Quantitative CT Imaging in Progressive Pulmonary Fibrosis: Clinical Usefulness and Meaningful Threshold Definition.

Abstract

Although quantitative CT imaging offers objective evaluation of radiologic progression in non-idiopathic pulmonary fibrosis (IPF) fibrosing interstitial lung disease (ILD), clinically meaningful thresholds for defining progressive pulmonary fibrosis (PPF) remain unclear. What are the minimal clinically important differences (MCIDs) in quantitative CT imaging-based fibrosis score (FS) changes over 1 year and 6 months, and do these thresholds predict outcomes and enhance risk stratification in defining PPF among patients with non-IPF fibrosing ILD? This retrospective study included patients with non-IPF fibrosing ILD who underwent volumetric CT imaging at baseline and the 1-year follow-up. FS was calculated using a deep learning-based quantitative CT imaging algorithm. The MCID for FS change was determined using anchor-based methods, referencing absolute 1-year FVC change. The association of FS change MCID with transplant-free survival (TFS) and its alignment with PPF criteria were analyzed using Cox regression. Concordance between quantitative CT imaging-based and visual assessments was also assessed. Among 476 patients, the 1-year and 6-month MCIDs were 2.24% and 1.34%, respectively. Exceeding the 1-year MCID was independently associated with poorer TFS (adjusted hazard ratio [HR], 3.01; 95% CI, 2.19-4.14). Quantitative CT imaging-based progression provided additional risk stratification in patients with discordant PPF criteria, including those with disagreement on visual progression (P = .02). Patients with both visual and quantitative CT imaging-based progression showed worse outcomes than those with visual progression alone (P < .001). FS changes of more than the 6-month MCID were also associated with worse outcome (adjusted HR, 2.82; 95% CI, 1.57-5.04). Quantitative CT imaging-based PPF definition using 1-year change in FS was prognostic across patients with non-IPF fibrosing ILDs and enhanced risk stratification in patients with discordant PPF assessments.