Electron linear accelerator for radiotherapy equipment in X-ray operation

Abstract

The invention discloses an electron linear accelerator for radiotherapy equipment in an X-ray operation. The microwave power source sequentially passes through the circulator and the power divider and then is connected with the first coupler and the second coupler, the first coupler is connected with the first acceleration cavity to provide an independent microwave magnetic field, and the second coupler is connected with the second acceleration cavity to provide an independent microwave magnetic field. An electron gun of the electron linear accelerator is sequentially connected with the first acceleration cavity and the second acceleration cavity and then outputs electron beams; the first coupler inputs the microwave power to the first acceleration cavity, so that the first acceleration cavity optimizes the electron beam energy spectrum monochromaticity; and the second coupler inputs the microwave power into the second acceleration cavity, so that the second acceleration cavity accelerates the electron beam to required energy. According to the electron linear accelerator, the needed electron beam energy can be achieved only through the two cavities, a large amount of energy of the finally obtained electron beam is concentrated on the needed energy through the acceleration mode, and in other words, the energy spectrum monochromaticity is better.

Description

Technical Field

[0001] The invention belongs to the field of X-ray intraoperative radiotherapy equipment, and in particular relates to an electron linear accelerator used for X-ray intraoperative radiotherapy equipment. Background Art

[0002] The means of treating tumors include: surgery, radiotherapy, chemotherapy, hormone therapy, targeted therapy, etc. In clinical treatment principles, surgery has the highest priority. However, in surgical treatment, incomplete resection of local tumors or residual cancer cells in the tumor bed may lead to tumor recurrence. In order to reduce the recurrence rate of tumors, a method of combining surgery with radiotherapy, namely intraoperative radiotherapy, has been developed. Intraoperative radiotherapy is defined as radiotherapy performed during surgery. Usually, after surgical resection of the tumor, a single large dose of irradiation is given to the tumor bed and the unresectable part to achieve the purpose of inhibiting tumor growth or preventing tumor recurrence. Internationally, intraoperative radiotherapy equipment technology has developed rapidly and has a high degree of maturity. It is mainly in Europe and the United States. It has been widely used in breast cancer, pancreatic cancer, gastrointestinal tumors, brain tumors, head and neck tumors, skin cancer, spinal metastases, etc., and is applicable to many types of cases and a large base. Typical electron beam intraoperative radiotherapy equipment is represented by the United States and Italy, including Mobetron, LIAC and Novac-7. X-ray intraoperative radiotherapy equipment includes Intrabeam from Zeiss in Germany and Xoft Axxent from iCAD in the United States. However, the progress of intraoperative radiotherapy technology in China is slow. Currently, the electronic beam intraoperative radiotherapy equipment includes the mobile electron beam intraoperative radiotherapy system developed by Hunan Huachuang Medical Technology Co., Ltd., but there is no prototype of X-ray intraoperative radiotherapy equipment.

[0003] Considering that the X-ray intraoperative radiotherapy equipment needs to use the electron beam generated by the accelerator to hit the target and generate X-rays, and generally only a small part of the electron beam will be converted into X-rays, with a conversion rate of no more than 10%. Therefore, the electrons at the exit of the accelerator tube need to meet the energy requirements as much as possible, that is, the monochromaticity of the electron beam energy spectrum needs to be as good as possible. Summary of the invention

[0004] In order to overcome the shortcomings and deficiencies of the prior art, an object of the present invention is to provide an electron linear accelerator for use in an X-ray intraoperative radiotherapy device.

[0005] The present invention is implemented as follows: an electron linear accelerator for X-ray intraoperative radiotherapy equipment, wherein the electron linear accelerator is connected to a first coupler and a second coupler through a microwave power source, which passes through a circulator and a power distributor in sequence. The first coupler is connected to a first accelerating cavity to provide an independent microwave magnetic field, and the second coupler is connected to a second accelerating cavity to provide an independent microwave magnetic field. The electron gun of the electron linear accelerator is connected to the first accelerating cavity and the second accelerating cavity in sequence to output an electron beam; wherein the first coupler inputs microwave power to the first accelerating cavity so that the first accelerating cavity optimizes the monochromaticity of the electron beam energy spectrum; and the second coupler inputs microwave power to the second accelerating cavity so that the second accelerating cavity accelerates the electron beam to the required energy.

[0006] Preferably, the first coupler is connected to the end surface of the first accelerating chamber body; the second coupler is connected to the end surface of the second accelerating chamber body.

[0007] Preferably, the coupling degree of the first accelerating cavity is 1.2, and the coupling degree of the second accelerating cavity is 1.

[0008] Preferably, the resonant frequency in the first accelerating cavity and the second accelerating cavity is 9.3 GHz.

[0009] Preferably, the coupling degree of the first accelerating cavity input coupler is 1.18; and the coupling degree of the second accelerating cavity input coupler is 1.03.

[0010] Preferably, the power distributor distributes power to the first accelerating cavity and the second accelerating cavity in a manner that satisfies the following relationship:

[0011] S 21 / S 31 =0.34601

[0012] Among them, S 21 is the microwave power transmitted by the power divider to the first accelerating cavity, S 32 It is the microwave power transmitted by the power divider to the second accelerating cavity.

[0013] Preferably, the power distributor is a 4-port type power distributor, wherein the two input ports are isolated from each other, and the two output ports are isolated from each other.

[0014] The present invention overcomes the shortcomings of the prior art and provides an electron linear accelerator for X-ray intraoperative radiotherapy equipment. The electron linear accelerator of the present invention uses X-band microwave technology, and the working resonant frequency is 9.3 GHZ. The microwave structure of this frequency band is extremely compact, which well meets the requirement of small device size required for intraoperative radiotherapy equipment. In the electron linear accelerator, only two cavities are required to achieve the required electron beam energy, and the acceleration mode is used so that a large amount of energy of the electron beam is finally concentrated on the required energy, that is, the energy spectrum has better monochromaticity.

[0015] Compared with the shortcomings and deficiencies of the prior art, the present invention has the following beneficial effects:

[0016] (1) The present invention utilizes a novel acceleration mode and adjusts the phases of the first accelerating cavity and the second accelerating cavity so that the first accelerating cavity is used to optimize the electron beam energy spectrum and the second accelerating cavity is used to accelerate the electron beam, thereby finally obtaining an electron beam that meets the target energy and has a better energy spectrum monochromaticity;

[0017] (2) The present invention utilizes a novel acceleration structure, a power divider and two microwave resonant cavities (i.e., a first acceleration cavity and a second acceleration cavity) to achieve energy acceleration and energy spectrum optimization at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of the electron linear accelerator of the present invention;

[0019] Figure 2 It is a model structure diagram of a power distributor, a coupler, and an accelerating cavity in the electron linear accelerator of the present invention;

[0020] Figure 3 is the field distribution diagram (cross section) of the first accelerating cavity obtained by CST calculation in the present invention;

[0021] Figure 4 is the field distribution diagram (cross section) of the second accelerating cavity obtained by CST calculation in the present invention;

[0022] Figure 5 is the frequency calculation result of the first accelerating cavity;

[0023] Figure 6 is the frequency calculation result of the second accelerating cavity;

[0024] Figure 7 is a schematic diagram of the connection structure between the second accelerating cavity and the second coupler;

[0025] Figure 8 is the initial intrinsic quality factor of the first accelerating cavity;

[0026] Fig. 9 is the initial external quality factor of the first accelerating cavity;

[0027] Fig.10 The Smith chart calculation results of the first accelerating cavity;

[0028] Fig.11 is the final intrinsic quality factor of the first accelerating cavity;

[0029] Fig.12 is the final external quality factor of the first accelerating cavity;

[0030] Fig.13 is the Smith chart calculation result of the second accelerating cavity;

[0031] Fig.14 It is the axis field distribution derived by the first accelerating cavity using CST;

[0032] Fig.15 It is the axis field distribution derived by the second accelerating cavity using CST;

[0033] Fig.16 is the field distribution diagram of the power divider;

[0034] Fig.17 is the S parameter of the power divider calculated by CST;

[0035] Fig.18 is the electron beam energy spectrum at the exit of the second accelerating cavity;

[0036] Fig.19 is the electron energy variation at the exit of the second accelerating cavity (distributed along the z axis);

[0037] Fig. 20 is the axial electric field distribution of the two cavities;

[0038] Fig.21 is the electron beam energy spectrum at the exit of the first accelerating cavity. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0040] The present invention discloses an electron linear accelerator for an X-ray intraoperative radiotherapy device, such as Figure 1As shown, the electron linear accelerator is connected to the first coupler and the second coupler through a microwave power source, which passes through a circulator and a power divider in sequence. The first coupler is connected to the first accelerating cavity to provide an independent microwave magnetic field, and the second coupler is connected to the second accelerating cavity to provide an independent microwave magnetic field. The electron gun of the electron linear accelerator is connected to the first accelerating cavity and the second accelerating cavity in sequence to output an electron beam; wherein the first coupler inputs microwave power to the first accelerating cavity so that the first accelerating cavity optimizes the monochromaticity of the electron beam energy spectrum; and the second coupler inputs microwave power to the second accelerating cavity so that the second accelerating cavity accelerates the electron beam to the required energy.

[0041] In the embodiment of the present invention, the center of the electron gun, the center of the first accelerating cavity and the center of the second accelerating cavity are on the same axis. In addition, there is no coupling between the first accelerating cavity and the second accelerating cavity, that is, there is no energy exchange, and the microwave power in the cavity is fed in through the power divider and the first coupler and the second coupler respectively. The first accelerating cavity is used to optimize the electron beam energy spectrum so that the electron beam energy spectrum at the accelerating tube outlet has good monochromaticity, and then the second accelerating cavity is used to accelerate the electron beam so that the electron beam energy at the final accelerating tube outlet meets the requirements.

[0042] like Figure 2 As shown in the figure, the first and second accelerating cavities use a nose cone structure. Compared with the cylindrical cavity, the nose cone structure reduces the edges and corners and increases the arc while ensuring the cavity length and resonant frequency are constant, making the cavity surface smoother and reducing the loss of the cavity. In addition, the field distribution results calculated using CST Figures 3 to 6 As shown in the figure, the resonant frequencies of the first accelerating cavity and the second accelerating cavity are both around 9.3 GHz. By CST calculation and parameter adjustment, it can be finally obtained that the frequencies of the first accelerating cavity and the second accelerating cavity are 9.301472 GHz and 9.30058 GHz respectively, both of which meet the design requirements.

[0043] In the further implementation process, considering the portability of the later cavity processing, the present invention arranges the coupler on the end surface of the accelerating cavity, such as Figure 7 The schematic diagram of the connection structure between the second accelerating cavity and the second coupler is shown, and the input end of the second coupler is connected to the outer end face of the second accelerating cavity. Similarly, the first accelerating cavity and the first coupler have the same connection structure, that is, the input end of the first coupler is connected to the outer end face of the first accelerating cavity.

[0044] In the embodiment of the present invention, the coupling degree is an important indicator of the coupler design, and its definition is:

[0045]

[0046] Among them, P ext and P cThey are the external load loss power and the internal cavity loss power, Q0 and Q e They are intrinsic quality factor and external quality factor respectively.

[0047] When the coupling degree β = 1, the power loss of the load outside the cavity is equal to the power loss inside the cavity, which is the critical coupling state. However, when a beam passes through the cavity, the beam absorbs part of the power from the cavity. Therefore, the coupling degree can be calculated as:

[0048]

[0049] Among them, P B is the beam power.

[0050] According to formula (2), the final simulation value of the coupling degree of the first accelerating cavity should be around 1.2, and the calculated value of the coupling degree of the second accelerating cavity should be around 1. By adjusting the coupling hole size and the accelerating cavity radius and other parameters, the coupling hole size will affect the coupling degree, because the connection between the coupler and the accelerating cavity is connected by the coupling hole. Secondly, the accelerating cavity radius will affect the accelerating cavity frequency. After adding the coupler, the original accelerating cavity frequency will change. In order to control the frequency at 9.3 GHz, it is necessary to adjust the accelerating cavity radius. The intrinsic quality factor and external quality factor of the first accelerating cavity are calculated as follows: Figure 8 , Fig. 9 shown.

[0051] Therefore, the final calculated coupling result of the first accelerating cavity is:

[0052]

[0053] In addition, the Smith chart calculation is performed on the first accelerating cavity, such as Fig.10 As shown in Figure 2, the first accelerating cavity is in an over-coupled state, that is, the point where the red circle exceeds the center of the circle. Finally, the intrinsic quality factor and external quality factor of the first accelerating cavity are calculated as follows: Fig.11 , Fig.12 shown.

[0054] Similarly, the coupling degree of the second accelerating cavity is:

[0055]

[0056] Perform Smith chart calculation on the second accelerating cavity, such as Fig.13 As shown, the second accelerating cavity is in a critical coupling state, that is, the point where the red circle just passes through the center of the circle.

[0057] In the embodiment of the present invention, the function of the power divider is to divide the microwave power of the power source and finally inject it into the two cavities. In the further implementation process, in order to accurately determine the power required by the first accelerating cavity and the second accelerating cavity respectively, it is necessary to optimize the microwave structure of the power divider.

[0058] In the embodiment of the present invention, the S parameter is an important indicator of its design, and its physical meaning is to measure the transmission and reflection properties of microwaves in the waveguide. The power required by the first accelerating cavity and the second accelerating cavity can be calculated by using beam dynamics. 21 , S 31 The relationship between S 21 / S 31 The theoretical value is calculated as follows:

[0059]

[0060] In the formula, S 21 represents the microwave power transmission from the power divider to the first accelerating cavity, S 32 It represents the transmission of microwave power to the second accelerating cavity by the power divider, P2 is the microwave power required by the first accelerating cavity, P3 is the microwave power required by the second accelerating cavity, and P1 is the total power of the two cavities.

[0061] The power calculation needs to use beam dynamics. Since the size of the accelerating cavity field calculated by the model established in CST is very large, and such a large field is not required in the actual application of the present invention during acceleration or energy spectrum optimization, it is necessary to use the relationship between the field and power for adjustment. The specific relationship is as follows:

[0062]

[0063] Where E1 represents the field required by the first accelerating cavity, E 10 is the field calculated by the CST of the first accelerating cavity, P2 is the microwave power required by the first accelerating cavity, and P 20 is the microwave power of the first accelerating cavity calculated by CST.

[0064]

[0065] Among them, E2 represents the final field required by the second accelerating cavity, E 20 is the field calculated by the CST of the second accelerating cavity, P3 is the microwave power required by the second accelerating cavity, and P 30 is the microwave power of the second accelerating cavity calculated by CST.

[0066] The first accelerating cavity uses the CST-derived axial field distribution as follows Fig.14 The axial field distribution of the second accelerating cavity derived by CST is shown as Fig.15 shown.

[0067] Therefore, E 10 =752.37MV / m, E 20 =678.78MV / m, P 20 and P 30As can be seen from the figure above for calculating the intrinsic quality factor, Loss is the power loss, that is:

[0068] P 20 =1.17331×10 7 W, P 30 =8.4305×10 6 W.

[0069] The axial field distribution is imported into the beam dynamics calculation software. In order to obtain the energy spectrum at the accelerating tube exit that meets the requirements, the values ​​of E1 and E2 are adjusted. Finally, E1=19.57MV / m, E2=17.5MV / m can be obtained. By calculating with the above formula, we can get:

[0070] P2=1.1726×10 4 W, P3=5.6037×10 3 W;

[0071] P1=P2+P3=1.7330×10 4 W.

[0072] Finally, we can get S 21 / S 31 =0.34601.

[0073] Using CST to establish the model and calculate the S parameters, the power distribution field distribution can be obtained as follows: Fig.16 shown.

[0074] In the further implementation process, in order to prevent microwave power reflection between ports, in the embodiment of the present invention, the power divider is selected as a 4-port type. In the present invention, if the power divider is designed as a 3-port type, the microwave power of the two output ports will reflect each other and will be reflected back to the input port, while the 4-port type power divider can well avoid this situation, because the two input ports will be isolated from each other, and the two output ports will also be isolated from each other, for example Fig.16 Port 2 and port 3 in the figure are isolated from each other, that is, there is no mutual reflection of microwave power. The calculation of its S parameters is as follows: Fig.17 As shown. Fig.17 Available, S 21 / S 31 The simulated value is: 0.34667, which is very close to the theoretical value of 0.34601.

[0075] Based on the above-described implementation of the electron linear accelerator, further beam dynamics simulation is performed for the embodiment of the present invention. In order to optimize the electron beam energy spectrum by the first accelerating cavity, accelerate the electron beam by the second accelerating cavity, obtain the final accelerating cavity length, and calculate the correct electron capture rate, beam dynamics simulation is finally required. The phase difference between the two cavities is set to 90°, the electric field of the first accelerating cavity is set to 19.7MV / m, and the maximum electric field of the second accelerating cavity is set to 17.5MV / m. Finally, the electron beam energy spectrum, the distribution of the electric fields of the two cavities along the z-axis, and the electron energy increase value are calculated as follows: Figures 18 to 20 As shown in the figure, it can be seen that the electron beam energy spectrum has a good monochromaticity and the electron beam energy is around 50keV.

[0076] In order to prove the optimization effect of the first accelerating cavity on the electron beam energy spectrum, the electron beam energy spectrum at the exit of the first accelerating cavity is calculated, as shown in Fig.21 As shown in the figure, since the electrons entering the first accelerating cavity are all set to 8keV, and the energy spectrum at the exit of the first accelerating cavity is energy-optimized so that its energy spectrum has a distribution of 0 to 8keV, more electrons can be accelerated when entering the second accelerating cavity. Finally, it can be concluded that Fig.18 , there are as many electrons as possible with an energy of 50keV, that is, the energy spectrum is more monochromatic.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An electron linear accelerator for X-ray intraoperative radiotherapy equipment, characterized in that: The electron linear accelerator is connected to a first coupler and a second coupler through a microwave power source, which passes through a circulator and a power distributor in sequence. The first coupler is connected to a first accelerating cavity to provide an independent microwave magnetic field, and the second coupler is connected to a second accelerating cavity to provide an independent microwave magnetic field. The electron gun of the electron linear accelerator is connected to the first accelerating cavity and the second accelerating cavity in sequence to output an electron beam; wherein the first coupler inputs microwave power to the first accelerating cavity so that the first accelerating cavity optimizes the monochromaticity of the electron beam energy spectrum; and the second coupler inputs microwave power to the second accelerating cavity so that the second accelerating cavity accelerates the electron beam to the required energy.

2. The electron linear accelerator according to claim 1, characterized in that: The first coupler is connected to the end surface of the first accelerating cavity; the second coupler is connected to the end surface of the second accelerating cavity.

3. The electron linear accelerator according to claim 1, characterized in that: The coupling degree of the first accelerating cavity is 1.2, and the coupling degree of the second accelerating cavity is 1.

4. The electron linear accelerator according to claim 1, characterized in that: The resonant frequency in the first accelerating cavity and the second accelerating cavity is 9.3 GHz.

5. The electron linear accelerator according to claim 1, characterized in that: The coupling degree of the first accelerating cavity input coupler is 1.18; the coupling degree of the second accelerating cavity input coupler is 1.

03.

6. The electron linear accelerator according to claim 1, characterized in that: The relationship between the power distribution of the first accelerating cavity and the second accelerating cavity by the power distributor satisfies the following relationship: S 21 / S 31 =0.34601 Among them, S 21 is the microwave power transmitted by the power divider to the first accelerating cavity, S 32 It is the microwave power transmitted by the power divider to the second accelerating cavity.

7. The electron linear accelerator according to claim 1, characterized in that: The power distributor is a 4-port type power distributor, wherein the two input ports are isolated from each other, and the two output ports are isolated from each other.

Images