1. A radiation therapy system comprising: a radiation source that moves about a path and directs a beam of radiation towards an object; a cone-beam computer tomography system comprising: an x-ray source that emits an x-ray beam in a cone-beam form towards said object; an amorphous silicon flat-panel imager receiving x-rays after they pass through the object, said imager providing an image of said object; and a computer connected to said radiation source and said cone beam computerized tomography system, wherein said computer receives said image of said object and based on said image sends a signal to said radiation source that controls said path of said radiation source.