Disagreement of diameter and volume measurements for pulmonary nodule size estimation in CT lung cancer screening

We studied 2240 indeterminate solid nodules (volume 50-500mm 3) to determine the correlation of diameter and semi-automated volume measurements for pulmonary nodule size estimation. Intra-nodular diameter variation, defined as maximum minus minimum diameter through the nodule's center, varied by 2.8 mm (median, IQR:2.2-3.7 mm), so above the 1.5 mm cutoff for nodule growth used in Lung CT Screening Reporting and Data System (Lung-RADS). Using mean or maximum axial diameter to assess nodule volume led to a substantial mean overestimation of nodule volume of 47.2% and 85.1%, respectively, compared to semi-automated volume. Thus, size of indeterminate nodules is poorly represented by diameter. Trial registration number Pre-results, ISRCTN63545820.