1. A system for treating a patient's target tissue with radiation, the system comprising: a radiation source having a collimator that collimates radiation emitted from the radiation source during a treatment period; a targeting module that emits a target light that corresponds to a beam spot of the emitted radiation; an imaging system that repeatedly images the target tissue, during the treatment period, with visible or infrared light; a mapping module that maps a location of the target tissue, based on the images of the imaging system during the treatment period, in a coordinate system; and a movement module that moves the radiation source, based on the mapped location of the target tissue in the coordinate system, to delivery radiation to the target tissue.