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

Area of Science:

• Pulmonary Medicine
• Radiology
• Quantitative Imaging

Background:

• Quantitative CT (QCT) enables objective assessment of fibrosing interstitial lung disease (ILD) progression.
• Clinically significant thresholds for defining progressive pulmonary fibrosis (PPF) using QCT are not well-established for non-idiopathic pulmonary fibrosis (IPF) ILD.

Purpose of the Study:

• Determine minimal clinically important differences (MCIDs) in quantitative CT-based fibrosis score changes (ΔFS) over 1 year and 6 months in non-IPF fibrosing ILD.
• Evaluate if these ΔFS thresholds predict outcomes and enhance risk stratification for PPF.

Main Methods:

• Retrospective analysis of 476 patients with non-IPF fibrosing ILD undergoing volumetric CT scans.
• Fibrosis score (FS) calculated using a deep learning-based QCT algorithm.
• MCID for ΔFS determined using anchor-based methods referencing forced vital capacity (FVC) change; association with transplant-free survival (TFS) analyzed via Cox regression.

Main Results:

• 1-year and 6-month MCIDs for ΔFS were 2.24% and 1.34%, respectively.
• Exceeding the 1-year MCID was independently associated with poorer TFS (aHR=3.01) and enhanced risk stratification.
• ΔFS above the 6-month MCID also correlated with increased mortality (aHR=2.82).

Conclusions:

• A QCT-based definition of PPF using 1-year ΔFS is prognostic in non-IPF fibrosing ILDs.
• This QCT approach improves risk stratification, particularly in patients with discordant PPF assessments.
• Established MCIDs provide objective criteria for identifying disease progression and guiding clinical management.