Goodman et al3 presented results on the variability of volumetric measurements made with a commercial semiautomated software program (Advantage Lung Analysis; GE Healthcare). The evaluation was performed on 50 nodules across three repeat scans read by three observers. The second and third scans were acquired during two breath holds performed 10 to 20 min after the first scan. Nodule volume was estimated as the average volume measurement of the three observers at the first scan and was used as the baseline truth to measure interobserver variability. This measure of interobserver variability is inherently biased because each observer is compared against a standard that is based, in part, on his/her own contours. Interscan variability was measured as the percentage difference between the average volume measurements and the estimated volume. The results revealed significant interscan variability (on the order of 13%) but minimal interobserver variability. Findings from several other studies have demonstrated differences in the volumetric measurement error, ranging from 10% to 40%, between scans acquired with thin and thick section widths. Even with these limitations, we can generally conclude that section thickness/width is one of the most important CT scan acquisition parameters to control. In a recent article about nodule volumetry with phantom correlation, Xie et al4 reported that the CT scan-derived volume of small nodules is largely underestimated, with considerable variation.