.

[0063] The tracking error (position error) of a single blade is defined as:

[0064] e=x d -x(3);

[0065] Among them, x d is the expected position, x is the actual operating position. In the multi-leaf collimator control system, the synchronization requirements of each leaf may not be exactly the same, but in order to simplify the design, it is assumed that the synchronization requirements of each leaf are the same, that is, e1 = e2 = ... = e n .

[0066] In the synchronous control strategy, the difference between the position tracking error of the current blade and the next adjacent blade is defined as the synchronization error between the blades, such as:

[0067] ε1=C1e1-C2e2, ε2=C2e2-C3e3,…,ε n-1 =C n-1 e n-1 -C n e n (4);

[0068] Among them, ε i is the synchronization error of the i-th blade, C i is the synchronization coefficient, so that ε i →0 (i=1,2,…,n), then the synchronization control requirements are met, and the synchronization error is expressed as ε=Te, where e=[e1,e2,…,e n ] T , T is the synchronization transfer matrix. The coupling position error between blades is defined as the difference between the position tracking errors of two adjacent blades, expressed as:

[0069] E=e+αε (5)

[0070] Where α is a diagonal positive definite matrix, E is the control gain of the coupled position error, and substituting equation (5) into ε = Te yields:

[0071] E=(I+αT)e (6)

[0072] Based on this, a synchronous controller based on cross-coupled PD is designed:

[0073] τ=K P E+K D E+(I+αT) -1 K e e (7)

[0074] Among them, K P , K D , K e The controller's position control proportional gain, differential gain and compensation gain. The main purpose of the third term on the right side of the formula is to make the exchange rate make the system stable. Substituting formula (7) into formula (2) yields:

[0075]

[0076] When t→∞, e→0, ε→0, that is, the control law can ensure the tracking error and position error, and generate a comprehensive error which is superimposed on the output of each single blade controller and used for control respectively.

[0077] Embodiment 2:

[0078] This implementation provides a multi-leaf collimator for radiotherapy, which adopts the leaf arrangement scheme and the leaf drive control scheme described in Example 1.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A leaf structure of a multi-leaf collimator for radiotherapy, It is characterized in that include: A plurality of first blades, a plurality of second blades and a plurality of third blades, wherein the thickness of the first blades is smaller than the thickness of the second blades, and the thickness of the second blades is smaller than the thickness of the third blades; The first blades are all located in the central area, the third blades are located in the peripheral area, and the second blades are located in the middle area between the central area and the peripheral area.

2. The leaf structure of a multi-leaf collimator for radiotherapy according to claim 1, characterized in that: The thickness of the first blade is 5 mm, the thickness of the second blade is 7.5 mm, and the thickness of the third blade is 10 mm.

3. The leaf structure of a multi-leaf collimator for radiotherapy according to claim 1 or 2, characterized in that: The first blade includes 60 pieces, the second blade includes 40 pieces, and the third blade includes 20 pieces.

4. The leaf structure of a multi-leaf collimator for radiotherapy according to claim 1 or 2, characterized in that: The cross-sections of the first blade, the second blade and the third blade are all designed in an inverted trapezoidal shape, with the two side surfaces parallel to the direction of the ray, and the upper and lower surfaces inclined to the center line of the beam. Adjacent blades reduce leakage by overlapping inverted trapezoidal steps, and adopt an arc-shaped front end face to ensure that the edge of the ray is always tangent to the end face during movement.

5. The leaf structure of a multi-leaf collimator for radiotherapy according to claim 2, characterized in that: Each blade corresponds to a motor. The blades are arranged in pairs, including 60 pairs of blades. The 60 pairs of blades are divided into 15 groups. Each group includes 4 pairs of blades. Each group uses a control circuit consisting of a main control chip, two driver chips and their peripheral circuits to control the motor. The control circuits of the 15 groups are the same.

6. The leaf structure of a multi-leaf collimator for radiotherapy according to claim 5, characterized in that: The motor uses a vane motor with a built-in incremental rotary encoder. The rotation of the motor is converted into the horizontal displacement of the blade through the action of the lead screw. The pulse equivalent of the blade displacement is: Every time the rotary encoder generates a feedback pulse, the displacement of the blade is L; Among them, a is the pitch of the driving screw, the speed ratio of the motor reduction box is 4:1, and the number of pulses fed back by the built-in incremental rotary encoder of the motor is 12 per rotation.

7. A method for controlling the leaf structure of a multi-leaf collimator for radiotherapy, characterized in that: Using the multi-leaf collimator for radiotherapy according to any one of claims 1 to 6, The process includes: The single blade position controller controls the blade drive mechanism according to the blade tracking error, and the errors between each controlled blade and the adjacent blades are input into the cross-coupling controller for synchronization error calculation; The synchronization error is superimposed on the output of each controlled single blade position controller for controlling the blade drive mechanism.

8. The method for controlling the leaf structure of a multi-leaf collimator for radiotherapy according to claim 7, characterized in that: The control model of the cross-coupled controller is: Among them, K P , K D and K e are the proportional gain, differential gain and compensation gain for position control respectively, E=e+αε, M(·) is the positive definite inertia matrix, C(·) is the Coriolis force vector, α is the diagonal positive definite matrix, E is the control gain of the coupled position error, e is the synchronization error vector, x is the comprehensive error of the output, and T is the synchronization transfer matrix.

9. The method for controlling the leaf structure of a multi-leaf collimator for radiotherapy according to claim 8, characterized in that: Synchronization error vector e=[e1,e2,…,e n ] T , where n is the number of blades, e1 represents the tracking error of the first blade, e2 represents the tracking error of the first blade, and e n Represents the tracking error of the first blade.

10. A multi-leaf collimator for radiotherapy, characterized in that: A leaf structure of a multi-leaf collimator for radiotherapy comprising any one of claims 1-6.

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