Determination of patient-specific internal gross tumor volumes for lung cancer using four-dimensional computed tomography

Background To determine the optimal approach to delineating patient-specific internal gross target volumes (IGTV) from four-dimensional (4-D) computed tomography (CT) image data sets used in the planning of radiation treatment for lung cancers. Methods We analyzed 4D-CT image data sets of 27 consecutive patients with non-small-cell lung cancer (stage I: 17, stage III: 10). The IGTV, defined to be the envelope of respiratory motion of the gross tumor volume in each 4D-CT data set was delineated manually using four techniques: ( 1 ) combining the gross tumor volume (GTV) contours from ten respiratory phases (IGTV AllPhases ); ( 2 ) combining the GTV contours from two extreme respiratory phases (0% and 50%) (IGTV 2Phases ); ( 3 ) defining the GTV contour using the maximum intensity projection (MIP) (IGTV MIP ); and ( 4 ) defining the GTV contour using the MIP with modification based on visual verification of contours in individual respiratory phase (IGTV MIP-Modified ). Using the IGTV AllPhases as the optimum IGTV, we compared volumes, matching indices, and extent of target missing using the IGTVs based on the other three approaches. Results The IGTV MIP and IGTV 2Phases were significantly smaller than the IGTV AllPhases ( p < 0.006 for stage I and p < 0.002 for stage III). However, the values of the IGTV MIP-Modified were close to those determined from IGTV AllPhases ( p = 0.08). IGTV MIP-Modified also matched the best with IGTV AllPhases . Conclusion IGTV MIP and IGTV 2Phases underestimate IGTVs. IGTV MIP-Modified is recommended to improve IGTV delineation in lung cancer.

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