A bi-directional scanning magnet for radiotherapy

Abstract

The application relates to a bidirectional scanning magnet for radiotherapy, a first scanning coil is an X-direction scanning coil, a second scanning coil is a Y-direction scanning coil, the first scanning coil is located on the radial inner side of the second scanning coil and is integrated with the second scanning coil through a framework or a tool, the two are coaxially arranged and the extension length of the first scanning coil is less than the extension length of the second scanning coil, so that a conical air gap structure of the bidirectional scanning magnet is defined to deflect a beam in a plane perpendicular to the beam direction Z. According to the bidirectional scanning magnet for radiotherapy, with the increase of the coil radius, the coil extension length gradually becomes long, so that a conical air gap structure is formed at the end of the scanning magnet, the originally separated X-direction scanning coil and Y-direction scanning coil are integrated together, space is saved, the magnet source axle distance is effectively reduced, the rotating gantry radius is reduced, and the weight and volume of the rotating gantry are reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to medical equipment, more particularly to a bidirectional scanning magnet for radiotherapy. BACKGROUND

[0002] With the rapid development of social economy, people's living standards have been greatly improved, and medical and health conditions have been further improved. However, cancer is still the main obstacle to further improve the level of human health. Common cancer treatment methods mainly include surgical treatment, chemotherapy and radiotherapy. The particles used in radiotherapy include electrons, photons, protons, heavy ions, etc.

[0003] Proton therapy and heavy ion therapy are used for tumor treatment due to their unique Bragg peak, have the advantages of precision, high efficiency, small side effects and wide application range, and are the current international research hotspot. Compared with traditional radiotherapy, chemotherapy and surgery, using proton beams or heavy ion beams to treat tumors is one of the techniques that cause the least harm to patients.

[0004] The particle therapy device mainly consists of a particle accelerator, a beam transport system, an injection and extraction system, a treatment head system, a treatment control system, and a magnet power supply system. The particle beam is generated by the accelerator, transmitted to the treatment head through the beam transport system, and finally incident into the human body after the direction modulation and position dose verification of the beam in the treatment head.

[0005] The scanning magnet is a key component of the particle therapy device, which is installed on the rotating gantry. The size of the space occupied by the scanning magnet determines the overall size of the rotating gantry to some extent. When the particle beam passes through the scanning magnet, the accelerated charged ions are affected by the magnetic field, and the direction of motion is deflected. The scanning power supply changes the size of the magnetic field strength by controlling the excitation current to guide the movement of the charged ions, which expands the beam irradiation range from a point to the entire tumor section, and releases energy in the irradiation area to kill cancer cells. It changes the beam trajectory of the pencil beam to accurately and uniformly irradiate the target tumor area.

[0006] The scanning magnet used in the current common particle therapy device is usually composed of two independent dipole magnets placed orthogonally, which respectively realize the deflection of the particle beam in the X direction and the Y direction. There is also a drift distance between them, which leads to a larger longitudinal (Z direction) space occupied by the separated structure, making the overall treatment head longer. For the rotating gantry, its mass is approximately proportional to the square of its rotating radius, and the rotating radius mainly depends on the length of the treatment head. Therefore, in order to reduce the overall size of the rotating gantry, it is necessary to reduce the space occupied by the scanning magnet installed on it. SUMMARY

[0007] In order to solve the problems of the prior art, such as the too large rotating gantry, the application provides a bidirectional scanning magnet for radiotherapy.

[0008] The bidirectional scanning magnet for radiotherapy according to the application comprises a first scanning coil and a second scanning coil, wherein the first scanning coil is an X-direction scanning coil, the second scanning coil is a Y-direction scanning coil, the first scanning coil is a cylindrical scanning magnet with a first diameter and a first length, the second scanning coil is a cylindrical scanning magnet with a second diameter and a second length, the first diameter is smaller than the second diameter, the first scanning coil is located on the radial inner side of the second scanning coil and is integrated with the second scanning coil through a skeleton or a tool, the two are coaxially arranged and the first length is smaller than the second length to define a tapered air gap structure of the bidirectional scanning magnet to deflect the beam in a plane perpendicular to the beam direction Z.

[0009] Preferably, the first ends of the first scanning coils and the second scanning coils are aligned, and the second end of the second scanning coil extends beyond the second end of the first scanning coil to provide the tapered air gap structure.

[0010] Preferably, the bidirectional scanning magnet comprises a plurality of first scanning coils and a plurality of second scanning coils, wherein the first scanning coils and the second scanning coils are alternately distributed.

[0011] Preferably, one layer of first scanning coils and one layer of second scanning coils form a magnet group, the extension length of the outer magnet group is greater than the extension length of the inner magnet group, and the extension length of the outer scanning coil in each magnet group is greater than the extension length of the inner scanning coil, thereby providing the tapered air gap structure.

[0012] Preferably, the bidirectional scanning magnet comprises a plurality of first scanning coils and a plurality of second scanning coils, wherein the first scanning coils and the second scanning coils are centrally distributed.

[0013] Preferably, a plurality of first scanning coils form a first magnet coil group, a plurality of second scanning coils form a second magnet coil group, the extension length of the second magnet coil group is greater than the extension length of the first magnet coil group, and the extension length of the outer scanning coil in each magnet coil group is greater than the extension length of the inner scanning coil, thereby providing the tapered air gap structure.

[0014] Preferably, the first scanning coil and the second scanning coil are respectively composed of two symmetrical halves, and each half is composed of a plurality of nested ladder-shaped coil conductors.

[0015] Preferably, the coil conductors are distributed in a Cosine-Theta form.

[0016] Preferably, the bidirectional scanning magnet further comprises a yoke, which is a cylindrical structure arranged on the radial outer side of the second scanning coil.

[0017] Preferably, the magnetic yoke has a plurality of slots that are uniformly distributed in the circumferential direction and extend radially outward from its inner surface.

[0018] According to the present invention, the bidirectional scanning magnet for radiotherapy gradually increases in length as the coil radius increases, thereby forming a tapered air gap structure at the end of the scanning magnet. This integrates the originally separate X-direction and Y-direction scanning coils, saving space. Therefore, the scanning magnet system of the present invention can effectively reduce the magnet source axial distance, thereby reducing the radius of the rotating gantry, which helps to reduce the weight and volume of the rotating gantry and promotes the miniaturization and functionalization of particle therapy devices. Attached Figure Description

[0019] Figure 1 A bidirectional scanning magnet for radiotherapy, according to a preferred embodiment of the present invention, comprises an X-direction scanning coil and a Y-direction scanning coil.

[0020] Figure 2 Show Figure 1 The integration path of the bidirectional scanning magnet.

[0021] Figure 3 exist Figure 1 Add a magnetic yoke to the existing structure.

[0022] Figure 4 A bidirectional scanning magnet for radiotherapy, illustrating another preferred embodiment of the invention, comprises two layers of X-direction scanning coils and two layers of Y-direction scanning coils.

[0023] Figure 5 Show Figure 4 The deflection angle and scanning range of the bidirectional scanning magnet along the direction of the particle beam's advance (Z direction).

[0024] Figure 6 Show Figure 4 The alternating distribution of bidirectional scanning magnets.

[0025] Figure 7 Corresponding to Figure 6 This illustrates a concentrated distribution of bidirectional scanning magnets for radiotherapy according to yet another preferred embodiment of the invention.

[0026] Figure 8 This illustrates a larger taper of a bidirectional scanning magnet for radiotherapy according to yet another preferred embodiment of the invention.

[0027] Figure 9 This illustrates a smaller taper of a bidirectional scanning magnet for radiotherapy according to yet another preferred embodiment of the invention. Detailed Implementation

[0028] In view of the defects of the scanning magnet in the existing particle therapy device, the application provides a bidirectional scanning magnet for radiotherapy, which integrates an X-direction scanning coil and a Y-direction scanning coil together to replace the traditional two separate dipole magnets, so as to realize the miniaturization and compactness of the particle therapy device.

[0029] The preferred embodiments of the application are described in detail below with reference to the drawings.

[0030] As shown in the drawings, Figures 1-2 The bidirectional scanning magnet for radiotherapy according to one preferred embodiment of the application comprises a first scanning coil 1 and a second scanning coil 2, wherein the first scanning coil 1 is a cylindrical scanning magnet with a first diameter and a first length, the second scanning coil 2 is a cylindrical scanning magnet with a second diameter and a second length, the first diameter is smaller than the second diameter, the first scanning coil 1 is located on the radial inner side of the second scanning coil 2 and is integrated with the second scanning coil 2 through a skeleton or tooling (not shown in the drawings), the first length is smaller than the second length, the first ends (i.e. the incident ends) of the first scanning coil 1 and the second scanning coil 2 are aligned, and the second end (i.e. the outgoing end) of the second scanning coil 2 extends beyond the second end of the first scanning coil 1, thereby providing a tapered air gap structure. When the beam passes through the magnetic field between the scanning magnets, the beam envelope gradually increases outward along the central axis of the bidirectional scanning magnet under the action of the Lorentz force.

[0031] As shown in the drawings, Figure 3 The bidirectional scanning magnet according to the embodiment further comprises a magnetic yoke 3 arranged on the radial outer side of the second scanning coil 2 to improve the excitation efficiency of the coil and reduce the leakage magnetic field. It should be understood that the magnetic yoke 3 is also commonly referred to as a core.

[0032] In the embodiment, the first scanning coil 1, the second scanning coil 2 and the magnetic yoke 3 are all cylindrical structures. In order to reduce the eddy current effect, the material of the magnetic yoke 3 can be selected from silicon steel sheet, ferrite, iron-based nanometer alloy and iron-based amorphous alloy. In order to reduce the adjustment time of the scanning magnetic field, the eddy current effect can be reduced by slotting the magnetic yoke pole head, therefore, the magnetic yoke 3 can have a plurality of slots 31 extending radially outward from the inner surface thereof, and the slots 31 are uniformly distributed in the circumferential direction. It should be understood that the cylindrical structure here can be a right circular cylindrical structure, an elliptical cylindrical structure, a square cylindrical structure, etc.

[0033] As shown in the drawings, Figures 4-6As shown, a bidirectional scanning magnet for radiotherapy according to another preferred embodiment of the present invention includes two first scanning coils 1 and two second scanning coils 2, wherein the first scanning coils 1 and the second scanning coils 2 are alternately integrated together, with one first scanning coil 1 located radially inside one second scanning coil 2, and the other first scanning coil 1 located radially outside the second scanning coil 2, and the other second scanning coil 2 located radially outside the other first scanning coil 1, i.e., one layer of first scanning coil 1, one layer of second scanning coil 2, one layer of first scanning coil 1, and one layer of second scanning coil 2, thereby satisfying a higher integration field requirement compared to the previous embodiment. In particular, the first ends of the two first scanning coils 1 and the two second scanning coils 2 are aligned, the second end of one second scanning coil 2 extends beyond the second end of one first scanning coil 1, the second end of the other first scanning coil 1 extends beyond the second end of one second scanning coil 2, and the second end of the other second scanning coil 2 extends beyond the second end of the other first scanning coil 1, thereby providing a tapered air gap structure by changing the extension length of each layer of scanning coils 1, 2. A two-layer structure consisting of a first scanning coil 1 and a second scanning coil 2 is referred to as a magnet group. This embodiment provides an example of two magnet groups. It should be understood that the bidirectional scanning magnet for radiotherapy according to the present invention can also include more magnet groups, as long as the extension length of the outer magnet group is greater than the extension length of the inner magnet group, and the extension length of the outer scanning coil in each magnet group is greater than the extension length of the inner scanning coil, thereby providing a tapered air gap structure. Furthermore, by alternating the placement of the first scanning coil 1 and the second scanning coil 2, the excitation efficiency of the coils by the yoke can be improved.

[0034] like Figure 7 As shown, a bidirectional scanning magnet for radiotherapy according to another preferred embodiment of the present invention includes two first scanning coils 1 and two second scanning coils 2, wherein the first scanning coils 1 and the second scanning coils 2 are centrally distributed, with the two first scanning coils 1 located radially inside the two second scanning coils 2, i.e., the two layers of first scanning coils 1 are placed on the innermost side, and the two layers of second scanning coils 2 are placed on the outermost side. It should be understood that the number of first scanning coils 1 placed on the inner side is not limited to two layers, and the number of second scanning coils 2 placed on the outer side is not limited to two layers, nor do they necessarily have to be the same; they can be adjusted according to the specific requirements of the scanning magnet.

[0035] like Figures 1-5As shown, the first scanning coil 1 is an X-direction scanning coil, and the second scanning coil 2 is a Y-direction scanning coil, which are coaxially arranged (the central axis is the Z-direction) to deflect the pencil beam in the plane perpendicular to the beam direction. The beam is incident along the Z-direction, and as the scanning coil radius gradually increases (since the outer scanning coil gradually expands not only in diameter but also in Z-direction extension relative to the inner scanning coil), a tapered air gap structure is formed to adapt to the gradually changing trajectory of the beam, thereby saving space. Specifically, the taper of the tapered air gap structure can be the circular cone shown in the embodiment, or the square cone not shown. It should be understood that the taper of the tapered air gap structure at the end of the scanning magnet is mainly related to the scanning magnet radius, the source-magnet distance, and the scanning range. When the scanning magnet radius is large, the source-magnet distance is long, and the scanning range is small, the taper at the end of the scanning magnet needs to be set as shown in Figure 8 When the scanning magnet radius is small, the source-magnet distance is short, and the scanning range is large, the taper at the end of the scanning magnet needs to be set as shown in Figure 9 For example, to reduce the coil energy storage as much as possible and thus reduce the power requirement of the coil, the radius should be as small as possible, and in addition, the beam envelope should not hit the inner wall of the vacuum chamber, so the taper at the end of the scanning magnet needs to be set as shown in Figure 9

[0036] The deflection angle of the particle beam in the magnetic field is determined by the magnetic rigidity of the particle and the trajectory integral field along the integral path S (see Figure 2 ). For different particles, their deflection in the same scanning magnet is also different. The greater the particle energy, the greater the magnetic rigidity, the more difficult the deflection, and the smaller the taper of the scanning magnet. The magnetic rigidity is used to evaluate whether the particle is easy to deflect under the action of the Lorentz force in the magnetic field, so the taper of the scanning magnet is different for different types of particles.

[0037] Compared with the traditional split scanning magnet, this scanning magnet system can significantly reduce the source-magnet distance from the original 3 meters of the traditional split scanning magnet to about 1 meter, significantly reducing the space occupied by the magnet, and further reducing the space occupied by the treatment head, which can significantly reduce the volume and weight of the rotating gantry, making the rotating gantry more compact, and greatly reducing the difficulty of controlling the rotating gantry, thereby significantly improving the treatment accuracy.

[0038] The source-magnet distance of the traditional split scanning magnet is different, which increases the complexity of the treatment plan, while the source-magnet distance of the X-direction scanning coil and the Y-direction scanning coil of this scanning magnet can be the same or different, greatly reducing the difficulty and complexity of treatment.

[0039] ​The current required by the conical gap scanning magnet for deflecting the particle beam of the same energy is lower than that of the equidistant gap scanning magnet, so that the excitation current of the magnet can be effectively reduced, the coil energy storage and inductance can be reduced, the coil power can be reduced, the eddy current loss of the coil can be reduced, and a very high scanning speed can be met.

[0040] As shown in Figure 1 The scanning coils 1, 2 are respectively composed of two symmetrical halves, and each half is composed of a plurality of nested coil conductors similar to trapezoids. In the embodiment, the first scanning coil 1 is composed of two halves on the left and right, and the second scanning coil 2 is composed of two halves on the top and bottom. The coil conductor distribution of the bidirectional scanning magnet according to the application conforms to the Cosine-Theta form, and good magnetic field quality can be obtained. In addition, the position distribution of the coil wire can be adjusted according to the requirements of the magnet, and the uniformity of the integrated field can be improved. For different types of particles, the required integrated field can be increased by increasing the number of coil layers, and the integrated field of the scanning magnet is proportional to the deflection angle and determines the size of the scanning range. It should be understood that the scanning coils 1, 2 can be wound using copper stranded wires or inner water-cooled copper pipes. It should be understood that the two halves are arranged to facilitate pipe winding.

[0041] In summary, the bidirectional scanning magnet according to the application can replace the conventional two separate dipole magnets by integrating the first and second scanning coils together, so as to realize the miniaturization and compactness of the particle therapy device.

[0042] The above is only a preferred embodiment of the application, and is not intended to limit the scope of the application. The above embodiment of the application can be variously changed. That is, any simple, equivalent changes and modifications made according to the content of the claims and the specification of the application fall within the scope of protection of the patent. The application is not described in detail, which is a conventional technical content.

Claims

1. A bidirectional scanning magnet for radiotherapy, characterized in that, The bidirectional scanning magnet includes a first scanning coil and a second scanning coil, each consisting of two symmetrical halves. Each half is composed of several nested trapezoidal coil conductors, with the conductor distribution conforming to the Cosine-Theta form. The first scanning coil is an X-direction scanning coil, and the second scanning coil is a Y-direction scanning coil. The first scanning coil is a cylindrical scanning magnet with a first diameter and a first length, and the second scanning coil is a cylindrical scanning magnet with a second diameter and a second length. The first diameter is smaller than the second diameter. The first scanning coil is located radially inside the second scanning coil and integrated with it via a frame or tooling. The two are coaxially arranged, and the incident ends of the first and second scanning coils are aligned. The exit end of the second scanning coil extends beyond the exit end of the first scanning coil. The tapered air gap structure of the bidirectional scanning magnet is defined by the first length being smaller than the second length, so as to deflect the beam in a plane perpendicular to the beam direction Z.

2. The bidirectional scanning magnet according to claim 1, characterized in that, The bidirectional scanning magnet includes a plurality of first scanning coils and a plurality of second scanning coils, wherein the first scanning coils and the second scanning coils are alternately distributed.

3. The bidirectional scanning magnet according to claim 2, characterized in that, A first scanning coil and a second scanning coil form a magnet group. The extension length of the outer magnet group is greater than that of the inner magnet group, and the extension length of the outer scanning coil in each magnet group is greater than that of the inner scanning coil, thereby providing a tapered air gap structure.

4. The bidirectional scanning magnet according to claim 1, characterized in that, The bidirectional scanning magnet includes several first scanning coils and several second scanning coils, wherein the first scanning coils and the second scanning coils are distributed in a concentrated manner.

5. The bidirectional scanning magnet according to claim 4, characterized in that, A number of first scanning coils form a first magnet coil group, and a number of second scanning coils form a second magnet coil group. The extension length of the second magnet coil group is greater than the extension length of the first magnet coil group, and the extension length of the outer layer scanning coil in each magnet coil group is greater than the extension length of the inner layer scanning coil, thereby providing a tapered air gap structure.

6. The bidirectional scanning magnet according to claim 1, characterized in that, The bidirectional scanning magnet also includes a magnetic yoke, which is a cylindrical structure located radially outside the second scanning coil.

7. The bidirectional scanning magnet according to claim 6, characterized in that, The magnetic yoke has a number of slots that are evenly distributed in the circumferential direction, extending radially outward from its inner surface.

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