A scanning magnet system for radiotherapy

Abstract

The application relates to a scanning magnet system for radiotherapy, a first scanning coil is a first variable-aperture cylindrical scanning magnet, a second scanning coil is a second variable-aperture cylindrical scanning magnet, 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, the first scanning coil is an X-direction scanning magnet, the second scanning coil is a Y-direction scanning magnet, both are coaxially arranged and define a conical air gap structure of the variable-aperture bidirectional scanning magnet to deflect a beam in a plane perpendicular to the beam direction Z. According to the scanning magnet system for radiotherapy, the variable-aperture mode is adopted to reduce the energy storage, thereby reducing the inductance, further reducing the requirement of the scanning magnet on the power supply, the originally separated scanning magnets are integrated through the framework, the space occupied by the scanning magnets is greatly reduced, the rotating gantry can be reduced, and the miniaturization and compactness of a particle therapy device can be realized.

Description

TECHNICAL FIELD

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

[0002] In recent years, cancer has become one of the major problems threatening human health, and there are currently three basic means for treating cancer, namely surgical treatment, chemotherapy and radiotherapy. Particle therapy (such as proton therapy and heavy ion therapy) is a common way of radiotherapy, which effectively kills cancer cells in the human body by utilizing the unique Bragg peak characteristics of charged particles, has the advantages of precision, high efficiency, small side effects and wide adaptation, and has become one of the most advanced cancer treatment methods in the world.

[0003] A particle therapy device mainly consists of a particle accelerator, a beam transport system and a treatment head system. The charged 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 beam direction modulation and position dose verification in the treatment head.

[0004] The scanning magnet is a key component of the particle therapy device, which is installed on the rotating gantry, and the size of the space it occupies determines the overall size of the rotating gantry to some extent. It changes the beam trajectory of the pencil beam to accurately irradiate the target tumor region.

[0005] The scanning magnet is used to deflect the charged particle beam to uniformly irradiate the tumor tissue, and the beam is expanded in the transverse direction by the deflection of the magnetic field. When the beam passes through the magnet aperture, it is deflected in the plane perpendicular to the beam direction due to the influence of the Lorentz force.

[0006] The scanning magnet used in the common particle therapy device at present is usually composed of two independent dipole magnets placed orthogonally, which respectively realize the deflection of the charged particle beam in the X direction and the Y direction, and there is a drift distance between them, which leads to the large longitudinal (Z direction) space occupied by the separated structure, making the length of the treatment head longer. For the rotating gantry, its mass is approximately proportional to the square of its rotation radius, and the rotation radius mainly depends on the length of the treatment head. Therefore, the overall size of the rotating gantry of the particle therapy device in the prior art is too large. SUMMARY

[0007] In order to solve the problem of the rotating gantry being too large in the prior art, the present application provides a scanning magnet system for radiotherapy.

[0008] The scanning magnet system for radiotherapy according to the present application comprises a first scanning coil and a second scanning coil, wherein the first scanning coil is a first variable-aperture cylindrical scanning magnet, the second scanning coil is a second variable-aperture cylindrical scanning magnet, the first scanning coil is located radially inside the second scanning coil and integrated with the second scanning coil through a backbone, the first scanning coil is an X-direction scanning magnet, the second scanning coil is a Y-direction scanning magnet, both of which are coaxially arranged and define a conical air gap structure of the variable-aperture two-direction scanning magnet to deflect the beam in a plane perpendicular to the beam direction Z. It should be understood that the X-direction scanning magnet is provided by at least one first scanning coil, and the Y-direction scanning magnet is provided by at least one second scanning coil, and the specific combination thereof can be adjusted as needed. From the inside to the outside, the layout can be the first scanning coil and the second scanning coil, the first scanning coil, another first scanning coil and the second scanning coil, the first scanning coil, the second scanning coil, another first scanning coil and another second scanning coil, the first scanning coil, another first scanning coil, the second scanning coil and another second scanning coil, the first scanning coil, the second scanning coil, another first scanning coil, another second scanning coil and yet another second scanning coil, and the like.

[0009] Preferably, the first scanning coil and the second scanning coil have the same or different source axis distances.

[0010] Preferably, the first scanning coil and the second scanning coil are respectively composed of two symmetrical halves, each of which is composed of a plurality of nested ladder-shaped coil conductors.

[0011] Preferably, the coil conductors are distributed in accordance with the Cosine-Theta form.

[0012] Preferably, the first scanning coil and the second scanning coil have the same or different extension lengths.

[0013] Preferably, the first scanning coil has a linearly increasing first inner diameter, and the second scanning coil has a linearly increasing second inner diameter, and the increasing degree of the first inner diameter is equal to the increasing degree of the second inner diameter.

[0014] Preferably, the scanning magnet system further comprises a magnetic yoke, which is a cylindrical structure arranged radially outside the second scanning coil.

[0015] Preferably, the magnetic yoke has a plurality of slots uniformly distributed in the circumferential direction extending radially outward from the inner surface thereof.

[0016] Preferably, the scanning magnet system comprises two first scanning coils and two second scanning coils, wherein the first scanning coils and the second scanning coils are integrated alternately, one first scanning coil is located radially inside one second scanning coil, the other first scanning coil is located radially outside the second scanning coil, and the other second scanning coil is located radially outside the other first scanning coil. That is, from inside to outside, the layout is first scanning coil, second scanning coil, another first scanning coil, and another second scanning coil.

[0017] Preferably, the scanning magnet system comprises two first scanning coils and one second scanning coil, wherein one first scanning coil is located radially inside the other first scanning coil, and the second scanning coil is located radially outside the other first scanning coil. That is, from inside to outside, the layout is first scanning coil, another first scanning coil, and second scanning coil.

[0018] The scanning magnet system for radiotherapy according to the present application reduces the energy storage in a variable-aperture manner, thereby reducing the inductance and further reducing the requirements of the scanning magnet on the power supply. The originally separated scanning magnets are integrated together through the skeleton, the space occupied by the scanning magnets is greatly reduced, the rotating gantry is reduced in size, and the miniaturization and compactness of the particle therapy device can be realized. In summary, the scanning magnet system for radiotherapy according to the present application can effectively reduce the magnet source wheelbase, thereby reducing the rotating gantry radius, which helps to reduce the weight and volume of the rotating gantry. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a structural schematic diagram of a scanning magnet system for radiotherapy according to a preferred embodiment of the present application.

[0020] Figure 2 shows Figure 1 the integral path of the scanning magnet of the scanning magnet system.

[0021] Figure 3 shows Figure 1 the deflection angle and scanning range of the beam of the scanning magnet system.

[0022] Figure 4 is an exploded view of the scanning magnet system. Figure 1

[0023] Figure 5 is a structural schematic diagram of a scanning magnet system for radiotherapy according to another preferred embodiment of the present application. DETAILED DESCRIPTION

[0024] The preferred embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0025] As​Figures 1-2 As shown, a preferred embodiment of the scanning magnet system for radiotherapy according to the present invention includes a first scanning coil 1, a second scanning coil 2, and a magnetic yoke 3. The first scanning coil 1 is a first variable-aperture cylindrical scanning magnet, and the second scanning coil 2 is a second variable-aperture cylindrical scanning magnet. The first scanning coil 1 is located radially inside the second scanning coil 2 and integrated with it via a frame (not shown). The magnetic yoke 3 is disposed radially outside 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 an iron core.

[0026] In this embodiment, the first scanning coil 1, the second scanning coil 2, and the magnetic yoke 3 are all cylindrical structures. To reduce the eddy current effect, the magnetic yoke 3 can be made of laminated silicon steel sheets. It should be understood that the material of the magnetic yoke 3 can also be ferrite, iron-based nanocrystals, or iron-based amorphous materials. 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 several slots 31 extending radially outward from its inner surface, and these slots 31 are uniformly distributed in the circumferential direction. It should be understood that the cylindrical structure here can be a perfect cylindrical structure, an elliptical cylindrical structure, a square cylindrical structure, etc.

[0027] like Figure 3 As shown, the first scanning coil 1 is a scanning magnet in the X direction, and the second scanning coil 2 is a scanning magnet in the Y direction. Both are coaxially arranged (with the central axis in the Z direction) and define a tapered (e.g., conical or square pyramidal) air gap structure for the variable aperture bidirectional scanning magnet, used to deflect the pencil beam in a plane perpendicular to the beam direction. The beam is incident along the Z direction, and as it passes through the magnetic field of the magnet gap, under the action of the Lorentz force, the beam envelope gradually increases outward along the central axis Z of the scanning magnet. Specifically, the first scanning coil 1 and the second scanning coil 2 can have the same Z-direction extension length. The first scanning coil 1 has a linearly increasing first inner diameter, and the second scanning coil 2 has a linearly increasing second inner diameter. The degree of increase in the first inner diameter is equal to the degree of increase in the second inner diameter; this degree of increase is also referred to as the taper. In particular, the inner diameters of the scanning magnets 1 and 2 can be designed as a tapered air gap structure adapted to the gradually changing trajectory of the beam. It should be understood that the extension lengths of the first scanning coil 1 and the second scanning coil 2 can also be different.

[0028] The deflection angle of the beam in the magnetic field is determined by the magnetic stiffness of the particles (protons or heavy ions) and the angle along the integral path S (see...). Figure 2 The trajectory integration field determines the deflection of different particles on the same scanning magnet. The higher the particle energy, the greater its magnetic stiffness, making it more difficult to deflect, and the smaller the taper of the scanning magnet can be. Therefore, the taper of the scanning magnet is different for particles with different energies.

[0029] Compared to traditional separate scanning magnets, the variable aperture bidirectional scanning magnet of the present invention can significantly reduce the source axis distance from 3 meters to about 1 meter. The space occupied by the magnet is significantly reduced, which in turn reduces the space occupied by the treatment head. This can significantly reduce the volume and weight of the rotating gantry, making the rotating gantry more compact. The difficulty of controlling the rotating gantry is also greatly reduced, and the treatment accuracy is significantly improved.

[0030] Traditional split-type scanning magnets have different source axis distances, increasing the complexity of treatment planning. However, the variable aperture bidirectional scanning magnet of the present invention allows the source axis distances of the X-direction and Y-direction scanning magnets to be the same, greatly reducing the difficulty and complexity of treatment. It should be understood that the source axis distances can also be designed to be different.

[0031] Using a scanning magnet to deflect a beam of charged particles with the same energy, the current required for a conical air gap scanning magnet is lower than that for an equal-spaced air gap scanning magnet. Therefore, using this variable aperture bidirectional scanning magnet can effectively reduce the magnet's excitation current, reduce coil energy storage and inductance, thereby reducing coil power and eddy current losses, which can meet very high scanning speeds.

[0032] like Figure 4 As shown, scanning magnets 1 and 2 are each composed of two symmetrical halves, each half consisting of several nested trapezoidal coil conductors. In this embodiment, the first scanning coil 1 is composed of upper and lower halves, and the second scanning coil 2 is composed of left and right halves. The coil conductor distribution of the variable aperture bidirectional scanning magnet according to the present invention conforms to the Cosine-Theta form, and the position distribution of the coil wires can be adjusted according to the magnet requirements to improve the uniformity of the integrated field. For particles of different energies, the required integrated field can be increased by increasing the number of coil layers. 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 scanning magnets 1 and 2 can be formed using Litz wire or internally water-cooled copper tubing. It should be understood that the arrangement of the two halves facilitates the winding of the tubing.

[0033] like Figure 5As shown, the scanning magnet system for radiotherapy according to another preferred embodiment of the present application comprises two first scanning coils 1 and two second scanning coils 2, wherein the first scanning coils 1 and the second scanning coils 2 are integrated alternately, one first scanning coil 1 is located radially inside one second scanning coil 2, another first scanning coil 1 is located radially outside the second scanning coil 2, and another second scanning coil 2 is located radially outside the another first scanning coil 1, so that higher integral field requirement can be met compared with the previous embodiment. The two-layer structure of one first scanning coil 1 and one second scanning coil 2 is referred to as one magnet group, and two magnet groups are given in the embodiment, and it should be understood that the scanning magnet system for radiotherapy according to the present application can also comprise more magnet groups. In addition, by placing the first scanning coils 1 and the second scanning coils 2 alternately, the excitation efficiency of the magnetic yoke to the coils can be improved.

[0034] The scanning magnet system for radiotherapy according to another preferred embodiment of the present application comprises two first scanning coils and one second scanning coil, wherein one first scanning coil is located radially inside another first scanning coil, and the second scanning coil is located radially outside the another first scanning coil.

[0035] In summary, by integrating the first and second scanning coils, the scanning magnet system according to the present application can replace the conventional two separate dipole magnets, so as to realize the miniaturization and compactness of the particle therapy device.

[0036] The above description is only for the preferred embodiments of the present application, and is not intended to limit the scope of the present application. The above embodiments of the present application can be variously changed. Any simple, equivalent changes and modifications made according to the content of the claims and the description of the present application fall within the scope of protection of the present application. The present application is not described in detail, which is conventional technical content.

Claims

1. A scanning magnet system for radiotherapy, characterized in that, The scanning magnet system 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 a first variable-aperture cylindrical scanning magnet, and the second scanning coil is a second variable-aperture cylindrical scanning magnet. The first scanning coil is located radially inside the second scanning coil and integrated with it via a frame. The first scanning coil is an X-direction scanning magnet with a first inner diameter that increases linearly along the beam direction Z, and the second scanning coil is a Y-direction scanning magnet with a second inner diameter that increases linearly along the beam direction Z. The linearly increasing taper of the first inner diameter is equal to that of the second inner diameter, and both are coaxially arranged to define the tapered air gap structure of the variable-aperture bidirectional scanning magnet to deflect the beam in a plane perpendicular to the beam direction Z.

2. The scanning magnet system according to claim 1, characterized in that, The first and second scanning coils may have the same or different source axis pitches.

3. The scanning magnet system according to claim 1, characterized in that, The first and second scanning coils have the same or different extension lengths.

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

5. The scanning magnet system according to claim 4, 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.

6. The scanning magnet system according to claim 1, characterized in that, The scanning magnet system includes two first scanning coils and two second scanning coils, wherein the first scanning coils and the second scanning coils are alternately integrated together, with one first scanning coil located radially inside one second scanning coil and another first scanning coil located radially outside the second scanning coil, and another second scanning coil located radially outside the other first scanning coil.

7. The scanning magnet system according to claim 1, characterized in that, The scanning magnet system includes two first scanning coils and one second scanning coil, wherein one first scanning coil is located radially inside the other first scanning coil and the second scanning coil is located radially outside the other first scanning coil.

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