RATIONALE AND OBJECTIVESDetermine inter- and intraobserver variability of computed tomography (CT) tumor volume measurements in advanced non-small-cell lung cancer (NSCLC) patients treated in a Phase II clinical trial using chest CT.MATERIALS AND METHODSTwenty-three advanced NSCLC patients with a total of 53 measurable lung lesions enrolled in a Phase II, multicenter, open-label clinical trial of erlotinib were retrospectively studied with institutional review board approval. Two radiologists independently measured the tumor size, volume, and CT attenuation coefficient using commercially available volume analysis software. Concordance correlation coefficients (CCCs) and Bland-Altman plots were used to assess inter- and intraobserver agreement.RESULTSHigh CCCs (0.949-0.990) were observed in all types of measurements for interobserver agreement. The 95% limits of agreements for volume, unidimensional, and bidimensional measurements were (-26.0%, 18.6%), (-23.1%, 24.4%), and (-34.0%, 48.6%), respectively. Volume measurement had slightly higher CCC and narrower 95% limits of agreement compared to uni- and bidimensional measurements. CCCs for intraobserver agreement were high (range, 0.946-0.996) with CCC for volume being slightly higher than CCCs of uni- and bidimensional measurements. The smaller the tumor volume was, the larger the interobserver difference of CT attenuation. Location, morphology, or adjacent atelectasis had no significant impact on inter- or intraobserver variability.CONCLUSIONCT tumor volume measurement in advanced NSCLC patients using clinical chest CT and commercially available software demonstrated high inter- and intraobserver agreement, indicating that the method may be used routinely in clinical practice.