Timing of fluorodeoxyglucose positron emission tomography maximum standardized uptake value for diagnosis of local recurrence of non-small cell lung cancer after stereotactic body radiation therapy.

Introduction: After treatment with stereotactic body radiation therapy (SBRT), local recurrence of non-small cell cancer (NSCLC) can be difficult to differentiate from radiation-induced changes. Maximum standardized uptake value (SUVmax), measured with 18-F-Fluorodeoxyglucose positron emission tomography (FDG-PET), can have false positives due to acute radiation inflammation. The primary study objective was to determine the utility of SUVmax > 5 to identify local recurrence later than 9 months after SBRT. Method: A retrospective review was performed of FDG-PET scans for suspicious CT findings after SBRT treatment of stage 1 NSCLC. SUVmax was measured including surrounding opacification. Outcome measures were local recurrence, progression free survival, and overall survival. Receiver operator curve analysis, sensitivity, specificity, and Kaplan-Meier analysis were performed.

Results: Of 118 patients treated, 42 patients had eligible FDG-PET scans. They received SBRT (48-60Gy in 3-8 fractions) for 49 NSCLC and had 101 follow-up PET scans. The median time to first PET scan was 9.3 months, and the median follow-up period was 22.4 months. Local recurrence was diagnosed in 12 patients, at a median of 16 months. Due to selection bias, the included patients had poorer outcomes than the entire cohort, with progression free survival (PFS) at 1, 2, and 3 years of 82.7%, 57.8%, and 45.8%; and overall survival of 97.9%, 79.9%, and 59.1%, respectively. Thirty FDG-PET scans were performed within 9 months, of which 17% were false positives. A total of 71 FDG-PET scans were performed beyond 9 months, and the median SUVmax was significantly higher for patients with local recurrence (7.48 vs. 2.14, P < .0001). SUVmax > 5 has a sensitivity of 91% (95% CI 62%-99.8%) and 100% (89.1%-100%).

Conclusion: For local recurrence of NSCLC, SUVmax > 5 on FDG-PET scan has good sensitivity and specificity after 6 months, but is highest beyond 9 months after SBRT.