Interstitial Lung Disease Outcome Prediction Using Quantitative Densitometry Indices on Baseline Chest Computed Tomography

<b>Background/Objectives</b>: Accurate prognostication for interstitial lung disease (ILD) remains challenging, limiting clinicians' ability to optimize patient management strategies. This study aimed to evaluate the prognostic value of baseline quantitative CT-derived indices, including total lung volume (TLVcm³), normal lung volume% (NLV%), and fibrotic lung volume% (FLV%), for predicting three-year mortality in interstitial lung disease (ILD) patients. <b>Methods</b>: A total of 101 ILD patients were retrospectively enrolled. Baseline CT-derived indices, including TLVcm³, NLV% (-950 to -700 HU), and FLV% (-600 to +50 HU), were measured on chest CT. Baseline forced vital capacity(FVC)% predicted and diffuse capacity of lungs for carbon monoxide (DLCO)% predicted were collected. Survival analysis used Kaplan-Meier's curves and log-rank tests. Uni- and multivariate Cox's proportional hazards regression were performed. Pearson's correlation was used between CT-derived indices, FVC% predicted, and DLCO% predicted. <b>Results</b>: During 3-year follow-up, 30 of 101 patients (29.70%) died. Deceased patients had a significantly lower baseline NLV% (59.27% ± 7.61% vs. 65.02% ± 7.82%, <i>p</i> = 0.001) and a higher FLV% (17.64% ± 7.98% vs. 13.34% ± 7.48%, <i>p</i> = 0.011) compared with survivors. Multivariate analysis identified baseline NLV% (adjusted hazard ratio 0.88, 95% CI: 0.78-0.99, <i>p</i> = 0.034) and DLCO% predicted (adjusted hazard ratio 0.97, 95% CI: 0.95-0.99, <i>p</i> = 0.007) as independent predictors of three-year mortality. Patients with NLV% ≤ 64.15 and FLV% ≥ 14.12 showed significantly worse survival outcomes (21.78% vs. 7.92%, <i>p</i> < 0.001;19.80% (20/101) vs. 9.90% (10/101), <i>p</i> < 0.001). CT-derived indices moderately correlated with FVC% predicted and DLCO% predicted. <b>Conclusions</b>: Baseline FLV% ≥ 14.12 and NLV% ≤ 64.15 can effectively stratify and differentiate outcomes in ILD patients. Baseline NLV% has the potential as a prognostic indicator for 3-year survival in ILD.