In this study, we have developed a three-dimensional (3D) optical flow program that includes a multi-resolution feature and applied to 3D anatomic structure and gross tumor volume(GTV) contour mapping for four-dimensional computed tomography((4D CT) data. Actual 4D CT data sets from one lung cancer patient and one esophageal tumor patient, 10 phases were reconstructed per respiratory cycle respectively. On the four-dimensional (4D) data sets, a physician contoured anatomic structures and GTV on the end-inspiration phase. The motion fields calculated by 3D optical flow algorithm that includes a multi-resolution feature. The contours of lung, esophageal and tumor elastically mapped from end-expiration to all the other respiration phases using optical flow. The mapped contours in 4D CT images of lungs, esophageal, GTV and other structures for actual patient using 3D optical flow program that included multi-resolution feature are acceptable to clinicians. The 3D optical flow algorithm that includes a multi-resolution feature can be used for 4D radiation therapy to determine the ITV.