Systems for delivering radiation dose to a target area within a subject comprise: a radiation source for outputting a radiation beam； a support for supporting the subject； a movement mechanism for moving the radiation source relative to the subject along a trajectory； one or more sensors for monitoring a position of the subject； and a controller configured, in accordance with a radiation delivery plan, to: determine the position from one or more signals received from the one or more sensors； deactivate delivery of the treatment radiation beam upon determining that the position is outside of an acceptable range； and reactivate delivery of the treatment radiation beam upon determining that the position is within the acceptable range, to thereby deliver dose to the subject according to the radiation delivery plan.
