A method and system for compensating for isochronous magnetic fields in a medical cyclotron accelerator

Abstract

This application relates to the field of magnetic field compensation technology, specifically to a method and system for isochronous magnetic field compensation in a medical cyclotron accelerator. The method includes: collecting the magnetic field strength at various locations within the magnetic field region of the medical cyclotron accelerator; determining the local magnetic field inhomogeneity at each location; evenly dividing the magnetic pole surface of the magnetic field region into a predetermined number of magnetic pole steps, and determining the compensation property of each magnetic pole step; based on the correlation between the compensation properties of each magnetic pole step, classifying all magnetic pole steps into Class I and Class II magnetic pole steps; determining the compensation complexity of each Class I magnetic pole step; based on the difference in compensation property before and after compensation for Class I magnetic pole steps, combined with the compensation complexity, and the difference in compensation property before and after compensation for Class II magnetic pole steps, determining a fitness function; and using a particle swarm optimization algorithm to obtain the optimal height for magnetic field compensation of each magnetic pole step. This improves the accuracy of isochronous magnetic field compensation in a medical cyclotron accelerator.

Description

Technical Field

[0001] This application relates to the field of magnetic field padding technology, specifically to a method and system for isochronous magnetic field padding in a medical cyclotron accelerator. Background Technology

[0002] A medical cyclotron is a device used to generate high-energy particles, primarily for applications in radiotherapy and medical imaging. It accelerates charged particles (usually protons or ions) to extremely high speeds, causing these particles to collide with a target material and produce radioactive isotopes used for medical diagnosis and treatment.

[0003] In the design and construction of medical cyclotrons, to eliminate magnetic field distortion caused by the non-ideal magnetic properties of ferromagnetic materials, machining and assembly errors, and magnet structural deformation, and to obtain the theoretically designed isochronous magnetic field, accurate padding of the actual magnetic field is required. Traditional padding techniques often focus on a plane or a single dimension, while magnetic fields are typically three-dimensional. How to accurately determine the padding height in a three-dimensional magnetic field is a crucial problem in magnetic field padding. Summary of the Invention

[0004] To address the aforementioned technical problems, the purpose of this application is to provide a method and system for compensating for the isochronous magnetic field of a medical cyclotron accelerator. The specific technical solution adopted is as follows:

[0005] In a first aspect, embodiments of this application provide a method for compensating for the isochronous magnetic field of a medical cyclotron accelerator, the method comprising the following steps:

[0006] The magnetic field strength was collected at various locations within the magnetic field region of the medical cyclotron.

[0007] The difference in magnetic field strength between each location and its radial neighbor is analyzed, and the spatial distance between each location and its radial neighbor is considered to determine the local magnetic field inhomogeneity at each location. A predetermined number of magnetic pole steps are evenly distributed on the magnetic pole surface of the magnetic field region. The difference between the magnetic field strength at each location in the three-dimensional region corresponding to each magnetic pole step and the target magnetic field strength is analyzed. The padding performance of each magnetic pole step is determined based on the local magnetic field inhomogeneity.

[0008] Based on the correlation between the padding properties of each magnetic pole step, all magnetic pole steps are divided into Class I magnetic pole steps and Class II magnetic pole steps. For each Class I magnetic pole step, the distribution of local magnetic field inhomogeneity at all locations in the three-dimensional region corresponding to it in the magnetic field is analyzed, as well as the difference between the local magnetic field inhomogeneity at each location and the axially adjacent location. Combined with the padding properties, the padding complexity of each Class I magnetic pole step is determined.

[0009] Based on the difference in padding properties before and after padding of a type I magnetic pole step, combined with the padding complexity, and the difference in padding properties before and after padding of a type II magnetic pole step, a fitness function is determined, and an intelligent optimization algorithm is used to obtain the optimal height for magnetic field padding of each magnetic pole step.

[0010] In one embodiment, determining the local magnetic field inhomogeneity includes:

[0011] The difference between the axial components of the magnetic field strength at each location and its radial neighbor locations is calculated and denoted as the first difference. The ratio of the first difference to the spatial distance is calculated, and the local magnetic field inhomogeneity is the result of the fusion of the ratios at each location and all its radial neighbor locations.

[0012] In one embodiment, the local magnetic field inhomogeneity is the sum of the ratios at each location to all its radially adjacent locations.

[0013] In one embodiment, the target magnetic field strength is the magnetic field strength at which isochronous magnetic fields need to be maintained at various locations in the magnetic field region.

[0014] In one embodiment, the determination of the padding properties includes:

[0015] The difference between the axial component of the magnetic field strength at each location and its target magnetic field strength is denoted as the second difference. The product of the local magnetic field inhomogeneity at each location and the second difference is calculated. The padding property is the fusion result of the product of all locations in the three-dimensional region corresponding to each magnetic pole step in the magnetic field.

[0016] In one embodiment, classifying all magnetic pole steps into Class I magnetic pole steps and Class II magnetic pole steps includes:

[0017] Clustering algorithms are used to cluster the padding properties of all magnetic pole steps, dividing all magnetic pole steps into two clusters. The mean value of the padding properties of all magnetic pole steps in each cluster is calculated. The magnetic pole steps in the cluster with the maximum mean value are denoted as Class I magnetic pole steps, and the magnetic pole steps in the remaining clusters are denoted as Class II magnetic pole steps.

[0018] In one embodiment, determining the padding complexity includes:

[0019] The difference in local magnetic field inhomogeneity at each location within the three-dimensional region corresponding to each type of magnetic pole step in the magnetic field and its axially adjacent location is calculated and denoted as the third difference. The fusion value of the third difference at all locations within the three-dimensional region corresponding to each type of magnetic pole step in the magnetic field is calculated. The disorder of local magnetic field inhomogeneity at all locations within the three-dimensional region corresponding to each type of magnetic pole step in the magnetic field is calculated. Based on the disorder, the fusion value, and the padding property, the padding complexity of each type of magnetic pole step is determined.

[0020] In one embodiment, the padding complexity is the product of the disorder, the fusion value, and the padding property of each type of magnetic pole step.

[0021] In one embodiment, the fitness function is expressed as:

[0022] In the formula, S represents the fitness function, C1 is the number of first-class magnetic pole steps, and C2 is the number of second-class magnetic pole steps. The padding complexity for the i-th type I magnetic pole step, The padding properties before the i-th type I magnetic pole step padding, The padding performance after padding the i-th type of magnetic pole step is given. The padding properties before padding the j-th type II magnetic pole step. The padding performance after padding the j-th type II magnetic pole step is given. The default value is greater than 0.

[0023] Secondly, embodiments of this application also provide an isochronous magnetic field compensation system for a medical cyclotron accelerator, including a memory, a processor, and a computer program stored in the memory and running on the processor, wherein the processor executes the computer program to implement the steps of any of the methods described above.

[0024] This application has at least the following beneficial effects:

[0025] This application collects magnetic field strength data at various locations within the magnetic field region of a medical cyclotron accelerator; analyzes the difference in magnetic field strength between each location and its radially adjacent locations; and, combined with the spatial distance between each location and its radially adjacent locations, determines the local magnetic field inhomogeneity at each location. Local magnetic field inhomogeneity reflects the degree of inconsistency in magnetic field changes at each location, highlighting the necessity of magnetic field padding at each location to maintain isochronous magnetic fields, thus improving the reliability of magnetic field padding analysis. A predetermined number of magnetic pole steps are evenly distributed on the magnetic pole surface of the magnetic field region. The difference between the magnetic field strength at each location within the three-dimensional region corresponding to each magnetic pole step and the target magnetic field strength is analyzed. Combined with the aforementioned local magnetic field inhomogeneity, the padding suitability of each magnetic pole step is determined. Padding suitability reflects the urgency of magnetic field padding within the three-dimensional region corresponding to each magnetic pole step, improving the accuracy of magnetic field padding location determination. Based on the correlation between the padding suitability of each magnetic pole step, all magnetic pole steps are classified into one type of magnetic pole step and... Two types of magnetic pole steps are identified. By dividing magnetic pole steps into Class I and Class II, those requiring significant padding are selected, improving the accuracy of subsequent height determination. For each Class I magnetic pole step, the distribution of local magnetic field inhomogeneity at all locations within its corresponding three-dimensional region in the magnetic field is analyzed, along with the difference in local magnetic field inhomogeneity between each location and its axially adjacent locations. Combined with the padding properties, the padding complexity of each Class I magnetic pole step is determined. Padding complexity reflects the difficulty of padding each Class I magnetic pole step, and this is used as a weight to improve the rationality of subsequent fitness function determination. Based on the difference in padding properties before and after padding of Class I magnetic pole steps, combined with the padding complexity, and the difference in padding complexity before and after padding of Class II magnetic pole steps, the fitness function is determined, improving the optimization ability of the particle swarm optimization algorithm. Using the particle swarm optimization algorithm, the optimal height for magnetic field padding of each magnetic pole step is obtained, ultimately improving the accuracy of height determination for magnetic field padding of each magnetic pole step. Attached Figure Description

[0026] To more clearly illustrate the technical solutions and advantages in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 A flowchart illustrating the steps of an isochronous magnetic field compensation method for a medical cyclotron accelerator, provided as an embodiment of this application;

[0028] Figure 2 This is a schematic diagram of the magnetic field response curve;

[0029] Figure 3 Determine the flowchart for the fitness function. Detailed Implementation

[0030] To further illustrate the technical means and effects adopted by this application to achieve the intended purpose of the invention, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of a medical cyclotron isochronous magnetic field compensation method and system proposed in this application. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0031] 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 pertains.

[0032] The following description, in conjunction with the accompanying drawings, details the specific scheme of the isochronous magnetic field compensation method and system for a medical cyclotron accelerator provided in this application.

[0033] Please see Figure 1 The document illustrates a flowchart of a method for compensating for the isochronous magnetic field of a medical cyclotron accelerator according to an embodiment of this application. The method includes the following steps:

[0034] S1 collects the magnetic field strength at various locations within the magnetic field region of the medical cyclotron.

[0035] In a medical cyclotron, the region corresponding to the trajectory of a particle in a magnetic field is denoted as the characteristic magnetic field region. In this embodiment, the finite cloud method is used to simulate the three-dimensional magnetic field between the two magnetic poles of a medical cyclotron, i.e., the characteristic magnetic field region. In this embodiment, N preset positions are selected in the characteristic magnetic field region and denoted as N measurement points. The process of obtaining N measurement points is as follows: U horizontal magnetic pole surfaces are uniformly obtained in the characteristic magnetic field region, and n measurement points are uniformly selected on each horizontal magnetic pole surface. Then N = n × U. In this embodiment, N = 1000 and U = 10. Implementers can set them according to the actual situation. This embodiment does not impose any restrictions.

[0036] It should be noted that the finite cloud method is a well-known existing technology. Implementers may choose other feasible simulation algorithms based on the actual situation. This embodiment does not impose any restrictions on this method.

[0037] In this embodiment, a Hall-Gauss meter is used to measure the magnetic field strength at each measurement point in a characteristic magnetic field region.

[0038] S2, analyze the difference in magnetic field strength between each location and its radial neighbor, and determine the local magnetic field inhomogeneity at each location by combining the spatial distance between each location and its radial neighbor; divide the magnetic pole surface of the magnetic field region into a predetermined number of magnetic pole steps, analyze the difference between the magnetic field strength at each location in the three-dimensional region corresponding to each magnetic pole step and the target magnetic field strength, and determine the padding of each magnetic pole step by combining the local magnetic field inhomogeneity.

[0039] In medical cyclotrons, an isochronous magnetic field typically refers to a magnetic field whose strength and direction do not change over time; that is, it is a constant magnetic field. The magnetic field within a medical cyclotron is usually isochronous, meaning that during acceleration, the strength and direction of the magnetic field do not change, thus keeping particles moving in a fixed orbit. During this process, the isochronous magnetic field needs to ensure that particles maintain a stable orbit and that their trajectory is not affected by fluctuations in the magnetic field. Therefore, the design of medical cyclotrons typically relies on a uniform and constant magnetic field.

[0040] However, in reality, magnetic fields often exhibit inhomogeneity due to manufacturing errors, current fluctuations, core saturation, and other issues. This inhomogeneity leads to deviations and instability in particle trajectories, thus affecting acceleration efficiency. The step-filling method is primarily used to correct magnetic field inhomogeneity. By arranging specific compensating magnetic fields within the accelerator, discontinuities in magnetic field variations are eliminated or reduced, ensuring stable particle trajectories.

[0041] In this embodiment, the entire magnetic pole surface of the bottom magnet is uniformly divided into M steps along the radial direction to keep the width of each step uniform. In this embodiment, M=5. The implementer can set it according to the actual situation. This embodiment does not impose any restrictions here.

[0042] When filling the isochronous magnetic field of a medical cyclotron, the magnetic field distribution in the characteristic magnetic field region of the cyclotron must first be analyzed to obtain the non-uniform areas of the magnetic field, and then the non-uniform areas are filled. Specifically, for each measurement point, R neighboring measurement points are selected in its radial direction. In this embodiment, R=10. The implementer can set it according to the actual situation, and this embodiment does not impose any restrictions.

[0043] The local magnetic field inhomogeneity of each measurement point is calculated by the difference in magnetic field strength between local measurement points in the radial direction. Specifically, the difference in the axial component of the magnetic field strength of each measurement point and its neighboring measurement points in the radial direction is calculated and denoted as the first difference. The ratio of the first difference to the spatial distance is calculated. The local magnetic field inhomogeneity is the result of the fusion of the ratios of each measurement point and all its neighboring measurement points in the radial direction.

[0044] It should be noted that difference represents the degree of difference between two variables, which can be calculated using methods such as the absolute value of the difference or the square of the difference. This embodiment uses the absolute value of the difference as the calculation method. Fusion represents the combination of multiple variables, which can be calculated using methods such as multiplication, addition, or a combination of addition and multiplication. This embodiment uses addition as the calculation method for fusion. In addition, for calculating the difference of the axial component of the magnetic field strength, the axial component is the component in the vertical direction. Since the particles move along a circular track in the horizontal plane in the cyclotron, the magnetic field formed between the two magnetic poles is perpendicular to the horizontal plane. The magnetic field strength in the vertical direction, that is, the axial component of the magnetic field strength, has the most significant impact on the particle motion. Therefore, the difference of the axial component of the magnetic field strength between the measurement points is analyzed.

[0045] In this embodiment, the calculation method for the local magnetic field non-uniformity at each measurement point is as follows: In the formula, For the local magnetic field inhomogeneity at the q-th measurement point, Let be the amplitude of the axial component of the magnetic field strength at the q-th measurement point. Let be the magnitude of the magnetic field strength along the axial component of the magnetic field strength at the z-th measurement point adjacent to the q-th measurement point in the radial direction. Let be the spatial distance between the q-th measurement point and its radially adjacent z-th measurement point. This is denoted as the first difference.

[0046] It should be noted that the spatial distance is calculated using Euclidean distance, and the radial direction refers to the measurement point located on the same diameter as the q-th measurement point. If the spatial distance between each measurement point and its neighboring measurement points in the radial direction is closer, and the difference in magnetic field strength amplitude is greater, it indicates that the magnetic field in the local area of ​​that measurement point is more non-uniform, and more need for padding treatment. Therefore, the local magnetic field non-uniformity is greater.

[0047] When using padding blocks to fill in the uneven magnetic field at measurement points, the magnetic field emitted by the blocks mainly affects the area above the blocks, indirectly affecting the entire magnetic field area. Therefore, if the determination of whether to use padding is based solely on the unevenness of the magnetic field at the measurement point, the following phenomenon may occur: Since the characteristic magnetic field area is a three-dimensional area, unevenness in the radial direction of the measurement point does not guarantee that unevenness also exists in the axial direction of the measurement point. Therefore, when padding is performed directly, the measurement points above or below may experience a renewed uneven magnetic field under the influence of the magnetic field of the padding blocks.

[0048] Therefore, in this embodiment, the area between each step surface vertically upward to the magnetic pole surface of the top magnet is denoted as each three-dimensional step area. Each measurement point within the three-dimensional step area has a corresponding local magnetic field inhomogeneity. Furthermore, by combining the difference between the magnetic field strength of each measurement point and the target magnetic field strength, the necessity of padding the three-dimensional step area is determined. Specifically, the difference between the axial component of the magnetic field strength of each measurement point and its target magnetic field strength is denoted as the second difference. The product of the local magnetic field inhomogeneity of each measurement point and the second difference is calculated. The padding of each magnetic pole step is the fusion result of the product of all measurement points within the three-dimensional step area corresponding to each magnetic pole step in the magnetic field.

[0049] It should be noted that the target magnetic field strength is the magnetic field strength that a particle needs to achieve at each position to maintain isochronism when moving along a circular orbit in the magnetic field.

[0050] In this embodiment, the compensation method for each magnetic pole step is as follows: In the formula, For the padding property of the k-th magnetic pole step, Let be the number of measurement points within the three-dimensional step region corresponding to the k-th magnetic pole step. The local magnetic field inhomogeneity at the v-th measurement point within the three-dimensional step region corresponding to the k-th magnetic pole step. Let V be the amplitude of the magnetic field strength at the v-th measurement point within the three-dimensional step region corresponding to the k-th magnetic pole step, along with the axial component of the magnetic field strength. Let V be the amplitude of the target magnetic field strength at the v-th measurement point within the three-dimensional step region corresponding to the k-th magnetic pole step. This is denoted as the second difference.

[0051] It should be understood that the greater the difference between the magnetic field strength at each measurement point within the three-dimensional step area and the target magnetic field strength, and the greater the local magnetic field inhomogeneity at the measurement point, the more padding treatment is needed in the three-dimensional step area. Therefore, the padding of the corresponding magnetic pole step is greater.

[0052] S3. Based on the correlation between the padding properties of each magnetic pole step, all magnetic pole steps are divided into Class I magnetic pole steps and Class II magnetic pole steps. For each Class I magnetic pole step, the distribution of local magnetic field inhomogeneity at all locations in the three-dimensional region corresponding to it in the magnetic field is analyzed, as well as the difference between the local magnetic field inhomogeneity at each location and the axially adjacent location. Combined with the padding properties, the padding complexity of each Class I magnetic pole step is determined.

[0053] The padding properties of all magnetic pole steps are clustered using the K-means clustering algorithm, with clustering parameter K=2. The distance metric is the absolute value of the difference in padding properties of the magnetic pole steps. The K-means clustering algorithm is a well-known existing technology. Implementers can choose other feasible existing clustering algorithms according to the actual situation. This embodiment does not impose any restrictions here.

[0054] Based on the above clustering results, all magnetic pole steps are divided into two clusters. The mean of the padding of all magnetic pole steps in each cluster is calculated. All magnetic pole steps in the cluster with the maximum mean are denoted as Class I magnetic pole steps, and all magnetic pole steps in the remaining clusters are denoted as Class II magnetic pole steps. Among them, Class I magnetic pole steps are those that need significant padding, and the magnetic field inhomogeneity in the corresponding three-dimensional step region is more obvious. Therefore, Class I magnetic pole steps are regarded as magnetic pole steps to be padded. By distinguishing the magnetic pole steps, Class I and Class II magnetic pole steps are divided into Class I and Class II magnetic pole steps, so as to more accurately perform padding processing on the magnetic pole steps.

[0055] When padding a three-dimensional step area, the magnetic field strength at a certain location is the sum of the magnetic field strengths generated by multiple different magnetic pole steps. The magnetic field strength values ​​at the same location are often different for magnetic pole steps at different locations and heights. That is, the more uneven the magnetic field strength distribution in the three-dimensional step area, the more magnetic pole steps are needed, and the more complex the height setting of the magnetic pole steps is.

[0056] Therefore, this embodiment calculates the padding complexity of each type of magnetic pole step for each type of magnetic pole step. Specifically, it calculates the difference in local magnetic field inhomogeneity between each measurement point in the three-dimensional step region corresponding to each type of magnetic pole step in the magnetic field and its axially adjacent measurement point, denoted as the third difference. It calculates the fusion value of the third difference of all measurement points in the three-dimensional step region corresponding to each type of magnetic pole step in the magnetic field, calculates the disorder of local magnetic field inhomogeneity of all measurement points in the three-dimensional step region corresponding to each type of magnetic pole step in the magnetic field, and determines the padding complexity of each type of magnetic pole step based on the disorder, the fusion value, and the padding.

[0057] It should be noted that the disorder degree is calculated using information entropy in this embodiment. If the implementer can measure the degree of disorder of the distribution of local magnetic field non-uniformity at all measurement points, they can choose other existing feasible algorithms for calculation. This embodiment does not impose any restrictions on this.

[0058] In this embodiment, the calculation method for the padding complexity of each type of magnetic pole step is as follows: In the formula, The padding complexity for the xth type-I magnetic pole step, For the padding property of the xth type I magnetic pole step, Let be the information entropy of the local magnetic field inhomogeneity at all measurement points within the three-dimensional step region corresponding to the x-th type-I magnetic pole step. The local magnetic field inhomogeneity at the v-th measurement point within the three-dimensional step region corresponding to the x-th type-I magnetic pole step. The local magnetic field inhomogeneity of the v-th measurement point within the three-dimensional step region corresponding to the x-th type-I magnetic pole step is located axially above the measurement point closest to it. Let be the number of all measurement points within the three-dimensional step region corresponding to the x-th type-I magnetic pole step. This is denoted as the third difference. This is denoted as the fusion value of the third difference.

[0059] It should be noted that, in the process of calculating the padding complexity of each type of magnetic pole step, if there is no nearest measurement point above the axial direction of the measurement point in the three-dimensional step area corresponding to each type of magnetic pole step, then the nearest measurement point below the axial direction of the measurement point is selected.

[0060] The third difference reflects the non-uniformity of the axial magnetic field strength distribution at the measurement points in the three-dimensional step region. The larger the third difference, the more non-uniform the axial magnetic field strength distribution, and the more difficult it is to pad the magnetic pole step. In addition, the more chaotic the distribution of local magnetic field non-uniformity at all measurement points in the three-dimensional step region, the greater the calculated information entropy, which also indicates that the magnetic field in the region is more non-uniform, and correspondingly, the greater the padding complexity.

[0061] S4. Based on the difference in padding properties before and after padding of a type of magnetic pole step, combined with the padding complexity, and the difference in padding properties before and after padding of a type of magnetic pole step, a fitness function is determined, and the optimal height for magnetic field padding of each magnetic pole step is obtained using a particle swarm optimization algorithm.

[0062] After placing a magnetic pole step of arbitrary height at any position on the magnetic pole surface of a magnet, the magnetic field strength generated by the magnetic pole step will be linearly superimposed with the magnetic field strength of the original magnet. Therefore, the magnetic field strength at each measurement point is repeatedly obtained using a Hall-Gauss meter, and a new three-dimensional magnetic field generated by the characteristic magnetic field region between the two magnetic poles of a medical cyclotron is simulated using the finite cloud method. This yields the magnetic field response curve of the magnetic pole step pad at the arbitrary height and position. Similarly, magnetic field response curves for magnetic pole step pads at different positions and heights can be obtained. The magnetic field response curves typically approximate a Gaussian distribution, with the amplitude increasing closer to the center of the magnetic pole step and decreasing rapidly further away. That is, the magnetic field strength is greatest directly above the pad, gradually decreasing towards both sides. The magnetic field response curves provide the magnetic field strength of each pad at different positions and heights. A schematic diagram of the magnetic field response curve is shown below. Figure 2 As shown, Figure 2 The horizontal axis represents distance, indicating that the amplitude decreases rapidly with increasing distance from the magnetic pole step. Figure 2 The left vertical axis represents the magnetic field strength, and the right vertical axis represents the height, indicating the height of the magnetic pole step.

[0063] Before and after padding the magnetic pole steps, the padding performance can be calculated using the aforementioned padding performance calculation method. This embodiment uses a particle swarm optimization algorithm to obtain the optimal height for each magnetic pole step during padding. The optimal solution of the particle swarm optimization algorithm has a dimension of M, corresponding to the optimal height of M magnetic pole steps. In this embodiment, the number of particles in the particle swarm optimization algorithm is 200, the maximum number of iterations is 500, the inertia weight is 0.8, and both the individual learning factor and the social learning factor are 1.5. Implementers can set these values ​​according to their actual situation; this embodiment does not impose any restrictions. The fitness function of the particle swarm optimization algorithm is... In the formula, S represents the fitness function, C1 is the number of first-class magnetic pole steps, and C2 is the number of second-class magnetic pole steps. The padding complexity for the i-th type I magnetic pole step, The padding properties before the i-th type I magnetic pole step padding, The padding performance after padding the i-th type of magnetic pole step is given. The padding properties before padding the j-th type II magnetic pole step. The padding performance after padding the j-th type II magnetic pole step is given. To ensure that the value is greater than 0 and to avoid a denominator of 0, this embodiment... The implementer can set the parameters according to the actual situation; this embodiment does not impose any restrictions. The flowchart for determining the fitness function is as follows: Figure 3 As shown.

[0064] In this embodiment, the optimization process of the particle swarm optimization algorithm is to maximize the fitness function. For a type I magnetic pole step, the more non-uniform the magnetic field in the corresponding three-dimensional step region, the greater the difference in the padding property before and after padding, and the smaller the padding property after padding. For a type II magnetic pole step, compared with a type I magnetic pole step, the magnetic field in the corresponding three-dimensional step region is more uniform, so the difference in the padding property before and after padding is smaller.

[0065] Finally, the optimal solution corresponding to maximizing the fitness function, that is, the padding height corresponding to the padding performance after padding, is taken as the optimal height of each magnetic pole step. The particle swarm optimization algorithm optimization process is a well-known existing technology, and will not be described in detail in this embodiment.

[0066] Based on the same inventive concept as the above method, this application embodiment also provides a medical cyclotron isochronous magnetic field padding system, 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-described medical cyclotron isochronous magnetic field padding methods.

[0067] It should be noted that the order of the embodiments described above is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. Furthermore, specific embodiments of this specification have been described above. Additionally, the processes depicted in the accompanying drawings do not necessarily require a specific or sequential order to achieve the desired results. In some implementations, multitasking and parallel processing are possible or may be advantageous.

[0068] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0069] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the principles of this application should be included within the protection scope of this application.

Claims

1. A method for compensating for the isochronous magnetic field of a medical cyclotron accelerator, characterized in that, The method includes the following steps: The magnetic field strength was collected at various locations within the magnetic field region of the medical cyclotron. The differences in magnetic field strength between each location and its radially adjacent locations are analyzed. Combined with the spatial distance between each location and its radially adjacent locations, the difference in the axial component of the magnetic field strength between each location and its radially adjacent locations is calculated and denoted as the first difference. The ratio of the first difference to the spatial distance is calculated, and the local magnetic field inhomogeneity is the fusion result of the ratios between each location and all its radially adjacent locations. A predetermined number of magnetic pole steps are evenly distributed on the magnetic pole surface of the magnetic field region. The differences in magnetic field strength at each location within the three-dimensional region corresponding to each magnetic pole step in the magnetic field are analyzed and denoted as the target magnetic field strength. The difference in the axial component of the magnetic field strength at each location compared to the target magnetic field strength is denoted as the second difference. The product of the local magnetic field inhomogeneity at each location and the second difference is calculated, and the padding property is the fusion result of the product of the products at all locations within the three-dimensional region corresponding to each magnetic pole step in the magnetic field. Based on the correlation between the padding properties of each magnetic pole step, all magnetic pole steps are divided into Class I and Class II magnetic pole steps. For each Class I magnetic pole step, the distribution of local magnetic field inhomogeneity at all locations within the three-dimensional region corresponding to it in the magnetic field is analyzed, as well as the difference between the local magnetic field inhomogeneity at each location and the axially adjacent location. The difference between the local magnetic field inhomogeneity at each location and the axially adjacent location within the three-dimensional region corresponding to each Class I magnetic pole step in the magnetic field is calculated and denoted as the third difference. The fusion value of the third difference at all locations within the three-dimensional region corresponding to each Class I magnetic pole step in the magnetic field is calculated, and the disorder of the local magnetic field inhomogeneity at all locations within the three-dimensional region corresponding to each Class I magnetic pole step in the magnetic field is calculated. Based on the disorder, the fusion value, and the padding property, the padding complexity of each Class I magnetic pole step is determined. Based on the difference in padding properties before and after padding of a type I magnetic pole step, combined with the padding complexity, and the difference in padding properties before and after padding of a type II magnetic pole step, a fitness function is determined, and an intelligent optimization algorithm is used to obtain the optimal height of each magnetic pole step when performing magnetic field padding. The expression for the fitness function is: In the formula, S represents the fitness function, C1 is the number of first-class magnetic pole steps, and C2 is the number of second-class magnetic pole steps. The padding complexity for the i-th type I magnetic pole step, The padding properties before the i-th type I magnetic pole step padding, The padding performance after padding the i-th type of magnetic pole step is given. The padding properties before padding the j-th type II magnetic pole step. The padding performance after padding the j-th type II magnetic pole step is given. The default value is greater than 0.

2. The method for compensating for the isochronous magnetic field of a medical cyclotron accelerator as described in claim 1, characterized in that, The local magnetic field inhomogeneity is the sum of the ratios at each location to all its radial neighboring locations.

3. The method for compensating for the isochronous magnetic field of a medical cyclotron accelerator as described in claim 1, characterized in that, The target magnetic field strength is the magnetic field strength required to maintain an isochronous magnetic field at various locations within the magnetic field region.

4. The method for compensating for the isochronous magnetic field of a medical cyclotron accelerator as described in claim 1, characterized in that, The classification of all magnetic pole steps into Class I and Class II magnetic pole steps includes: Clustering algorithms are used to cluster the padding properties of all magnetic pole steps, dividing all magnetic pole steps into two clusters. The mean value of the padding properties of all magnetic pole steps in each cluster is calculated. The magnetic pole steps in the cluster with the maximum mean value are denoted as Class I magnetic pole steps, and the magnetic pole steps in the remaining clusters are denoted as Class II magnetic pole steps.

5. The method for compensating for the isochronous magnetic field of a medical cyclotron accelerator as described in claim 1, characterized in that, The padding complexity is the product of the disorder, the fusion value, and the padding property of each type of magnetic pole step.

6. A medical cyclotron isochronous magnetic field compensation system, 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 as described in any one of claims 1-5.

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