A ring beam delivery method and system for radiotherapy

Abstract

The application belongs to the technical field of medical devices, and relates to a ring-shaped beam irradiation method and system for radiotherapy. The application provides a ring-shaped beam irradiation system for ultra-high dose rate radiotherapy, which comprises an electron beam generating device, a beam focusing and transmission system, an initial beam deflection system, a main ring beam deflection system and a beam blocker; wherein the electron beam deflection system comprises a 90-degree combined deflection assembly comprising a Kicker magnet. The control method of the application comprises: dynamically scheduling the magnetic field of each Kicker at a millisecond level through electromagnetic control, realizing instant extraction of the beam at any predetermined angle on the ring-shaped main beam line, and completing multi-angle irradiation without mechanical movement and delay. The system can be expanded into a multi-treatment room system sharing the same accelerator. The application realizes an ultra-high dose rate radiotherapy platform with small floor area, short treatment time and sustainable upgrade, and is suitable for next-generation precise radiotherapy.

Description

Technical Field

[0001] This invention belongs to the field of medical device technology, specifically relating to a ring beam irradiation method and system for radiotherapy. Background Technology

[0002] Radiation therapy is one of the main methods of cancer treatment. Its core goal is to concentrate the radiation dose on the tumor target area to the maximum extent possible, while protecting the surrounding normal tissues to the greatest extent possible. In recent years, ultra-high rate radiotherapy, or FLASH radiotherapy, has become a revolutionary research hotspot due to its ability to significantly reduce toxicity to normal tissues while maintaining the same or even better tumor-killing effect. This technology typically requires a dose rate far exceeding the conventional standard, ≥40 Gy / s, to achieve an extremely short irradiation time in the millisecond range.

[0003] The current standard clinical protocol for multi-angle irradiation uses a rotating gantry to carry the radiation device (such as a linear accelerator) for mechanical rotation. However, this traditional mechanical motion mode has inherent and insurmountable drawbacks, fundamentally contradicting the requirements of FLASH technology: First, heavy gantry units, due to their large moment of inertia and limited acceleration, require several seconds or even longer to complete an angle switch, failing to meet the millisecond-level instantaneous multi-angle switching required by FLASH technology, thus making it difficult to implement multi-angle FLASH-level dose delivery in a very short time. Second, the gantry inevitably generates mechanical vibrations during startup, rotation, and braking, affecting the pointing accuracy and isocentric stability of the radiation beam, posing a risk to treatment precision. Simultaneously, to accommodate the large rotating structure, the treatment room requires a huge safety clearance, resulting in a large footprint (typically ≥35m²). 2The high cost of infrastructure construction limits its deployment and widespread adoption within existing spaces. Furthermore, core mechanical components such as bearings and slip rings are easily damaged and require frequent maintenance, posing challenges to the stability and reliability of continuous system operation. This is particularly true for photon FLASH radiotherapy, where multi-angle irradiation is especially difficult. High-energy photon FLASH requires higher instantaneous power and more complex beam control technology compared to electron beam FLASH. Current research mainly relies on modifying traditional linear accelerators for single-angle experiments or using fixed beam devices (such as directional LINACs), while multi-angle irradiation still solely depends on rotating gantry structures, exposing all the aforementioned bottlenecks (rate, vibration, and space). In addition, international research teams are actively exploring the use of multiple fixed linear accelerator arrays to achieve electronic beam switching, such as Stanford University's "PHASER" research scheme, which uses 16 independent linear accelerator modules arranged around the patient to complete beam switching at different angles within milliseconds. It is worth noting that most of these technologies are currently still in the proof-of-concept or preliminary experimental stages and require multiple linear accelerators, resulting in relatively high costs. Therefore, there is a serious lack of solutions in the existing technology that can truly be compatible with the characteristics of photonic FLASH, achieve multi-angle instantaneous irradiation, and have a relatively low cost.

[0004] In summary, there is an urgent need in this field for an innovative system that can completely eliminate the limitations of mechanical rotation, achieve millisecond-level switching times, fundamentally eliminate mechanical vibration, and improve accuracy and reliability. This would meet the stringent requirements of multi-angle photon FLASH radiotherapy and drive the breakthrough of this cutting-edge technology from the laboratory to clinical applications. Summary of the Invention

[0005] This invention aims to solve the problems commonly found in existing radiotherapy equipment under multi-angle irradiation scenarios, such as large inertia of mechanical rotating mechanisms, slow switching speed, accumulation of positioning errors, large system size, and the need for multiple accelerators. It provides a regular polygonal ring static multi-angle beam projection system for ultra-high dose rate radiotherapy (including FLASH therapy).

[0006] This invention provides a ring beam projection system for radiotherapy, comprising an electron beam generating device 1, a beam focusing and transmission system 20, an initial beam deflection system 200, N-1 main ring beam deflection systems 300, and a beam blocker 7. The initial beam deflection system 200 is a set of combined deflection components 30. The main ring beam deflection system 300 includes a set of main ring deflection components 40 and a set of combined deflection components 30 arranged sequentially. The N combined deflection components 30 are arranged in an N-order rotationally symmetrical manner and are tangent to the line connecting the midpoint of each side of a regular N-gon to the center point of the regular N-gon, where 4≤N≤12.

[0007] The beam focusing and transmission system 20 is composed of a quadrupole 2;

[0008] The combined deflection assembly 30 includes the following components arranged in sequence: Kicker magnet 3, front focusing assembly, combined deflection assembly deflecting diode 4, rear focusing assembly, and treatment head 6; the treatment head is a regular N-gon whose center and the center point of its sides are perpendicularly intersected by a line that intersects the corresponding area of ​​the side.

[0009] The main ring deflection assembly 40 includes the following components arranged in sequence: main ring deflection assembly deflecting diode 5, quadrupole 2, and main ring deflection assembly deflecting diode 5.

[0010] Furthermore, the parameters of the annular beam projection system for radiotherapy are determined by a multi-objective optimization method;

[0011] The decision variable parameters of the multi-objective optimization method include the following in the main loop deflection component 40: quadrupole magnetic field, effective length of the deflecting dipole, effective length of the quadrupole, size of the quadrupole good field region, air gap of the dipole, edge angle of the dipole, and length of the drift segment.

[0012] The objective function of the multi-objective optimization method is:

[0013] ;

[0014] in, , , They represent the objective functions respectively. , , The weights;

[0015] The objective function is to minimize the system's geometric dimensions.

[0016] ,

[0017] in, The deflection radius of the combined deflection assembly deflects the diode 4. This indicates the effective length of grade IV iron. The length of the drift segment between the quadrupoles in the combined deflection assembly 30. The drift segment length between the deflection diode 4 in the combined deflection assembly and the quadrupole in the front focusing assembly is determined. The drift segment length between the deflection diode 4 in the combined deflection assembly and the quadrupole in the post-focusing assembly is determined. To focus on the length of the drift segment between the quadrupoles in the component, The length of the drift segment between the post-focusing assembly and the electron beam target point of the treatment head. The distance from the electronic target position of the treatment head to the center point of the regular N-gon;

[0018] Let be the beam safety margin function.

[0019] ,

[0020] Where k represents the number of any set of beam parameters, and s represents the path coordinates along the beam propagation path. This represents the Twiss-β function in the horizontal direction at position s. This represents the beam emittance in the horizontal direction of the k-th group. This represents the Twiss-β function in the vertical direction at position s. This represents the beam emittance in the vertical direction of the k-th group. This represents the horizontal dispersion function at position s;

[0021] For the dispersive residual function,

[0022] Where j represents the sampling point number, This represents the path coordinates of the j-th sampling point along the transmission direction. Indicates the location The horizontal dispersion function at that point, Indicates position The horizontal dispersion slope at N p This indicates the total number of sampling points.

[0023] Furthermore, the termination condition of the multi-objective optimization method includes: or ,

[0024] in, This represents the difference between the parameters of the decision variable before and after the latest iteration;

[0025] And / or, the constraints of the objective function of the multi-objective optimization method include: , , , , ;

[0026] in, The deflection radius of the combined deflection assembly deflects the diode 4. This indicates the effective length of grade IV iron. The length of the drift segment between the quadrupoles in the combined deflection assembly 30. The drift segment length between the deflection diode 4 in the combined deflection assembly and the quadrupole in the front focusing assembly is determined. These represent the drift segment length before the inlet of the main ring deflection component 40 and the drift segment length from the outlet to the matching point, respectively. The matching point refers to the center point of the i-th side of the regular N-gon, where i represents the side number. This indicates transmission efficiency.

[0027] Furthermore, the following physical and engineering constraints are simultaneously applied during the multi-objective optimization process: symmetric refractive index. Double waistband at matching point Achromatic transmission Aperture constraint ; Quadrupole magnetic field gradient Effective length of quadrupole ; Dipolar magnetic field strength The air gap of the diode is ;

[0028] Wherein, the matching point refers to the center point of the i-th side of the regular N-gon, denoted as CPi, where i represents the side number. Indicates the beam emittance in the horizontal direction. Indicates beam emittance in the vertical direction. express The mean square value of the horizontal displacement in the matrix. express The mean square value of the vertical displacement in the matrix. express Horizontal displacement-angle correlation in the matrix This indicates a vertical displacement-azimuth correlation. express The mean square value of the horizontal divergence angle in the matrix. express The mean square value of the vertical divergence angle in the matrix. This represents the momentum dispersion function in the linear transfer matrix R. Let βx represent the slope of the momentum dispersion function in the linear transfer matrix R, and let βx represent the Twiss-β function in the horizontal direction. Let βy represent the horizontal beam emittance of the k-th beam parameter group, and let βy represent the vertical Twiss-β function. This represents the beam emittance in the vertical direction of the k-th group of beam parameters.

[0029] Furthermore, the N-1 main ring beam deflection systems have the same beam parameters, and the center point of the i-th side of the regular N-gon is CP. i 'i' represents the edge number, and each CP i Located at the beam waist and with consistent beam parameters;

[0030] The beam parameters of the annular beam projection system for radiotherapy at each CPi include: beam spot size x, beam emission angle y = 2x, and emissivity ε = xy.

[0031] Furthermore, the beam parameters at each CPi point include: beam spot size 1≤x≤3 mm, beam emittance 2π mm·mrad≤ε≤18π mm·mrad.

[0032] Furthermore, at the Kicker magnet inlet of the combined deflection assembly, the beam spot size is x. k = x + L·y, emission angle x' k = y, L is the distance from the i-th Kicker magnet to CP i The distance, and the beam is in a converging state;

[0033] And / or, the size of the band spot at the entrance of the treatment head 6 is the same, all being 1-3 mm, and located at the waist position, CP i-1 The electron beam center trajectory path to the treatment head inlet BMi is equal, CP i The straight-line distances to the treatment head inlet BMi are also equal, all <1 m; preferably, CP i The straight-line distance to the treatment head inlet BMi is 0.8~1m.

[0034] And / or, the deflection angle of the combined deflection component 30 is 90°; the deflection angle of the main ring deflection component 40 is 360° / N;

[0035] The main ring deflection assembly 40 includes two main ring deflection assemblies deflecting dipoles 5 and three quadrupoles, with the quadrupoles located between the two main ring deflection assemblies deflecting dipoles 5; the combined deflection assembly 30 includes one kicker magnet 3 and one combined deflection assembly deflecting dipole 4. The front focusing assembly and the rear focusing assembly are the same, each including two sets of two-in-one quadrupoles; the distance from the beam focusing and transmission system 20 to K1 is equal to the distance from the quadrupole in the main ring deflection assembly 40 to the corresponding kicker magnet, and the first kicker magnet into which the electron beam enters is set as K1.

[0036] Preferably, the deflection angle of both the Kicker magnet 3 and the combined deflection assembly deflects the dipole 4 by 45°.

[0037] And / or, the distance from the beam focusing and transmission system 20 to the Kicker magnet in the initial beam deflection system is equal to the distance from the quadrupole of the main ring deflection assembly to the corresponding Ki;

[0038] The distance from the first beam focusing and transmission system 20 to K1 is a, and the distance from the first beam focusing and transmission system 20 to the first main ring deflection component 40 is b, where a:b = 0.20-0.24:1.16-1.42.

[0039] Preferably, a:b = 0.22:1.29.

[0040] Furthermore, the beam focusing and transmission system 20 includes two sets of two-in-one quadrupole irons 2; the quadrupole iron, the combined deflection component deflection dipolar iron, and the main ring deflection component deflection dipolar iron are all wound with quadrupole coils, the effective length of the quadrupole coils is ≤50mm, the spacing between the coils is ≤50mm, the aperture radius of the quadrupole iron is 5-10mm, and the quadrupole magnetic field gradient is 15T / m;

[0041] And / or, the beam energy E of the electron beam output by the electron beam generating device 1 is 6-9 MeV;

[0042] And / or, the dose rate delivered by the annular beam irradiation system is ≥40 Gy / s, the shut-off time of the Kicker magnet is ≤5ms, and the total time used for irradiation by the annular beam irradiation system is less than 500ms;

[0043] And / or, the air gap and magnetic field strength of the combined deflection assembly deflecting dipolar iron, the main ring deflection assembly deflecting dipolar iron, and the Kicker magnet are all the same, with an air gap of 5-10mm and a magnetic field strength of ≤0.15T.

[0044] And / or, the combined deflection assembly has a horizontal projection distance of ≤0.5 m, and the combined deflection assembly deflects the same radius of the dipolar iron and the Kicker magnet, both of which are <0.2 m;

[0045] And / or, the electron beam generating device 1 is selected from a linear accelerator, a cyclotron accelerator, a petal accelerator, a high-energy electron beam source of 20-100MeV, a proton source of 70-250MeV, or a heavy ion accelerator of 150-430MeV / u.

[0046] And / or, the annular beam delivery system for radiotherapy further includes a field-programmable gate array control system;

[0047] And / or, the side length of the regular N-gon is s, and the perpendicular distance from the center of the regular N-gon to each side is R, satisfying the formula: , R < 2 m.

[0048] Preferably, the results output by the multi-objective optimization method include the following in the main ring deflection component 40: the focusing quadrupole magnetic field is 0.1339T, the diffuse quadrupole magnetic field is -0.0871T, the effective length of the deflecting dipole is 120mm, the effective length of the quadrupole is 50mm, the size of the quadrupole good field region is 17mm, the size of the dipole air gap is 10mm, the dipole edge angle is 7.5°, and the drift segment lengths of each segment from the drift segment at the inlet of the main ring deflection component to the drift segment at the outlet of the main ring deflection component are 500mm, 50mm, 40mm, 40mm, 50mm, and 500mm, respectively.

[0049] This invention provides a method for radiotherapy using a ring beam projection system as described in any of the preceding claims, which is a non-therapeutic method of radiotherapy, comprising:

[0050] Step 1: Keep all Kicker magnets off and turn on the electron beam generating device;

[0051] Step 2: Simultaneously activate all Kicker magnets;

[0052] Step 3: Starting with the first Kicker magnet into which the electron beam enters, turn off the Kicker magnets counterclockwise in sequence until all Kicker magnets are turned off.

[0053] Furthermore, the total time used for the illumination satisfies the following formula:

[0054]

[0055] in, This indicates the total time taken to obtain the certificate. This represents the exit time of the i-th field, which is equal to the number of hops in the i-th field divided by the dose rate. This represents the closing time of the i-th Kicker magnet, and n represents the number of Kicker magnets. The number of the first Kicker magnet into which the electron beam enters is set to i=1, and the value of i is an integer between 1 and n.

[0056] Furthermore, the total time used for ultra-high dose rate single breath-hold irradiation using the irradiation method is... Less than 15 seconds.

[0057] In this invention, "sequential setting" refers to setting the electron beam sequentially according to its transmission direction.

[0058] A "beam" refers to a group of particles that are confined into a bundle and move at high speed in the same direction.

[0059] The "beam waist position" refers to the location where the radius or diameter of the beam reaches its minimum value in the propagation direction. At this position, the beam is most concentrated and the beam size is smallest.

[0060] "Corresponding" means that the edges of a regular N-gon that are tangent to the same beam deflection system or the same beam deflection system correspond to each other; for example, "the treatment head in the edge-corresponding region" refers to the treatment head in the beam deflection system that is tangent to that edge, and "the distance from the quadrupole iron in the main ring deflection assembly 40 to the corresponding Kicker magnet" refers to the distance from the quadrupole iron in the main ring deflection assembly 40 that is tangent to the Kicker magnet in the same beam deflection system.

[0061] The numbering of the beam deflection system and its components or components within the same system is consistent with the numbering of the sides of the regular N-gon tangent to that system. For example, the beam deflection system tangent to the i-th side of the regular N-gon is numbered as the i-th beam deflection system, the Kicker magnet is numbered Ki, and the treatment head inlet is numbered BMi. In this invention, starting from the electron beam generating device, the first beam focusing and transmission system into which the electron beam enters is called the "first beam focusing and transmission system," the first main ring deflection component into which the electron beam enters is called the "first main ring deflection component," the first Kicker magnet into which the electron beam enters is called K1, and so on.

[0062] "Convergence state" refers to a state where the beam envelope (lateral dimension) gradually decreases along the propagation direction, the particles are "approaching the axis", the Twiss parameter α < 0, and the beam belongs to any segment before the beam waist.

[0063] "Irradiation field" refers to the irradiation field formed by the beam from the Kicker magnet to the entrance of the treatment head within the same beam deflection system.

[0064] "Good field area of ​​quadrupole iron" refers to the area where the magnetic field gradient deviation (ΔG / G0) meets the design tolerance (usually <±0.05%), and is usually expressed as the inscribed circle diameter of the available aperture.

[0065] The "air gap" of a dipolar iron refers to the vertical height (Gap) of the net space between the upper and lower magnetic pole surfaces of the dipolar iron.

[0066] The "effective length" of a deflecting dipole refers to the length of the ideal rectangular magnetic field (LD) equivalent to the actual magnetic field integrated along the central orbit. eff = ∫Bds).

[0067] The "effective length" of a quadrupole is the integral length of the magnetic field after equivalent processing of the longitudinal gradient distribution of the quadrupole (LQ). eff = ∫Gds).

[0068] The "edge angle" of a dipolar magnet refers to the angle between the normal to the magnet and the tangent to the magnet when the magnet enters / exits the center track of the beam.

[0069] Numerical designations such as "first," "second," and "third" serve to distinguish different terms and are ordered according to the direction of electron beam transmission. They do not limit the scope of the technical features described.

[0070] The terms "front focusing assembly" and "rear focusing assembly" serve to distinguish different terms and are ordered according to the direction of electron beam transmission. They do not limit the scope of the technical features described.

[0071] This invention provides a regular polygonal annular static multi-angle beam projection system for ultra-high dose rate radiotherapy (including FLASH therapy). The system utilizes pure electromagnetic deflection to achieve millisecond-level switching between arbitrary angles and employs a highly symmetric N-gonal structure (4 ≤ N ≤ 12) to ensure equivalent beam paths, unified optical parameters, and modular scalability. This invention is particularly suitable for high instantaneous dose rate electron FLASH radiotherapy, and also possesses scalability for upgrading to high-energy electron beam FLASH, proton FLASH, heavy ion FLASH, and other platforms, and can support novel treatment modes such as single-shot irradiation.

[0072] The static rack of this invention adopts a regular N-gon geometric layout, with N = 12 being a preferred embodiment. The rack consists of N-1 identical deflection segments forming a non-closed main loop, with the start and end points of each segment located at the center points CP1, CP2...CP of the sides of the regular polygon, respectively. 12 This results in the main ring exhibiting strict geometric symmetry. For a regular N-gon with side length s, the distance R from its center to each side satisfies:

[0073]

[0074] This distance determines the position of the deflecting magnets, the quadrupole arrangement, and the initial geometry of the beam propagation. Each segment of the main ring uses identical magnet combinations, including a combined quadrupole (QF / QD) and several dipoles with fixed and identical magnetic field strengths, resulting in n-1 periodic beam optical structures in the main ring. The beam size x is approximately 1-3 mm, the divergence angle y is 2-6 mrad, the emittance ε is 2-18 (π mm mrad), the energy is 6-9 MeV, and the energy dispersion is ±3%. At any CP... iAt the target point, a beam channel is drawn out, containing two 45° deflection magnets. The first is a fast-switching kicker with a switching speed of less than 5ms, and the second is a fixed-magnetic-field dipolar iron, coupled with several quadrupole irons for optical matching. All beam channels use completely identical magnet models, the same optical parameters, and the same deflection angles to ensure strictly consistent beam properties in all 12 directions. The source-target distance from the exit of each beam system to the treatment target is uniformly 100 cm for easy dose calibration.

[0075] The electron beam is generated by a horizontally mounted ground-based electron accelerator, capable of outputting an ultra-high current electron beam of 6-9 MeV to meet FLASH dose rate requirements. This invention selectively guides the beam to any single treatment head via a purely electromagnetic method. Each treatment head includes a target material (such as a tungsten target) and beam shaping components (collimator, MLC, or fixed beam limiter), and beam measurement devices are arranged as needed. The collimator's movement direction is perpendicular to the beam direction to reduce broadening errors and scattering effects.

[0076] In terms of treatment sequence control, this invention employs a Kicker fast deflection magnet as the only high-speed switchable element, with a magnetic field setup and decay time ≤ 5 ms. Initially, all Ki magnets are in the on state, allowing the beam to flow in the main loop according to CP1→CP2→…→CP. n The sequence propagates steadily. During the illumination of the i-th direction, the system ensures that only K... i Keep it open while the preceding Kicker (K1... K) {i-1} All switches are closed to prevent the beam from being mistakenly drawn out to the completed angle. When K i After the corresponding field of illumination ends, the controller shuts down K within a time window of no more than 5 ms. i And at the same time maintain the subsequent Kicker (K {i+1} …K n The beam is in the open state, allowing it to continue propagating to the rear of the main ring and preparing for the next extraction. The last field of fire (K) n After completion, a beam termination unit (beam blocker) is installed at the tail of the main ring to safely absorb any remaining unextracted beam.

[0077] For the complete treatment sequence, the magnetic field settling time T for each radiation field total satisfy:

[0078] Field 1:

[0079]

[0080] Field 2:

[0081]

[0082] Field n:

[0083]

[0084] TMU i Tk is the exit time of the i-th field. i Let be the time for the i-th Kicker switch. This time model allows the treatment planning system to accurately assess whether the FLASH conditions are strictly met.

[0085] This invention, based on high-speed switching, absence of mechanical movement, and controllable and stable beam path, can also achieve single-shot irradiation mode, that is, outputting the entire therapeutic dose within a single Kicker extraction cycle, maximizing both timeliness and biological effects by utilizing the ultra-high dose rate FLASH effect. Furthermore, because this invention has no mechanical rotating mechanism, it can achieve an isocenter error ≤0.5 mm and a mean time between failures ≥10,000 hours, while the system footprint can be controlled within 10-15 square meters, significantly superior to traditional radiotherapy equipment.

[0086] In summary, this invention constructs a multi-angle ultra-high dose rate radiotherapy system that significantly outperforms existing technologies in terms of angle switching speed, space efficiency, treatment accuracy, structural scalability, and functional richness through a regular polygonal static gantry, periodic main ring optics, 12 fully equivalent beam channels, a millisecond-level electromagnetic switching Kicker system, a multi-room shared architecture, and a scalable FLASH technology platform. This system not only overcomes the speed and accuracy bottlenecks of existing mechanical rotating equipment but also provides a novel system architecture and engineering implementation path for FLASH radiotherapy and future clinical applications of particle FLASH.

[0087] Obviously, based on the above description of the present invention, and according to common technical knowledge and conventional methods in the field, various other modifications, substitutions or alterations can be made without departing from the basic technical concept of the present invention.

[0088] The following detailed embodiments further illustrate the above-described content of the present invention. However, this should not be construed as limiting the scope of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Attached Figure Description

[0089] Figure 1 This is a schematic diagram of the regular dodecagonal layout structure of the system of the present invention.

[0090] Figure 2This is a schematic diagram of the main ring structure formed by connecting 11 main ring deflection components at 30°; where CP represents the matching point, K represents the Kicker magnet, and BM represents the treatment head inlet.

[0091] Figure 3 The beam optical diagrams for beam propagation of 11 30° main ring deflection components are shown. The lines from top to bottom in the first quadrant and from bottom to top in the second quadrant represent the beam optical diagrams under the beam conditions of parameters 5, 4, 3, 2, and 1 shown in Table 1, respectively. The horizontal axis represents the path length S along the beam propagation path, i.e., the S-axis, and the vertical axis represents the beam spot size. Below the S-axis represents the horizontal beam spot size x, and above the S-axis represents the vertical beam spot size y.

[0092] Figure 4 The beam optical diagram is for the beam transmission of a single 30° main ring deflection component; wherein, the lines from top to bottom in the first quadrant and from bottom to top in the second quadrant represent the beam optical diagrams under the beam conditions of parameters 5, 4, 3, 2, and 1 shown in Table 1, respectively. This indicates the effective length of each quadrupole. This indicates the effective length of the dipole. B represents the length of the drift segment from the inlet of the main ring deflection assembly to the magnetic element at the outlet of the main ring deflection assembly. D1 B represents the magnetic field strength of the deflecting dipole in the first main ring deflection assembly. D2 B represents the magnetic field strength of the deflecting dipole in the second main ring deflection assembly. Q1 B represents the magnetic field strength of the first quadrupole iron in the main ring deflection assembly 40. Q2 B represents the magnetic field strength of the second quadrupole iron in the main ring deflection assembly 40. Q3 This indicates the magnetic field strength of the third quadrupole iron in the main ring deflection assembly 40.

[0093] Figure 5 Open the beam optical diagrams for each beam deflected by the kicker. The lines from top to bottom in the first quadrant and from bottom to top in the second quadrant represent the beam optical diagrams under the beam conditions of parameters 5, 4, 3, 2, and 1 shown in Table 1, respectively. The horizontal axis represents the path length S along the beam propagation path, i.e., the S-axis. The vertical axis represents the beam spot size. Below the S-axis represents the horizontal beam spot size x, and above the S-axis represents the vertical beam spot size y.

[0094] Figure 6 This is a schematic diagram of the system's Kicker timing control method.

[0095] Figure 7 This is a flowchart of the projection time control for a ring-shaped static multi-field beam system.

[0096] Figure 8 This is a schematic diagram of the combined deflection component 40 corresponding to the regular N-gon (4≤N≤12) layout structure of the present invention; where θ represents the deflection angle of the main ring deflection component and N represents the number of sides of the regular N-gon.

[0097] Figure 9 The main view of the engineering model of the system of the present invention when N=12; wherein, the microwave power source is used to provide microwave power to the accelerating tube.

[0098] Figure 10 When N=12, the three-dimensional view of the engineering model observed by the system of the present invention from the right-top-front perspective.

[0099] Figure 11 When N=12, the three-dimensional diagram of the engineering model observed by the system of the present invention from the left-top-back perspective.

[0100] Figure 12 This is a schematic diagram of the system layout when there are two treatment rooms, and the two treatment rooms have the same layout structure.

[0101] Figure 13 This is a schematic diagram of the system layout when there are two treatment rooms, and the layout of the two treatment rooms is mirrored.

[0102] Figure 14 This is a schematic diagram of the system layout when there are 6 treatment rooms.

[0103] In the attached figures, the reference numerals are as follows: 1-Electron beam generating device, 2-Quadrupole, 20-Beam focusing and transmission system, 100-Beam deflection and path selection system, 200-Initial beam deflection system, 300-Main ring beam deflection system, 30-Combined deflection assembly, 40-Main ring deflection assembly, 3-Kicker magnet, 4-Combined deflection assembly deflecting dipolar iron, 5-Main ring deflection assembly deflecting dipolar iron, 6-Treatment head, 7-Beam blocker, 8-Microwave power source, 9-Treatment bed, 10-Central beam transmission combined deflection assembly. Detailed Implementation

[0104] In the following embodiments and experimental examples, the algorithms for data acquisition, transmission, storage, and processing steps not specifically described, as well as the hardware structures and circuit connections not specifically described, can all be implemented using the content already disclosed in the prior art.

[0105] Example 1: A regular polygonal ring static multi-angle beam projection system and projection method for XFLASH ultra-high dose rate radiotherapy

[0106] I. Photo Transmission System

[0107] The system structure in this embodiment is as follows: Figure 1As shown, it consists of the following components:

[0108] (1) A rigid static frame with a regular N-gon (4≤N≤12, specifically 12 in this embodiment) structure, specifically, the side length of the regular N-gon is 1.07m and the radius of the inscribed circle is 1.85m;

[0109] (2) An electron beam generating device 1, specifically a medical electron accelerator, with an output electron beam energy of E of 6-9 MeV, specifically 6 MeV;

[0110] (3) A beam focusing and transmission system 20, which consists of two sets of two-in-one quadrupoles 2. The length of a single quadrupole is 50 mm, the center-to-center distance between adjacent two-in-one quadrupoles is 50 mm, the quadrupole magnetic field gradient is 15 T / m, the focusing quadrupole magnetic field is 0.1339 T, the divergence quadrupole magnetic field is -0.0871 T, and the good field area of ​​the quadrupole is 17 mm. It is configured before each of the following beam deflection systems (initial beam deflection system 200, main ring beam deflection system 300). Among them, except for the beam focusing and transmission system 20 before the initial beam deflection system 200, the other beam focusing and transmission systems 20 mainly serve as safety redundancy and can also be omitted.

[0111] The two-in-one quadrupole iron refers to two independent quadrupole irons that are close together along the bundle direction, each with its own coil and its own power supply; the quadrupole iron is wound with a quadrupole coil, that is, each quadrupole iron is wound with 4 sets of coils in the NSNS sequence, and after being energized, it generates a "quadrupole magnetic field" - the magnetic field strength at the center is zero, and it has a linear gradient along the X and Y directions.

[0112] (4) Beam deflection and path selection system 100, which consists of N beam deflection systems, namely: 1 initial beam deflection system 200 and N-1 main ring beam deflection systems 300;

[0113] The initial beam deflection system 200 is a set of combined deflection components 30; a main ring beam deflection system 300 is a set of main ring deflection components 40 and a set of combined deflection components 30 arranged sequentially; wherein, the combined deflection components 30 in the initial beam deflection system 200 and the combined deflection components 30 in the main ring beam deflection system 300 constitute N combined deflection components, and the N combined deflection components 30 are arranged in an Nth order rotationally symmetric manner and are tangent to the line connecting the midpoint of each side of a regular N-gon to the center point of the regular N-gon;

[0114] The combined deflection assembly 30 consists of the following components arranged sequentially: one Kicker magnet 3, one combined deflection assembly deflecting diode 4, and one treatment head 6. A focusing assembly is located downstream of both the Kicker magnet 3 and the combined deflection assembly deflecting diode 4. The focusing assembly downstream of the Kicker magnet 3 is called the front focusing assembly, and the focusing assembly downstream of the combined deflection assembly deflecting diode 4 is called the rear focusing assembly. Specifically, this focusing assembly consists of two sets of two-in-one quadrupoles. Since the deflection angles of both the Kicker magnet 3 and the combined deflection assembly deflecting diode 4 are 45°, the deflection angle of the combined deflection assembly 30 is 90°. The line connecting the center of the regular N-gon to the center point of one of its sides intersects perpendicularly at the treatment head in the corresponding region of the side. The combined deflection assembly 30 deflects the electron beam to the treatment head 6. The electron beam is then directed to the treatment head 6 to generate an X-ray beam.

[0115] Each main ring deflection assembly 40 specifically comprises the following components: two main ring deflection assemblies deflecting diodes 5 and three quadrupoles, with the quadrupoles located between the two main ring deflection assemblies deflecting diodes 5; the deflection angle of each main ring deflection assembly is 360° / N, i.e., 30°, and the deflection angle of each main ring deflection assembly deflecting diode 5 is 15°; in the main ring deflection assembly 40, the drift distances of each segment between the first main ring deflection assembly deflecting diodes and the second main ring deflection assembly deflecting diodes are 50mm, 40mm, 40mm, and 50mm, respectively; the main ring deflection system deflects the electron beam to a regular N-sided main ring;

[0116] The distance from the quadrupole (i.e., the first beam focusing and transmission system) matched between the electron beam generating device 1 and the main ring to K1 is 0.22m, which is equal to the distance from the quadrupole of the main ring deflection component to the corresponding Ki; the distance from the exit position of the electron accelerator to the center position of the quadrupole in the first beam focusing and transmission system is specifically 0.1m; the distances from each of the other beam focusing and transmission systems 20 to the entrance of the corresponding main ring deflection component 40 are equal, all being 0.1m;

[0117] In this embodiment, both the 15° deflecting dipole (i.e., the deflecting dipole of the main ring deflection assembly) and the quadrupole are wound with quadrupole coils. The effective length of the quadrupole coil is 50mm, and the spacing between the coils is also 50mm. A dipole coil is also wound on the dipole. The magnetic field of the dipole is 0.1417T, and the effective length of the deflecting dipole is 120mm.

[0118] In this embodiment, the central beam aperture of the quadrupole (i.e., the radius of the circular channel in the coil that allows the particle beam to pass through, which is the physical size of the beam channel) is r=10mm, and the maximum magnetic field (i.e., the peak magnetic field strength that the coil can reach at the aperture r=10 mm position) is 0.13T. If the maximum aperture r=5mm, the maximum magnetic field is 0.065T; the specific central beam aperture in this embodiment is r=10mm.

[0119] In this embodiment, the magnetic field of all deflecting magnets (Kicker magnets, deflecting dipoles) is 0.1417T, the inscribed circle radius of the system's regular N-gon is 1.85m, and the horizontal projection distance of the 90° combined deflection assembly is ≤0.5m, specifically 0.5m. All deflecting magnets (Kicker magnets, deflecting dipoles) have the same air gap of 5-10mm, specifically 10mm, and the edge angle of the dipole is 7.5°.

[0120] (5) A beam blocker 7;

[0121] (6) Control system, specifically the components of the timing control system using a field-programmable gate array (FPGA) control system.

[0122] The following is a detailed description of each component:

[0123] The system in this embodiment adopts a static rack with a regular N-gon (4≤N≤12) geometric layout, such as... Figure 2 As shown, it consists of N-1 identical deflection segments (i.e., the main ring deflection component 40 + beam focusing and transmission system 20) forming a non-closed main ring. The start and end points of each segment are located at the center points CP1, CP2...CP of the sides of the regular polygon, respectively. N This results in the main ring exhibiting strict geometric symmetry. Specifically, this embodiment employs a static frame with a regular dodecagonal (N=12) shape, consisting of 11 identical deflection segments forming a non-closed main ring. The start and end points of each segment are located at the center points CP1, CP2...CP3 of the sides of the regular polygon. 12 .

[0124] For a regular N-gon with side length s, the distance R from its center to each side (i.e., the radius of the incircle of the regular N-gon) satisfies:

[0125]

[0126] This parameter determines the geometry of the main ring, the magnet layout, the treatment head spacing, and the beam optics layout. In this embodiment, the lines connecting the center points of the twelve sides to the system center form the center lines of the twelve irradiation beams. A treatment head is placed at the end of each center line, ensuring that the angle between each treatment direction is θ = 360° / N = 30°, guaranteeing the system's uniformity and geometric equivalence. Adjacent center points CP i With CP i+1 The 30° combination deflection structure parameters are completely consistent, ensuring that the main ring beam parameters remain equivalent in the 12 side segments.

[0127] The electron beam generating device can be a linear accelerator, cyclotron accelerator, or petal accelerator, capable of generating high-current electron beams of 6–10 MeV. It can also be upgraded to a high-energy electron beam source of 20–100 MeV for FLASH radiotherapy. Furthermore, it can be replaced with a proton accelerator of 70–250 MeV or a heavy ion accelerator of 150–430 MeV / u to achieve proton FLASH or heavy ion FLASH radiotherapy. The beam path topology of this invention does not change with the particle type; upgrades can be achieved simply by redefining the magnetic field strength and beam optical parameters. In this embodiment, the electron beam generating device used is a medical linear accelerator.

[0128] The system in this embodiment includes 12 radiation field paths, corresponding to K1→BM1, K2→BM2, ..., K12→BM12, respectively. BMMi refers to the position where the beam enters the i-th treatment head; each radiation field is controlled by a 45° fast-switching kicker magnet K. i (Switching time ≤ 5 ms) It consists of a 45° ordinary deflecting dipole and two sets of combined quadrupole focusing components. The 45° Kicker magnet and the 45° ordinary deflecting dipole together achieve a 90° extraction angle. The treatment head 6 is located at the end of each radiation field path and contains an X-ray target, collimator, and dose shaping components. After the beam bombards the target material in the treatment head, it forms an XFLASH ultra-high dose rate X-ray beam for rapid irradiation of the patient's target area. The radiation field collimator does not have MLC switching action. The MLC is turned on once before treatment and remains stationary. Each radiation field is a single subfield irradiation, avoiding the additional time and uncertainty introduced by dynamic MLC and ensuring that the FLASH dose rate can be maintained stably.

[0129] II. Projection Method

[0130] When the system is in standby mode, all kickers (K1 to K12) remain off, and the electron beam circulates along the main ring. The physical results of beam transmission through the 11 deflection structures are as follows: Figure 3-4 As shown, the main ring deflection assembly deflects the beam normally as expected, and the beam is eventually absorbed by the beam blocker and will not enter any treatment direction; for the sake of simplicity, the combined quadruple ferromagnetic field in the beam focusing and transmission system 20 before each main ring beam deflection system 300 is 0, which is equivalent to the vacuum drift section.

[0131] To achieve sequential multi-angle irradiation during treatment preparation, this invention employs a unique "overall activation, individual deactivation" Kicker control mode. Before treatment begins, the system simultaneously activates K1 to K12, allowing the beam to enter any of the irradiation paths, such as... Figure 5As shown, the exit beam parameters are the same for each beam. The beam size x is approximately 1-3 mm, the divergence angle y is 2-6 mrad, the emittance ε is 2-18π mm mrad, the energy is 6-9 MeV, and the energy dispersion is ±3%.

[0132] System kicker timing control method as follows Figure 6 As shown, when executing field 1 (K1→BM1→treatment head 50), since K1 is in the on state, the beam is introduced into field 1 and enters the first treatment head for irradiation along a 90° deflection path. At this time, the total magnetic field stabilization time of field 1 is equal to its exit time TMU1 (equal to the number of jumps (MU) of the field divided by the dose rate), and no switching time is required, i.e.:

[0133]

[0134] After field 1 is completed, the controller shuts off K1 within 5 ms to prevent the beam from entering the field 1 path. When the beam travels along the main ring to CP2, since K2-K12 remain on, the beam automatically deflects to the field 2 path (K2→BM2→treatment head). At this time, the total magnetic field stabilization time of field 2 is the sum of its beam exit time and one kicker switching time, where T... k1 The closing time for K1:

[0135]

[0136] Similarly, during the sequential execution of field 1 to field n (12 fields in this embodiment), after the irradiation of the i-th field is completed, the control system shuts off Ki within ≤5 ms, allowing the beam to continue to propagate along the main loop direction to CP(i+1), and then through K... i+1 →BM i+1 Proceed to the next firing field. For the nth firing field, its total magnetic field settling time is equal to the sum of the beam exit times of all firing fields and the kicker switching times of the previous n-1 times:

[0137]

[0138] In this embodiment, n=12, therefore for the 12th firing field, we have:

[0139]

[0140] After field 12 is irradiated, K12 is shut off within ≤5 ms. The beam then travels along the main ring to CP12 and is safely absorbed by beam blocker 7, terminating the irradiation sequence. The total treatment time for the entire process is... The time window must be less than 500ms to meet the stringent requirements of XFLASH's ultra-high dose rate for the overall time window. If it does not meet these requirements... When the requirement is less than 500ms, follow Figure 7 Adjust as shown.

[0141] During beam switching, all dipole and quadrupole magnets maintain a constant magnetic field, with only the kicker magnet Ki undergoing millisecond-level shut-off, resulting in extremely high stability and repeatability. Throughout the irradiation process, the kicker's shut-off state gradually decreases: initially, K1 to K12 are all on; after completing field 1, K1 is shut off; after completing field 2, K2 is shut off; and so on, until field 12 is completed, at which point all K1 to K12 are shut off. Once all kickers are off, the beam no longer enters any field path but flows to the beam blocker, ensuring system safety. Since all magnets except the kicker do not require dynamic adjustment, the system optics remain strictly consistent, and the dose distribution is stable. This embodiment achieves unidirectional, non-backtracking, multi-angle sequential beam irradiation through a strategy of "closing only the kickers in completed fields, while keeping subsequent kickers always on." Its switching logic does not require adjustment of other magnet parameters, thus obtaining reliable, stable, and repeatable beam transmission conditions.

[0142] In this embodiment, the regular dodecagonal structure allows the treatment heads to be distributed at 30° equiangular intervals, resulting in a total footprint of less than approximately 15 m². 2 Compared to systems that emit beams simultaneously in the same number of directions, this invention requires only one electron beam generation device to complete sequential irradiation in 12 directions, significantly reducing system cost and space requirements. Furthermore, since all magnets (except the kicker) employ a fixed magnetic field design, its beam stability and maintenance costs are significantly superior to complex dynamic magnetic field systems. The frame is made of a material that combines structural strength and magnetic shielding performance, resulting in a smaller overall footprint.

[0143] In this embodiment, ensuring complete consistency of beam parameters at the 12 beam exits is crucial. To guarantee this consistency, assuming all 12 combined deflection components are identical, the beam parameters at the entrance of each Kicker magnet (K1-K12) must also be identical. Since K2-K12 are repeating structures, it is only necessary to ensure consistency of beam parameters at the center points (CP1-CP12) of each side of the regular polygon.

[0144] Since the distances from each center point CP1-CP11 to the inlet of each Kicker magnet are equal, and with the kicker closed, the area from the kicker inlet to the center point is a vacuum drift segment without magnetic field constraint, the beam parameters of CP2-CP12 are completely identical, assuming that the 11 main ring beam deflection systems are identical. Therefore, to ensure that the beam parameters of CP1-CP12 are consistent, it is only necessary to ensure that the beam parameters of CP1 and CP2 are consistent. To achieve this, the magnetic field control, positional relationship, and dimensional design of the initial beam deflection system's 200° and 30° deflection components (i.e., the main ring deflection components) are crucial.

[0145] First, the distance from the quadrupole (i.e., the initial beam deflection system) matched between the electron beam generating device 1 and the main ring to K1 is equal to the distance from the quadrupole of the main ring deflection assembly to the corresponding Ki.

[0146] In the initial beam deflection system 200, two sets of two-in-one quadrupoles focus the beam. The effective length of the quadrupole coils is 50 mm, and the spacing between the coils is also 50 mm. The maximum quadrupole field gradient G generated by the quadrupole coils is 15 T / m. The aperture of the quadrupole (i.e., the radius of the circular channel in the coil that allows the particle beam to pass through, which is the physical size of the beam channel) is r. q =10mm, the maximum magnetic field Bmax (i.e., the peak magnetic field strength that the coil can reach at the position with an aperture r=10 mm) is 0.13T. Since the magnetic field gradient G=B / r, where B is the magnetic field strength at a distance r from the quadrupole, if the maximum aperture r q If the aperture is 5mm, then the maximum magnetic field is 0.065T; the relationship between the maximum magnetic field of the quadrupole iron and the half-aperture is B=0.13. r q / 10.

[0147] In the 30° deflection assembly (i.e., the main ring deflection assembly), the magnetic field strength of the deflecting dipole is controlled within 0.15T, specifically 0.1417T, and the air gap of the deflecting dipole is 5-10mm, specifically 10mm; there is a set of three-in-one quadrupoles between the two 15° deflecting dipoles, and the magnetic field and size settings of the quadrupoles are consistent with those of the quadrupoles in the initial beam deflection system 200.

[0148] In order to be consistent with the initial beam deflection system 200 and the main ring deflection assembly, the magnetic field control and size of the deflection magnets (Kicker magnet and deflection secondary iron) in the combined deflection assembly are consistent with the deflection secondary iron of the main ring deflection assembly, and the magnetic field and size settings of the quaternary iron are consistent with the quaternary iron in the initial beam deflection system 200.

[0149] In addition, to ensure the ring can be installed in an existing radiotherapy room, its diameter should not be too large; R needs to be less than 2m. This is based on the formula for the distance from the center point to each side. When n=12 and R=1.85m, s=1.07m (s represents the side length of a regular N-gon). Therefore, the projected distance of the 90° combined deflection assembly in the horizontal direction must be less than or equal to 0.5m, specifically 0.5m; the radius of the deflection magnet (Kicker magnet and deflecting secondary iron) must be less than 0.2m, specifically 0.15m; the length of the quadrupole iron or quadrupole coil must be less than or equal to 0.05m, specifically 0.05m, otherwise the space requirements for practical use cannot be met. The source-target distance from the exit of each beam system to the treatment target point is uniformly 100 cm, CP i The straight-line distance to the treatment head inlet BMi is equal and all <1 m, specifically 0.85 m.

[0150] In this embodiment, the parameters for the regular polygonal annular static multi-angle beam projection system and projection method have all been rigorously optimized and calculated. This invention is based on the linear beam transmission principle and the internationally used software TRANSPROT, and addresses the periodic structure of the annular beam transmission system composed of the main ring deflection component 40, as follows: Figure 4 A multi-objective optimization calculation method is proposed. This method unifies the system geometry, beam envelope, dispersion function, transmission efficiency, stability and engineering feasibility into a multi-objective constrained optimization problem, and determines the optimal combination of magnet parameters through automatic iterative fitting to achieve efficient, stable and compact matching design of beam optics. For simplicity, in the optimization process, the beam focusing and the two-in-one four-level ferromagnetic field in the transmission system 20 before each main ring beam deflection system 300 are 0, which is equivalent to the vacuum drift section. The physical design boundary conditions of the beam optics of the periodic matching section of the ring machine main beam transmission system are determined as follows: (1) Symmetrical beam emittance, = (2) Double waist at the matching point, , , (3) Achromatic transmission, (4) Keep the 2σ beam spot size within the aperture (R=10 mm), and the specific parameters are shown in Table 1 below.

[0151] Table 1 Beam parameters for different emittances

[0152]

[0153] in, , , , , , x represents the horizontal beam size, xp represents the horizontal divergence angle of the beam center, y represents the vertical beam size, yp represents the vertical divergence angle of the beam center, and ε represents the emittance. Indicates the beam emittance in the horizontal direction. Indicates beam emittance in the vertical direction. express The mean square value of the horizontal displacement in the matrix. express The mean square value of the vertical displacement in the matrix. express Horizontal displacement-angle correlation in the matrix This indicates a vertical displacement-azimuth correlation. express The mean square value of the horizontal divergence angle in the matrix. express The mean square value of the vertical divergence angle in the matrix. This represents the momentum dispersion function in the linear transfer matrix R. This represents the slope of the momentum dispersion function in the linear transfer matrix R. The matrix is ​​the beam envelope matrix.

[0154] In the multi-objective optimization, each drift segment, quadrupole magnet, and dipole magnet in the system is equivalent to a linear transfer matrix element, and the initial beam envelope matrix is ​​set as follows:

[0155]

[0156] in, The matrix is ​​the beam envelope matrix. express The mean square value of the horizontal displacement in the matrix. σ represents the horizontal beam spot size-divergence correlation moment. 21 =σ 12 , σ 22 σ represents the mean square value of the horizontal divergence angle. 33 σ represents the mean square value of the vertical displacement. 34 σ represents the vertical beam spot size-divergence correlation moment. 43 =σ 34 , σ 44 This represents the mean square value of the vertical divergence angle.

[0157] The beam transmission system contains n transmission elements, whose linear transmission matrices are respectively Then the beam parameters at the outlet of any element are obtained recursively by the following formula:

[0158]

[0159] Where i represents the number of any of the n transmission elements, and T is the matrix transpose symbol.

[0160] The relationship between the horizontal particle coordinates and the transfer matrix of a dipolar iron particle:

[0161]

[0162] The linear transmission equation and transmission matrix expression for a dipole iron in the vertical direction are as follows:

[0163]

[0164] in The horizontal focusing constant, , The vertical focusing constant, , The quadrupole field index. Let be the curvature at the particle's central orbit. Let L be the deflection radius of the dipolar magnet, and L be the arc length (equivalent length) of the dipolar magnet.

[0165] Horizontal transfer matrix of the drift segment: Vertical transmission matrix: , where L is the length of the drift segment.

[0166] Four-pole horizontal transmission matrix ,

[0167] Perpendicular direction of quadrupole:

[0168] Where L is the length of the quadrupole. It is the focusing constant of the tetrapolar iron. Let be the magnetic field strength at a position with a radius of a0 from the center of the quadrupole. Let h be the magnetic field strength of the particle, and h = 1 / → 0.

[0169] The Twiss parameters and dispersion function are obtained from the σ matrix and the transfer matrix:

[0170]

[0171] Where, β x α x β y α y These are Twiss parameters, representing the horizontal β function, horizontal α function, vertical β function, and vertical α function, respectively. Represents the horizontal dispersion function. Indicates the horizontal dispersion slope, This represents the momentum dispersion function in the linear transfer matrix R. This represents the slope of the momentum dispersion function in the linear transfer matrix R.

[0172] In TRANSPORT, the following parameters in the main ring deflection assembly 40 are defined as optimization decision variables: quadrupole magnetic field, effective length of the dipolar and quadrupole, good field size, dipolar air gap, dipolar edge angle, and drift segment length.

[0173]

[0174] in, These represent the magnetic fields of the three quadrupole iron pieces, with the positive and negative signs indicating the focusing / defocusing direction. This indicates the effective length of each quadrupole. This indicates the effective length of the dipole. Indicates the edge angle of the diode. This indicates the air gap of the diode. These represent the drift segment lengths from the inlet of the main ring deflection assembly to the magnet at the outlet of the main ring deflection assembly.

[0175] Its initial values ​​are set as follows: focusing quadrupole magnetic field 0.05 T, defocusing quadrupole magnetic field −0.05 T, effective quadrupole length 40 mm, good field radius 5 mm, effective dipolar magnet length 150 mm, air gap 7.5 mm, dipolar magnet edge angle 7.5°, distance between quadrupoles 40 mm, and distance between dipolar magnets and quadrupoles 50 mm. .

[0176] The objective function is constructed in the multi-objective optimization as follows:

[0177] (1) Objective function for minimizing system geometry f 1 Defined as:

[0178]

[0179] in, The deflection radius of the combined deflection assembly deflects the diode 4. This indicates the effective length of grade IV iron. The length of the drift segment between the quadrupoles in the combined deflection assembly 30. The drift segment length between the deflection diode 4 in the combined deflection assembly and the quadrupole in the front focusing assembly is determined. The drift segment length between the deflection diode 4 in the combined deflection assembly and the quadrupole in the post-focusing assembly is determined. To focus on the length of the drift segment between the two pairs of two-in-one quadrupoles in the component, The length of the drift segment between the post-focusing assembly and the electron beam target point of the treatment head. The distance from the electronic target position of the treatment head to the center point of the regular N-gon is equal to 1m, and a constraint is applied:

[0180]

[0181]

[0182] (2) To ensure that the beam does not collide with the tube wall throughout the entire path and to meet the clinical transmission efficiency requirements, the envelope function, dispersion function, and transmission efficiency are jointly constructed as the beam safety margin function, i.e., the second objective function. f 2 First, the transmission efficiency under the k-th beam condition (any one of the 5 beam parameters shown in Table 1) is defined as:

[0183]

[0184] in, For the number of injected particles, Let this be the number of particles reaching the exit without aperture loss or exceeding the good field limit. f 2 Defined as:

[0185]

[0186] Where k represents the number of any one of the five sets of beam parameters shown in Table 1, and s represents the path coordinates along the beam propagation path. This represents the Twiss-β function in the horizontal direction at position s. This represents the beam emittance in the horizontal direction of the k-th group of beam parameters. This represents the Twiss-β function in the vertical direction at position s. This represents the beam emittance in the vertical direction of the k-th set of beam parameters. Let represent the horizontal dispersion function at position s.

[0187] And apply hard constraints: .

[0188] (3) To avoid the influence of energy dispersion on the beam spot, an anti-dispersion condition is applied at the second diode iron outlet, the center point CPi of the periodic segment, and the isocenter point. The fitting error is defined as the third objective function. f 3 (Achromatic residual function):

[0189]

[0190] Where j represents the sampling point number, This represents the path coordinates of the j-th sampling point along the transmission direction. Indicates the location The horizontal dispersion function at that point, Indicates position The horizontal dispersion slope at N p This indicates the total number of sampling points, which are the second diode iron outlet, the center point CPi of the periodic segment, and the isocenter point.

[0191] And impose constraints: .

[0192] The following physical and engineering constraints are simultaneously applied during the multi-objective optimization process: symmetric emissivity Double waistband at matching point Achromatic transmission Aperture constraint ; Quadrupole magnetic field gradient Effective length of quadrupole ; Dipolar magnetic field strength Diode air gap .

[0193] (4) In TRANSPORT, the above multi-objective functions are uniformly constructed into a weighted least squares scalar objective function:

[0194]

[0195] in And use weights: , , ; The smaller the better.

[0196] The corresponding fitting form in TRANSPORT is:

[0197]

[0198] in For the physical quantity to be fitted (β function, R) 16 R 26 (Envelope radius, magnet gradient, system radius) This corresponds to the target value.

[0199] (5) To ensure that the system can operate stably under different beam parameters, a multi-condition joint optimization strategy is adopted to optimize the five sets of input beam parameters in Table 1. Simultaneously apply fitting constraints to construct a robust objective function:

[0200]

[0201] The same set of magnet parameters must simultaneously meet the following requirements under all operating conditions:

[0202]

[0203] in, This represents the horizontal dispersion function under the k-th set of beam parameters. This represents the horizontal dispersion slope under the k-th set of beam parameters. This represents the transmission efficiency under the k-th group of beam parameters. This represents the β function in the horizontal direction under the k-th set of beam parameters. This represents the beam emittance in the horizontal direction under the k-th set of beam parameters.

[0204] During the solution process, TRANSPORT uses a weighted least squares iterative algorithm to update the variables:

[0205]

[0206] Where J is the sensitivity matrix of the fitted quantity to the variable, W is the weight matrix, t represents the iteration number, and T is the matrix transpose symbol.

[0207] When the following conditions are met: The iteration terminates at time 1, outputting the optimal quadrupole magnetic field parameters (-0.0871 T, 0.1339 T, -0.0871 T), effective length of the dipole (120 mm), effective length of the quadrupole (50 mm), air gap size of the dipole (10 mm) and edge angle (7.5°), good field region of the quadrupole (17 mm), and drift segment length. The final design values ​​are 500mm, 50mm, 40mm, 40mm, 50mm, and 500mm, respectively, to obtain a ring beam transmission system beam optics scheme that meets the requirements of a transmission efficiency of not less than 95%, a system radius of not more than 2 m, and stable and reliable beam operation.

[0208] In other embodiments, the beam energy E of the electron beam output by the electron beam generating device can also be adjusted within the range of 6-9 MeV, and the relationship between momentum P and energy E is P=(E (E+2 0.511)) 1 / 2 The relationship between the magnetic stiffness and momentum of electron beams with different energies is Bρ = 0.0033356. P, the radius of all deflecting dipolar iron and Kicker magnets is 0.15m, and the corresponding magnetic field is B=0.02234. P, the magnetic field of the electron beam deflector magnet with different energies can be obtained by scaling the relationship between momentum P and energy E and the relationship between magnetic stiffness and momentum.

[0209] The annular beam projection system for radiotherapy of the present invention can also be other regular polygons, such as... Figure 8 As shown, when 4 ≤ N ≤ 12, the deflection angle of the regular polygonal main ring deflection component 40 is adaptively adjusted. When N = 12, the model diagram of the system of the present invention is as follows. Figure 9-11 As shown.

[0210] Example 2: Multi-chamber system based on a linear accelerator

[0211] This embodiment provides a multi-chamber system based on a single linear accelerator. The system employs m sets of regular N-gonal annular projection systems as described in Embodiment 1. These m sets of regular polygonal annular systems share the same accelerator through a central beam transmission system, using time multiplexing, energy zone multiplexing, or time-division pulse multiplexing. One accelerator can simultaneously provide FLASH, electron, proton, or heavy ion beam services to multiple treatment chambers, significantly improving equipment resource utilization and economy. Each set of regular N-gonal annular projection systems forms one treatment chamber.

[0212] When there are two treatment rooms, and the two treatment rooms have the same layout, such as Figure 12 As shown. The annular layout of each treatment room in this system is the same as in Embodiment 1. The central beam transmission system is positioned between the electron beam generating device 1 and the initial beam deflection system 200, and consists of two sets of central beam transmission combined deflection components 10. The deflection angle of the central beam transmission system is 360 degrees, perpendicularly intersecting the sides of the N-sided polygon, but not overlapping with the annular gantry. When there are two treatment rooms, and the layout of the two treatment rooms is mirror-image, as... Figure 13 As shown, the central beam transmission system undergoes adaptive adjustments.

[0213] Using a ring-shaped layout similar to the two treatment rooms, the system in this embodiment can also be expanded to three to six treatment rooms, such as... Figure 14 As shown.

[0214] As can be seen from the above embodiments, the present invention provides a static multi-angle beam projection system for ultra-high dose rate radiotherapy (FLASH). The system adopts a regular N-gon (4≤N≤12) static rigid annular gantry structure, completely abandoning the traditional rotating gantry, and achieving multi-angle irradiation through electromagnetic deflection. The system includes: a medical linear accelerator for generating the therapeutic electron beam; a beam focusing and transmission system located downstream of the accelerator; N-1 main ring deflection components with a deflection angle of 360° / N for constructing the annular main beamline; and N sets of 90° combined deflection components, each set consisting of a fast-switching kicker and an auxiliary deflecting dipole, and equipped with a two-in-one quadrupole for beam optical matching. The system arranges N treatment heads along the inscribed circle direction of the regular polygon to bombard the target material with the deflected electron beam to generate X-rays. The core control concept of this invention is to dynamically schedule the magnetic fields of each kicker at the millisecond level (≤5 ms) using an FPGA / RTOS real-time control architecture. This allows for sequential "closing the preceding sequence and opening the following sequence" to advance the beam segment by segment along the annular main beamline, achieving instantaneous extraction at any predetermined angle, thus completing multi-angle irradiation without mechanical movement or delay. The system's beam optics employ a fully periodic design to ensure consistent beam parameters at all angles, enabling single-shot irradiation, multi-angle FLASH, arbitrary sequence switching, and millisecond-level dose segmentation. The device can be expanded to allow multiple treatment rooms to share the same accelerator and can be upgraded for high-energy electron, proton, and heavy ion FLASH therapy. This invention overcomes the technical bottlenecks of traditional rotating gantry systems, such as slow switching speed, large mechanical inertia, large vibration errors, and large footprint. It achieves a small footprint, fast switching speed, short treatment time (total irradiation time less than 500 ms), and sustainable upgradeability, making it suitable for next-generation precision radiotherapy.

Claims

1. A ring beam projection system for radiotherapy, characterized in that, The system includes an electron beam generating device (1), a beam focusing and transmission system (20), an initial beam deflection system (200), N-1 main ring beam deflection systems (300), and a beam blocker (7). The initial beam deflection system (200) is a set of combined deflection components (30). The main ring beam deflection system (300) includes a set of main ring deflection components (40) and a set of combined deflection components (30) arranged in sequence. The N combined deflection components (30) are arranged in an N-order rotationally symmetric manner and are tangent to the line connecting the midpoint of each side of a regular N-sided polygon and the center point of the regular N-sided polygon, where 4≤N≤12. The beam focusing and transmission system (20) is composed of a quadrupole (2); The combined deflection assembly (30) includes the following components arranged in sequence: Kicker magnet (3), front focusing assembly, combined deflection assembly deflecting diode (4), rear focusing assembly, and treatment head (6); the treatment head is formed by connecting the center of a regular N-gon with the center point of one of its sides perpendicularly intersecting the corresponding area of ​​the side. The main ring deflection assembly (40) includes the following components arranged in sequence: main ring deflection assembly deflecting dipolar iron (5), quadrupole iron (2), and main ring deflection assembly deflecting dipolar iron (5).

2. The annular beam projection system for radiotherapy according to claim 1, characterized in that: The parameters of the annular beam projection system used for radiotherapy were determined by a multi-objective optimization method; The decision variable parameters of the multi-objective optimization method include the following in the main loop deflection component (40): quadrupole magnetic field, effective length of the deflecting dipole, effective length of the quadrupole, size of the quadrupole good field region, air gap of the dipole, edge angle of the dipole, and length of the drift segment. The objective function of the multi-objective optimization method is: ； in, , , They represent the objective functions respectively. , , The weights; The objective function is to minimize the system's geometric dimensions. ， in, To determine the deflection radius of the deflection diode (4) in the combined deflection assembly, This indicates the effective length of grade IV iron. The length of the drift segment between the quadrupoles in the combined deflection assembly (30) is given. The drift segment length between the deflecting diode (4) in the combined deflection assembly and the quadrupole in the front focusing assembly is given. The drift length between the deflection diode (4) in the combined deflection assembly and the quadrupole in the post-focusing assembly is given. To focus on the length of the drift segment between the quadrupoles in the component, The length of the drift segment between the post-focusing assembly and the electron beam target point of the treatment head. The distance from the electronic target position of the treatment head to the center point of the regular N-gon; Let be the beam safety margin function. ， Where k represents the number of any set of beam parameters, and s represents the path coordinates along the beam propagation path. This represents the Twiss-β function in the horizontal direction at position s. This represents the beam emittance in the horizontal direction of the k-th group. This represents the Twiss-β function in the vertical direction at position s. This represents the beam emittance in the vertical direction of the k-th group. This represents the horizontal dispersion function at position s; For the dispersive residual function, Where j represents the sampling point number, This represents the path coordinates of the j-th sampling point along the transmission direction. Indicates the location The horizontal dispersion function at that point, Indicates position The horizontal dispersion slope at N p This indicates the total number of sampling points.

3. The annular beam projection system for radiotherapy according to claim 2, characterized in that, The termination conditions of the multi-objective optimization method include: or , in, This represents the difference between the parameters of the decision variable before and after the latest iteration; And / or, the constraints of the objective function of the multi-objective optimization method include: , , , , ; in, To determine the deflection radius of the deflection diode (4) in the combined deflection assembly, This indicates the effective length of grade IV iron. The length of the drift segment between the quadrupoles in the combined deflection assembly (30) is given. The drift segment length between the deflecting diode (4) in the combined deflection assembly and the quadrupole in the front focusing assembly is given. These represent the drift segment length before the entrance of the main ring deflection component (40) and the drift segment length from the exit to the matching point, respectively. The matching point refers to the center point of the i-th side of the regular N-gon, where i represents the side number. This indicates transmission efficiency.

4. The annular beam projection system for radiotherapy according to claim 2, characterized in that: The multi-objective optimization process simultaneously applies the following physical and engineering constraints: symmetric emissivity Double waistband at matching point Achromatic transmission Aperture constraint ; Quadrupole magnetic field gradient Effective length of quadrupole ; Dipolar magnetic field strength The air gap of the diode is ; The matching point refers to the center point of the i-th side of the regular N-gon, denoted as CP. i , where i represents the edge number. Indicates the beam emittance in the horizontal direction. Indicates beam emittance in the vertical direction. express The mean square value of the horizontal displacement in the matrix. express The mean square value of the vertical displacement in the matrix. express Horizontal displacement-angle correlation in the matrix This indicates a vertical displacement-azimuth correlation. express The mean square value of the horizontal divergence angle in the matrix. express The mean square value of the vertical divergence angle in the matrix. This represents the momentum dispersion function in the linear transfer matrix R. β represents the slope of the momentum dispersion function in the linear transfer matrix R. x Represents the Twiss-β function in the horizontal direction. β represents the beam emittance in the horizontal direction of the k-th beam parameter group. y Represents the vertical Twiss-β function. This represents the beam emittance in the vertical direction of the k-th group of beam parameters.

5. The annular beam projection system for radiotherapy according to claim 4, characterized in that: The N-1 main ring beam deflection systems (300) have the same beam parameters, and the center point of the i-th side of the regular N-gon is CP. i 'i' represents the edge number, and each CP i Located at the beam waist and with consistent beam parameters; The beam parameters of the annular beam projection system for radiotherapy at each CPi include: beam spot size x, beam emission angle y = 2x, and emissivity ε = xy.

6. The annular beam projection system for radiotherapy according to claim 5, characterized in that, Each CP i The beam parameters at the point include: beam spot size 1≤x≤3 mm, beam emittance 2π mm·mrad≤ε≤18π mm·mrad.

7. The annular beam projection system for radiotherapy according to claim 1 or 2, characterized in that: At the Kicker magnet inlet of the combined deflection assembly, the beam spot size is x. k = x + L·y, emission angle x' k = y, L is the distance from the i-th Kicker magnet to CP i The distance, and the beam is in a converging state; And / or, the size of the band spot at the entrance of the treatment head (6) is the same, 1-3 mm, and located at the waist position, CP i-1 The electron beam center trajectory path to the treatment head inlet BMi is equal, CP i The straight-line distances to the treatment head inlet BMi are also equal, all <1m; And / or, the deflection angle of the combined deflection assembly (30) is 90°; the deflection angle of the main ring deflection assembly (40) is 360° / N; The main ring deflection assembly (40) includes two main ring deflection assembly deflecting dipoles (5) and three quadrupoles, with the quadrupoles located between the two main ring deflection assembly deflecting dipoles (5); the combined deflection assembly (30) includes one Kicker magnet (3) and one combined deflection assembly deflecting dipole (4), the front focusing assembly and the rear focusing assembly are the same, both including two sets of two-in-one quadrupoles; the distance from the beam focusing and transmission system (20) to K1 is equal to the distance from the quadrupole in the main ring deflection assembly (40) to the corresponding Kicker magnet, and the first Kicker magnet into which the electron beam enters is set as K1; And / or, the beam focusing and transmission system (20) includes two sets of two-in-one quadrupole irons (2); the quadrupole iron, the combined deflection component deflection dipolar iron and the main ring deflection component deflection dipolar iron are all wound with quadrupole coils, the effective length of the quadrupole coil is ≤50mm, the spacing between the coils is ≤50mm, and the hole radius of the quadrupole iron is 5-10mm. And / or, the electron beam generating device (1) outputs an electron beam with a beam energy E of 6-9 MeV; And / or, the dose rate delivered by the annular beam irradiation system is ≥40 Gy / s, the shut-off time of the Kicker magnet is ≤5ms, and the total time used for irradiation by the annular beam irradiation system is less than 500ms; And / or, the air gap and magnetic field strength of the combined deflection assembly deflecting dipolar iron, the main ring deflection assembly deflecting dipolar iron, and the Kicker magnet are all the same, with an air gap of 5-10mm and a magnetic field strength of ≤0.15T. And / or, the combined deflection assembly has a horizontal projection distance of ≤0.5 m, and the combined deflection assembly deflects the same radius of the dipolar iron and the Kicker magnet, both of which are <0.2 m; And / or, the electron beam generating device (1) is selected from linear accelerators, cyclotron accelerators, petal accelerators, high-energy electron beam sources of 20-100MeV, proton sources of 70-250MeV, or heavy ion accelerators of 150-430MeV / u. And / or, the side length of the regular N-gon is s, and the perpendicular distance from the center of the regular N-gon to each side is R, satisfying the formula: , R < 2 m.

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