1. In radiation therapy using a radiation delivery system having a radiation source that directs a radiation beam to a beam isocenter, an apparatus for locating and tracking a treatment target in a patient comprising: a wireless marker configured to be implanted in the patient at a site relative to the treatment target wherein the marker is energized or excited by an excitation source positioned exterior of the patient; a plurality of sensors in a fixed and known geometry relative to each other that obtain position information about the location and/or orientation of the marker; and a computer operatively coupled to the sensors, the computer having a computer operable medium containing instructions that cause the computer to (a) receive the position information data from the sensors 12 or more times per minute, (b) determine an actual location of the treatment target, and (c) compute a displacement between the treatment target and the beam isocenter while the sensors obtain the position information.