Diameter of the Solid Component in Subsolid Nodules on Low-Dose Unenhanced Chest Computed Tomography: Measurement Accuracy for the Prediction of Invasive Component in Lung Adenocarcinoma

Objective: To determine if measurement of the diameter of the solid component in subsolid nodules (SSNs) on low-dose unenhanced chest computed tomography (CT) is as accurate as on standard-dose enhanced CT in prediction of pathological size of invasive component of lung adenocarcinoma. Materials and Methods: From February 2012 to October 2015, 114 SSNs were identified in 105 patients that underwent low-dose unenhanced and standard-dose enhanced CT pre-operatively. Three radiologists independently measured the largest diameter of the solid component. Intraclass correlation coefficients (ICCs) were used to assess inter-reader agreement. We estimated measurement differences between the size of solid component and that of invasive component. We measured diagnostic accuracy of the prediction of invasive adenocarcinoma using a size criterion of a solid component ${\geq}6mm$, and compared them using a generalized linear mixed model. Results: Inter-reader agreement was excellent (ICC, 0.84-0.89). The mean ${\pm}$ standard deviation of absolute measurement differences between the solid component and invasive component was $4{\pm}4mm$ in low-dose unenhanced CT and $5{\pm}4mm$ in standard-dose enhanced CT. Diagnostic accuracy was 81.3% (95% confidence interval, 76.7-85.3%) in low-dose unenhanced CT and 76.6% (71.8-81.0%) in standard-dose enhanced CT, with no statistically significant difference (p = 0.130). Conclusion: Measurement of the diameter of the solid component of SSNs on low-dose unenhanced chest CT was as accurate as on standard-dose enhanced CT for predicting the invasive component. Thus, low-dose unenhanced CT may be used safely in the evaluation of patients with SSNs.