Dose adjustment mechanism and radiation therapy device

A radiation therapy apparatus comprising:

• a radiation irradiation apparatus;
• a gantry configured to rotate the radiation irradiation apparatus around an isocenter;
• a patient support device configured to support a patient such that a therapy target site is positioned at the isocenter;
• and
• a dose adjustment mechanism configured to adjust a dose of radiation emitted by the radiation irradiation apparatus, wherein
• the dose adjustment mechanism includes
• an actuator disposed apart from a radiation axis irradiated with radiation by a radiation therapy apparatus, and
• an interference element configured to move in a direction perpendicular to the radiation axis by an operation of the actuator and switch between a state in which the interference element is disposed on an axis of the radiation axis and a state in which the interference element is not disposed on the axis of the radiation axis, and
• an operation shaft of the actuator does not intersect the radiation axis.