Reduced Margin Stereotactic Body Radiation Therapy for Early Stage Non-Small Cell Lung Cancers

Abstract

Purpose: To report the clinical outcomes of patients treated with reducedmargin, fiducial-guided stereotactic body radiation therapy (SBRT) for early stage non-small cell lung cancer (NSCLC). We also sought to assess the effect of histologic subtype on local control. Methodology:We retrospectively reviewed the charts of all patients treated with SBRT for early stage NSCLC between 2007 and 2017 at our institution. All patients who had implanted fiducial markers, had planning target volume margins of 5 mm or less, and were treated with curative intent were included in this analysis. Local failure was defined as tumor recurrence on radiographic imaging or by biopsy within 1 cm of the previously treated volume, and time to local failure was measured from the beginning of SBRT. Estimates of local control were generated using the Kaplan-Meier method and differences between survival curves were assessed using the log-rank test. Patients without evidence of local failure were censored at the time of last follow-up or death. Results: A total of 194 patients met the inclusion criteria for this analysis with a median follow-up of 12 months. Patients received 54 Gy in 3 fractions for peripheral tumors and 48-52.5 Gy in 4-5 fractions for central tumors. Treatments were respiratory-gated with intrafraction fidu-cial tracking by on-board kVradiographs in the majority of cases. NSCLC histology was adenocarcinoma in 89 (45.9%) cases, squamous cell carcinoma in 78 (40.2%) cases, and other or non-subtyped in 27 (13.9%) of cases. Across the entire cohort the 2-year estimate of local control was 88.5%. When histology was considered, the 2-year estimate of local control among patients with adenocarcinoma was 100% as compared to 84.5% for patients with squamous cell carcinoma (p = 0.044) and 77.5% for patients with other histologies (p = 0.003). Conclusion: Fiducial-guided, reduced-margin SBRT did not compromise local control as compared to historical standards. In this series, patients with adenocarcinoma experienced improved local control as compared to squamous cell carcinoma.