Patent Number: 
Section: claims

1. A method of modulating ions comprising:(a) generating an area beam of ions directed along an axis and having a longitudinal and latitudinal extent in cross-section and divided into latitudinally adjacent beamlets of ions;(b) occluding the area beam with a set of latitudinally arrayed ion-blocking shutters each having a latitudinal width substantially equal to a latitudinal width of a beamlet, the ion-blocking shutters controllably extended to different longitudinal distances at the cross-section according to a desired intensity of a beamlet of ions to block only a controllable portion of the longitudinal extent of the beamlet and to pass without blocking a remaining portion of the beamlet so that the intensity of the beamlet is substantially nonuniform in a longitudinal direction, some of the different longitudinal distances at the cross-section being less than a length of the longitudinal extent of the area beam; wherein an average intensity of the beamlet is defined by a portion of the beamlet occluded by a given shutter; and(c) refocussing the occluded area beam with a lens system to collapsing the area beam and beamlets in the longitudinal direction to form a fan beam directable toward a patient for radiation therapy to provide a substantially uniform longitudinal intensity in each collapsed beamlet. 2. The method of claim 1 further including the step of occluding the fan beam with a set of latitudinally adjacent ion attenuating wedges controllably extended to different longitudinal distances according to a desired energy of a beamlet of ions defined by a portion of the area beam occludable by a given wedge. 3. The method of claim 1 wherein each wedge is matched to a corresponding wedge providing mirror movement to the wedge to present a uniform thickness of material within the fan beam. 4. The method of claim 1 wherein step of the collapsing the area beam passes the area beam through a pair of quadrupole lenses aligned in rotation with each other about the axis. 5. The method of claim 1 wherein the step of generating the area beam passes a pencil beam through a scattering foil to form the area beam. 6. The method of claim 1 wherein the area beam is a proton beam. 7. The method of claim 1 including the step of rotating the fan beam with respect to the patient about a longitudinal axis while controllably varying the longitudinal distances of the shutters. 8. A modulator for ions comprising:(a) a beam generator generating an area beam of ions directed along an axis and having a longitudinal and latitudinal extent in cross-section composed of latitudinally adjacent beamlets of ions;(b) an intensity modulator occluding the area beam with a set of latitudinally arrayed ion-blocking shutters each having a latitudinal width substantially equal to a latitudinal width of a beamlet, the ion-blocking shutters controllably extended to different longitudinal distances at the cross-section according to a desired intensity of a beamlet of ions to block only a controllable portion of the longitudinal extent of the beamlet and to pass without blocking a remaining portion of the beamlet so that the intensity of the beamlet is substantially nonuniform in a longitudinal direction, some of the different longitudinal distances at the cross-section being less than a length of the longitudinal extent of the area beam; wherein an average intensity of the beamlet is defined by a portion of the beamlet occluded by a given shutter; and(c) a lens system receiving the area beam from the intensity modulator, the lens system collapsing the area beam and beamlets in the longitudinal direction to form a fan beam directable toward a patient for radiation therapy to provide a substantially uniform longitudinal intensity in each collapsed beamlet. 9. The modulator of claim 8 further including an energy modulator having a set of latitudinally adjacent ion attenuating wedges controllably extended to different longitudinal distances according to a desired energy of a beamlet of ions defined by a portion of the area beam occludable by a given wedge. 10. The modulator of claim 8 wherein each wedge is matched to a corresponding wedge providing minor movement to the wedge to present a uniform thickness of material within the fan beam. 11. The modulator of claim 8 wherein the lens system is a pair of quadrupole lenses aligned in rotation about the axis. 12. The modulator of claim 8 wherein the beam generator is a scattering foil receiving a pencil beam to spread it into an area beam. 13. The modulator of claim 8 wherein the beam generator generates a proton beam. 14. The modulator of claim 8 including a gantry holding the modulator for rotation of the fan beam with respect to the patient about a longitudinal axis while controllably varying the longitudinal distances of the shutters.