A medical cyclotron accelerating voltage control method and device

Abstract

The present application relates to the technical field of cyclotron voltage control, and specifically to a method and device for controlling the accelerating voltage of a medical cyclotron. The method comprises: dividing the alternating voltage signal into three stages according to the sudden change of the alternating voltage signal within a conversion cycle; analyzing the periodic fluctuations of the high-level stage and the low-level stage, the rate of change of the transition edge stage, and the degree of disorder of the change, to obtain the control intervention degree of the conversion cycle; obtaining an adjustment coefficient according to the stage to which the voltage amplitude at the same moment in the alternating voltage signal at the current moment in the previous conversion cycle belongs; and obtaining a control proportional coefficient at the current moment by combining the change in magnetic field intensity at the current moment, the adjustment coefficient, and the control intervention degree of the previous conversion cycle at the current moment, and performing feedback control on the alternating voltage signal. The present application can improve the control accuracy of the accelerating voltage of a medical cyclotron.

Description

Technical Field

[0001] The present application relates to the technical field of cyclotron voltage control, and in particular to a method and device for controlling the acceleration voltage of a medical cyclotron. Background Art

[0002] A medical cyclotron is a particle accelerator primarily used to produce positron-emitting radionuclides for applications such as PET / CT imaging and radiotherapy. The cyclotron's primary operating principle utilizes a magnetic field and an alternating electric field to induce a cyclotron motion in the magnetic field, where charged particles are repeatedly accelerated to achieve the desired particle energy.

[0003] In typical medical cyclotron accelerators, an LLRF (Low-Level Radio Frequency) system is used to control the operating state of the high-frequency radio frequency (RF) system, ensuring stable particle beam acceleration. Control of the RF field within the accelerating cavity (Dee) is primarily achieved through the voltage amplitude and phase of the alternating electric field. This is typically achieved through DSP digital signals obtained through ADC sampling on an amplitude and phase control board. Feedback control is then used to control the voltage and phase of the RF field. This control strategy often uses a fixed proportional coefficient, resulting in overshoot or lag in the regulation of the accelerating voltage within the accelerating cavity under different scenarios, resulting in poor control accuracy. 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. The technical solutions adopted are as follows:

[0005] In a first aspect, an embodiment of the present application provides a method for controlling the accelerating voltage of a medical cyclotron, the method comprising the following steps:

[0006] S1, obtaining the alternating voltage signal of each conversion cycle during the operation of the medical cyclotron;

[0007] S2, based on the sudden changes of the alternating voltage signal during the conversion cycle, divide the alternating voltage signal into a high-level stage, a transition edge stage, and a low-level stage; obtain the level stage stability based on the periodic fluctuations of the alternating voltage signal during the high-level stage and the low-level stage; obtain the transition overshoot disorder value based on the rate of change of the alternating voltage signal during the transition edge stage and the degree of disorder of the change; and obtain the control intervention degree of the conversion cycle by integrating the level stage stability and the transition overshoot disorder value;

[0008] S3, obtaining an adjustment coefficient at the current moment based on the stage to which the voltage amplitude at the same moment in the alternating voltage signal in the previous conversion cycle belongs; obtaining the magnetic field strength at each moment; and obtaining a control proportional coefficient at the current moment by combining the change in magnetic field strength at the current moment, the adjustment coefficient, and the control intervention degree in the previous conversion cycle at the current moment;

[0009] S4, performing feedback control on the alternating voltage signal according to the control proportional coefficient at the current moment.

[0010] Furthermore, the alternating voltage signal is divided into a high level phase, a transition edge phase and a low level phase according to the mutation of the alternating voltage signal within the conversion period, including:

[0011] The alternating voltage signal in each conversion cycle is subjected to inflection point detection to obtain each inflection point; the alternating voltage signal of the first inflection point and before it is recorded as a high-level stage; the alternating voltage signal between the first inflection point and the last inflection point is recorded as a jump edge stage; the alternating voltage signal of the last inflection point and after it is recorded as a low-level stage.

[0012] Furthermore, the method for obtaining the level phase stability includes: recording the level phase stability of the current cycle as A; Where, 、 Respectively represent the autocorrelation functions based on the high level phase and low level phase of the current cycle, Indicates selecting the maximum value of the autocorrelation function in the value range, 、 Represent the standard deviation of the high level stage and the low level stage respectively.

[0013] Furthermore, the method for obtaining the jump overshoot disorder value includes:

[0014] Perform linear fitting on the alternating voltage signal during the transition phase to obtain a fitted straight line; the acute angle between the fitted straight line and the vertical direction is taken as the inclination of the fitted straight line; wherein the horizontal coordinate of the two-dimensional plane where the fitted straight line exists is time, and the vertical coordinate is voltage amplitude;

[0015] Obtaining an oscillation characteristic value based on the central symmetry feature of the alternating voltage signal in the transition edge phase; obtaining an average distance between data points of all elements in the alternating voltage signal in the transition edge phase mapped on a two-dimensional plane and a fitting straight line; and calculating a sum of the oscillation characteristic value and the average distance;

[0016] The product of the angle value of the fitting straight line inclination and the sum value is used as the jump overshoot disorder value.

[0017] Furthermore, the method for obtaining the oscillation characteristic value includes:

[0018] All elements in the alternating voltage signal during the transition phase are rearranged in time from back to front to obtain a symmetrical voltage signal. The mean difference between all elements at the same position in the alternating voltage signal during the transition phase and the symmetrical voltage signal is calculated as the oscillation characteristic value.

[0019] Furthermore, the method for obtaining the control intervention degree of the conversion cycle includes: taking the sum of the level stage stability and the jump overshoot disorder value as the control intervention degree of the conversion cycle.

[0020] Furthermore, the method for obtaining the adjustment coefficient at the current moment includes:

[0021] The voltage amplitude of the alternating voltage signal at the same moment in the previous conversion cycle is recorded as ;like belongs to the high level stage or the low level stage, the adjustment coefficient at the current moment is the first preset value; if If it is in the transition edge stage, the adjustment coefficient at the current moment is the second preset value; wherein the first preset value is smaller than the second preset value.

[0022] Furthermore, the method for obtaining the control proportional coefficient at the current moment includes:

[0023] The difference in magnetic field intensity between the current moment and the previous moment is taken as the variable magnetic interference degree at the current moment;

[0024] The control proportional coefficient at the current moment i is recorded as , ;in, is the preset initial scale factor; norm() is the linear normalization function; Indicates the control intervention degree of the transformation cycle before the current moment; Indicates the variable magnetic interference degree at the current moment i; is the adjustment coefficient at the current moment i.

[0025] Furthermore, the feedback control of the alternating voltage signal according to the control proportional coefficient at the current moment specifically includes:

[0026] 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.

[0027] In a second aspect, an embodiment of the present application also provides a medical cyclotron acceleration voltage control device, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, wherein when the processor executes the computer program, the steps of any one of the above-mentioned medical cyclotron acceleration voltage control methods are implemented.

[0028] This application has at least the following beneficial effects:

[0029] The present application analyzes the influence of internal mechanical vibration and electromagnetic interference of the accelerating cavity on the stability control of the acceleration of charged particles in the accelerating cavity of a medical cyclotron accelerator; firstly, the voltage variation characteristics of the alternating electric field of the accelerating cavity caused by mechanical vibration at different stages are analyzed, and the control intervention degree is mainly obtained based on the voltage fluctuation and mechanical vibration in the high and low level stages, as well as the convergence and overshoot of the voltage along the jump edge, which reflects the fluctuation of the voltage signal due to the interference of the circuit noise, and further more accurately evaluates the degree of control intervention required for the voltage signal; further analysis is made of the electromagnetic interference on the conversion and stability of the alternating electric field of the accelerating cavity during the conversion of the alternating electric field, and based on the change of the magnetic field strength, the variable magnetic interference degree is obtained, which reflects the obstruction of the magnetic field to the alternating electric field; comprehensively considering the influence of mechanical vibration and electromagnetic interference, by quantifying the relationship between the interference degree and the voltage control strength, the control proportional coefficient is finally obtained, and the feedback control algorithm is used to realize the control of the accelerating voltage of the accelerating cavity. Compared with setting a fixed proportional coefficient in the traditional control process, this solution mainly analyzes the fluctuation of sensor data collected by the mechanical vibration of the medical cyclotron and the obstructive effect of electromagnetic interference during equipment operation, and adjusts the proportional coefficient in real time. It can achieve precise control of the alternating electric field voltage, avoid control lag or overshoot oscillation, and improve the control accuracy of the medical cyclotron acceleration voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions and advantages of the embodiments of the present application or the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0031] Figure 1 A flowchart of a method for controlling the accelerating voltage of a medical cyclotron provided in one embodiment of the present application;

[0032] Figure 2 A schematic diagram of the structural entity of a cyclotron provided in one embodiment of the present application. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. In the absence of conflict, the embodiments of this application and the technical features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0034] Unless defined otherwise, 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.

[0035] The following describes in detail a medical cyclotron acceleration voltage control method and device provided by the present application with reference to the accompanying drawings.

[0036] See also Figure 1 , which shows a flowchart of a method for controlling the accelerating voltage of a medical cyclotron provided by one embodiment of the present application, the method comprising the following steps:

[0037] S1, obtaining the alternating voltage signal of each conversion cycle during the operation of the medical cyclotron.

[0038] A specific implementation scenario of the present application is the acceleration voltage control scenario of a cyclotron; the structural entity of the cyclotron is as follows: Figure 2 As shown, Figure 2 In the figure, 1 represents the particle source generator, 2 represents the alternating electric field of the accelerating chamber, 3 represents the high-frequency radio frequency accelerating chamber, 4 represents the single magnetic field chamber, and 5 represents the particle outflow port and particle emission direction. The principle of a cyclotron accelerator is as follows: a particle source generator generates a beam of charged particles. These particles are accelerated by the Coulomb force in the accelerating chamber's alternating electric field. From there, they enter a uniform magnetic field and, under the influence of the Lorentz force, move in a circular motion. This allows the charged particles to repeatedly enter the accelerating chamber for acceleration, ultimately achieving high energies for medical treatment.

[0039] In order to ensure that charged particles can be stably accelerated in the accelerating cavity, the direction of the electric field is opposite each time the charged particles pass through the accelerating cavity; and in order to ensure that the energy obtained by all charged particles through the accelerating cavity each time is equal, the electric field needs to remain stable.

[0040] Under ideal conditions, the entire medical cyclotron is in a vacuum state. The accelerating cavity is responsible for accelerating the charged particles, while the magnetic field cavity is responsible for causing the charged particles to perform cyclotron circular motion. Under the action of the magnetic field, the period of the charged particles' circular motion is Where m represents the mass of the charged particle, q represents the charge of the particle, both of which depend on the type of particle source generator, and B represents the magnetic field strength within the magnetic field chamber. The calculated period of motion of the charged particle is the switching period of the alternating electric field, from which the operating frequency of the alternating electric field can be determined. The operating frequency is the inverse of the switching period.

[0041] To obtain the operating status of the alternating electric field in the accelerating cavity of a medical cyclotron accelerator, this solution utilizes an FPGA amplitude and phase control board with analog circuitry, using an ADC to sample the high-frequency signal, generating an alternating voltage signal for each conversion cycle within the accelerating cavity. The ADC sampling frequency satisfies the Nyquist sampling theorem, which determines the frequency of the alternating electric field based on the mass and charge of the particles emitted by the particle source. In this embodiment, the ADC sampling frequency is set to 100 times the calculated charge motion frequency. A Hall-effect magnetometer is also deployed within the accelerating cavity to obtain the induced magnetic field within the accelerating cavity, with the sampling frequency being consistent with that of the alternating voltage signal.

[0042] To address the problem of overshoot or lag in the acceleration voltage control within the accelerating cavity caused by the use of a fixed proportional coefficient set by PID calculation during amplitude and phase control of the RF field accelerating cavity in the LLRF system of a medical cyclotron, this embodiment analyzes the periodic variation of the alternating voltage signal within the accelerating cavity, the interference from high and low level fluctuations and mechanical vibration, and the obstruction of the alternating electric field caused by the electromagnetic interference magnetic field changes within the accelerating cavity. The control proportional coefficient is then derived and feedback control calculations are performed to achieve regulation of the voltage signal.

[0043] S2, according to the sudden change of the alternating voltage signal in the conversion cycle, 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 of the alternating voltage signal in the high-level stage and the low-level stage, the level stage stability is obtained; according to the change rate of the alternating voltage signal in the jump edge stage and the degree of chaos of its change, the jump overshoot disorder value is obtained; the control intervention degree of the conversion cycle is obtained by integrating the level stage stability and the jump overshoot disorder value.

[0044] Ideally, when an alternating electric field is able to stably accelerate charged particles, on the one hand, it is necessary to ensure stability during the acceleration phase, that is, stability at high or low levels. On the other hand, in order to improve the overall focused beam effect on the particle beam, it is necessary to quickly converge when the high and low levels jump. Therefore, the alternating electric field waveform is a rectangular wave signal with a period of T alternating positive and negative. However, during actual operation, due to the influence of mechanical vibrations inside the medical cyclotron and electromagnetic interference in the acceleration cavity, the voltage in the acceleration cavity overshoots and oscillates during the feedback control process, affecting the final particle acceleration and focused beam effect. Therefore, this embodiment analyzes the fluctuations of the alternating voltage within the period to show that the particles are affected by the mechanical vibrations inside the medical cyclotron and electromagnetic interference in the acceleration cavity.

[0045] First, the inflection point detection is performed on the alternating voltage signal in each conversion cycle to obtain each inflection point; based on the inflection point detection algorithm, two inflection points of high-low level conversion are obtained, thereby dividing the voltage window sequence into three sections: the alternating voltage signal of the first inflection point and before it is a high-level stage; the alternating voltage signal between the first inflection point and the last inflection point is a jump edge stage; the alternating voltage signal of the last inflection point and after it is a low-level stage.

[0046] Because a particle source generator produces not just one particle but a stream of particles, all particles within the entire stream must be accelerated within the acceleration chamber, requiring the high and low voltage levels to remain stable during the switching cycle. However, in practice, when maintaining the high or low voltage levels in the acceleration chamber, circuit noise can cause a certain degree of random fluctuation in the output voltage. Furthermore, during operation, the medical cyclotron may experience mechanical vibrations, which can cause fluctuations in the voltage data collected by the sensor. These fluctuations are due to sensor interference, not actual voltage fluctuations.

[0047] The real voltage data fluctuations caused by electrical noise are often randomly distributed, while the data fluctuations caused by mechanical vibration often have a certain periodicity. Therefore, this embodiment further analyzes the periodic fluctuations of the alternating voltage signal in the high and low level stages to determine the degree of influence of mechanical vibration.

[0048] Specifically, for the current cycle, the calculation formula for the level stage stability of the current cycle is:

[0049]

[0050] Where A represents the level stability of the current cycle, 、 Respectively represent the autocorrelation functions based on the high level phase and low level phase of the current cycle, Indicates selecting the maximum value of the autocorrelation function in the value range, 、 Represent the standard deviation of the high level phase and the low level phase respectively. It should be noted that if the standard deviation of any of the items is zero, the item is assigned a value of 5.

[0051] Ideally, the data is essentially maintained at one value during the high and low level stages, and the standard deviation of the sequence is zero. This results in a higher stability value for both the high and low levels. If there are large data fluctuations in the current voltage data sequence, the standard deviation of the sequence obtained at this time is larger. However, due to the periodicity of the misjudged data fluctuations caused by mechanical vibration, the maximum value of the autocorrelation function of the sequence is larger, resulting in a higher overall stability value for the level stage. However, due to the randomness of the data fluctuations caused by circuit noise, the correlation of the sequence autocorrelation function within the range of values ​​is weaker, resulting in a lower stability value for the level stage. The construction of the autocorrelation function of a time series is a well-known technique, and the specific process will not be described in detail.

[0052] In order to achieve a complete beam and focus for the entire particle flow, the jump time of the high and low levels of the alternating electric field in the accelerating cavity is required to be short enough. However, in the actual acceleration process, the jump is not completed instantly, but it slopes down from a high level to a low level. Even when the control is not good, overshoot oscillation will occur, causing the data to have a large oscillation at the endpoint of the jump. Therefore, in order to measure the oscillation of the jump edge within the transformation cycle, a linear fit is performed on the alternating voltage signal in the jump edge stage of the current transformation cycle to obtain a fitting straight line, the horizontal coordinate of the fitting straight line is time, and the vertical coordinate is voltage amplitude. This embodiment represents the rate of change of the alternating voltage signal in the jump edge stage by the degree of inclination of the fitting straight line; and represents the oscillation change of the alternating voltage signal by analyzing the central symmetry feature of the alternating voltage signal in the jump edge stage.

[0053] In this embodiment, an oscillation characteristic value is obtained based on the central symmetry characteristics of the alternating voltage signal during the transition phase. Specifically, all elements in the alternating voltage signal during the transition phase are rearranged in chronological order to obtain a symmetrical voltage signal. For example, the first element of the alternating voltage signal is the last element of the symmetrical voltage signal. The mean difference between the alternating voltage signal during the transition phase and all elements in the symmetrical voltage signal at the same position is calculated as the oscillation characteristic value, where the difference is specifically the absolute value of the calculated difference.

[0054] When the alternating voltage has a poor jump control effect, due to the influence of overshoot, the difference between the corresponding elements after the sequence rotation is large, that is, the rate of voltage rise or fall is unstable, and an oscillation phenomenon occurs, resulting in a large oscillation characteristic value.

[0055] The central symmetry characteristics of the alternating voltage signal during the transition phase and the inclination of the fitted straight line are further combined to obtain the transition overshoot disorder value of the conversion cycle. The transition overshoot disorder value of the current conversion cycle is recorded as V, and the calculation formula of the transition overshoot disorder value is:

[0056]

[0057] Where, The average distance between the data points of all elements in the alternating voltage signal at the transition edge stage mapped on the two-dimensional plane and the fitted straight line is specifically the mean of the Euclidean distance. represents the oscillation eigenvalue; Indicates the inclination of the fitted line, specifically the acute angle between the fitted line and the vertical direction.

[0058] If the alternating voltage in the cyclotron accelerating chamber is poorly regulated during the transition, resulting in overshoot, the sequence will contain more outliers, increasing the distance between the sequence and the fitting line segment. Furthermore, due to the overshoot, the oscillation characteristic value is larger. Furthermore, due to poor regulation, the transition between high and low levels is slow, causing the slope angle of the fitting line segment to deviate significantly from a right angle, ultimately resulting in a larger transition overshoot disorder value. Conversely, if the regulation is good, the transition edges of the high and low levels are symmetrical and almost perpendicular to the horizontal and vertical directions, resulting in a smaller transition overshoot disorder value.

[0059] To measure the overall stability and control effect of the voltage signal within the cyclotron accelerating cavity during a conversion cycle, the control intervention degree C is calculated based on the level phase stability A and the jump overshoot disturbance value V. Specifically, the sum of the level phase stability A and the jump overshoot disturbance value V is used as the control intervention degree C for the conversion cycle.

[0060] If the alternating voltage signal within the cyclotron's accelerating cavity exhibits significant fluctuations within a single conversion cycle, with delayed transitions and overshoot, this indicates that the accelerating cavity voltage signal within that conversion cycle is poorly accelerating and focusing the entire particle beam. In this case, increased control intervention of the voltage signal is necessary. Therefore, under the current state, the greater the level stage stability, the greater the periodicity of the data fluctuations caused by mechanical vibration, resulting in a greater control intervention value, necessitating increased control intensity.

[0061] S3, according to the stage to which the voltage amplitude at the same moment in the alternating voltage signal in the previous conversion cycle belongs at the current moment, obtain the adjustment coefficient at the current moment; obtain the magnetic field strength at each moment; and obtain the control proportional coefficient at the current moment by combining the change in magnetic field strength at the current moment, the adjustment coefficient and the control intervention degree of the previous conversion cycle at the current moment.

[0062] Generally speaking, the mass of the charged particles produced by the particle source generator in the cyclotron accelerator is relatively small, so the cycle of the alternating voltage in the accelerating cavity is relatively short, while the change of the external environment is a relatively slow process. Therefore, it can be simply assumed that the external environment is unchanged in two adjacent cycles. Therefore, the voltage amplitude of the current conversion cycle can be controlled according to the alternating voltage situation in the accelerating cavity in the previous conversion cycle.

[0063] 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 transition edge stage, the voltage needs to change rapidly and converge quickly. Therefore, when the voltage amplitude is regulated in real time in this embodiment, it is necessary to continue the voltage stage of the previous conversion cycle, and determine the degree of regulation at the current moment based on the stage to which the voltage amplitude at each moment in the alternating voltage signal in the previous conversion cycle belongs. In this embodiment, a specific example is given with the first preset value of 0.4 and the second preset value of 2. The method for constructing the adjustment coefficient at the current moment is:

[0064]

[0065] in, is the adjustment coefficient at the current moment i; It represents the voltage amplitude at the same moment in the alternating voltage signal in the previous conversion cycle. For example, the alternating voltage signal between the 60th and 77th sampling moments in the previous conversion cycle is in the transition edge stage. If the current sampling moment is numbered between the 60th and 77th sampling moments in the current conversion cycle, then the current moment is considered to be in the transition edge 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.

[0066] The goal of the high and low level phases is to maintain level stability, so a smaller adjustment coefficient is set. The goal of the transition phase is to achieve rapid transition and convergence between high and low frequency conversion, so a larger adjustment coefficient is required. It should be noted that when the cyclotron initially operates, the generation of the alternating electric field requires a crystal oscillator startup process, so the data from the first five conversion cycles is not analyzed.

[0067] Ideally, there is no magnetic field in the accelerating cavity of the cyclotron. However, due to the overflow of the alternating electric field or the magnetic field in the cavity, electromagnetic interference exists in the accelerating cavity. The interfering magnetic field hinders the change of the electric field. Therefore, the voltage of the alternating electric field needs to be further regulated according to the electromagnetic interference situation.

[0068] According to Faraday's law of electromagnetic induction, the obstruction of the magnetic field to the electric field mainly depends on the change of the magnetic flux. Here it is simplified to the change of the magnetic field. The greater the change in the magnetic field strength in the acceleration cavity between two adjacent sampling moments, the greater the obstruction of the induced electric field to the conversion of the alternating electric field.

[0069] Based on the above analysis, the variable magnetic interference degree is calculated according to the difference in magnetic field strength between the current moment and the previous moment:

[0070]

[0071] Where, represents the variable magnetic interference degree at the i-th sampling moment, and represent the magnetic field strength at the i-th moment and the i-1-th moment respectively.

[0072] The greater the change in magnetic field strength between two adjacent sampling moments, the greater the effect of the induced electric field on the electric field within the accelerating cavity, resulting in a larger value for the variable magnetic interference. Conversely, the smaller the change in magnetic field strength between two adjacent sampling moments, the smaller the effect on the alternating electric field, resulting in a smaller value for the variable magnetic interference.

[0073] When regulating a voltage signal, the degree of regulation varies at different voltage stages. For example, at high and low levels, fine-tuning is required to ensure voltage stability, while at the transition phase, the voltage needs to change rapidly and converge quickly. Therefore, based on the different phases of the voltage signal at the current sampling moment, the control proportional coefficient at the current sampling moment is obtained:

[0074]

[0075] represents the control proportional coefficient at the current moment i, represents the initial scale factor, which is set to 10 in this embodiment, norm() is a linear normalization function, Indicates the control intervention degree of the previous transformation cycle at the current moment, represents the variable magnetic interference degree at the i-th sampling moment; is the adjustment coefficient at the current moment i.

[0076] The control intervention degree value in the previous conversion cycle is large, and the external environment changes relatively slowly, so a greater degree of intervention is required at the current sampling moment. At the same time, the larger the value of the variable magnetic interference degree, the stronger the electromagnetic interference's obstruction to the alternating electric field. At this time, the intervention force on the voltage should be greater, and the overall normalized value is larger, thereby amplifying the initial proportional coefficient and improving the control force on the voltage signal. Conversely, if the voltage signal remains relatively stable as a whole and the magnetic field remains basically unchanged, the normalized value is smaller, reducing the initial proportional coefficient and reducing the control force on the voltage signal.

[0077] S4, performing feedback control on the alternating voltage signal according to the control proportional coefficient at the current moment.

[0078] The control proportional coefficient at the current moment obtained through the above steps analyzes the impact of the cyclotron's working phase and magnetic field changes on voltage stability at the current moment, indicating the degree to which the voltage at the current moment needs to be controlled. In this embodiment, a PID controller is used to achieve real-time control of the voltage by controlling the control quantity of the voltage regulating device. Specifically, the voltage amplitude at the current moment and the preset target voltage value are used as inputs to the PID controller. In the PID operation, the proportional coefficient is set to the control proportional coefficient at the current moment, and the integral coefficient and differential coefficient are set to 0.8 and 0.3, respectively. The control signal obtained through the PID operation controls the voltage regulating device, thereby achieving voltage control of the alternating electric field in the accelerating cavity of the cyclotron through voltage compensation.

[0079] In this solution, the proportional coefficient is mainly controlled. The proportional coefficient determines the response strength during the control process, is more helpful in maintaining the stability of the control, and ensures rapid convergence during high and low level conversion.

[0080] Based on the same inventive concept as the above method, an embodiment of the present application also provides a medical cyclotron acceleration voltage control device, 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-mentioned medical cyclotron acceleration voltage control methods.

[0081] Through the above description of the implementation method in combination with the accompanying drawings, technical personnel in the relevant field can understand that for the convenience and simplicity of description, only the division of the above-mentioned functional modules is used as an example. In actual applications, the above-mentioned functions can be distributed and completed by different functional modules as needed, that is, the internal structure of the device can be divided into different functional modules to complete all or part of the functions described above.

[0082] The above content is only a specific implementation method of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with this technical field can easily think of changes or replacements within the technical scope disclosed in this application, and they should all 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, obtaining the alternating voltage signal of each conversion cycle during the operation of the medical cyclotron; S2, based on the sudden changes of the alternating voltage signal during the conversion cycle, divide the alternating voltage signal into a high-level stage, a transition edge stage, and a low-level stage; obtain the level stage stability based on the periodic fluctuations of the alternating voltage signal during the high-level stage and the low-level stage; obtain the transition overshoot disorder value based on the rate of change of the alternating voltage signal during the transition edge stage and the degree of disorder of the change; and obtain the control intervention degree of the conversion cycle by integrating the level stage stability and the transition overshoot disorder value; S3, obtaining an adjustment coefficient at the current moment based on the stage to which the voltage amplitude at the same moment in the alternating voltage signal in the previous conversion cycle belongs; obtaining the magnetic field strength at each moment; and obtaining a control proportional coefficient at the current moment by combining the change in magnetic field strength at the current moment, the adjustment coefficient, and the control intervention degree in the previous conversion cycle at the current moment; S4, performing feedback control on the alternating voltage signal according to the control proportional coefficient at the current moment; The method for obtaining the jump overshoot disorder value includes: Perform linear fitting on the alternating voltage signal during the transition phase to obtain a fitted straight line; the acute angle between the fitted straight line and the vertical direction is taken as the inclination of the fitted straight line; wherein the horizontal coordinate of the two-dimensional plane where the fitted straight line exists is time, and the vertical coordinate is voltage amplitude; Obtaining an oscillation characteristic value based on the central symmetry feature of the alternating voltage signal in the transition edge phase; obtaining an average distance between data points of all elements in the alternating voltage signal in the transition edge phase mapped on a two-dimensional plane and a fitting straight line; and calculating a sum of the oscillation characteristic value and the average distance; The product of the angle value of the fitting straight line inclination and the sum value is used as the jump overshoot disorder value; The method for obtaining the oscillation characteristic value includes: All elements in the alternating voltage signal during the transition phase are rearranged in time order to obtain a symmetrical voltage signal; the mean difference between all elements at the same position in the alternating voltage signal during the transition phase and the symmetrical voltage signal is calculated as the oscillation characteristic value; The method for obtaining the control intervention degree of the conversion cycle includes: taking the sum of the level stage stability and the jump overshoot disorder value as the control intervention degree of the conversion cycle.

2. The method for controlling the accelerating voltage of a medical cyclotron according to claim 1, wherein: The method of dividing the alternating voltage signal into a high level phase, a transition edge phase and a low level phase according to the sudden change of the alternating voltage signal within the conversion period includes: The alternating voltage signal in each conversion cycle is subjected to inflection point detection to obtain each inflection point; the alternating voltage signal of the first inflection point and before it is recorded as a high-level stage; the alternating voltage signal between the first inflection point and the last inflection point is recorded as a jump edge stage; the alternating voltage signal of the last inflection point and after it is recorded as a low-level stage.

3. The method for controlling the accelerating voltage of a medical cyclotron according to claim 1, wherein: The method for obtaining the level phase stability includes: recording the level phase stability of the current cycle as A; Where, 、 Respectively represent the autocorrelation functions based on the high level phase and low level phase of the current cycle, Indicates selecting the maximum value of the autocorrelation function in the value range, 、 Represent the standard deviation of the high level stage and the low level stage respectively.

4. The method for controlling the accelerating voltage of a medical cyclotron according to claim 1, wherein: The method for obtaining the adjustment coefficient at the current moment includes: The voltage amplitude of the alternating voltage signal at the same moment in the previous conversion cycle is recorded as ;like belongs to the high level stage or the low level stage, the adjustment coefficient at the current moment is the first preset value; if If it is in the transition edge stage, the adjustment coefficient at the current moment is the second preset value; wherein the first preset value is smaller than the second preset value.

5. The method for controlling the accelerating voltage of a medical cyclotron according to claim 1, wherein: The method for obtaining the control proportional coefficient at the current moment includes: The difference in magnetic field intensity between the current moment and the previous moment is taken as the variable magnetic interference degree at the current moment; The control proportional coefficient at the current moment i is recorded as , ;in, is the preset initial scale factor; norm() is the linear normalization function; Indicates the control intervention degree of the transformation cycle before the current moment; Indicates the variable magnetic interference degree at the current moment i; is the adjustment coefficient at the current moment i.

6. The method for controlling the accelerating voltage of a medical cyclotron according to claim 1, wherein: 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, 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.

7. A medical cyclotron acceleration voltage control device, 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, the steps of the medical cyclotron acceleration voltage control method according to any one of claims 1 to 6 are implemented.

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