Patent Number: 
Section: claims

1. A neutron capture therapy system, comprising:a beam shaping assembly and a vacuum tube disposed in the beam shaping assembly, wherein the beam shaping assembly comprises:a beam entrance,an accommodating cavity for accommodating the vacuum tube,a moderator adjacent to an end of the accommodating cavity, wherein the moderator moderates neutrons generated from a target to an epithermal neutron energy range,a reflector surrounding the moderator, wherein the reflector guides deflecting neutrons back to the moderator to enhance an intensity of an epithermal neutron beam,a radiation shield disposed in the beam shaping assembly, wherein the radiation shield is configured to shield against leaked neutrons and photons to reduce a dose to a normal tissue in a non-irradiation area, anda beam exit, wherein the target is disposed at an end of the vacuum tube, the target undergoes a nuclear reaction with a charged particle beam entering through the beam entrance to generate neutrons, the neutrons form a neutron beam, and the neutron beam is emitted from the beam exit and defines a neutron beam axis, andwherein the moderator at least comprises two cylindrical moderating members with different outer diameters respectively, the moderator has a first end close to the beam entrance and a second end close to the beam exit, and the target is accommodated between the first end and the second end. 2. The neutron capture therapy system according to claim 1, wherein the moderator comprises a first moderating unit close to the beam entrance and a second moderating unit closely attached to the first moderating unit and close to the beam exit, the first moderating unit at least comprises two cylindrical moderating members with different outer diameters respectively, wherein all of the beam entrance, the moderator and the beam exit are extended along the neutron beam axis, and wherein a distance from the target to the beam exit is less than a distance from the first end to the beam exit. 3. The neutron capture therapy system according to claim 2, wherein the first moderating unit comprises three cylindrical moderating members with different outer diameters respectively, the first moderating unit comprises a first moderating portion close to the beam entrance, a second moderating portion closely attached to the first moderating portion, and a third moderating portion closely attached to the second moderating portion, the first moderating portion, the second moderating portion and the third moderating portion are sequentially arranged along an axial direction of the neutron beam, the first moderating portion defines a first outer diameter, the second moderating portion defines a second outer diameter greater than the first outer diameter, the third moderating portion defines a third outer diameter greater than the second outer diameter, the second moderating unit defines a fourth outer diameter equal to the third outer diameter. 4. The neutron capture therapy system according to claim 3, wherein the first moderating portion comprises a first front end surface close to the beam entrance, a first rear end surface close to the beam exit and a first outer circumferential surface, the second moderating portion comprises a second front end surface closely attached to the first rear end surface, a second rear end surface close to the beam exit and a second outer circumferential surface, the third moderating portion comprises a third front end surface closely attached to the second rear end surface, a third rear end surface close to the beam exit and a third outer circumferential surface, the second moderating unit comprises a fourth front end surface closely attached to the third rear end surface, a fourth rear end surface close to the beam exit and a fourth outer circumferential surface, in the tangent surface passing through the neutron beam axis, the first front end surface intersects the first outer circumferential surface to obtain a first intersection point, the second front end surface intersects the second outer circumferential surface to obtain a second intersection point, the third front end surface intersects the third outer circumferential surface to obtain a third intersection point, and the first intersection point, the second intersection point and the third intersection point are located on a same straight line or one arc lin. 5. The neutron capture therapy system according to claim 2, wherein a cross section of the second moderating unit is conical or cylindrical or steped-shaped. 6. The neutron capture therapy system according to claim 2, wherein a depth of the target entering into the moderator is less than or equal to a length of the first moderating unit in an axial direction of the neutron beam. 7. The neutron capture therapy system according to claim 1, wherein a reflection compensator is filled between the accommodating cavity and the vacuum tube, and the reflection compensator is lead or Al or C. 8. The neutron capture therapy system according to claim 1, wherein the first end protrudes from the target along the neutron beam axis in a direction towards the beam entrance, and the second end protrudes from the target along the neutron beam axis in a direction towards the beam exit. 9. The neutron capture therapy system according to claim 1, wherein the reflector protrudes from the moderator on both sides of the neutron beam axis, the accommodating cavity comprises a reflector accommodating cavity surrounded by the reflector and a moderator accommodating cavity extending from the reflector accommodating cavity and surrounded by the moderator, the vacuum tube comprises an extending section accommodated in the reflector accommodating cavity and an insertion section extending from the extending section and accommodated in the moderator accommodating cavity, and the target is disposed at an end of the insertion section. 10. The neutron capture therapy system according to claim 1, wherein the neutron capture therapy system further comprises at least one cooling device, at least one accommodating pipe disposed in the beam shaping assembly for accommodating the cooling device and a lead alloy or an aluminum alloy filled between the cooling device and an inner wall of the accommodating pipe. 11. The neutron capture therapy system according to claim 1, wherein the neutron capture therapy system further comprises a shielding assembly disposed at the beam entrance and closely attached to the beam shaping assembly. 12. The neutron capture therapy system according to claim 10, wherein the cooling device comprises a first cooling portion arranged in a vertical direction and located in front of the target for cooling the target and a second cooling portion and a third cooling portion extending in an axial direction of the neutron beam and respectively located on two sides of the vacuum tube, the first cooling portion is connected between the second cooling portion and the third cooling portion, the second cooling portion inputs a cooling medium into the first cooling portion, and the third cooling portion outputs the cooling medium in the first cooling portion. 13. A neutron capture therapy system, comprising:a beam shaping assembly,a vacuum tube disposed in the beam shaping assembly, anda target disposed at an end of the vacuum tube, wherein the target undergoes a nuclear reactions with a charged particle beam entering through the beam entrance to generate neutrons,wherein the beam shaping assembly comprises:a beam entrance,an accommodating cavity for accommodating the vacuum tube,a moderator adjacent to an end of the accommodating cavity, wherein the moderator at least comprises two hollow cylindrical moderating members with different outer diameters and same inner diameter respectively,a reflector surrounding the moderator, anda beam exit. 14. The neutron capture therapy system according to claim 13, wherein a reflection compensator is filled between the accommodating cavity and the vacuum tube, and the reflection compensator is lead or Al or C. 15. The neutron capture therapy system according to claim 13, wherein the neutron capture therapy system further comprises at least one cooling device, at least one accommodating pipe disposed in the beam shaping assembly for accommodating the cooling device, and a lead alloy or an aluminum alloy is filled between the cooling device and an inner wall of the accommodating pipe. 16. The neutron capture therapy system according to claim 13, wherein the moderator comprises a first end close to the beam entrance and a second end close to the beam exit, and the target is accommodated between the first end and the second end. 17. A neutron capture therapy system, comprising:a beam shaping assembly, the beam shaping assembly comprises:a beam entrance,a moderator,a reflector surrounding the moderator, anda beam exit,wherein the moderator at least comprises two hollow cylindrical moderating members with different outer diameters respectively. 18. The neutron capture therapy system according to claim 17, wherein the moderator comprises a first moderating unit close to the beam entrance and a second moderating unit closely attached to the first moderating unit and close to the beam exit, the first moderating unit at least comprises two hollow cylindrical moderating members with different outer diameters respectively. 19. The neutron capture therapy system according to claim 17, wherein the neutron capture therapy system further comprises at least one cooling device, at least one accommodating pipe disposed in the beam shaping assembly for accommodating the cooling device and a lead alloy or an aluminum alloy filled between the cooling device and an inner wall of the accommodating pipe. 20. The neutron capture therapy system according to claim 17, wherein the neutron capture therapy system further comprises a vacuum tube disposed in the beam shaping assembly, the beam shaping assembly further comprises an accommodating cavity for accommodating the vacuum tube, a reflection compensator is filled between the accommodating cavity and the vacuum tube, and the reflection compensator is lead or Al or C.