“…There are several techniques and methods that can be applied to tracking organs: the Point Distribution Model (PDM) or active contours [1,3,20,21,25,43,32,50], the Kalman filter [14,52], segmentation methods based on gradient and morphological operations like erosion and dilatation [44], geometrical models [34,40,39], based on camera calibration [18], applying register [27,29,24], using a commercial specialized system such as CyberKnife [17,49] or IRIS, [4] and using external and internal markers [9,54,49]. Murphy performs a comprehensive review of the work on tracking organs in real-time [35].…”