Method to estimate real-time rotation and translation of a target with a single x-ray imager

A method of real-time estimation of target rotation and translation in 6 degrees of freedom, comprising:

• a. using an x-ray imager, during radiation treatment delivery, to acquire sequential images of the projected 2D positions of at least three fiducial markers implanted in a host, wherein a series of said fiducial markers in 2D images are determined;
• b. determining, using an appropriately programmed computer, a covariance matrix of said fiducial marker locations and mean point fiducial marker locations by fitting a probability distribution function (PDF) to said series of fiducial marker locations in 2D images using a maximum likelihood estimation, wherein said series of fiducial markers location in 2D images are used to determine projected 3D points of said at least three fiducial markers in said host;
• c. inputting said projected 3D points of said at least three fiducial markers to an iterative closest point (ICP) algorithm using said appropriately programmed computer to determine a real-time target rotation and translation about a center of mass of said at least three fiducial markers;
• and
• d. outputting 3D locations of said at least three fiducial markers rotated around a right-left direction, an anterior-posterior direction, and a superior-inferior direction of said host.