Visual Emphysema as a Category Modifier in Lung-RADS: Secondary Analysis of National Lung Screening Trial.

Objective: The Lung CT Reporting and Data System (Lung-RADS) does not consider emphysema, a lung cancer risk factor detectable on CT, when assessing nodule risk. This study aimed to evaluate the impact of incorporating emphysema into Lung-RADS on lung cancer diagnosis.

Methods: In this secondary analysis of the National Lung Screening Trial data, CT arm participants with noncalcified nodules were assigned to Lung-RADS categories, and their emphysema severity was visually dichotomized. Lung cancer rates within each Lung-RADS category were compared based on emphysema severity. A modified Lung-RADS, reclassifying nodules with significant emphysema into a higher category, was evaluated against standard Lung-RADS.

Results: A study of 9444 participants (782 [8.3%] with lung cancer) revealed difference in lung cancer rates across Lung-RADS categories based on visual emphysema severity: category 2 (2.6% vs. 4.9%; P = 0.007), 3 (4.9% vs. 9.0%; P < 0.001), 4A (9.2% vs. 15.5%; P = 0.01), 4B (16.1% vs. 24.1%; P = 0.12), and 4X (25.3% vs. 33.2%; P = 0.008) without or with significant emphysema. Compared to standard Lung-RADS, modified Lung-RADS demonstrated a comparable area under the curve (AUC) (0.73 vs. 0.74, P = 0.009), increased sensitivity (61.3% vs. 67.6%, P < 0.001), decreased specificity (77.2% vs. 71.4%, P < 0.001), and improved goodness of fit (P = 0.008) for predicting lung cancer.

Discussion: Lung cancer rates differ by emphysema severity within Lung-RADS categories. Using the visual emphysema severity as a category modifier in Lung-RADS increased sensitivity while achieving comparable AUC for lung cancer.