An apparatus, comprising: a rotatable gantry; a translatable treatment couch coupled to the rotatable gantry via a communications network; a control computer for receiving a treatment plan to instruct the apparatus to at least adjust a therapeutic megavoltage radiation source into position to align a treatment volume with the therapeutic megavoltage radiation source; first means for applying a first cone-beam radiation beam coupled to the rotatable gantry, wherein the first means for applying includes a kilovoltage radiation source; second means for applying a second cone-beam radiation beam coupled to the rotatable gantry using the treatment plan, wherein the second means for applying includes the therapeutic megavoltage radiation source; first means for capturing first image projection data applied by the kilovoltage radiation source with a first flat-panel kilovoltage radiation imager, which is coupled to the rotatable gantry; second means for capturing second image projection data applied by the megavoltage radiation source with a different, second flat-panel megavoltage radiation imager, which is coupled to the rotatable gantry; means for storing the captured image projection data coupled to the rotatable gantry via a communications network; means for generating cone-beam computed tomography volumetric image data from the captured image projection data captured by the first flat-panel imager; characterised in that said control computer is configured for determining the patient repositioning required to begin a treatment based on a comparison of the second image projection data with at least one reference image a rotatable gantry; a translatable treatment couch coupled to the rotatable gantry via a communications network; a control computer for receiving a treatment plan to instruct the apparatus to at least adjust a therapeutic megavoltage radiation source into position to align a treatment volume with the therapeutic megavoltage radiation source; first means for applying a first cone-beam radiation beam coupled to the rotatable gantry, wherein the first means for applying includes a kilovoltage radiation source; second means for applying a second cone-beam radiation beam coupled to the rotatable gantry using the treatment plan, wherein the second means for applying includes the therapeutic megavoltage radiation source; first means for capturing first image projection data applied by the kilovoltage radiation source with a first flat-panel kilovoltage radiation imager, which is coupled to the rotatable gantry; second means for capturing second image projection data applied by the megavoltage radiation source with a different, second flat-panel megavoltage radiation imager, which is coupled to the rotatable gantry; means for storing the captured image projection data coupled to the rotatable gantry via a communications network; means for generating cone-beam computed tomography volumetric image data from the captured image projection data captured by the first flat-panel imager; characterised in that said control computer is configured for determining the patient repositioning required to begin a treatment based on a comparison of the second image projection data with at least one reference image