Method and device for controlling acceleration voltage of medical cyclotron

Abstract

The invention relates to the technical field of cyclotron voltage control, in particular to a medical cyclotron acceleration voltage control method and device, and the method comprises the steps: dividing an alternating voltage signal into three stages according to the sudden change condition of the alternating voltage signal in a conversion period; the periodic fluctuation conditions of the high level stage and the low level stage, the change rate of the jump edge stage and the chaos degree of the change are analyzed, and the regulation and control intervention degree of the conversion period is obtained; obtaining an adjustment coefficient according to the subordinate stage of the voltage amplitude at the same moment in the alternating voltage signal in the previous conversion period at the current moment; and integrating the magnetic field intensity change at the current moment, the adjustment coefficient and the regulation intervention degree of the previous conversion period at the current moment to obtain a control proportionality coefficient at the current moment, and carrying out feedback control on the alternating voltage signal. The control precision of the acceleration voltage of the medical cyclotron can be improved.

Description

Technical Field

[0001] This application relates to the technical field of cyclotron voltage control, and particularly relates to a method and device for controlling the accelerating voltage of a medical cyclotron. Background Art

[0002] A medical cyclotron is a particle accelerator mainly used for producing positron radionuclides, which are applied in aspects such as PET / CT imaging or radioactive therapy. The main working principle of the cyclotron is to use a magnetic field and an alternating electric field to make charged particles move in a circular motion in the magnetic field and be repeatedly accelerated in the alternating electric field so that they can reach the expected particle energy.

[0003] In a general medical cyclotron, an LLRF high-frequency low-level system is used to control the working state of the high-frequency radio frequency (RF) system to ensure the stable acceleration of the particle beam. The control of the RF field in the accelerating cavity Dee is mainly through the voltage amplitude and phase of the alternating electric field. Basically, an analog-to-digital converter (ADC) sampling is used by a amplitude-phase control board to obtain a digital signal of a digital signal processor (DSP), and feedback control is used to control the voltage and phase of the RF field; in this control strategy, a fixed proportional coefficient is often set, resulting in overshoot or lag phenomena in the regulation of the accelerating voltage in the accelerating cavity under different scenarios, and the control accuracy of the accelerating voltage is poor. Summary of the Invention

[0004] In order to solve the above technical problems, the purpose of this application is to provide a method and device for controlling the accelerating voltage of a medical cyclotron, and the specific technical solutions adopted are as follows: In the first aspect, an embodiment of this application provides a method for controlling the accelerating voltage of a medical cyclotron, and the method includes the following steps: S1, obtaining the alternating voltage signals of each transformation period during the operation of the medical cyclotron; S2, according to the mutation situation of the alternating voltage signals within the transformation period, dividing the alternating voltage signals into a high-level stage, a jump edge stage, and a low-level stage; according to the periodic fluctuation situation of the alternating voltage signals in the high-level stage and the low-level stage, obtaining the stability of the level stage; according to the change rate and the degree of chaos of the change of the alternating voltage signals within the jump edge stage, obtaining the jump overshoot disorder value; fusing the stability of the level stage and the jump overshoot disorder value to obtain the regulation intervention degree of the transformation period; S3, obtaining the adjustment coefficient at the current moment according to the stage to which the voltage amplitude at the same moment in the alternating voltage signals in the previous transformation period belongs; obtaining the magnetic field intensity at each moment; comprehensively considering the change of the magnetic field intensity at the current moment, the adjustment coefficient, and the regulation intervention degree of the previous transformation period before the current moment, obtaining the control proportional coefficient at the current moment; S4, performing feedback control on the alternating voltage signals according to the control proportional coefficient at the current moment.

[0005] Further, dividing the alternating voltage signal into a high-level stage, a transition edge stage, and a low-level stage according to the mutation situation of the alternating voltage signal within the transformation period includes: Detecting the inflection points of the alternating voltage signal in each transformation period to obtain each inflection point; denoting the alternating voltage signal before the first inflection point and the first inflection point as the high-level stage; denoting the alternating voltage signal between the first inflection point and the last inflection point as the transition edge stage; and denoting the alternating voltage signal after the last inflection point and the last inflection point as the low-level stage.

[0006] Further, the method for obtaining the stability of the level stage includes: denoting the stability of the level stage in the current period as A; ; where and respectively represent the autocorrelation functions based on the high-level stage and the low-level stage in the current period, represents selecting the maximum value within the value range of the autocorrelation function, and respectively represent the standard deviations of the high-level stage and the low-level stage.

[0007] Further, the method for obtaining the jump overshoot disorder value includes: Performing linear fitting on the alternating voltage signal in the transition edge stage to obtain a fitting straight line; taking the acute angle between the fitting straight line and the vertical direction as the inclination angle of the fitting straight line; where the abscissa of the two-dimensional plane where the fitting straight line exists is time and the ordinate is the voltage amplitude; According to the central symmetry feature of the alternating voltage signal in the transition edge stage, obtaining an oscillation feature value; obtaining the average distance between the data points of all elements in the alternating voltage signal in the transition edge stage mapped in the two-dimensional plane and the fitting straight line; calculating the sum value of the oscillation feature value and the average distance; Taking the product of the angle value of the inclination angle of the fitting straight line and the sum value as the jump overshoot disorder value.

[0008] Further, the method for obtaining the oscillation feature value includes: Rearranging all elements in the alternating voltage signal in the transition edge stage in the order from the back to the front in terms of time to obtain a symmetric voltage signal; calculating the average difference of the elements at the same positions in the alternating voltage signal in the transition edge stage and the symmetric voltage signal as the oscillation feature value.

[0009] Further, the method for obtaining the regulation intervention degree of the transformation period includes: taking the sum of the stability of the level stage and the jump overshoot disorder value as the regulation intervention degree of the transformation period.

[0010] Further, the method for obtaining the adjustment coefficient at the current moment includes: Denote the voltage amplitude at the same moment in the alternating voltage signal within the previous transformation period as the current moment ; If belongs to the high-level stage or the low-level stage, the adjustment coefficient at the current moment is the first preset value; if belongs to the edge-transition stage, the adjustment coefficient at the current moment is the second preset value; wherein, the first preset value is less than the second preset value.

[0011] Furthermore, the method for obtaining the control proportional coefficient at the current moment includes: Take the difference in magnetic field intensity between the current moment and the previous moment as the magnetic-variation interference degree at the current moment; Denote the control proportional coefficient at the current moment i as , wherein, is the preset initial proportional coefficient; norm() is the linear normalization function; represents the regulation intervention degree of the previous transformation period before the current moment; represents the magnetic-variation interference degree at the current moment i; is the adjustment coefficient at the current moment i.

[0012] Furthermore, the feedback control of the alternating voltage signal according to the control proportional coefficient at the current moment specifically includes: According to the difference between the voltage amplitude at the current moment and the preset target voltage value, use a PID controller to calculate the control signal and control the voltage regulation device; wherein, take the control proportional coefficient at the current moment as the proportional coefficient in the PID controller.

[0013] In a second aspect, an accelerating voltage control device for a medical cyclotron provided by an embodiment of the present application includes a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, the steps of the method for controlling the accelerating voltage of a medical cyclotron described in any one of the above are implemented.

[0014] The present application has at least the following beneficial effects: This application analyzes the influence of internal mechanical vibration and electromagnetic interference in the acceleration cavity of a medical cyclotron on the stability control of charged particle acceleration. First, it analyzes the voltage change characteristics of the alternating electric field in the acceleration cavity caused by mechanical vibration, mainly obtaining the regulation intervention degree based on the voltage fluctuation and mechanical vibration conditions in the high and low level stages, as well as the convergence and overshoot of the voltage at the jump edge, which reflects the fluctuation of the voltage signal affected by circuit noise interference, and further more accurately evaluates the degree of regulation intervention required for the voltage signal. Further, it analyzes the electromagnetic interference suffered by the conversion and stability of the alternating electric field in the acceleration cavity during the conversion process of the alternating electric field, and obtains the variable magnetic interference degree based on the change of the magnetic field intensity, which reflects the obstruction of the magnetic field to the alternating electric field. Considering the influence of mechanical vibration and electromagnetic interference comprehensively, by quantifying the relationship between the interference degree and the voltage control intensity, the control proportional coefficient is finally obtained, and the feedback control algorithm is used to realize the control of the acceleration voltage in the acceleration cavity. Compared with setting a fixed proportional coefficient in the traditional control process, this solution mainly analyzes the fluctuation of the data collected by the sensor caused by the mechanical vibration of the medical cyclotron and the obstruction of the electromagnetic interference during the operation of the equipment, adjusts the proportional coefficient in real time, can achieve precise control of the alternating electric field voltage, avoid the situation of regulation lag or overshoot oscillation, and improve the control accuracy of the acceleration voltage of the medical cyclotron. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present application or the prior art, the drawings required for use in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0016] Figure 1 It is a step flowchart of a method for controlling the acceleration voltage of a medical cyclotron provided by an embodiment of the present application; Figure 2 It is a schematic structural diagram of a cyclotron provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Without conflict, the embodiments of the present application and the technical features in the embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present application.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0019] The following specifically describes the specific solutions of a method and device for controlling the accelerating voltage of a medical cyclotron provided by this application in conjunction with the accompanying drawings.

[0020] Please refer to Figure 1 , which shows a flowchart of the steps of a method for controlling the accelerating voltage of a medical cyclotron provided by an embodiment of this application. The method includes the following steps: S1. Obtain the alternating voltage signals of each transformation period during the operation of the medical cyclotron.

[0021] A specific implementation scenario of this application is the scenario of controlling the accelerating voltage of the cyclotron; the structural entity of the cyclotron is as Figure 2 shown, Figure 2 in which, 1 represents the particle source generator, 2 represents the alternating electric field of the acceleration cavity, 3 represents the high-frequency RF acceleration cavity, 4 represents a single magnetic field cavity, and 5 represents the particle flow outlet and the particle ejection direction. The principle of the cyclotron is: a beam of charged particles is generated by the particle source generator, and the charged particles are accelerated by the Coulomb force under the alternating electric field of the acceleration cavity, and then enter the uniform magnetic field, where they move in a circular motion under the action of the Lorentz force. The charged particles can repeatedly enter the acceleration cavity for acceleration, and finally the charged particles have high energy for medical treatment.

[0022] In order to ensure that the charged particles can be stably accelerated in the acceleration cavity, the direction of the electric field is opposite each time the charged particles pass through the acceleration cavity; and in order to ensure that all charged particles obtain equal energy each time they pass through the acceleration cavity, the electric field needs to be kept stable.

[0023] In an ideal situation, the entire medical cyclotron is in a vacuum state. The acceleration cavity is responsible for accelerating the charged particles, and the magnetic field cavity is responsible for making the charged particles move in a circular motion. Under the action of the magnetic field, the period of the charged particles moving in a circular motion is ; where, m represents the mass of the charged particles, q represents the charge of the charged particles, both of which are related to the type of the particle source generator, and B represents the magnetic field strength in the magnetic field cavity. The calculated period of the charged particles' motion is also the transformation period of the alternating electric field, and thus the operating frequency of the alternating electric field can be determined, and the operating frequency is the reciprocal of the transformation period.

[0024] Therefore, in order to obtain the operating conditions of the alternating electric field in the acceleration cavity of a medical cyclotron, in this solution, an FPGA amplitude-phase control board is used to adopt an analog circuit, and an ADC is used to sample the high-frequency signal to obtain the alternating voltage signal of each transformation period in the acceleration cavity. The sampling frequency of the ADC satisfies the Nyquist sampling theorem, that is, the frequency of the alternating electric field is obtained based on the mass and charge of the particles emitted by the particle source. In this embodiment, the ADC is set to a sampling frequency that is 100 times the calculated charge movement frequency. At the same time, a Hall effect magnetometer is deployed inside the acceleration cavity to obtain the induced magnetic field in the acceleration cavity, and the sampling frequency is the same as that of the alternating voltage signal.

[0025] To solve the problem of overshoot or hysteresis in the acceleration voltage regulation in the acceleration cavity during the amplitude-phase control of the RF field acceleration cavity in the high-frequency low-level system LLRF of a medical cyclotron, in this embodiment, based on the periodic change of the alternating voltage signal in the acceleration cavity, its interference conditions under high and low level fluctuations and mechanical vibrations, as well as the obstruction of the alternating electric field by the change of the electromagnetic interference magnetic field in the acceleration cavity, are analyzed to obtain the control proportional coefficient, and feedback control operation is performed, thereby realizing the regulation of the voltage signal.

[0026] S2. According to the mutation situation of the alternating voltage signal within the transformation period, the alternating voltage signal is divided into a high-level stage, a jump edge stage, and a low-level stage; according to the periodic fluctuation situation of the alternating voltage signal in the high-level stage and the low-level stage, the stability of the level stage is obtained; according to the change rate and the degree of chaos of the change of the alternating voltage signal within the jump edge stage, the jump overshoot disorder value is obtained; the regulation intervention degree of the transformation period is obtained by fusing the stability of the level stage and the jump overshoot disorder value.

[0027] Ideally, when the alternating electric field can stably accelerate charged particles, on the one hand, it is necessary to ensure the stability of the acceleration stage, that is, the stability at high or low levels, and on the other hand, in order to improve the focusing beam current effect on the overall particle beam, that is, to quickly converge when jumping between high and low levels. Therefore, the waveform diagram of the alternating electric field is a rectangular wave signal that alternates positively and negatively with a period of T. However, during the actual operation process, affected by the internal mechanical vibration of the medical cyclotron and the electromagnetic interference in the acceleration cavity, in the feedback control process, the voltage in the acceleration cavity has overshoot and oscillation phenomena, affecting the final acceleration and focusing beam current effect of the particles. Therefore, in this embodiment, the influence of the internal mechanical vibration of the medical cyclotron and the electromagnetic interference in the acceleration cavity on the particles is represented by analyzing the fluctuation change of the alternating voltage within the period.

[0028] First, perform inflection point detection on the alternating voltage signal within each transformation period to obtain each inflection point. Based on the inflection point detection algorithm, the two turning points of the high and low level conversion are obtained. Thus, the voltage window sequence is divided into three segments. The alternating voltage signal before and including the first inflection point is the high level stage; the alternating voltage signal between the first inflection point and the last inflection point is the transition edge stage; the alternating voltage signal after and including the last inflection point is the low level stage.

[0029] Since the particle source generator generates not just one particle but a beam of particle flow, in the acceleration cavity, it is necessary to accelerate all the particles within the entire beam of particle flow. It is required that during the transformation period, the high and low levels need to be maintained continuously and stably. However, in the actual process, when maintaining the high level or low level of the acceleration cavity, affected by circuit noise, the high and low levels output by the device may show a certain degree of random fluctuation. At the same time, when the device is operating, mechanical vibrations may occur in the medical cyclotron, resulting in data fluctuations when the sensor collects voltage data. The data fluctuations caused by mechanical vibrations are due to sensor interference and are not real voltage fluctuations.

[0030] The real voltage data fluctuations caused by electrical noise are often randomly distributed; while the data fluctuations caused by mechanical vibrations often have a certain periodicity. Therefore, in this embodiment, the periodic fluctuations of the alternating voltage signal in the high and low level stages are further analyzed to determine the degree of influence of mechanical vibrations.

[0031] Specifically, for the current period, the calculation formula for the stability of the level stage of the current period is: In the formula, A represents the stability of the level stage of the current period, 、 respectively represent the autocorrelation functions based on the high level stage and the low level stage of the current period, represents the maximum value selected from the value range of the autocorrelation function, 、 respectively represent the standard deviations of the high level stage and the low level stage. It should be noted that if the standard deviation of any one of them is zero, that item is assigned a value of 5.

[0032] Ideally, the data remains basically at one value during the high and low level phases. At this time, the standard deviation of the sequence is zero, and a relatively large value of the stability of the high and low levels can be obtained. If there are large data fluctuations in the current voltage data sequence, the standard deviation of the obtained sequence is relatively large. For the data fluctuations caused by mechanical vibration, which are periodic, the maximum value in the autocorrelation function of the obtained sequence is relatively large, and finally the overall stability of the level phase is on the high side. For the data fluctuations caused by circuit noise, which have a certain degree of randomness, the correlation within the value range of the autocorrelation function of the sequence is weak, and the stability of the level phase obtained is small. The construction of the autocorrelation function of the time series is a well-known technology, and the specific process will not be elaborated here.

[0033] To achieve the complete beam current and focusing of the entire beam of particle flow, it is required that the jump time of the alternating electric field between high and low levels in the acceleration cavity is short enough. However, in the actual acceleration process, the jump does not occur instantaneously. Instead, it slopes down from the high level to reach the low level, and even overshoot oscillations may occur when the regulation is not good, resulting in large oscillations in the data at the jump endpoints. Therefore, in order to measure the oscillation situation of the jump edge within the transformation period, for the alternating voltage signal at the jump edge stage of the current transformation period, a linear fit is performed to obtain a fitted straight line. The abscissa of the fitted straight line is time, and the ordinate is the voltage amplitude. In this embodiment, the slope of the fitted straight line represents the change rate of the alternating voltage signal at the jump edge stage; the oscillation change of the alternating voltage signal is represented by analyzing the central symmetry characteristics of the alternating voltage signal at the jump edge stage.

[0034] In this embodiment, according to the central symmetry characteristics of the alternating voltage signal at the jump edge stage, an oscillation characteristic value is obtained. Specifically, all the elements in the alternating voltage signal at the jump edge stage are rearranged in the order from the back to the front in terms of time to obtain a symmetric voltage signal. For example, the first element of the alternating voltage signal is the last element of the symmetric voltage signal. The average difference of the elements at the same positions in the alternating voltage signal at the jump edge stage and the symmetric voltage signal is calculated as the oscillation characteristic value, where the difference is specifically calculated as the absolute value of the difference.

[0035] When the regulation effect of the alternating voltage at the jump is poor, due to the influence of overshoot, after the sequence is rotated, the difference between the corresponding elements is relatively large, that is, the rate of increase or decrease of the voltage is unstable, and an oscillation phenomenon occurs, resulting in a relatively large oscillation characteristic value.

[0036] Furthermore, by comprehensively considering the central symmetry characteristics of the alternating voltage signal at the jump edge stage and the slope of its fitted straight line, the jump overshoot disorder value of the transformation period is obtained. Denote the jump overshoot disorder value of the current transformation period as V, and the calculation formula for the jump overshoot disorder value is: In the formula, It represents the average distance between the data points of all elements in the alternating voltage signal in the edge transition stage mapped on the two-dimensional plane and the fitting line. The average distance is specifically the mean value of the Euclidean distance. It represents the oscillation eigenvalue. It represents the inclination angle of the fitting line, specifically the acute angle between the fitting line and the vertical direction.

[0037] If, within the acceleration cavity of the cyclotron during the transformation period, the regulation of the alternating voltage during the jump is poor, resulting in overshoot during the jump, then there will be more outliers in the sequence, causing a larger distance from the sequence to the fitting line segment. At the same time, due to the influence of overshoot, the oscillation eigenvalue is larger, and due to poor regulation, the conversion between high and low levels is slower, making the included angle between the slope of the fitting line segment and the right angle differ greatly. Eventually, the value of the jump overshoot disorder value is larger. On the contrary, if the regulation is good, at this time, the jump edges of the high and low levels are symmetric and almost perpendicular to the horizontal and vertical directions, resulting in a smaller jump overshoot disorder value.

[0038] Therefore, in order to measure the overall stability and regulation effect of the voltage signal in the acceleration cavity of the cyclotron during the transformation period, based on the stability A of the level stage and the jump overshoot disorder value V, the regulation intervention degree C is obtained. Specifically, the sum of the stability A of the level stage and the jump overshoot disorder value V is used as the regulation intervention degree C of the transformation period.

[0039] If the alternating voltage signal of a single transformation period in the acceleration cavity of the cyclotron shows a large real fluctuation, with untimely jumps and overshoots during the jump, it indicates that the acceleration and focusing beam effects of the acceleration cavity voltage signal in the transformation period on the entire beam of charged particles are poor. At this time, it is necessary to increase the regulation intervention intensity on the voltage signal. Thus, in the current state, the greater the stability of the level stage, the greater the periodicity of the data fluctuations caused by misjudgment during mechanical vibration, and finally the larger the value of the regulation intervention degree, and the regulation intensity needs to be increased.

[0040] S3. According to the stage to which the voltage amplitude at the same moment in the alternating voltage signal in the previous transformation period belongs at the current moment, obtain the adjustment coefficient at the current moment; obtain the magnetic field intensity at each moment; comprehensively consider the change in the magnetic field intensity at the current moment, the adjustment coefficient, and the regulation intervention degree of the previous transformation period before the current moment to obtain the control proportional coefficient at the current moment.

[0041] Generally speaking, the mass of the charged particles generated by the particle source generator in the cyclotron is small, so the period of the alternating voltage in the acceleration cavity is short, while the change in the external environment is a relatively slow process. Therefore, it can be simply assumed that the external environment remains unchanged under two adjacent periods. Thus, the voltage amplitude of the current transformation period can be regulated according to the situation of the alternating voltage in the acceleration cavity in the previous transformation period.

[0042] It should be noted that when regulating the voltage signal, the degree of regulation is different at different stages of the voltage. For example, at high and low levels, fine-tuning is required to ensure the stability of the voltage, while at the edge transition stage, the voltage needs to change rapidly and converge quickly. Therefore, when the present embodiment performs real-time regulation on the voltage amplitude, it is necessary to continue the voltage stage of the previous conversion period, and determine the degree of regulation at the current moment according to the stage to which the voltage amplitude at each moment in the alternating voltage signal in the previous conversion period belongs. In the present embodiment, taking the first preset value as 0.4 and the second preset value as 2 as a specific example, the construction method of the adjustment coefficient at the current moment is as follows: Wherein, is the adjustment coefficient at the current moment i; represents the voltage amplitude at the same moment in the alternating voltage signal in the previous conversion period at the current moment; for example, the alternating voltage signal between the 60th to 77th sampling moments in the previous conversion period is the edge transition stage. If the arrangement serial number of the current sampling moment in the current conversion period is between the 60th to 77th sampling moments, it is determined that the current moment is in the edge transition stage, and the adjustment coefficient is 2. Otherwise, it belongs to the high level stage or the low level stage, and the adjustment coefficient is 0.4.

[0043] For the high and low level stages, the purpose is to maintain the stability of the level, so a smaller adjustment coefficient is set. For the edge transition stage, the purpose is to quickly transform and converge the high and low frequencies, so a larger adjustment coefficient is required. It should be noted that when the cyclotron starts to work for the first time, the generation of the alternating electric field requires the process of the crystal oscillator starting to oscillate. Therefore, the data of the first 5 conversion periods are not analyzed.

[0044] Ideally, there is no magnetic field in the acceleration cavity of the cyclotron. However, due to the overflow of the alternating electric field or the magnetic field in the cavity, there is electromagnetic interference in the acceleration cavity. The action of the interfering magnetic field hinders the change of the electric field. Therefore, it is necessary to further regulate the voltage of the alternating electric field according to the situation of the electromagnetic interference.

[0045] According to Faraday's law of electromagnetic induction, the situation of the magnetic field hindering the electric field mainly depends on the change of the magnetic flux. Here, it is simplified to the change of the magnetic field. If the change degree of the magnetic field intensity in the acceleration cavity between two adjacent sampling moments is greater, the degree of hindrance of the induced electric field to the transformation of the alternating electric field is greater.

[0046] Based on the above analysis, according to the magnetic field intensity difference between the current moment and the previous moment, calculate the variable magnetic interference degree: In the formula, represents the variable magnetic interference degree at the i-th sampling moment, and respectively represent the magnetic field intensities at the \(i\)-th moment and the \((i - 1)\)-th moment.

[0047] If the change amount of the magnetic field intensity between two adjacent sampling moments is larger, the induced electric field generated has a stronger hindering effect on the electric field in the acceleration cavity, so that the value of the magnetic field change interference degree is larger. On the contrary, if the change amount of the magnetic field intensity between adjacent relevant sampling moments is smaller, the hindering effect on the alternating electric field is smaller, and thus the value of the magnetic field change interference degree is smaller.

[0048] When regulating the voltage signal, the regulation degree is different in different stages of the voltage. For example, at high and low levels, fine-tuning is required to ensure the stability of the voltage, while at the edge transition stage, the voltage needs to change rapidly and converge quickly. Therefore, based on the different stages of the voltage signal at the current sampling moment, the control proportional coefficient at the current sampling moment is obtained: represents the control proportional coefficient at the current moment \(i\), represents the initial proportional coefficient, which is set to 10 in this embodiment, and norm() is a linear normalization function, represents the regulation intervention degree in the previous transformation period before the current moment, represents the magnetic field change interference degree at the \(i\)-th sampling moment; is the adjustment coefficient at the current moment \(i\).

[0049] For the regulation intervention degree value in the previous transformation period being larger and the external environment changing relatively slowly, a larger intervention degree is required for the current sampling moment; at the same time, the larger the value of the magnetic field change interference degree, the stronger the hindering effect of electromagnetic interference on the alternating electric field. At this time, the intervention strength on the voltage should be greater, and the overall normalized value obtained is larger, thereby realizing the amplification of the initial proportional coefficient and improving the control strength of the voltage signal. On the contrary, if the voltage signal remains relatively stable as a whole and the magnetic field remains basically unchanged, the normalized value at this time is smaller, realizing the reduction of the initial proportional coefficient and reducing the regulation of the voltage signal.

[0050] S4. Perform feedback control on the alternating voltage signal according to the control proportional coefficient at the current moment.

[0051] The control proportional coefficient at the current moment obtained through the above steps analyzes the working stage of the cyclotron and the influence of magnetic field changes on voltage stability at the current moment, and represents the degree of voltage control required at the current moment. In this embodiment, a PID controller is used to achieve real-time voltage control by controlling the control amount of the voltage regulating device. Specifically, the voltage amplitude at the current moment and the preset target voltage value are used as the inputs of the PID controller. In the PID operation, the proportional coefficient is set to the control proportional coefficient at the current moment, while the integral coefficient and the differential coefficient are set to 0.8 and 0.3 respectively. A control signal is obtained through the PID operation to control the voltage regulating device, and thus the voltage control of the alternating electric field in the acceleration cavity of the cyclotron is achieved through the method of voltage compensation.

[0052] In this solution, the main control is the proportional coefficient. The proportional coefficient determines the response intensity in the control process, which is more conducive to maintaining the stability of the control and ensuring rapid convergence during the high and low level conversion.

[0053] Based on the same inventive concept as the above method, an embodiment of the present application also provides a device for controlling the acceleration voltage of a medical cyclotron, including a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, it implements the steps of any one of the above methods for controlling the acceleration voltage of a medical cyclotron.

[0054] Through the above description of the embodiments in conjunction with the drawings, those skilled in the art can understand that for the convenience and simplicity of description, only the above division of each functional module is used as an example. In practical applications, the above functions can be allocated to different functional modules according to needs, that is, the internal structure of the device is divided into different functional modules to complete all or part of the functions described above.

[0055] The above content is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present application, and all should be covered by the protection scope of the present application.

Claims

1. A method for controlling the accelerating voltage of a medical cyclotron, characterized in that The method comprises the following steps: S1. Obtain the alternating voltage signals of each transformation period during the operation of the medical cyclotron; S2. According to the mutation situation of the alternating voltage signal within the transformation period, divide the alternating voltage signal into a high-level stage, a jump edge stage, and a low-level stage; according to the periodic fluctuation situation of the alternating voltage signals in the high-level stage and the low-level stage, obtain the stability of the level stage; according to the change rate and the degree of chaos of the change of the alternating voltage signal within the jump edge stage, obtain the jump overshoot disorder value; fuse the stability of the level stage and the jump overshoot disorder value to obtain the regulation intervention degree of the transformation period; S3. According to the stage to which the voltage amplitude at the same moment in the alternating voltage signal in the previous transformation period belongs at the current moment, obtain the adjustment coefficient at the current moment; obtain the magnetic field intensity at each moment; comprehensively consider the change of the magnetic field intensity at the current moment, the adjustment coefficient, and the regulation intervention degree of the previous transformation period before the current moment to obtain the control proportional coefficient at the current moment; S4. Perform feedback control on the alternating voltage signal according to the control proportional coefficient at the current moment.

2. The method for controlling the accelerating voltage of a medical cyclotron as described in claim 1, wherein, The step of dividing the alternating voltage signal into a high-level stage, a jump edge stage, and a low-level stage according to the mutation situation of the alternating voltage signal within the transformation period includes: Perform inflection point detection on the alternating voltage signal in each transformation period to obtain each inflection point; record the alternating voltage signal before the first inflection point and the first inflection point as the high-level stage; record the alternating voltage signal between the first inflection point and the last inflection point as the jump edge stage; record the alternating voltage signal after the last inflection point and the last inflection point as the low-level stage.

3. A method for controlling the accelerating voltage of a medical cyclotron as described in claim 1, characterized in that, The method for obtaining the level stage stability includes: recording the level stage stability of the current cycle as A; ; In the formula, , respectively represent the autocorrelation functions based on the high level stage and the low level stage of the current cycle, represents selecting the maximum value of the autocorrelation function within the value range, , respectively represent the standard deviations of the high level stage and the low level stage.

4. A method for controlling the accelerating voltage of a medical cyclotron according to claim 1, characterized in that, The method for obtaining the jump overshoot disorder value includes: Perform linear fitting on the alternating voltage signal in the jump edge stage to obtain a fitting line; take the acute angle between the fitting line and the vertical direction as the inclination angle of the fitting line; wherein, the abscissa of the two-dimensional plane where the fitting line exists is time, and the ordinate is the voltage amplitude; According to the central symmetry feature of the alternating voltage signal in the jump edge stage, obtain the oscillation feature value; obtain the average distance between all the data points of the elements in the alternating voltage signal in the jump edge stage mapped on the two-dimensional plane and the fitting line; calculate the sum value of the oscillation feature value and the average distance; Take the product of the angle value of the inclination angle of the fitting line and the sum value as the jump overshoot disorder value.

5. The acceleration voltage control method of a medical cyclotron according to claim 4, characterized in that The method for obtaining the oscillation feature value includes: Rearrange all the elements in the alternating voltage signal in the jump edge stage in the order from the back to the front in terms of time to obtain a symmetric voltage signal; calculate the average difference of the elements at the same positions in the alternating voltage signal in the jump edge stage and the symmetric voltage signal as the oscillation feature value.

6. The method for controlling the accelerating voltage of a medical cyclotron according to claim 1, wherein The method for obtaining the regulation intervention degree of the transformation period includes: taking the sum of the stability of the level stage and the jump overshoot disorder value as the regulation intervention degree of the transformation period.

7. The method for controlling the accelerating voltage of a medical cyclotron according to claim 1, characterized in that The method for obtaining the adjustment coefficient at the current moment includes: Denote the voltage amplitude at the same moment in the alternating voltage signal in the previous transformation period at the current moment as ; if belongs to the high-level stage or the low-level stage, the adjustment coefficient at the current moment is the first preset value; if belongs to the edge transition stage, the adjustment coefficient at the current moment is the second preset value; where the first preset value is less than the second preset value.

8. The acceleration voltage control method of a medical cyclotron according to claim 1, wherein, The method for obtaining the control proportional coefficient at the current moment includes: Take the difference between the magnetic field intensity at the current moment and the magnetic field intensity at the previous moment as the variable magnetic interference degree at the current moment; Denote the control proportionality coefficient at the current moment \(i\) as , ; where is the preset initial proportionality coefficient; norm() is the linear normalization function; represents the regulation intervention degree in the previous transformation period before the current moment; represents the variable magnetic interference degree at the current moment \(i\); is the adjustment coefficient at the current moment \(i\).

9. The method for controlling the accelerating voltage of a medical cyclotron according to claim 1, wherein, The specific implementation of performing feedback control on the alternating voltage signal according to the control proportional coefficient at the current moment includes: According to the difference between the voltage amplitude at the current moment and the preset target voltage value, a control signal is calculated using a PID controller to control the voltage regulating device; wherein, the control proportional coefficient at the current moment is used as the proportional coefficient in the PID controller.

10. A device for controlling the accelerating voltage of a medical cyclotron, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method for controlling the accelerating voltage of a medical cyclotron according to any one of claims 1-9.

Images