A radiation therapy system comprising a therapeutic radiation system (e.g., an MV X-ray source, and/or a linac) and a co-planar imaging system (e.g., a kV X-ray system) on a fast rotating ring gantry frame. The therapeutic radiation system and the imaging system are separated by a gantry angle, and the gantry frame may rotate in a direction such that the imaging system leads the MV system. The radiation sources of both the therapeutic and imaging radiation systems are each collimated by a dynamic multi-leaf collimator (DMLC) disposed in the beam path of the MV X-ray source and the kV X-ray source, respectively. In one variation, the imaging system identifies patient tumor(s) positions in real-time. The DMLC for the imaging radiation source limits the kV X-ray beam spread to the tumor(s) and/or immediate tumor regions, and helps to reduce irradiation of healthy tissue (e.g., reduce the dose-area product).
