Patent Number: 
Section: claims

1. A particle therapy gantry for delivering a particle beam to a patient comprising:beam tube having a curvature defining a particle beam path; anda plurality of fixed field magnets sequentially arranged along said beam tube for guiding the particle beam along said particle path wherein each of said fixed field magnets is a combined function magnet performing a first function of bending the particle beam along said particle path and a second function of focusing or defocusing the particle beam, and wherein said combined function fixed field magnets are arranged in triplets, each triplet comprising two focusing magnets and a defocusing magnet disposed between said focusing magnets, said focusing magnets performing the combined function of bending the particle beam and focusing the particle beam and said defocusing magnet performing the combined function of bending the particle beam and defocusing the particle beam. 2. A gantry as defined in claim 1, wherein said defocusing magnets are positive bending magnets for bending the particle beam along an arc defined by a positive center of curvature and wherein said focusing magnets are negative bending magnets for bending the particle beam along an arc defined by a negative center of curvature, said positive and negative centers of curvature being oriented on opposite sides of said beam pipe. 3. A gantry as defined in claim 2, wherein said fixed field magnets are permanent magnets comprising a ferromagnetic core having a curvature defined by a center of curvature and forming a beam tube receiving cavity having said beam tube supported therein, said core being shaped to provide a magnetic field in said beam tube which grows stronger in a direction toward said core center of curvature. 4. A gantry as defined in claim 2, wherein said fixed field magnets comprise superconducting coils adjacent said beam tube for providing said combined function. 5. A gantry as defined in claim 1, wherein said beam tube includes a particle beam entry point, a transition point, a particle beam exit point, a first curved particle beam path arc length extending between said entry point and said transition point and a second curved particle beam path arc length extending between said transition point and said exit point, said first arc length bending about ninety degrees and said second arc length bending about one hundred eighty degrees in a direction opposite said first arc length. 6. A gantry as defined in claim 5, wherein said combined function fixed field magnets comprise two half-triplets disposed in juxtaposed orientation at said beam tube transition point, each of said half-triplets comprising a defocusing magnet and a focusing magnet, said focusing magnet performing the combined function of bending the particle beam and focusing the particle beam and said defocusing magnet performing the combined function of bending the particle beam and defocusing the particle beam. 7. A gantry as defined in claim 5, wherein said combined function fixed field magnets comprise a half-triplet disposed at said beam tube entry point and a half-triplet disposed at said beam tube exit point, each of said half-triplets comprising a defocusing magnet and a focusing magnet, said focusing magnet performing the combined function of bending the particle beam and focusing the particle beam and said defocusing magnet performing the combined function of bending the particle beam and defocusing the particle beam. 8. A method for delivering a particle beam to a patient through a gantry comprising the steps of:bending the particle beam with a plurality of fixed field magnets sequentially arranged along a beam tube of the gantry, the particle beam traveling in said beam tube;alternately focusing and defocusing the particle beam traveling in said beam tube with alternately arranged combined function focusing and defocusing fixed field magnets; anddelivering said particle beam from said gantry to a patient, wherein said beam is strongly focused in both the horizontal and vertical planes,wherein said combined function fixed field magnets are arranged in triplets, each triplet comprising two focusing magnets and a defocusing magnet disposed between said focusing magnets, said focusing magnets performing the combined function of bending the particle beam and focusing the particle beam and said defocusing magnet performing the combined function of bending the particle beam and defocusing the particle beam. 9. A method as defined in claim 8, wherein said defocusing magnets are positive bending magnets for bending the particle beam along an arc defined by a positive center of curvature and wherein said focusing magnets are negative bending magnets for bending the particle beam along an arc defined by a negative center of curvature, said positive and negative centers of curvature being oriented on opposite sides of said beam pipe. 10. A particle beam therapy system comprising:a source of particles;an accelerator for accelerating the particles as a particle beam;an injector for transporting particles from said source to said accelerator;a patient treatment station including a rotatable gantry for delivering a particle beam to a patient, said gantry including a beam tube having a curvature defining a particle beam path and a plurality of fixed field magnets sequentially arranged along said beam tube for guiding the particle beam along said particle path; anda beam transport system for transporting the accelerated beam from said accelerator to said patient treatment station, wherein each of said fixed field magnets of said gantry is a combined function magnet performing a first function of bending the particle beam along said particle path and a second function of focusing or defocusing the particle beam, and wherein said combined function fixed field magnets of said gantry are arranged in triplets, each triplet comprising two focusing magnets and a defocusing magnet disposed between said focusing magnets, said focusing magnets performing the combined function of bending the particle beam and focusing the particle beam and said defocusing magnet performing the combined function of bending the particle beam and defocusing the particle beam. 11. A particle beam therapy system as defined in claim 10, wherein said defocusing magnets of said gantry are positive bending magnets for bending the particle beam along an arc defined by a positive center of curvature, and wherein said focusing magnets of said gantry are negative bonding magnets for bending the particle beam along an arc defined by a negative center of curvature, said positive and negative centers of curvature being oriented on opposite sides of said beam pipe. 12. A particle beam therapy system as defined in claim 11, wherein said fixed field magnets of said gantry are permanent magnets comprising a ferromagnetic core having a curvature defined by a center of curvature and forming a beam tube receiving cavity having said beam tube supported therein, said core being shaped to provide a magnetic field in said beam tube which grows stronger in a direction toward said core center of curvature. 13. A particle beam therapy system as defined in claim 11, wherein said fixed field magnets of said gantry comprise superconducting coils adjacent said beam tube for providing said combined function. 14. A particle beam therapy system as defined in claim 10, wherein said beam tube of said gantry includes a particle beam entry point, a transition point, a particle beam exit point, a first curved particle beam path arc length extending between said entry point and said transition point and a second curved particle beam path arc length extending between said transition point and said exit point, said first arc length bending about ninety degrees and said second arc length bending about one hundred eighty degrees in a direction opposite said first arc length. 15. A particle beam therapy system as defined in claim 14, wherein said combined function fixed field magnets of said gantry comprise two half-triplets disposed in juxtaposed orientation at said beam tube transition point, each of said half-triplets comprising a defocusing magnet and a focusing magnet, said focusing magnet performing the combined function of bending the particle beam and focusing the particle beam and said defocusing magnet performing the combined function of bending the particle beam and defocusing the particle beam. 16. A particle beam therapy system as defined in claim 14, wherein said combined function fixed field magnets of said gantry comprise a half-triplet disposed at said beam tube entry point and a half-triplet disposed at said beam tube exit point, each of said half-triplets comprising a defocusing magnet and a focusing magnet, said focusing magnet performing the combined function of bending the particle beam and focusing the particle beam and said defocusing magnet performing the combined function of bending the particle beam and defocusing the particle beam.