Prognostic Value of Dual-Time-Point ^sup 18^ F-FDG PET for Idiopathic Pulmonary Fibrosis

The aim of this prospective study was to clarify whether dual-time-point 18F-FDG PET imaging results are useful to predict long-term survival of idiopathic pulmonary fibrosis (IPF) patients. Fifty IPF patients underwent 18F-FDG PET examinations at 2 time points: 60 min (early imaging) and 180 min (delayed imaging) after 18F-FDG injection. The standardized uptake value (SUV) at each point and retention index value (RI-SUV) calculated from those were evaluated, and then the results were compared with overall and progression-free survival. A multivariate Cox proportional hazards model showed higher RI-SUV and higher extent of fibrosis score as independent predictors of shorter progression-free survival. The median progression-free survival for patients with negative RI-SUV was better than that for those with positive RI-SUV (27.9 vs. 13.3 mo, P = 0.0002). On the other hand, multivariate Cox analysis showed higher RI-SUV and lower forced vital capacity to be independent predictors of shorter overall survival. The 5-y survival rate for patients with negative RI-SUV was better than that for those with positive RI-SUV (76.8% vs. 14.3%, P = 0.00001). In addition, a univariate Cox model showed that positive RI-SUV as a binary variable was a significant indicator of mortality (hazard ratio, 7.31; 95% confidence interval, 2.64-20.3; P = 0.0001). Our results demonstrate that positive RI-SUV is strongly predictive of earlier deterioration of pulmonary function and higher mortality in patients with IPF.