Energy degrader for radiation therapy system

Abstract

An energy degrading device for attenuating energy of a particle beam with reduced emittance growth. An energy degrader comprises an emittance control material that can preferentially scatter the beam particles that is incident on a surface with a shallow angle. In one approach, the energy degrader may include alternating layers of a low-Z and a high-Z material, wherein the low Z material serves to attenuate energy of the beam particles by virtue of scattering and the high Z material serves to suppress the emittance increase by scattering back the beam particles toward the beam axis. In another approach, the energy degrader may be composed of carbon nanotubes or a material with oriented crystalline structure that is substantially orientated in the incident direction of the particle beam. The carbon nanotubes may serve to preferentially scatter beam particles towards the central beam axis as well as attenuate energy thereof.

What is claimed is: 
     
         1 . A radiation therapy system comprising:
 an accelerator operable to generate a particle beam; and   an energy degrader coupled to said accelerator and operable to attenuate energy of said particle beam by virtue of particle scattering, wherein said particle scattering causes spatial emittance growth of said particle beam, wherein said energy degrader comprises a first material operable to constrain said spatial emittance growth by virtue of particle interactions.   
     
     
         2 . The radiation therapy systems of  claim 1 , wherein said energy degrader further comprises a second material operable to attenuate energy of said particle beam by said particle scattering, and wherein said first material and said second material have substantially different atomic or molecular weights. 
     
     
         3 . The radiation therapy systems of  claim 2 , wherein said second material is selected from a group consisting of Lucite, graphite, Al, C, and Be, and wherein said first material is selected from a group consisting of W, Pb, and Ta. 
     
     
         4 . The radiation therapy system of  claim 2 , wherein said energy degrader comprises a first layer sandwiched by a second layer and a third layer, wherein said first layer is made of said second material, and wherein said second member and said third member are made of said first material, wherein said first layer, said second layer and said third layer are parallel to an incident direction of said particle beam, and wherein said energy degrader is rotatable. 
     
     
         5 . The radiation therapy system of  claim 2 , wherein said energy degrader comprises a number of sections along an incident direction of said particle beam, wherein each section comprises a plurality of alternating layers made of said first material and said second material, wherein said plurality of alternating layers are parallel to said incident direction, and wherein layers of each two consecutive sections are disposed perpendicular to each other. 
     
     
         6 . The radiation therapy system of  claim 2 , wherein said energy degrader is of substantially cylindrical shape elongated along an incident direction of said particle beam, wherein said energy degrader comprises a plurality of concentric and alternating layers made of said first material and said second material, and wherein further each layer is approximately 1 mm in thickness. 
     
     
         7 . The radiation therapy system of  claim 1 , wherein said first material comprises carbon nanotubes oriented approximately in an incident direction of said particle beam. 
     
     
         8 . The radiation therapy system of  claim 7 , wherein said particle beam comprises a beam selected from a group consisting of proton beam, neutron beam, electron beam, He 2+  beam, and C 6+  beam. 
     
     
         9 . The radiation therapy system of  claim 1  further comprising a gantry, wherein said energy degrader material is integrated in said gantry. 
     
     
         10 . The radiation therapy system of  claim 1 , wherein said degrader material is disposed in a vacuum chamber. 
     
     
         11 . An energy degrader configured to attenuate energy of a particle beam by virtue of particle scattering, wherein said particle scattering causes bean diameter expansion of said particle beam, wherein said energy degrader comprises a first material operable to suppress said bean diameter expansion by virtue of particle interactions. 
     
     
         12 . The energy degrader of  claim 11  comprising a plurality of moveable members, wherein each moveable member comprises said first material and said second material. 
     
     
         13 . The energy degrader of  claim 11  further comprising a second material operable to attenuate energy of said particle beam, wherein said first material and said second material have substantially different atomic or molecular weights, wherein said second material is selected from a group consisting of Lucite, graphite, Al, C, and Be, and wherein said first material is selected from a group consisting of W, Pb, and Ta. 
     
     
         14 . The energy degrader of  claim 13 , wherein said energy degrader comprises one or more sections along an incident direction of said particle beam, wherein each section comprises a respective plurality of alternating layers of made of said first material and said second material, wherein layers in each two adjacent sections are oriented in different directions. 
     
     
         13 . (canceled) 
     
     
         14 . (canceled) 
     
     
         15 . The energy degrader of  claim 11 , wherein said first material comprises carbon nanotubes oriented approximately in an incident direction of said particle beam. 
     
     
         16 . The energy degrader of  claim 10 , wherein said particle beam comprises a beam selected from a group consisting of proton beam, neutron beam, electron beam, He 2+  beam, and C 6+  beam. 
     
     
         17 . A system configured to generate a particle beam in a controlled energy, said system comprising:
 a cyclotron coupled to a particle source;   a beam line assembly coupled to said cyclotron and operable to direct said particle beam to a target; and   an energy degrader disposed in said beam line assembly and configured to attenuate energy of said particle beam by virtue of particle scattering, wherein said particle scattering causes bean diameter expansion of said particle beam, wherein said energy degrader comprises a first material operable to suppress said bean diameter expansion by virtue of particle interactions.   
     
     
         18 . The system of  claim 17 , wherein said energy degrader further comprises a second material operable to attenuate energy of said particle beam, and wherein said first material and said second material have substantially different atomic or molecular weights. 
     
     
         19 . The system of  claim 18 , wherein said energy degrader comprises a plurality alternating layers made of said first material and said second material, wherein each layer is disposed in parallel to an incident direction of said particle beam. 
     
     
         20 . The system of  claim 17 , wherein said energy degrader comprises carbon nanotubes oriented approximately in an incident direction of said particle beam.