The purpose of this work is to demonstrate a method of automated contour segmentation by deformable registration on four-dimensional CT data. A deformable image registration method is used to map the original contour to other phases. A few control points are selected on a delineated phase. Then Fourier interpolation is used to complete the contour. Application of this approach to 4D CT images shows that displacements of geometrical center of delineated and generated contour are within 2mm and the maximum volume difference is just 1.5ml. The level of accuracy is acceptable for most radiotherapy applications. The robustness and accuracy of...