Variation in Screening CT-Detected Nodule Volumetry as a Function of Size

The objective of this study is to evaluate measurement variability in volumetric assessment of pulmonary nodules on low-dose CT images with a view toward determining how this variability is influenced by nodule size. A large CT screening database was reviewed to identify solid pulmonary nodules that had remained stable in size on the basis of findings from at least three scans obtained over a 2-year period. Two software packages (Lung VCAR and syngo.via) were used to assess the nodule volume on the two most recent CT scans, which were obtained at a slice thickness of 0.625 mm. The percentage of volume change was calculated for each nodule. The SD of the percentage of volume change was determined for nodules in each of the following nodule diameter size categories: less than 4 mm, 4-5 mm, 6-9 mm, and 10 mm or larger. The diameter was the mean of the length and width in the CT image that represented the largest cross-sectional area of the nodule. The 171 stable nodules that were identified in 117 CT screening participants (median age, 61 years) ranged in size from 2.2 to 18.7 mm. The time between acquisition of the first and last CT images ranged from 3.7 to 17.8 years (median, 11.5 years). For each of the four categories of diameter size (< 4, 4-5, 6-9, and ≥ 10 mm), the SD of the percentage of volume change was 20.4%, 17.7%, 14.6%, and 3.7%, with the use of Lung VCAR, and 59.5%, 24.3%, 9.1%, and 6.2%, with the use of syngo.via, respectively. The SD decreased with increasing nodule diameter, with the use of both software packages. Measurement variability decreased with increasing nodule diameter for both software packages and was different between the two software packages.