Use of three‐dimensional (3D) optical flow method in mapping 3D anatomic structure and tumor contours across four‐dimensional computed tomography data

Geoffrey Zhang,Kang‐Ping Lin,Craig Stevens,Thomas Guerrero,George Starkschall,Ken Forster,Tzung‐Chi Huang

doi:10.1120/jacmp.v9i1.2738

Abstract

A three‐dimensional (3D) optical flow program that includes a multi‐resolution feature has been developed and applied to 3D anatomic structure and gross tumor volume (GTV) contour mapping for four‐dimensional computed tomography (4D CT) data. The present study includes contour mapping for actual CT data sets from 3 patients and also for a thoracic phantom in which the displacement for each voxel was known. Of the CT data sets for the actual patients, one set was used to map lung and GTV contours over all respiration phases, and the other two were studied using only the end inspiration and end expiration phases, in which the displacements between phases were the largest. Including the residual motion in the 4D CT data and motion from table shaking, the optical flow calculation agrees with the known displacement to within 1 mm. Excluding errors not introduced by the optical flow algorithm, agreement for a displacement magnitude of 24 mm can be within 0.1 mm. The mapped contours in 4D CT images of lungs, liver, esophagus, GTV, and other structures for actual patients were acceptable to clinicians. The 3D optical flow program is a good tool for contour mapping of anatomic structure and tumor volume across 4D CT scans.PACS numbers: 87.55.D‐, 87.59.bd

Highlights

Zhang et al.: Use of three-dimensional (3D) optical flow method in...respiratory phase during treatment, and the treatment system determines the subplan to use based on the tracking system’s feedback
To reduce the clinician’s contouring time, we propose using a deformable image registration algorithm based on an optical flow method to assist the contouring process
Anderson Radiological Physics Center (RPC).(9) The phantom was placed on a table that allowed for programmable one-dimensional (1D) motion

Summary

INTRODUCTION

Zhang et al.: Use of three-dimensional (3D) optical flow method in. respiratory phase during treatment, and the treatment system determines the subplan to use based on the tracking system’s feedback. In planning for 3D conformal radiotherapy or intensity-modulated radiotherapy, normal anatomic structures and tumor volumes have to be contoured to define treatment fields and to calculate dose distributions. One set of contours for the anatomic structures and the tumor volumes would not fit all of the images involved. Contouring these structures for 4D treatment planning would take a considerable multiple of the time required for traditional 3D treatment planning. To reduce the clinician’s contouring time, we propose using a deformable image registration algorithm based on an optical flow method to assist the contouring process. The optical flow algorithm differs from other methods of image-deformable registration in its ease of use and precision in mapping structures of interest. A 3D optical flow program was implemented and validated based on an extension to Horn and Schunck’s gradient-based algorithm.[7,8] The gradient-based algorithm was chosen for considerations of accuracy

MATERIALS AND METHODS

RESULTS AND DISCUSSION

CONCLUSIONS