Lung Stereotactic Body Radiation Therapy: Regional Nodal Failure Is Not Predicted by Tumor Size

Introduction: To examine regional nodal failure patterns with respect to lesion size in medically inoperable early-stage non-small cell lung cancer (NSCLC) patients treated with definitive lung stereotactic body radiation therapy (SBRT). Methods: Between 2004 and 2012, 342 medically inoperable early-stage NSCLC patients treated with definitive SBRT were identified in our institutional review board-approved prospective registry. All patients were treated on a Novalis/BrainLAB system using ExacTrac for image guidance. Kaplan-Meier analysis was performed with the log-rank test used to detect differences between lesion size and nodal failure patterns. Cox-proportional hazard regression analysis was performed to identify predictors of nodal failure. Results: Median follow-up was 17.6 months (range, 0-84 months). Median tumor size, positron emission tomography maximum standardized uptake value, and dose/fractionation were 2.2 cm (range, 0.8-7.2 cm), 6.7 (range, 1-59), and 50 Gray (Gy)/five fractions, respectively. Of the 342 lesions evaluated, 14.6% (50 of 342) experienced nodal failure. Nodal failure rates were 17.45% (26 of 149), 10.3% (11 of 107), 14.1% (10 of 71), and 20% (3 of 15) for lesions less than or equal to 2 cm, 2.1 to 3 cm, 3.1 to 5 cm, and greater than 5 cm, respectively. Rates of nodal failure were not significantly different between the four different size groups (p = 0.15). On univariate analysis, 2.1 to 3 cm lesions versus less than or equal to 2 cm exhibited less nodal failure after SBRT (hazard ratio = 0.406; 95% confidence interval = 0.189-0.87; p = 0.0205). No other patient, tumor, or treatment factor significantly affected nodal failure. Conclusion: For early-stage NSCLC treated with SBRT, tumor size does not influence the rates of regional nodal failure. This finding warrants further investigation on the possible mechanisms of SBRT by which loco-regional control is improved.