Evaluation for local failure by 18F-FDG PET/CT in comparison with CT findings after stereotactic body radiotherapy (SBRT) for localized non-small-cell lung cancer

PurposeStereotactic body radiotherapy (SBRT) is the standard care for medically inoperable early non-small-cell lung cancer (NSCLC). However, it can be difficult to differentiate local recurrence from non-recurrence radiation-induced lung opacity. We retrospectively assessed 18F-FDG PET/CT to detect local recurrence after SBRT for NSCLC.MethodsBetween 2005 and 2011, 273 NSCLCs in 257 patients were treated with SBRT. Prescribed doses were 50 Gy and 40 Gy per 5 fractions for peripheral and central lesions, respectively. Tri-monthly follow-up CT scans were acquired. 18F-FDG PET/CT scans were scheduled for screening at one year after SBRT or when recurrence was highly suspected. The dual-time-point maximum standardized uptake values (SUVmaxs) and their retention indexes (RIs) were obtained.ResultsA total of 214 18F-FDG PET/CT scans were obtained for 164 localized NSCLC tumors in 154 patients. The median follow-up period was 24.9 months (range: 6.3–72.1). Among these, 21 scans of 17 tumors were diagnosed as local recurrence. The median SUVmaxs on early and late images of recurrence and their RI were 5.0 (range: 3.2–10.7), 6.3 (range: 4.2–13.4), and 0.20 (range; 0–0.41), respectively. These were significantly higher than the respective values of non-recurrence images of 1.8 (range: 0.5–4.6), 1.7 (range: 0.5–6.1), and 0.00 (range: −0.37–0.41) (all p < 0.05). For SUVmaxs on early and late images, optimal thresholds were identified as 3.2 and 4.2. Using each threshold, the sensitivity and specificity were 100% and 96–98%, respectively. CT findings were classified into ground-glass opacity (N = 9), scar or fibrotic change (N = 96), consolidation with air-bronchogram (N = 34), consolidation only (N = 22), and nodule (N = 17); the respective numbers of recurrence were 0, 0, 1, 3, and 17.ConclusionSUVmaxs of 18F-FDG PET/CT could detect local recurrence after SBRT for localized NSCLC. In contrast, CT scan results had a limited ability to diagnose local recurrence.