Patent Number: 
Section: claims

1. A method for irradiating a charged particle beam onto an irradiation subject, the method comprising:determining, by performing a treatment optimization calculation by a treatment planning apparatus, an arrangement of columnar irradiation fields at a first plurality of locations of the irradiation subject in accordance with a distal form of the irradiation subject and at a second plurality of locations of the irradiation subject in accordance with a distal form of portions of the irradiation subject;when it is determined that the arrangement of columnar irradiation fields at the determined first plurality of locations and the determined second plurality of locations includes overlapping columnar irradiation fields, adjusting, by an optimization calculation unit, the arrangement of the overlapping columnar irradiation fields such that portions where the columnar irradiation fields overlap are eliminated and an irradiation dose falls within a predetermined range;after at least said determination, generating, by a columnar-irradiation-field generation apparatus, a columnar irradiation field having a Spread Out Bragg Peak (SOBP) width, wherein said generated columnar irradiation field (i) is generated without scattering the charged particle beam in an X-Y direction perpendicular to the charged particle beam and (ii) has a depth in the irradiation subject in the direction of the charged particle beam that is larger than a cross-sectional dimension of the charged particle beam in the X-Y direction perpendicular to the charged particle beam on the irradiation subject;in accordance with the treatment optimization calculation, (i) initially scanning, by a scanning system, the charged particle beam with the generated columnar irradiation field at the first plurality of locations of the irradiation subject in accordance with the distal form of the irradiation subject, and (ii) subsequently scanning, by the scanning system, the charged particle beam with the generated columnar irradiation field at the second plurality of locations of the irradiation subject in accordance with the distal form of portions of the irradiation subject, other than the first plurality of locations irradiated in the initial scanning. 2. The method of claim 1, wherein, during the subsequent scanning, the columnar irradiation field has a SOBP width that differs from the SOBP width of the columnar irradiation field during the initial scanning. 3. The method of claim 1, wherein the columnar-irradiation field generation apparatus includes an apparatus for changing the energy of the columnar irradiation field, and wherein, during the scanning steps, the energy of the columnar irradiation field is changed in accordance with the distal form of the area of the irradiation subject that is to be irradiated. 4. The method of claim 3, wherein:the energy changing apparatus comprises a plurality of absorbers, one absorber including a uniform thickness that differs from a uniform thickness of another absorber, andthe step of changing the energy of the columnar irradiation fields include adjusting, by at least one driving device, a combined thickness of the plurality of absorbers. 5. The method of claim 4, wherein adjusting the combined thickness of the plurality of absorbers includes positioning at least two absorbers from the plurality of absorbers along a beam axis of the charged particle beam such that the at least two absorbers from the plurality of absorbers are in alignment with the charged particle beam. 6. The method of claim 3, wherein the energy changing apparatus comprises a range shifter whose thickness changes in a direction perpendicular to the charged particle beam, and wherein the steps of scanning the charged particle beam in accordance with a distal form of the irradiation subject include moving the charged particle beam in said perpendicular direction, by at least one deflection electromagnet, to a desired location in the range shifter. 7. The method of claim 1, wherein, during the initial scanning, the columnar irradiation field is scanned along an outer distal periphery of the irradiation subject. 8. The method of claim 7, wherein, during the subsequent scanning, the columnar irradiation field is scanned along locations interior of the outer periphery scanned during the initial scanning. 9. The method of claim 1, wherein the generated columnar irradiation field of the charged particle beam enters the irradiation subject from a plurality of different directions during each of the initial and subsequent scannings.