Lung tumor growth: assessment with CT--comparison of diameter and cross-sectional area with volume measurements.

PURPOSE To compare diameter and cross-sectional area measurements with volume measurements in the assessment of lung tumor growth with serial computed tomography (CT). MATERIALS AND METHODS Patients with lung cancer who underwent at least one pair of chest CT examinations 25 or more days apart before treatment and with a tumor size of T1 (< or =3-cm diameter) at the initial CT examination were identified. A total of 63 patients (62 men, one woman) who underwent 93 pairs of CT examinations were included. Images obtained at each examination were displayed, and the maximum diameter, cross-sectional area, and volume of the tumor were measured. For each measurement, the change between examinations was assessed to determine whether the change reached a detection threshold for growth, as determined in a prior study with simulated tumors. Results were then compared between measurement methods, with volume change serving as the reference standard, by calculating Spearman rank-order coefficients between examinations. Tumor size or section width were also evaluated with the two-tailed Fisher exact probability test to determine if they affected agreement about tumor growth between measurement methods. RESULTS Thresholds were as follows: diameter, 2.1 mm with hand-held calipers and 0.68 mm with electronic calipers; area, 9.4%; volume, 16.5%. The median time between examinations was 92 days (range, 25-1,221 days). Median diameter increased from 19.3 mm to 23.0 mm (19.2%), median area from 207 mm(2) to 267 mm(2) (29.0%), and median volume from 1,652 mm(3) to 2,443 mm(3) (47.9%). Growth assessment with these diameter (as assessed with hand-held and electronic calipers) and area thresholds disagreed with those obtained with volume in 34 (37%), 26 (28%), and 25 (27%) of the 93 pairs of CT examinations, respectively. Of diameter assessments with the hand-held caliper threshold, 28 (30%) were false-negative; false-negative results occurred with this diameter threshold and area threshold with examination intervals as long as 1 year. CONCLUSION Growth assessment of T1 lung tumors on serial CT scans with nonvolumetric measurements frequently disagrees with growth assessment with volumetric measurements.