Patent ID: 8447387

Claim:
A method for real-time tracking of a target in a human body, the method comprising the acts of: implanting into the target a plurality of physical positron emission fiducial markers having a low activity positron-emitting isotope source; detecting two annihilation gamma rays resulting from positron annihilation associated with each of a plurality of position-emitting nuclear decay events of the low activity positron-emitting isotope source using a plurality of position-sensitive detectors, wherein the plurality of position-sensitive detectors comprises two pairs of position-sensitive detector modules mounted external to the human body in an orthogonal orientation such that the angle between the two pairs of position-sensitive detector modules is between 65 degrees and 90 degrees; forming a coincident line from only the two detected annihilation gamma rays for each of the plurality of position-emitting nuclear decay events; sorting the coincident lines into clusters based on an iterative Expectation-Maximization clustering algorithm; determining the locations of the plurality of physical position emission fiducial markers using only said clusters; and tracking, during radiation therapy delivery, movement and change of orientation of the target in real-time based on a change in position and orientation of plurality of physical positron emission fiducial markers, wherein said tracking provides target movement information for use in performing said radiation therapy delivery.