Observer variation in contouring gross tumor volume in patients with poorly defined non-small-cell lung tumors on CT: The impact of (18)FDG-hybrid PET fusion

Purpose: To quantify interobserver variation in gross tumor volume (GTV) lo calization using CT images for patients with non-small-cell lung carcinoma and poorly defined tumors on CT and to determine whether variability would be reduced if coregistered 2-[F-18]fluoro-2-deoxy-D-glucose (FDG)-hybrid po sitron emission tomography (PET) with CT images were used. Methods and Materials: Prospectively, 30 patients with non-small-cell lung carcinoma had CT and FDG-hybrid PET examinations in radiation treatment pos ition on the same day. Images were coregistered using eight fiducial marker s. Guidelines were established for contouring GTVs. Three radiation oncolog ists performed localization independently. The coefficient of variation was used to assess interobserver variability. Results: The size of the GTV defined showed great variation among observers . The mean ratios of largest to smallest GTV were 2.31 and 1.56 for CT only and for CT/FDG coregistered data, respectively. The addition of PET reduce d this ratio in 23 of 30 cases and increased it in 7. The mean coefficient of variation for GTV based on the combined modalities was significantly sma ller (p < 0.01) than that for CT data only. Conclusions: High observer variability in CT-based definition of the GTV ca n occur. A more consistent definition of the GTV can often be obtained if c oregistered FDG-hybrid PET images are used. (C) 2001 Elsevier Science Inc.