| CPC A61N 5/1048 (2013.01) [A61N 5/103 (2013.01); A61N 5/1045 (2013.01); A61N 5/1081 (2013.01)] | 11 Claims |

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1. A radiation therapy system, comprising:
a radiation source;
a rotation mechanism that supports the radiation source and rotates the radiation source around an isocenter;
a couch that places a therapy target site of a patient at the isocenter;
a head swing mechanism that is disposed between the radiation source and the rotation mechanism and that swings an irradiation axis of a radiation emitted from the radiation source by swinging the radiation source; and
a controller that controls the radiation source, the rotation mechanism, and the head swing mechanism,
wherein in an irradiation range expansion mode the controller holds the head swing mechanism in a state where the irradiation axis of the radiation of the radiation source is shifted from the isocenter in a predetermined direction by a predetermined amount by the head swing mechanism and rotates the radiation source by the rotation mechanism while emitting the radiation from the radiation source while maintaining the state of the head swing mechanism.
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