Patent Number: 
Section: claims

1. A charged particle irradiation system comprising:an accelerator for extracting a charged particle beam;charged-particle-beam scanning equipment; anda charged-particle-beam-position monitor system,wherein said charged particle irradiation system further includes a control unit for calculating a beam position at a target position on the basis of a signal received from the charged-particle-beam-position monitor system to control the charged-particle-beam scanning equipment so that the charged particle beam is moved to a desired irradiation position at the target position, andwherein in each predetermined cycle of the accelerator, said control unit corrects the value of an excitation current applied to the charged-particle-beam scanning equipment on a specified cycle basis on the basis of information about the position and the angle of the charged particle beam. 2. The charged particle irradiation system according to claim 1, wherein:said charged particle irradiation system is equipped with two of the charged-particle-beam-position monitor systems; andwherein in each predetermined cycle of the accelerator, said control unit corrects the value of the excitation current applied to the charged-particle-beam scanning equipment on a specified cycle basis on the basis of information about the position and the angle of the charged particle beam which are obtained from a first charged-particle-beam position detected by a first charged-particle-beam-position monitor system and a second charged-particle-beam position detected by a second charged-particle-beam-position monitor system. 3. The charged particle irradiation system according to claim 2, wherein:in each extraction cycle of the accelerator, said control unit corrects the value of an excitation current applied to the charged-particle-beam scanning equipment on the basis of information about the position and the angle of the charged particle beam. 4. The charged particle irradiation system according to claim 2, wherein:said control unit sets an excitation current value for the charged-particle-beam scanning equipment such that in the next cycle, a point on the opposite side of the charged particle beam position with respect to the desired irradiation position, which point is away from the beam position by the distance between the beam position and the desired position at the target position, is irradiated with such a charged particle beam with which the beam position agrees with the desired irradiation position. 5. The charged particle irradiation system according to claim 2, wherein:even when the charged-particle-beam scanning equipment scans the charged particle beam, said control unit calculates the distance between the desired position and the charged particle beam position at the target position on the basis of the distance between the position of the charged particle beam traveling toward the desired irradiation position at the position of the charged-particle-beam-position monitor system and the path of the charged particle beam. 6. The charged particle irradiation system according to claim 2, wherein:said first charged-particle-beam-position monitor system is disposed upstream of the charged-particle-beam scanning equipment and said second charged-particle-beam-position monitor system is disposed downstream of the charged-particle-beam scanning equipment. 7. The charged particle irradiation system according to claim 2, wherein:said first and second charged-particle-beam-position monitor systems are disposed downstream of the charged-particle-beam scanning equipment. 8. The charged particle irradiation system according to claim 2, wherein:said first and second charged-particle-beam-position monitor systems are disposed upstream of the charged-particle-beam scanning equipment. 9. The charged particle irradiation system according to claim 3, wherein:said control unit identifies the progress of the phase of the extraction cycle from a radiated charge amount in the same extraction cycle. 10. The charged particle irradiation system according to claim 3, wherein:said control unit identifies the progress of the phase of the extraction cycle from a numerical value that is obtained by dividing a radiated charge amount in the same extraction cycle by an accumulated charge amount. 11. The charged particle irradiation system according to claim 3, wherein:said control unit corrects the charged particle beam irradiation position in the next extraction cycle by a function in which a position to which the charged particle beam irradiation position changes according to the phase in the extraction cycle is approximated by a phase function of the extraction cycle. 12. The charged particle irradiation system according to claim 1, wherein:said charged particle irradiation system is equipped with one charged-particle-beam-position monitor system, said monitor system being capable of measuring both the position and the angle of the charged particle beam. 13. The charged particle irradiation system according to claim 1, wherein:if the difference between the charged particle beam position and the desired irradiation position at the target position exceeds a threshold value, a safety interlock system is operated, said charged particle beam position having been calculated by the control unit. 14. The charged particle irradiation system according to claim 12, wherein:in each extraction cycle of the accelerator, said control unit corrects the value of an excitation current applied to the charged-particle-beam scanning equipment on the basis of information about the position and the angle of the charged particle beam. 15. The charged particle irradiation system according to claim 12, wherein:said control unit sets an excitation current value for the charged-particle-beam scanning equipment such that in the next cycle, a point on the opposite side of the charged particle beam position with respect to the desired irradiation position, which point is away from the beam position by the distance between the beam position and the desired position at the target position, is irradiated with such a charged particle beam with which the beam position agrees with the desired irradiation position. 16. The charged particle irradiation system according to claim 12, wherein:even when the charged-particle-beam scanning equipment scans the charged particle beam, said control unit calculates the distance between the desired position and the charged particle beam position at the target position on the basis of the distance between the position of the charged particle beam traveling toward the desired irradiation position at the position of the charged-particle-beam-position monitor system and the path of the charged particle beam. 17. The charged particle irradiation system according to claim 14, wherein:said control unit identifies the progress of the phase of the extraction cycle from a radiated charge amount in the same extraction cycle. 18. The charged particle irradiation system according to claim 14, wherein:said control unit identifies the progress of the phase of the extraction cycle from a numerical value that is obtained by dividing a radiated charge amount in the same extraction cycle by an accumulated charge amount. 19. The charged particle irradiation system according to claim 14, wherein:said control unit corrects the charged particle beam irradiation position in the next extraction cycle by a function in which a position to which the charged particle beam irradiation position changes according to the phase in the extraction cycle is approximated by a phase function of the extraction cycle.