A structure and method for broadening the Bragg peak of ion rays

Abstract

The present invention discloses a structure and a method for broadening the Bragg peak of ion rays. The ion beam Bragg peak broadening structure of the present invention is designed based on the characteristics of porous materials for broadening the Bragg peak of ion beams, and has excellent ion beam Bragg peak broadening effect. Compared with the ion beam Bragg peak broadening device such as a ridge filter, the present invention has the advantages of uniform beam and can be used close to the patient.

Description

Technical Field

[0001] The present invention relates to the technical field of the physics of ion beam radiotherapy, and particularly relates to a structure and a method for broadening the Bragg peak of an ion beam. Background Art

[0002] Ion beam radiotherapy is an advanced treatment technology in the field of radiotherapy. Since ion beams have a Bragg peak and can deposit energy rapidly in the Bragg peak region, ion beam radiotherapy technology has advantages in physical properties compared with traditional photon beam radiotherapy technology.

[0003] The Bragg peak width of ion beams, especially carbon ion beams (defined as the width at the 90%-90% dose level on the integral dose-depth curve) is very small, and ion beams with different energies need to be superimposed to obtain a relatively flat target area dose distribution. However, the energy layer switching time of a synchrotron ring ion accelerator is about 2 - 5 seconds. The superposition of too many ion beam energy layers requires a large amount of energy layer switching time, which affects the treatment efficiency. Usually, a passive energy modulation device is placed on the beam path to broaden the Bragg peak and improve the irradiation efficiency.

[0004] A common Bragg peak broadening device is a ripple filter. It is made of plexiglass material with a 3 - mm - thick pin structure. This structure has been applied in carbon ion beam therapy. However, after the beam passes through this device, it needs to be transported over a long distance (60 cm - 80 cm) to become uniform. Moreover, due to the scattering effect of this device, the lateral broadening of the proton beam will be significantly increased. Therefore, the ripple filter is usually not used in proton beam therapy.

[0005] The patent application No. 201911244477.3 discloses a method for broadening the Bragg peak of a point - scanned proton or heavy ion beam and a radiotherapy system. A porous material is placed on the path of the point - scanned proton or heavy ion beam, the porous material is perpendicular to the direction of beam travel, and the point - scanned proton or heavy ion beam produces energy straggling after passing through the porous material, thereby broadening the Bragg peak of the proton or heavy ion beam.

[0006] The above-mentioned patent solves the problem of non-uniform beam current when other Bragg peak broadening devices are used close to the patient, but there are still some deficiencies. Since the energy modulation of the ion beam by the porous material is uniform modulation, it is impossible to adjust the distal falloff width of the ion beam (defined as the width of the 80%-20% dose level at the end of the integral dose-depth curve), resulting in a larger distal falloff width of the porous material Bragg peak broadening device than that of the ridge filter, which in turn leads to a worse dose conformity and may also increase the irradiated dose of normal tissues at the end of the ray range. Summary of the Invention

[0007] The purpose of the present invention is to overcome the above-mentioned deficiencies existing in the prior art, and to provide a structure body for broadening the Bragg peak of ion rays with a reasonable structural design.

[0008] The technical solution adopted by the present invention to solve the above problems is: a structure body for broadening the Bragg peak of ion rays, characterized in that: it includes a carrier with pores, and solid strip-shaped components are arranged on the carrier with pores at equidistant intervals in a periodic manner;

[0009] The carrier includes a container and material units. The container is made of a non-metallic material, and the material units are stacked and filled in the container. Pores are formed by the stacking of adjacent particles of the material units or the material units have porous characteristics;

[0010] Wherein, the water equivalent depth of the solid strip-shaped component along the Z-axis direction of the coordinate system O-XYZ is defined as ; the water equivalent depth of the porous carrier along the Z-axis direction of the coordinate system O-XYZ is defined as ; among the selected porous materials and solid strip-shaped components .

[0011] Furthermore: The material unit adopts any one of plastic foam, coal-based activated carbon, coconut shell activated carbon, spherical nano mineral crystal, solid gel particles and solid plastic PP particles.

[0012] Furthermore: The porous carrier and the solid strip-shaped component are integrally formed by 3D printing.

[0013] The present invention relates to a method for broadening the Bragg peak of ion rays. The defined coordinate system of the structure body is denoted as O-XYZ, and a plurality of solid strip-shaped components are arranged along the XY plane of the coordinate system O-XYZ; the ion rays are incident along the Z-axis direction of the coordinate system O-XYZ, and the above-mentioned structure body is selected to broaden the width of the Bragg peak of the ion rays.

[0014] Furthermore: The ion rays are composed of any one of protons, helium ions and carbon ions.

[0015] Further: Define the length of the solid bar-shaped component along the Z-axis direction of the coordinate system O-XYZ as and define the total length of the porous carrier along the Z-axis direction of the coordinate system O-XYZ as . By adjusting the of the carrier, the desired broadening width of the ion ray Bragg peak is adjusted. By adjusting the of the solid bar-shaped component, the water equivalent depth of the solid bar-shaped component and the water equivalent depth of the porous material are obtained.

[0016] Further: Define the cross-sectional area of the container along the XY plane of the coordinate system O-XYZ as A, and define the number of solid bar-shaped components arranged periodically in the container as n. By iteratively adjusting the ratio of the total area of the solid bar-shaped component to the cross-sectional area A of the container, the optimal end-drop width of the ion ray is obtained.

[0017] Further: Define the cross-sectional area of a single solid bar-shaped component along the XY plane of the coordinate system O-XYZ as . Adjust the area of a single solid bar-shaped component according to the minimum full width at half maximum of the incident ion ray beam spot; the ratio of the minimum full width at half maximum of the beam spot to is >5.

[0018] Compared with the prior art, the present invention has the following advantages and effects:

[0019] (1) The ion beam Bragg peak broadening structure of the present invention is designed based on the characteristics of the porous material for broadening the ion beam Bragg peak, and has excellent ion beam Bragg peak broadening effect. Compared with the ion beam Bragg peak broadening devices such as the ridge filter, the present invention has the advantages of uniform beam and can be used close to the patient.

[0020] (2) The ion beam Bragg peak broadening structure of the present invention introduces periodically arranged solid bar-shaped components. Under the condition of having a similar ion beam Bragg peak broadening ability to other devices, it can provide a smaller ion beam end-drop width, thereby improving the conformality of the ion beam dose.

[0021] (3) The ion beam Bragg peak broadening structure and design method of the present invention can adjust the broadening ability, adjust the end-drop width, and adjust the water equivalent range as required. The structure of the present invention can be applied to different clinical application scenarios. Brief Description of the Drawings

[0022] Figure 1It is a schematic structural diagram of a structure for broadening the Bragg peak of ion rays according to an embodiment of the present invention.

[0023] Figure 2 It is a comparison diagram of the Bragg peak broadening effects produced by a carbon ion beam with an energy of 234.1 MeV / u in the present embodiment of the invention when applying this structure, a traditional ridge filter, and a conventional porous material respectively.

[0024] Figure 3 A comparison diagram of the broadening capabilities of the structure of the present embodiment of the invention, a traditional ridge filter, and a conventional porous material under an ion beam.

[0025] Figure 4 A comparison diagram of the end-drop widths of the structure of the present invention, a traditional ridge filter, and a conventional porous material under an ion beam.

[0026] Figure 5 It is a schematic structural diagram of a structure for broadening the Bragg peak of ion rays according to Embodiment 2 of the present invention.

[0027] Figure 6 It is a partially enlarged view of the structure of the structure for broadening the Bragg peak of ion rays according to Embodiment 2 of the present invention. Detailed implementation manners

[0028] The present invention will be further described in detail below in conjunction with the accompanying drawings and through embodiments. The following embodiments are explanations of the present invention, and the present invention is not limited to the following embodiments.

[0029] Embodiment 1:

[0030] Refer to Figure 1 As shown, in this embodiment, a structure for broadening the Bragg peak of ion rays includes a carrier with pores, and solid strip components are arranged on the carrier with pores at equidistant intervals in a periodic manner. Specifically, in this embodiment, the carrier includes a container and material units. The container is made of a hard non-metallic material, and the material units are stacked and filled in the container. Pores are formed by the stacking of adjacent particles of the material units or the material units have porous characteristics. In this embodiment:

[0031] The nano-mineral crystals forming the porous material are spheres with a diameter of 0.4 mm. According to the space utilization rate of the closest hexagonal packing being about 74.1%, it can be deduced that the ratio of the nano-mineral crystal solid material to air is about 3:1. The purpose of this embodiment is to obtain the same Bragg peak broadening effect as that of applying a traditional ridge filter. According to the above-mentioned size and ratio of the nano-mineral crystals, Monte Carlo simulation calculation is used to obtain the thickness of the porous material as 8.4 mm.

[0032] The ratio of the equivalent water thickness of the above-mentioned porous material per unit thickness to that of the PMMA solid material per unit thickness obtained from the previous measurement is approximately 13:12. According to this ratio and the actual thickness of the above-mentioned porous material, the actual thickness of the PMMA solid material is calculated to be 9.1 mm. After measurement and verification, the difference in water equivalent thickness between the two is within the design error range ( ). Therefore, the length of the cuboid PMMA is set to 9.1 mm.

[0033] To obtain the optimal ratio of the total area of the solid strip components to the cross-sectional area A of the container, carbon ion beams with an energy of 234.1 MeV / u are used to pass through the above-mentioned 8.4-mm-thick porous material and 9.1-mm-thick PMMA respectively, and two integrated depth dose distribution (IDD) curves are obtained. Keeping the second IDD curve (using 9.1-mm-thick PMMA) unchanged, the ratio of the first IDD curve (using 8.4-mm-thick porous material) is adjusted in steps of 5%. When the minimum end-drop width is finally obtained, the ratio of the two curves is 1:3. Therefore, the ratio of the total area of the cuboid PMMA to the cross-sectional area A of the container is 1:4.

[0034] The container in this embodiment: the inner length, width, and height are 10 cm 10 cm and is made of a 8.4-mm-thick carbon fiber board; the thickness of the carbon fiber board is 2 mm. Setting of the solid strip components: 1111 cuboid PMMAs with a side length of 1.5 mm are periodically inserted into the container, that is, the ratio of the total area of the solid strip components to the cross-sectional area A of the container is 1:4.

[0035] Subsequently, nano-mineral crystal particles are placed in the container to complete the materials required for this embodiment.

[0036] This embodiment is placed at the isocenter position during clinical treatment, and the center of it is vertically irradiated with 234.1 MeV / u carbon ion beams with a beam spot full width at half maximum of 3, 4, 5, 6, 7, 8, 9, and 10 mm respectively. The results show that when the beam spot full width at half maximum is 6, 7, 8, 9, and 10 mm, the difference in the width of the broadened Bragg peak is within 0.1 mm (5%), and the differences in other cases all exceed 0.1 mm (5%). Accordingly, the minimum full width at half maximum of the incident ion beam spot to the area of a single solid strip component should be >5.

[0037] The initial Bragg peak width of the 234.1 MeV / u carbon ion beam (beam spot full width at half maximum 6 mm) obtained from the previous measurement is 0.70 mm.

[0038] As Figure 3-4 shown, the Bragg peak widths obtained by passing the above-mentioned rays through this embodiment, the traditional ridge filter, and the conventional porous material are 2.73 mm, 2.7 mm, and 2.72 mm, respectively. And the ray end-drop widths of the above-mentioned rays passing through this embodiment, the ridge filter, and the porous material are 1.70 mm, 2.07 mm, and 3.11 mm, respectively.

[0039] The structure of this embodiment is simulated with ion rays of different energies and compared with the Bragg peak widths and end-drop widths of the traditional ridge filter and the conventional porous material. As Figure 3 shown, it can be seen that the end-drop widths of the structure of this embodiment are all smaller than those of the traditional ridge filter and the conventional porous material, with an average reduction of 18.8% and 46.2% in the end-drop width.

[0040] Embodiment 2:

[0041] Based on the structural characteristics of Embodiment 1, for the convenience of implementation and the control of the pore uniformity of the carrier, for example Figure 5-6 shown, in this embodiment, the porous carrier and the solid bar-shaped component are integrally formed by 3D printing, where the solid bar component and the carrier are printed with the same material and have the same density. Therefore, in the structure formed by 3D printing, the length Dr of the solid bar-shaped component along the Z-axis direction of the coordinate system O-XYZ < the length of the carrier along the Z-axis direction of the coordinate system O-XYZ .

[0042] By adjusting the line width and volume of the carrier grid structure, the pore ratio of the carrier is set; by adjusting the cross-sectional area and arrangement ratio of the carrier solid bar structure, the ratio of the carrier solid bar component to the total area is set; by adjusting the length of the carrier solid bar structure, the water equivalent depth of the solid bar structure is adjusted so that the difference in the water equivalent thickness between the solid bar structure and the grid structure is within the design error range ( ).

[0043] This embodiment is formed by establishing a 3D model and printing, with stronger practicability and adjustability, and a carrier with a suitable particle beam broadening ability can be obtained according to actual needs.

[0044] What is described above in this specification is only an example of the present invention. Those skilled in the technical field to which the present invention pertains can make various modifications or supplements to the specific embodiments described or use similar methods for substitution, as long as they do not deviate from the content of this specification of the present invention or exceed the scope defined by this claim book, they should all fall within the protection scope of the present invention.

Claims

1. A structure for broadening the Bragg peak of ion rays, characterized in that: It includes a porous carrier, on which solid strip-shaped components are arranged at equidistant intervals in a periodic manner; The porous carrier includes a container and material units. The container is made of a hard non-metallic material, and the material units are stacked and filled in the container. Pores are formed by stacking adjacent particles of the material units or the material units have porous characteristics; The water equivalent depth of the solid bar-shaped component in the Z-axis direction of the coordinate system O-XYZ is defined as , and the water equivalent depth of the porous carrier in the Z-axis direction of the coordinate system O-XYZ is defined as ; among the selected porous material and solid bar-shaped component .

2. The structure for broadening the Bragg peak of ion rays according to claim 1, characterized in that: The hard non-metallic material is made of carbon fiber material, and the material units are any one of plastic foam, coal-based activated carbon, coconut shell activated carbon, spherical nano mineral crystal, solid gel particles, and solid plastic PP particles.

3. The structure for broadening the Bragg peak of ion rays according to claim 1, characterized in that: The porous carrier and the solid strip-shaped components are integrally formed by 3D printing.

4. A method for broadening the Bragg peak of ion rays, characterized in that: Select the structure described in any one of claims 1-3 to broaden the Bragg peak width of ion rays. Define the coordinate system as O-XYZ. A plurality of solid strip-shaped components are arranged along the XY plane of the coordinate system O-XYZ; the ion rays are incident along the Z-axis direction of the coordinate system O-XYZ.

5. The method for broadening the Bragg peak of ion rays according to claim 4, characterized in that: The ion rays are composed of any one or a combination of protons, helium ions, and carbon ions.

6. The method for broadening the Bragg peak of ion rays according to claim 4, characterized in that: Define the length of the solid bar-shaped component along the Z-axis direction of the coordinate system O-XYZ as ; define the total length of the porous carrier along the Z-axis direction of the coordinate system O-XYZ as . By adjusting the of the carrier, adjust the required broadening width of the ion ray Bragg peak. By adjusting the of the solid bar-shaped component, make the water equivalent depth of the solid bar-shaped component and the water equivalent depth of the porous material .

7. The method for broadening the Bragg peak of ion rays according to claim 6, characterized in that: Define the cross-sectional area of the container in the XY plane of the coordinate system O-XYZ as A, and define the cross-sectional area of a single solid bar-shaped component in the XY plane of the coordinate system O-XYZ as , define the number of times the solid bar-shaped components are periodically arranged in the container as n, and obtain the optimal end-drop width of the ion beam by iteratively adjusting the ratio of the total area of the solid bar-shaped components to the cross-sectional area A of the container.

8. The method for broadening the Bragg peak of ion rays according to claim 4, characterized in that: Define the cross-sectional area of a single solid bar-shaped component in the XY plane of the coordinate system O-XYZ as , and adjust the area of a single solid bar-shaped component according to the minimum full width at half maximum (FWHM) of the incident ion beam spot ; the ratio of the minimum FWHM of the beam spot to is > 5.

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