Purpose: To investigate the prognostic value of [18F]fluorodeoxyglucose positron emission tomography (FDG-PET) uptake at 12 weeks after stereotactic ablative radiotherapy (SABR) for stage I non-small-cell lung cancer (NSCLC).Methods and Materials: From November 2006 to February 2010, 132 medically inoperable patients with proven Stage I NSCLC or FDG-PET-positive primary lung tumors were analyzed retrospectively. SABR consisted of 60 Gy delivered in 3 to 8 fractions. Maximum standardized uptake value (SUVmax) of the treated lesion was assessed 12 weeks after SABR, using FDG-PET. Patients were subsequently followed at regular intervals using computed tomography (CT) scans. Association between post-SABR SUVmax and local control (LC), mediastinal failure, distant failure, overall survival (OS), and disease-specific survival (DSS) was examined.Results: Median follow-up time was 17 months (range, 3–40 months). Median lesion size was 25 mm (range, 9–70 mm). There were 6 local failures: 15 mediastinal failures, 15 distant failures, 13 disease-related deaths, and 16 deaths from intercurrent diseases. Glucose corrected post-SABR median SUVmax was 3.0 (range, 0.55–14.50). Using SUVmax 5.0 as a cutoff, the 2-year LC was 80% versus 97.7% for high versus low SUVmax, yielding an adjusted subhazard ratio (SHR) for high post-SABR SUVmax of 7.3 (95% confidence interval [CI], 1.4–38.5; p = 0.019). Two-year DSS rates were 74% versus 91%, respectively, for high and low SUVmax values (SHR, 2.2; 95% CI, 0.8–6.3; p = 0.113). Two-year OS was 62% versus 81% (hazard ratio [HR], 1.6; 95% CI, 0.7–3.7; p = 0.268).Conclusions: Residual FDG uptake (SUVmax ≥5.0) 12 weeks after SABR signifies increased risk of local failure. A single FDG-PET scan at 12 weeks could be used to tailor further follow-up according to the risk of failure, especially in patients potentially eligible for salvage surgery.
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