Beam distribution system suitable for variable energy linear accelerator FLASH treatment

Abstract

The invention discloses a beam distribution system suitable for FLASH treatment of a variable-energy linear accelerator, which adopts a mode of combining variable energy of the linear accelerator and transverse scanning, realizes longitudinal depth coverage through rapid variable energy of the linear accelerator, has two transverse implementation modes, including two-dimensional spot scanning through a pencil beam, two-dimensional spot scanning through a linear beam, two-dimensional spot scanning through a linear beam, and two-dimensional spot scanning through a linear beam. And the three-dimensional conformal irradiation is directly completed without customizing a ridge-shaped filter, so that the manufacturing difficulty caused by the complex shape of the target region can be avoided, the cost is reduced, and the universality is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of irradiation radiotherapy, and in particular, relates to a beam delivery system suitable for variable energy linear accelerator FLASH treatment. Background Art

[0002] Existing conventional radiotherapy devices damage cancer cells through ionizing radiation, which in turn leads to cancer cell death. However, radiotherapy also causes acute and chronic toxicity to normal tissues around the tumor. These radiation-induced toxicities limit the radiation dose delivered to the tumor, thereby limiting the local control effect of radiotherapy on the tumor.

[0003] Flash (FLASH) radiotherapy refers to radiotherapy that uses the mechanism of ultra-high dose rate irradiation to protect normal tissues. FLASH radiotherapy requires irradiation of >40Gy in less than 1s, so the beam delivery method is also a major problem that hinders the application of FLASH radiotherapy. Currently, in the treatment or research to achieve the FLASH effect, the method to meet the ultra-high dose rate is to reduce the size of the target area, such as 2cm×2cm, 3cm×3cm. If you want to achieve the FLASH effect for a target area of ​​10cm×10cm×10cm, the average intensity of the scattered irradiation beam must be at least greater than 700nA.

[0004] Although passive delivery can achieve two-dimensional or three-dimensional conformality, the utilization rate of the beam is low. For example, when the incident energy of protons is 230MeV (~39cm), the beam transmission efficiency is only 10% when the energy drops to 170MeV (~17cm), and when it drops to 70MeV (~4cm), the beam transmission efficiency is less than 1%. If two-dimensional conformality is used, the dose received by normal tissue is high and the dose required for a single irradiation is also relatively high, and the patient may have greater side effects; if three-dimensional conformal irradiation is used, it is required that the grating needs to change its opening shape at the ms level in each energy layer, and the fastest grating change time is 0.2s. Therefore, with current technology, the passive delivery method cannot meet the irradiation requirements of FLASH radiotherapy.

[0005] Active delivery is used to perform three-dimensional conformal irradiation on the tumor layer by layer. For synchrotron and linear accelerators, when the output beam intensity is 700nA, the accelerator needs to provide multiple (for example, for a 10cm×10cm×10cm tumor, the typical value is 32) energy beams within 1s, and each energy layer needs to complete the scanning irradiation of thousands of targets within about 30ms, that is, the time spent on each target is 30µs, and the magnet scanning frequency is 30kHz. Currently, dose monitoring and scanning speed cannot meet the above conditions, and do not meet the dose rate distribution requirements of three-dimensional conformal irradiation required for FLASH radiotherapy.

[0006] Previously, the Chinese invention patent application with publication number CN114452550A provided a beam delivery system that combined longitudinal expansion and transverse scanning of a ridge filter, which can achieve dose delivery that meets the requirements of FLASH treatment using existing scanning technology. However, its ridge filter needs to be customized according to the depth direction and shape of the target area of ​​each patient, and its versatility is poor. In addition, if the target area is complex or irregular in shape, its manufacturing precision is extremely high, which may lead to a significant increase in process difficulty and cost.

[0007] In addition, low-frequency linear accelerators mostly use low operating frequencies of tens to hundreds of MHz, are long, have large lateral dimensions, high flux, and are expensive. They are mostly used in basic scientific research devices and are difficult to apply in the field of radiotherapy. High-frequency linear accelerators have the advantages of low cost and compactness, but low flux, with a maximum peak intensity of about 100 µA and an average flux of about 100 nA, and cannot meet the requirements of three-dimensional conformal FLASH radiotherapy. Summary of the invention

[0008] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a beam delivery system suitable for variable energy linear accelerator FLASH treatment, aiming to achieve three-dimensional conformal irradiation of proton beams and improve the accuracy and efficiency of cancer radiotherapy.

[0009] To achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a beam delivery system suitable for FLASH therapy with a variable energy linear accelerator, characterized in that it comprises a plurality of quadrupole magnets, a Y-direction scanning magnet, an X-direction scanning magnet, a stripe ionization chamber, a dose ionization chamber and a therapy control system arranged in sequence along the beam transmission direction; wherein the quadrupole magnet is used to expand the diameter of the field of view of the macro bunch of the proton beam emitted by the variable energy linear accelerator to a specified size; the Y-direction scanning magnet is used to deflect the beam in the transverse y direction; the X-direction scanning magnet is used to deflect the beam in the transverse x direction; the stripe ionization chamber is used to measure the position of the beam in real time; the dose ionization chamber is used to measure the irradiation dose of the beam in real time; the therapy control system comprises: a calibration module, used to perform dose calibration on the macro bunch of the proton beam of each energy layer; a demand setting module, used to determine the number of particles to be irradiated on each target point in the target area according to the FLASH irradiation requirements; an accelerator control module, used to control the variable energy linear accelerator to perform point-by-point irradiation in the transverse direction according to the determined number of particles using a pencil beam scanning mode.

[0010] Preferably, when the average beam intensity is increased to several µA, at the same dose, the quadrupole magnet increases the field of view of each macro bunch to a diameter of more than 20 mm.

[0011] Preferably, the variable energy linear accelerator changes energy rapidly by presetting the phases and amplitudes of multiple cavities. The energy is changed by fixed point and range energy change. The energy change time is in ms level. The energy change step is less than 1MeV. The macro bunch pulse length of the proton beam is controlled by a beam chopper. The pulse length change step is less than 2ns. A layered scanning method of first the far end and then the near end is adopted in the longitudinal direction.

[0012] In a second aspect, the present invention provides another beam delivery system suitable for variable energy linear accelerator FLASH treatment, characterized in that it comprises a plurality of quadrupole-octupole-dodecopole combination magnets arranged in sequence along the beam transmission direction, a scanning magnet, a stripe ionization chamber, a dose ionization chamber and a treatment control system; wherein the quadrupole-octupole-dodecopole combination magnet is used to stretch the macro bunch of the proton beam emitted by the variable energy linear accelerator in the transverse x direction; The scanning magnet is used to enable the macro bunch to realize triangular wave or sine wave one-dimensional scanning in the transverse y direction; the stripe ionization chamber is used to measure the position of the beam in real time; the dose ionization chamber is used to measure the irradiation dose of the beam in real time; the treatment control system includes: a calibration module, which is used to calibrate the dose of the macro bunch of the proton beam of each energy layer; a demand setting module, which is used to determine the number of particles to be irradiated on each target point in the target area according to the FLASH irradiation requirements; an accelerator control module, which is used to control the variable energy linear accelerator to adopt a triangular wave or sine wave one-dimensional scanning mode to perform point-by-point irradiation in the transverse y direction according to the determined number of particles.

[0013] Preferably, when the average beam intensity is increased by about 3-3.5 µA, at the same dose, the quadrupole-octupole-dodecopole combination magnet stretches each macro bunch in the transverse x direction to obtain a macro bunch with a length of less than 100 mm and a width of more than 4.3 mm.

[0014] Preferably, the variable energy linear accelerator changes energy rapidly by presetting the phases and amplitudes of multiple cavities. The energy is changed by fixed point and range energy change. The energy change time is in ms level. The energy change step is less than 1MeV. The macro bunch pulse length of the proton beam is controlled by a beam chopper. The pulse length change step is less than 2ns. A layered scanning method of first the far end and then the near end is adopted in the longitudinal direction.

[0015] The present invention adopts the above technical solution, which has the following advantages: 1. The beam distribution system provided by the present invention can achieve a significant change in the lateral size and distribution of the beam, with the maximum lateral size ratio of about 25 times, so that single-energy layer lateral scanning irradiation can be completed through one-dimensional scanning such as triangular wave or sine wave, thereby improving irradiation efficiency.

[0016] 2. The variable energy linear accelerator can adjust the beam energy in the ms level, provide a bunch with a maximum of about 32 energy points in the second level or 5-6 different energy points in less than 200ms, and flexibly combine the lateral active scanning and space segmentation effects to achieve efficient three-dimensional irradiation at a scanning frequency of less than 1kHz, meeting the dose rate requirements of three-dimensional conformal irradiation.

[0017] 3. The present invention realizes longitudinal depth coverage through rapid energy change of a linear accelerator and directly completes three-dimensional conformal irradiation by combining active lateral scanning without customized ridge filters, thus avoiding manufacturing difficulties caused by complex target area shapes, reducing costs and improving versatility. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Throughout the accompanying drawings, the same reference numerals are used to represent the same components. In the accompanying drawings: Figure 1 The scanning principle diagram of the pencil beam two-dimensional point scanning method; Figure 2 A schematic diagram of the structure of a pencil beam two-dimensional point scanning beam delivery system provided in Example 1 of the present invention; Figure 3 A flowchart of a pencil beam two-dimensional point scanning beam delivery method provided in Example 1 of the present invention; Figure 4 The scanning principle diagram of one-dimensional scanning methods such as triangle wave or sine wave; Figure 5 A schematic diagram of the structure of a one-dimensional scanning beam delivery system such as a triangular wave or a sine wave provided in Embodiment 2 of the present invention; Figure 6 This is a flow chart of a one-dimensional scanning beam delivery method such as a triangular wave or a sine wave provided in Example 2 of the present invention. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical scheme and advantages of the present invention clearer, the specific embodiments of the present invention are further described below in conjunction with the accompanying drawings. Although the exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0020] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0021] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is more than two, unless otherwise clearly and specifically defined.

[0022] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0023] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0024] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0025] In the following, a beam delivery system suitable for FLASH proton therapy provided by an embodiment of the present invention is described in detail with reference to the accompanying drawings.

[0026] The present invention provides a beam distribution system combining linear accelerator variable energy and transverse scanning. The variable energy linear accelerator realizes rapid beam energy change in the longitudinal direction, and there are two ways to realize it in the transverse direction, including pencil beam two-dimensional point scanning or triangular wave one-dimensional scanning, so as to complete the three-dimensional dose distribution of the entire target area. Due to the use of scanning irradiation, the proton utilization rate is high, the single point demand is one order of magnitude lower, and the number of particles required for each scanning point is 10e9-10e10.

[0027] Example 1 The present embodiment provides a pencil beam two-dimensional point scanning beam delivery system. In the present embodiment, when the average beam intensity is increased to several µA (for example, 3-3.5 µA), under the same dose, the field of view of each macro bunch can be increased to a diameter of more than 20 mm. Pencil beam two-dimensional point scanning is adopted with a step size of 20 mm, and each dimension is scanned 5 times, with a total of 25 two-dimensional scans. The number of bunches is sufficient, and the magnet scanning frequency does not exceed 1 kHz, which also meets the requirements. Figure 1 The scanning process of the pencil beam two-dimensional point scanning on an area of ​​10cm*10cm is shown, and the red arrow is the movement trajectory of the beam spot.

[0028] See also Figure 2The beam distribution system provided in this embodiment includes a plurality of quadrupole magnets 1, a Y-direction scanning magnet 2, an X-direction scanning magnet 3, a stripe ionization chamber 4, a dose ionization chamber 5 and a treatment control system (not shown in the figure) arranged in sequence along the beam transmission direction. Among them, the quadrupole magnet 1 is used to expand the diameter of the field of view of the macro bunch of the proton beam emitted by the variable energy linear accelerator to a specified size; the Y-direction scanning magnet 2 is used to deflect the beam in the lateral y direction; the X-direction scanning magnet 3 is used to deflect the beam in the lateral x direction; the stripe ionization chamber is used to measure the position of the beam in real time; the dose ionization chamber is used to measure the irradiation dose of the beam in real time; the treatment control system is provided with a calibration module, a demand setting module and an accelerator control module, the calibration module is used to calibrate the dose of the macro bunch of the proton beam of each energy layer; the demand setting module is used to determine the number of particles to be irradiated at each target point in the target area 8 according to the FLASH irradiation requirements; the accelerator control module is used to control the variable energy linear accelerator to use a pencil beam scanning mode to perform point-by-point irradiation in the lateral direction according to the determined number of particles (please refer to Figure 1 ).

[0029] Compared with the beam distribution system of the longitudinal modulation transverse scanning scheme of the monoenergetic proton beam, this embodiment realizes the rapid energy change and pulse length control of the exit beam through the variable energy linear accelerator, so that the pencil beam can irradiate the entire longitudinal depth of the target area and the dose is distributed as much as possible in front of the target area, so there is no need for a compensator and a ridge filter, which will greatly reduce the treatment cost and simplify the treatment process, and can also achieve precise control of the dose. The variable energy linear accelerator quickly changes the energy by presetting the phase and amplitude of multiple cavities. The energy change adopts the fixed point and range energy change method. The fixed energy is usually 150MeV, 230MeV, etc. The energy change time is at the ms level, and the energy change step can be less than 1MeV. The proton beam macro bunch pulse length is controlled by the beam chopper, and the pulse length change step can be less than 2ns. The longitudinal layered scanning method of the distal end first and the proximal end is adopted. The multiple quadrupole magnets 1 not only have the traditional function of maintaining high beam quality, but also undertake the function of expanding the diameter of the field of view of the macro bunch. As the average beam intensity increases, at the same dose, the field of view of each macrobeam group also increases. When the average beam intensity is about 3~3.5µA, the field of view of each macrobeam group can be increased to more than 20mm in diameter.

[0030] See also Figure 3 When the beam distribution system provided in the above embodiment is used, the process of completing the beam distribution is as follows: S100. Expanding the diameter of the field of view of the macro bunch of the pencil beam by using a plurality of quadrupole magnets 1 (for example, increasing the diameter to 20 mm); S200. Calibrate and adjust the dose of the macro bunch of pencil beam at each energy layer; S300. According to the requirements of FLASH irradiation, determine the number of particles to be irradiated at each target point on the target area 8; S400. The variable energy linear accelerator adopts pencil beam scanning mode to irradiate according to the number of particles determined in step S300. In order to accurately distribute the dose of the proton beam, it is also necessary to adjust the irradiation dose in combination with the variable energy linear accelerator to control the macro bunch pulse length of the proton beam, so as to finally provide a proton beam with a corresponding number of particles at the corresponding target point, and irradiate the corresponding target point in the target area 8 through the Y-axis scanning magnet 2, the X-axis scanning magnet 3, the stripe ionization chamber 4 and the dose ionization chamber 5 in sequence.

[0031] In the above embodiment, preferably, if the target area 8 is larger than the set area (for example, 10 cm*10 cm), when the dose rate required for FLASH irradiation during the irradiation process cannot meet the coverage of the entire target area 8, the target area 8 is irradiated in different regions, that is, the target area 8 is divided into several regions, and only the dose coverage of a certain area in the target area is performed in one cycle, so that the area meets the FLASH irradiation requirements, and so on, until the dose coverage of all areas in the target area 8 is completed.

[0032] Example 2 This embodiment provides a one-dimensional scanning beam delivery system such as a triangular wave or a sine wave. In this embodiment, when the average beam intensity is increased to several µA (for example, 3-3.5 µA), at the same dose, each macro bunch is stretched in the lateral x direction to obtain a macro bunch with a length of less than 100 mm and a width of more than 4.3 mm, and a one-dimensional scanning such as a triangular wave or a sine wave is performed in the lateral y direction with a step size of 3 mm. About 30 scans are required. The number of bunches is sufficient, and the magnet scanning frequency does not exceed 1 kHz, which also meets the requirements. Figure 4 It shows the scanning process of one-dimensional scanning such as triangular wave or sine wave on an area of ​​10cm*10cm. The red arrow is the movement trajectory of the beam spot.

[0033] See also Figure 5The beam delivery system provided in this embodiment includes a plurality of quadrupole-octupole-dodecopole combination magnets 6 arranged in sequence along the beam transmission direction, a scanning magnet 7, a stripe ionization chamber 4, a dose ionization chamber 5 and a treatment control system (not shown in the figure). Among them, the quadrupole-octupole-dodecopole combination magnet 6 is used to stretch the macro bunch of the proton beam emitted by the variable energy linear accelerator in the horizontal x direction to obtain a macro bunch with a size of 100mm*4.3mm; the scanning magnet 7 is used to enable the macro bunch to realize one-dimensional scanning such as triangular wave or sine wave in the horizontal y direction; the stripe ionization chamber 3 is used to measure the position of the beam in real time; the dose ionization chamber 4 is used to measure the irradiation dose of the beam in real time; the treatment control system is provided with a calibration module, a demand setting module and an accelerator control module, the calibration module is used to calibrate the dose of the macro bunch of the proton beam of each energy layer; the demand setting module is used to determine the number of particles to be irradiated on each target point in the target area 8 according to the FLASH irradiation requirements; the accelerator control module is used to control the variable energy linear accelerator to adopt a one-dimensional scanning mode such as triangular wave or sine wave to perform point-by-point irradiation in the horizontal y direction according to the determined number of particles.

[0034] Compared with Example 1, this embodiment no longer uses only the quadrupole magnet 1 to expand the diameter of the field of view of the macro bunch, but instead uses a quadrupole-octupole-dodecopole combination magnet 6 to stretch each macro bunch in the transverse x direction to obtain a macro bunch with a length of less than 100 mm and a width of more than 4.3 mm, and performs one-dimensional scanning such as triangular wave or sine wave in the transverse y direction. Therefore, compared with Solution 1, there is one less set of scanning magnets, which further reduces the production cost and improves the flexibility of use.

[0035] See also Figure 6 Based on the beam distribution system provided in the above embodiment, the present solution also provides a beam distribution method, comprising the following steps: S100. Each macro bunch is stretched in the transverse x direction by a quadrupole-octupole-dodecopole combination magnet 6 to obtain a macro bunch of size 100 mm*4.3 mm; S200. Calibrate and adjust the dose of the proton beam macro bunch of each energy layer; S300. According to the requirements of FLASH irradiation, determine the number of particles to be irradiated at each target point on the target area 8; S400. The variable energy linear accelerator uses a one-dimensional scanning mode such as a triangular wave or a sine wave to irradiate according to the number of particles determined in step S300. In order to accurately distribute the dose of the proton beam, it is also necessary to adjust the irradiation dose in combination with the linear accelerator to control the macro bunch pulse length of the proton beam, and finally provide a proton beam with a corresponding number of particles at the corresponding target point, and irradiate the corresponding target point in the target area 8 through the scanning magnet 3, the stripe ionization chamber 4 and the dose ionization chamber 5 in turn.

[0036] In the above embodiment, preferably, if the target area 8 is larger than the set area (for example, 10 cm*10 cm), when the dose rate required for FLASH irradiation during the irradiation process cannot meet the coverage of the entire target area 8, the target area 8 is irradiated in different regions, that is, the target area 8 is divided into several regions, and only the dose coverage of a certain area in the target area 8 is performed in one cycle, so that the area meets the FLASH irradiation requirements, and so on, until the dose coverage of all areas in the target area 8 is completed.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A beam delivery system suitable for variable energy linear accelerator FLASH therapy, characterized in that: It includes a plurality of quadrupole magnets arranged in sequence along the beam transmission direction, a Y-direction scanning magnet, an X-direction scanning magnet, a stripe ionization chamber, a dose ionization chamber and a treatment control system; wherein, The quadrupole magnet is used to expand the diameter of the field of view of the macro bunch of the proton beam emitted by the variable energy linear accelerator to a specified size; The Y-direction scanning magnet is used to deflect the beam in the transverse y-direction; The X-direction scanning magnet is used to deflect the beam in the transverse x-direction; The stripe ionization chamber is used to measure the position of the beam in real time; The dose ionization chamber is used to measure the irradiation dose of the beam in real time; The treatment control system comprises: A calibration module, used for performing dose calibration on the macro bunch of the proton beam at each energy layer; The demand setting module is used to determine the number of particles that should be irradiated on each target point in the target area according to the FLASH irradiation requirements; The accelerator control module is used to control the variable energy linear accelerator to adopt a pencil beam scanning mode to perform point-by-point irradiation in the horizontal direction according to a determined number of particles.

2. The beam distribution system according to claim 1, characterized in that: When the average beam intensity is increased to several µA, at the same dose, the quadrupole magnet increases the field of view of each macro bunch to more than 20 mm in diameter.

3. The beam distribution system according to claim 1, characterized in that: The variable energy linear accelerator changes energy rapidly by presetting the phases and amplitudes of multiple cavities. The energy is changed by fixed point and range energy change. The energy change time is in the ms level. The energy change step is less than 1MeV. The macro bunch pulse length of the proton beam is controlled by a beam chopper. The pulse length change step is less than 2ns. The longitudinal direction adopts a layered scanning method of first the far end and then the near end.

4. A beam delivery system suitable for variable energy linear accelerator FLASH therapy, characterized in that: It includes a plurality of quadrupole-octupole-dodecopole combination magnets arranged in sequence along the beam transmission direction, a scanning magnet, a stripe ionization chamber, a dose ionization chamber and a treatment control system; wherein, The quadrupole-octupole-dodecopole combination magnet is used to stretch the macro bunch of the proton beam emitted by the variable energy linear accelerator in the transverse x direction; The scanning magnet is used to enable the macro bunch to achieve triangular wave or sine wave one-dimensional scanning in the lateral y direction; The stripe ionization chamber is used to measure the position of the beam in real time; The dose ionization chamber is used to measure the irradiation dose of the beam in real time; The treatment control system comprises: A calibration module, used for performing dose calibration on the macro bunch of the proton beam at each energy layer; The demand setting module is used to determine the number of particles that should be irradiated on each target point in the target area according to the FLASH irradiation requirements; The accelerator control module is used to control the variable energy linear accelerator to use a triangular wave or a sine wave one-dimensional scanning mode to perform point-by-point irradiation in the horizontal y direction according to a determined number of particles.

5. The beam distribution system according to claim 4, characterized in that: When the average beam intensity is increased to several µA, at the same dose, the quadrupole-octupole-dodecopole combination magnet stretches each macro bunch in the transverse x direction to obtain a macro bunch with a length of less than 100 mm and a width of more than 4.3 mm.

6. The beam distribution system according to claim 4, characterized in that: The variable energy linear accelerator changes energy rapidly by presetting the phases and amplitudes of multiple cavities. The energy is changed by fixed point and range energy change. The energy change time is in the ms level. The energy change step is less than 1MeV. The macro bunch pulse length of the proton beam is controlled by a beam chopper. The pulse length change step is less than 2ns. The longitudinal direction adopts a layered scanning method of first the far end and then the near end.

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