Local Control After Stereotactic Body Radiation Therapy for Early-Stage Non-Small Cell Lung Cancer: A Tale of 2 Schedules?

Abstract

Stereotactic body radiation therapy (SBRT) for early-stage (T1-3, N0, and M0) non-small cell lung cancer (NSCLC) generally yields excellent local control rates. The optimal dose and fractionation schedule remains unknown, especially for the treatment of central tumors. At our institution, we typically treat early-stage NSCLC patients with 10-11 Gy x 5 fractions for central tumors and 18-20 Gy x 3 fractions for non-central tumors. We present our institutional experience with SBRT for early-stage NSCLC and examine if local control rates vary with SBRT schedule. We identified patients who were treated with SBRT for early-stage NSCLC between September 2009 and May 2015. Patients with T1-3, N0, M0 tumors were eligible. Patients with more advanced disease, lung nodules attributed to other diagnoses, or missing follow-up data were excluded. Actuarial local control rates and freedom from progression rates for the entire cohort and for subsets treated with 10-11 Gy x 5 (Schedule A) and 18-20 Gy x 3 (Schedule B) were calculated using the Kaplan-Meier method. Comparisons were made using log-rank testing. Toxicity grading was performed using Common Terminology Criteria for Adverse Events (CTCAE) or Radiation Therapy Oncology Group (RTOG) criteria. Sixty-one patients met all inclusion criteria. With a median follow-up of 15.0 months, four local failures were observed, and fifteen patients developed progressive disease. Actuarial local control rates at 1 and 2 years were 98% and 92%, respectively. Four out of 29 patients receiving Schedule A experienced local failure, compared to 0 out of 32 patients receiving Schedule B. The 2-year actuarial local control rate for patients treated with Schedule A was 83%, compared to 100% for patients treated with Schedule B (log-rank P=0.040). Actuarial freedom from progression rates at one and two years were 88% and 67%, respectively. The 2-year actuarial freedom from progression rate for patients treated with Schedule A was 64%, compared to 70% for patients treated with Schedule B (log-rank P=0.079). Mean tumor diameter was 2.5 cm for tumors treated with Schedule A and 1.9 cm for tumors treated with Schedule B (unpaired t-test P=0.011). No grade 3 or higher acute or late toxicities were observed. SBRT for early-stage NSCLC yields excellent rates of local control, with progression most often occurring at regional and/or distant sites. 10-11 Gy x 5 schedule and increased tumor size were associated with increased probability of local failure. Additional studies with higher numbers of local failures will be necessary to fully characterize the interplay between SBRT schedule and/or tumor size as predictive factors.