The purpose of this study was to investigate doubling time (DT) differences among solid, part-solid (PS) and non-solid (NS) types of lung cancers. We also compared inter-observer differences in size measurements between diameter and three-dimensional (3D) volume measurements of lung cancers, including PS- and NS-type nodules, using 3D computer-aided volumetry (3D-CAV).
The long-axis diameters and 3D volumes of lung tumours were measured using CAV by two chest radiologists for 71 consecutive patients with peripheral lung cancer who underwent at least two CT examinations before surgical resection. We evaluated the inter-observer variability for the ratio of diameter change (RCdiameter) and volume change (RCvolume), which were based on two CT images obtained at different times prior to resection. Inter-observer agreement was evaluated by Bland–Altman plots. Based on the volumes obtained from 3D-CAV, we calculated the DTs and compared DT differences between solid, PS and NS types of lung tumours.
The inter-observer Spearman's rank correlation coefficients were 0.87 for RCvolume and 0.64 for RCdiameter (p < 0.001). For all internal appearance types, the rs values for RCvolume were greater than those for RCdiameter. The median DT values for solid, PS and NS were 278, 347 and 584 days, respectively. NS- and PS-type tumours had significantly longer DTs (p = 0.024; by Spearman's rank correlation coefficient).
DT determinations using 3D-CAV had good correlations with the internal appearances of lung cancers. Lung tumour volume measurements by 3D-CAV exhibited better inter-observer correlations than did diameter measurements.