Method and system for controlling leaves of multi-leaf collimator based on electrical impedance imaging technology

Abstract

The present invention discloses a method and system for controlling the blades of a multi-leaf collimator based on electrical impedance imaging technology. The system obtains the current position of each multi-leaf collimator blade in real time; determines the center position of a target tumor based on the conductivity distribution of a reconstructed image; determines the relationship between the radius of the tumor section and the blade width; and controls the multi-leaf collimator to move the blades to the target position based on the determination result. The present invention uses electrical impedance imaging technology to replace traditional medical imaging methods, reducing the side effects of radiation during treatment. It enables real-time dynamic monitoring and tracking of target tumors during radiotherapy, improves the accuracy of tumor positioning, and effectively reduces the development cost of multi-leaf collimator equipment.

Description

Technical Field

[0001] The present invention relates to the field of medical imaging technology, and in particular to a method and system for controlling leaves of a multi-leaf collimator based on electrical impedance imaging technology. Background Art

[0002] During radiotherapy, normal cells can also be damaged by radiation, so it is necessary to accurately determine the location of the lesion and implement local radiotherapy to ensure minimal damage to normal healthy tissues and at the same time not omit the treatment of cancerous tissues. Intensity Modulated Radiation Therapy (IMRT) is a method of achieving uniform distribution of radiation dose by adjusting the radiation dose within the treatment area, and can adjust the radiation irradiation volume according to treatment needs. This method ensures that the geometry of the treatment area is consistent with the shape of the tumor within the radiation field, while minimizing the radiation dose to surrounding normal tissues and organs. To achieve this function, a multi-leaf collimator (MLC) is usually used. A multi-leaf collimator is a mechanical moving component that accurately locates the tumor target through the arrangement and movement of the leaves, thereby achieving conformal irradiation while achieving precise positioning to minimize the side effects caused by radiotherapy.

[0003] During intensity-modulated conformal radiotherapy, the target tumor may move due to factors such as positioning accuracy and patient breathing, causing the tumor to move out of the radiation range and expose normal tissue to radiation. This affects the accuracy and efficacy of treatment. To avoid radiation damage to normal tissue and improve treatment efficacy, accurate, real-time, and safe image-guided tracking of the target tumor is necessary. Current image-guided methods mainly use magnetic resonance imaging (MRI) and X-ray computed tomography (CT). However, these technologies only provide accurate static image assessments, which cannot meet the needs of real-time tracking of lung tumors and have certain side effects in actual operation. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide a non-invasive, safe, faster and more accurate method and system for controlling the leaves of a multi-leaf collimator based on electrical impedance imaging technology.

[0005] Studies have shown that the electrical characteristic parameters of human tissue are sensitive to cancer, and there are obvious differences in the impedance values ​​between cancerous tissue and normal tissue. The impedance values ​​of most cancerous tissues are higher than those of normal tissue. Therefore, the electrical impedance of human tissue can be used as a technical indicator for identifying cancer tumors. Electrical impedance tomography (EIT) is a non-invasive, non-invasive, and low-cost detection technology that collects electrical impedance information by applying a driving current or voltage on the surface of the human body through an electrode array, and reconstructs the electrical impedance distribution image based on this information. EIT technology has the advantage of high-speed acquisition, which can reach up to several hundred frames per second. It also has the characteristics of being radiation-free, low-cost, and easy to operate. Therefore, EIT technology is very suitable for real-time dynamic monitoring and tracking of tumors during radiotherapy.

[0006] Using electrical impedance imaging technology as an image guidance method, the multi-leaf collimator is accurately controlled in real time to solve the problem of excessive radiation and radiation damage caused by respiratory movement.

[0007] The first aspect of the present invention is a method for controlling the blades of a multi-leaf collimator based on electrical impedance tomography (EIT). This method, a tumor localization algorithm, is used to implement the multi-leaf collimator blade positioning function of an EIT data acquisition system, accurately determining the target movement position of the multi-leaf collimator blades. The method is applicable to multi-leaf collimators with different numbers of blades, and the number of blades can be adjusted according to cost and demand in practical applications.

[0008] For each leaf, the current position of each leaf is obtained in real time; the shape of the tumor is approximated to a circular shape;

[0009] The center position of the target tumor is obtained based on the reconstructed image, and the image is divided into four parts with this position as the axis;

[0010] Determine the relationship between the radius of the tumor section and the width of the blade; if the radius of the tumor section is less than or equal to half the width of the blade, only the blade at the center coordinate position of the tumor needs to be moved according to the new coordinate information; if the radius of the tumor section is greater than half the width of the blade, calculate the difference between the radius of the tumor section and half the width of the blade; calculate the multiple relationship between the difference and the width of a single blade, that is, how many blade widths can be included in the difference, and round the result up; the result obtained is the number of blades moved by the quarter with the center position coordinate as the axis; calculate the polar coordinates of each point on the circular contour based on the number of blades in the quarter, use the polar coordinates to calculate the rectangular coordinates of each point, and use the rectangular coordinates as the new target position; after obtaining the coordinates of all points on the contour through the above calculation method, control the blade to move to the corresponding position of these point coordinates.

[0011] Furthermore, the reconstructed image is composed of a matrix with an equal number of rows and columns. In order to adapt to the corresponding range of rectangular coordinate systems required when using different numbers of leaves, the matrix size is changed by interpolating the data matrix of the reconstructed image, so that the image matrix corresponds to the proportion of the rectangular coordinate system while ensuring the smoothness of the reconstructed image.

[0012] Furthermore, the center position of the tumor is determined based on the numerical value of the conductivity value at each pixel point of the reconstructed image. The concentrated area of ​​the part with higher conductivity values ​​in the reconstructed image is the location of the target tumor. A suitable threshold range is set for the conductivity value of the reconstructed image, and the center position of the tumor is the coordinate position of the pixel point with the largest value within this threshold range.

[0013] The leaf width is adjusted according to the number of leaves actually used. In most cases, the detection range of the multi-leaf collimator is usually fixed.

[0014] The calculation result of the number of leaves is rounded up to make the opening of the leaves after movement closer to the actual shape of the target tumor, thereby ensuring that healthy tissue is not damaged by radiation to the greatest extent.

[0015] The polar coordinates of each point on the target tumor contour are determined by the number of leaves actually moved, which is applicable to the case where the target tumor is circular in shape. By converting the polar coordinates into rectangular coordinates, the coordinate positions of each point that can be reflected on the contour can be included as much as possible.

[0016] A second aspect of the present invention provides a system for controlling leaves of a multi-leaf collimator based on electrical impedance tomography technology, comprising:

[0017] A data processing module is used to collect data in real time and convert the collected data into conductivity distribution for image reconstruction through calculation;

[0018] Communication module, used for data transmission between the multi-leaf collimator and the tumor simulation system;

[0019] An image reconstruction module, used for displaying a reconstructed image based on the conductivity distribution;

[0020] The leaf positioning module adopts the method of controlling the leaves of the multi-leaf collimator using the electrical impedance imaging technology to locate the contour position of the target tumor.

[0021] The system can realize real-time image reconstruction following the changes of the individual's body, establish communication between the various devices of the control system, realize data collection and processing, and complete the positioning of the leaves. The leaf positioning method is implemented based on the multi-leaf collimator control method proposed by the control system.

[0022] Furthermore, the multi-leaf collimator comprises:

[0023] Two sets of blade groups, the two sets of blade groups are arranged opposite to each other, each set of blade groups consists of multiple blades, and each blade moves independently;

[0024] Multiple stepper motors, the number of the stepper motors is equal to the number of the blades, each stepper motor controls one blade and provides driving force for the movement of the blades;

[0025] A circuit board that controls the operation of the motor, establishes communication connection control, data processing control, and logic operation control for each stepper motor, and ensures the stable operation of the stepper motor;

[0026] Multiple transmission mechanisms, each stepping motor is connected to a transmission mechanism. The transmission mechanism is a belt and gear.

[0027] Multiple ball screws, each transmission mechanism is connected to a ball screw, and a blade is installed on the slider of each ball screw to assist it in completing linear motion; the ball screw converts the rotational motion of the motor into linear motion, ensuring the linear motion mode of the blade and high motion efficiency;

[0028] The bracket includes an aluminum alloy base and a suspension bracket, which is used to support the multiple stepper motors, multiple transmission mechanisms and multiple ball screws to ensure the overall consistency of the equipment.

[0029] Furthermore, both ends of the long side of the blade are flipped in different directions respectively, the flipped portion of the blade is the overlapping portion between two adjacent blades, and the flipping direction is perpendicular to the plane of the blade.

[0030] Furthermore, the tumor simulation system includes a water tank and a glue stick, which simulates the shape of the target tumor. Multiple electrodes are evenly distributed horizontally on the inner wall of the water tank, and data is collected through the electrodes. The movement of the glue stick in the water tank simulates the movement of the tumor in the human body.

[0031] The technology provided by the present invention includes the following beneficial effects:

[0032] 1. This invention uses electrical impedance imaging technology to replace traditional medical imaging methods, reducing the side effects of radiation during treatment, enabling real-time dynamic monitoring and tracking of target tumors during radiotherapy, improving the accuracy of tumor positioning, and effectively reducing the development cost of multi-leaf collimator equipment.

[0033] 2. The present invention constructs a simulated multi-leaf collimator control system based on electrical impedance imaging, which can meet the research needs of different numbers of leaves and different control methods, truly demonstrates the working process and implementation principle of the multi-leaf collimator system, and accelerates the development and research process of the multi-leaf collimator system. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic structural diagram of a simulated multi-leaf collimator in an embodiment of the present invention;

[0035] Figure 2 1 is a three-view diagram of a simulated multi-leaf collimator blade in an embodiment of the present invention, (a) is a front view, (b) is a side view, and (c) is a top view;

[0036] Figure 3 1. This is a diagram simulating the arrangement of various accessories on a side suspension bracket of a multi-leaf collimator according to an embodiment of the present invention;

[0037] Figure 4 is a framework diagram of a simulated multi-leaf collimator control system based on electrical impedance imaging in an embodiment of the present invention;

[0038] Figure 5 4 is a flow chart of positioning leaves of a multi-leaf collimator according to an embodiment of the present invention.

[0039] In the figure: 1 is a stepper motor, 2 is a transmission mechanism, 3 is a ball screw, 4 is a suspension bracket, 5 is a stainless steel blade, and 6 is an aluminum alloy base. DETAILED DESCRIPTION

[0040] The technical solution of the simulated multi-leaf collimator control system based on electrical impedance imaging provided by the present invention will be described below with reference to the accompanying drawings. The embodiments of this application are non-limiting exemplary embodiments and should not be used to limit the scope of protection of the present invention.

[0041] In a first aspect, the technical solution of the simulated multi-leaf collimator device of the present invention is as follows:

[0042] The present invention provides a device for simulating a multi-leaf collimator. The schematic diagram of the structure of the whole device is shown as follows: Figure 1 As shown, its structure includes: stainless steel blades 5 arranged in pairs, a stepper motor 1 that provides power, a circuit board that controls the operation of the motor, a ball screw 3 that converts rotational motion into linear motion, a slider that assists linear motion, a transmission structure 2 responsible for the longitudinal transmission of the motor and the screw, an aluminum alloy base 6 and a suspension bracket 4 that carry various accessories.

[0043] (1) Stainless steel blades:

[0044] The blades of a multi-leaf collimator system are typically designed to be radiation-proof. The blades are paired, and each leaf can move independently. To prevent radiation leakage from the edges of the leaves during treatment, a certain degree of overlap is designed between each leaf. The number and shape of the blades in a system are fixed, making it suitable for patients with different conditions. By adjusting the positional relationship between the leaves, blades of different shapes can be installed, resulting in multiple irradiated areas of different shapes.

[0045] The purpose of designing the simulation device is to better demonstrate the working principle and to provide an intuitive simulation demonstration for the analysis of the principle. At the same time, the design cost is taken into consideration to minimize the difficulty of processing. The material of the blades is stainless steel, which has no actual radiation protection ability. The total number of blades of the simulation device is set to 16, and each blade is 120mm long and 22mm wide. The number of multi-leaf collimator blades can be adjusted as needed. The more blades, the better the shape fit of the target lesion, and the better the effect of achieving precise treatment and avoiding radiation to surrounding healthy tissues.

[0046] To simulate the overlapping design between blades, e.g. Figure 2 As shown in the figure, one end of the long side of the blade is slightly flipped upward, and the other end is flipped downward. The length of the flipped part is 4mm. The two flipped parts serve as the upper and lower edges of the long side of the blade. The blades are shielded from each other by the lower edge of one blade and the upper edge of another blade, so that the blades fit together and overlap, avoiding radiation leakage from the blade edges. The appearance design of a single blade is as follows Figure 2 shown.

[0047] (2) Stepper motor and control circuit board

[0048] A stepper motor is an open-loop control element that converts electrical pulse signals into angular or linear displacement. For every unit of angular rotation of the stepper motor used in the simulation device, the ball screw moves 1mm relative to the motor. The circuit board that controls the motor movement includes the following modules: a microcontroller module, a motor driver module, a voltage stabilizer module, a current amplifier module, and a communication module. The functions of each module are as follows:

[0049] The microcontroller module is responsible for controlling the entire analog device, establishing communication connections, data processing, logical operations, etc.; the motor drive module is responsible for controlling the rotation of the stepper motor. Each control circuit board has four motor drive modules, and each motor drive module controls the movement of a leaf of a multi-leaf collimator. Since the analog device has a total of 16 leaves, a total of four identical control circuit boards are configured; the voltage stabilizer module provides stable power supply for each module, stabilizing the input voltage at 3.3V; the current amplification module can enhance the ability to drive other modules by amplifying current, realize the drive and control of different power supplies or loads, and effectively manage the power supply; the communication establishment module is responsible for controlling the communication connection between the multi-leaf collimator device and the host computer, and provides serial port communication between the USB interface and the microcontroller module.

[0050] The stepper motor is driven as follows: When the motor driver module receives a pulse signal, it drives the stepper motor to rotate in the set direction and at a fixed step angle. By controlling the number of pulses, the angular displacement can be controlled, enabling precise positioning of the blades. By controlling the pulse frequency, the motor's rotational speed and acceleration can be controlled, achieving speed regulation of the blades.

[0051] The microcontroller module's logical operations enable a scientific judgment of the blade's current position and the newly received position. Upon receiving a new target position, the system first determines the relationship between the blade's current and new target positions. If the current position matches the target, the blade remains stationary. If the current position differs from the target, the motor is controlled to rotate toward the target based on the current position, ensuring that each blade movement achieves the minimum distance. This logical operation ensures that each position change is based on the previous stopping point, eliminating the need for frequent positioning operations and improving operational efficiency.

[0052] (3) Ball screw and slider

[0053] A ball screw is a device that uses balls to roll between threads and a screw to achieve mechanical transmission. It consists of a threaded shaft and a screw. The threads are covered with a certain number of balls, while the inside of the screw has guide grooves corresponding to the balls. The balls transmit and convert power by rolling, thereby achieving linear motion. The friction coefficient of the ball screw during the transmission process is lower than that of an ordinary screw, with higher efficiency and lower noise. The total stroke of the screw used in the simulation device is 110mm, and the lead per turn is 1mm. A small lead can achieve more precise position control, and a smaller screw can reduce the weight of the entire device. The bolt of the ball screw is driven by a motor, and a linear bearing is introduced to ensure that the nut does not rotate. The linear bearing is placed directly below the screw and parallel to the screw.

[0054] To ensure smooth linear movement of the blades, a slider is installed. It has two holes through which the ball screw bolts and linear bearings are connected. The top of the slider secures the blades. When the motor rotates to drive the bolts, the slider moves synchronously, allowing the blades to move linearly, thus achieving electric control of the blades.

[0055] (4) Transmission structure

[0056] The simulation device's transmission structure, composed of a combination of gears and belts, is responsible for longitudinal transmission of the motor and screw, reducing the overall system's size. Two 1:1 transmission gears are mounted on the shafts of each motor and screw, connected by a belt with the same tooth profile.

[0057] (5) System main bracket

[0058] The main bracket of the system consists of an aluminum alloy base and a suspension bracket. The length, width and height of the aluminum alloy base are 530mm, 238mm and 315mm respectively. There is a square opening area with a size of 180mm*157mm in the center of the base. A total of 16 sets of motors, ball screws and blades are installed in pairs on the left and right sides of the area. Each blade can be moved in or out of the opening area independently. The stepper motor, the circuit board that controls the operation of the motor, and the transmission structure are all assembled on the suspension brackets on both sides of the base. The suspension bracket is customized according to the size of each accessory, which can reduce the appearance of the entire system. The assembly layout of each accessory on the suspension bracket is as follows Figure 3 shown.

[0059] In a second aspect, the technical solution of the EIT data acquisition system of the present invention is as follows:

[0060] The EIT data acquisition system of the present invention primarily comprises an EIT data acquisition component and a method control component. This system, based on image-guided technology, adds a time scale. This system can observe changes in the treatment target's state over time, based on the rate of change in the individual's body, through real-time image reconstruction. The reconstructed image can be displayed on an interface controlled by the system software, clearly demonstrating the location and size ratio of the target tumor within the entire detection area.

[0061] The EIT data acquisition system includes the following modules: a data processing module, a communication establishment module, an image reconstruction module, and a leaf positioning module. The data processing module is the EIT data acquisition component of the system, while the communication establishment module, image reconstruction module, and leaf positioning module are the method control components of the system. The data processing module is responsible for collecting real-time voltage data, converting the voltage data into current data through voltage-to-current conversion, and obtaining the conductivity distribution based on the current data. The communication establishment module controls the IP routing connection of the EIT imaging system and the serial port connection of the multi-leaf collimator, thereby establishing communication between the multi-leaf collimator device, the EIT data acquisition device, and the host computer. Upon successful connection, data transmission between the devices can be completed. The image reconstruction module uses the processed conductivity distribution to reconstruct the image and display the imaging results, using different image reconstruction algorithms based on actual needs. The leaf positioning module is implemented based on the multi-leaf collimator control method proposed in the multi-leaf collimator control system. It can locate the contour of the target tumor and then position the corresponding leaves based on the contour location and the actual number of leaves required, thus enabling real-time adaptive adjustment of the leaf number.

[0062] The image reconstruction algorithm used by the data acquisition system is the Landweber iterative algorithm, which is a common method widely used to solve inverse problems. The algorithm updates the solution vector iteratively to approximate the true solution. The initial solution image x 0 The regularization equation of the Landweber iterative process is shown as follows:

[0063] x i =x i-1 -aJ T (Jx i-1 -f)-λR'(x)

[0064] where x i The result of the i-th iteration for the image parameter vector to be solved; x i-1 is the result of the (i-1)th iteration; α is the data fidelity coefficient; J is the sensitivity matrix; f is the voltage vector measured by the electrode sensor; λ is the regularization parameter; and R'(x) is the gradient of the regularization term. The Landweber iterative image reconstruction algorithm is simple to use, has good convergence, and produces excellent imaging results. It is suitable for relatively simple linear inverse problems and is therefore well-suited for use in the electrical impedance dynamic imaging method of this system.

[0065] The EIT data acquisition system determines the leaf position coordinates based on the recognition results of the target tumor contour and sends the coordinate information to the multi-leaf collimator. At the same time, it can display the simulated target tumor position in real time, verifying and monitoring the actual position of the multi-leaf collimator leaves, and ultimately achieving a visual comparison between the target tumor and the actual position of the leaves. The framework diagram of the simulated multi-leaf collimator control system based on electrical impedance imaging proposed in this invention is shown in the figure below. Figure 4 shown.

[0066] In a third aspect, the technical solution of the water tank simulation system (tumor simulation system) of the present invention is as follows:

[0067] The water tank simulation system of the present invention simulates the data acquisition process of the EIT data acquisition system. The simulation system is designed to test the feasibility of the present invention. The water tank is a cylindrical barrel made of acrylic material. A circle of copper cylinder electrodes arranged at equal intervals is embedded on the outer surface of the barrel. The number of electrodes used is 16. A cylindrical rubber stick is used to simulate the target tumor. These electrodes are evenly distributed along the circumference of the barrel to form an annular structure. The movement of the target tumor in the human body is simulated by moving the cylindrical rubber stick in the barrel water tank. The accuracy of the simulated multi-leaf collimator designed in this system is tested by comparing the position of the cylindrical rubber stick after movement with the position of the leaves.

[0068] In a fourth aspect, the multi-leaf collimator control method of the present invention is as follows:

[0069] The multi-leaf collimator control method provided by the present invention is mainly aimed at determining the target position of the leaves;

[0070] The method is applied in a blade positioning module of an EIT data acquisition system, which is one of the modules of the method control part of the EIT data acquisition system of the present invention;

[0071] The control portion of the method described in the present invention can obtain the change in the position of the target tumor based on the electrical impedance reconstruction image, and convert the change in position into the movement distance of the multi-leaf collimator leaves. The judgment method of this process is as follows:

[0072] A fixed threshold is set for the conductivity data of the electrical impedance reconstruction image, and the coordinates of the point with the largest numerical value in the threshold range are used as the coordinates of the center position of the simulated target tumor (x0, y0). Based on the horizontal and vertical directions of this center coordinate position, all coordinate positions are divided into four parts, namely the upper left, upper right, lower left and lower right parts. Assuming that the shape of the tumor is circular, the present invention uses a cylindrical glue stick to simulate the shape of the tumor, and sets the radius of the circular section in the glue stick to R and the width of the blade to d. Based on the judgment of the size relationship between R and d, the number of blades that need to be moved is divided into two cases: (1) If R≤d / 2, only the blades at the center coordinate position of the tumor need to be moved according to the new coordinate information; (2) If R>d / 2, the calculation formula for the number of blades n moved for one-quarter of the center coordinate is as follows:

[0073]

[0074] The symbols = indicates the result is rounded up. Since all coordinates are divided into four parts based on the center coordinate position, including the transverse blade where the center coordinate is located, determining the tumor location requires moving at most 4n+2 blades. Based on the center coordinates (x0, y0) of the target tumor and the radius R of the circular section in the glue stick, the following horizontal and vertical coordinates can be determined using the following formula:

[0075]

[0076] where x l is the horizontal coordinate of the left end of the center position on the target tumor contour, x r is the horizontal coordinate of the right end, y u is the vertical coordinate of the upper end of the center position on the target tumor contour, y d It is the vertical coordinate of the bottom end.

[0077] According to the above judgment and calculation process, the coordinates of the five points of the target object's outline can be determined, namely (x0, y0), (x l ,y0),(x r ,y0),(x0,y u ), (x0,y d ).

[0078] Since the target object's outline is a circle, the number of blades n that are moved by a portion of the center position coordinates can be used to calculate the coordinates of other points on the outline using polar coordinates. i The calculation method is as follows, where the interval between the polar angles is π / 2n.

[0079]

[0080] After calculating all polar angles, remove the polar coordinates of the four known points with angles of (π / 2), π, (3π / 2), and 2π, and the final number of polar coordinates obtained is (4n-4). After obtaining the polar coordinates of each point on the contour, convert the polar coordinates to rectangular coordinates according to the following formula.

[0081]

[0082] where x i is the horizontal coordinate of each point on the contour, y i is the ordinate of each point on the contour, x0 and y0 are the abscissa and ordinate of the center position of the target shape, R is the radius of the target shape, θ i is the polar angle of each point. After obtaining the coordinates of all points on the contour through the above calculation method, the blade is controlled to move to the corresponding position of these point coordinates, completing the blade positioning process of the entire control system. The flow chart of this process is as follows Figure 5 shown.

[0083] The above description is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept, and these all fall within the scope of protection of the present invention.

Claims

1. A system for controlling the leaves of a multi-leaf collimator based on electrical impedance tomography, characterized in that: include: A data processing module is used to collect data in real time and convert the collected data into conductivity distribution for image reconstruction through calculation; Communication module, used for data transmission between the multi-leaf collimator and the tumor simulation system; An image reconstruction module, used for displaying a reconstructed image based on the conductivity distribution; A leaf positioning module uses electrical impedance imaging technology to control the leaves of a multi-leaf collimator to locate the contour position of the target tumor; The method of controlling the leaves of a multi-leaf collimator using electrical impedance imaging technology can obtain the change in the position of the target tumor based on the electrical impedance reconstruction image, and at the same time convert the change in position into the movement distance of the leaves of the multi-leaf collimator; For each leaf, Get the current position of each blade in real time; The tumor shape was approximated as a quasi-circular shape; The center position of the target tumor is obtained from the reconstructed image, and the image is divided into four parts with the center position as the axis. The center position of the target tumor is the concentrated area of ​​the portion with higher conductivity values ​​in the electrical impedance reconstructed image. A suitable threshold range is set for the conductivity values ​​of the reconstructed image. The center position of the tumor is the coordinate position of the pixel with the largest value within this threshold range. Determine the relationship between the radius R of the tumor section and the blade width d; If the radius of the tumor section is less than or equal to half the blade width, R ≤ d / 2, then only the blade at the tumor center coordinate position needs to be moved according to the new coordinate information; If the radius of the tumor section is greater than half the blade width, R>d / 2, the difference between the radius of the tumor section and half the blade width is calculated; Calculate the relationship between the difference and the multiple of a single blade, that is, how many blades the difference can include in width, and round the result up. The result is the number of blades n that are moved by one-quarter of the center position coordinate. The calculation formula is as follows: Calculate the polar coordinates of each point on the circular contour based on the number of blades in the quarter. Use the polar coordinates to calculate the rectangular coordinates of each point, and use the rectangular coordinates as the new target position. The specific calculation method is as follows: The following horizontal and vertical coordinates are determined based on the center coordinates of the target tumor (x0, y0) and the radius R of the tumor section. The formulas are as follows: where x l is the horizontal coordinate of the left end of the center position on the target tumor contour, x r is the horizontal coordinate of the right end, y u is the vertical coordinate of the upper end of the center position on the target tumor contour, y d is the vertical coordinate of the lower end; According to the above judgment and calculation process, the coordinates of the five points of the target object's outline are determined, namely (x0, y0), (x l ,y0),(x r ,y0),(x0,y u ), (x0,y d ); Since the target object's outline is a circle, the number of blades n that are moved according to the center position coordinates is used to calculate the coordinates of other points on the outline using polar coordinates. The polar angle θ in the polar coordinates is i The calculation method is as follows, where the interval between polar angles is π / 2n, After all polar angles are calculated, the polar coordinates of the four known points with angles of (π / 2), π, (3π / 2) and 2π are removed. The number of polar coordinates obtained is (4n-4). After obtaining the polar coordinates of each point on the contour, the polar coordinates are converted to rectangular coordinates according to the following formula: where x i is the horizontal coordinate of each point on the contour, y i is the ordinate of each point on the contour, x0 and y0 are the abscissa and ordinate of the center position of the target shape, respectively, θ i is the polar angle of each point; After obtaining the coordinates of all points on each part of the contour through the above calculation method, the blade is controlled to move to the corresponding position of these point coordinates.

2. The system for controlling the leaves of a multi-leaf collimator based on electrical impedance imaging technology according to claim 1, characterized in that: It also includes a tumor simulation system, which includes a water tank and a glue stick. The shape of the target tumor is simulated by the glue stick. A plurality of electrode sheets are evenly distributed horizontally on the inner wall of the water tank. Data is collected by the electrode sheets, and the movement of the glue stick in the water tank is used to simulate the movement of the tumor in the human body. The accuracy of the simulated multi-leaf collimator designed in this system is detected by comparing the position of the cylindrical glue stick and the position of the leaves after movement.

3. The system for controlling the leaves of a multi-leaf collimator based on electrical impedance imaging technology according to claim 1, characterized in that: The multi-leaf collimator comprises: Two sets of blade groups, the two sets of blade groups are arranged opposite to each other, each set of blade groups consists of multiple blades, and each blade moves independently; Multiple stepper motors, the number of the stepper motors is equal to the number of blades, and each stepper motor controls one blade; Multiple transmission mechanisms, each stepping motor is connected to a transmission mechanism; Multiple ball screws, each transmission mechanism is connected to a ball screw, and a blade is installed on the slider of each ball screw; The bracket is used to support the multiple stepping motors, the multiple transmission mechanisms and the multiple ball screws.

4. The system for controlling the leaves of a multi-leaf collimator based on electrical impedance imaging technology according to claim 1, characterized in that: The reconstructed image is a conductivity data matrix obtained by applying an imaging algorithm to the collected voltage values ​​using electrical impedance imaging technology. The reconstructed image is composed of a matrix with an equal number of rows and columns. The change in the matrix size is achieved by interpolating the data matrix of the reconstructed image.

5. The system for controlling the leaves of a multi-leaf collimator based on electrical impedance imaging technology according to claim 3, characterized in that: The two ends of the long side of the blade are respectively turned in different directions, the turned portion of the blade is the overlapping portion between two adjacent blades, and the turning direction is perpendicular to the plane of the blade.

Images