Clinical Outcomes Following Stereotactic Body Radiation Therapy (SBRT) for Stage I Medically Inoperable Small Cell Lung Carcinoma

OBJECTIVES: To utilize the RSSearch Patient Registry (RSSPR) to examine local control (LC), overall survival (OS), and toxicities following stereotactic body radiation therapy (SBRT) for stage I (T1-T2/N0) medically inoperable small cell lung carcinoma (SCLC). MATERIALS AND METHODS: We searched the RSSPR for medically inoperable stage I SCLC patients treated with definitive SBRT. Potential predictive factors of OS were estimated using the Kaplan-Meier method as well as a Cox proportional hazards model. RESULTS: Twenty-one patients were identified with medically inoperable stage I SCLC that met inclusion criteria. Fourteen patients had stage IA SCLC (T1N0) and 7 patients had stage IB SCLC (T2N0) with a median gross tumor volume of 10.1 cm (range: 0.72 to 41.4 cm). The median number of fractions was 4 (range: 3 to 5), and the median BED10 was 105.6 Gy10 (range: 72 to 239.7 Gy10). Four patients received adjuvant chemotherapy. One- and 2-year actuarial OS rates were 73.1% (95% confidence interval [CI]: 36.8%-90.1%) and 36.6% (95% CI: 9.0%-65.7%), respectively. Factors found to be associated with 1-year OS on univariate analysis included T2 disease (85.5% vs. 33.3%; P=0.03), adjuvant chemotherapy (100% vs. 66.3%; P=0.11), and gross tumor volume ≥10 cm (100% vs. 52.5%; P=0.10). On multivariate analysis, adjuvant chemotherapy was associated with improved OS (hazard ratio=0.07 [95% CI: 0.13-0.37; P=0.002]). The 1-, 2-, and 3-year LC rates were 100%, and 1- and 2-year progression-free survival (PFS) rates were 85.7% (95% CI: 33.4-97.9%) and 42.9% (95% CI: 1.1-85.3%), respectively. Similar to OS, patients with T1N0 disease had superior PFS as compared to T2N0 disease (P=0.01). Toxicities were reported by 3/21 (14.3%) of patients with none ≥ grade 3 and no esophageal toxicities. CONCLUSIONS: SBRT was well-tolerated in the treatment of stage I SCLC with excellent LC achieved. Patients with T1N0 stage IA SCLC were noted to have improved PFS and OS following SBRT as compared with T2N0 Stage IB SCLC. Adjuvant chemotherapy was found to result in improved OS for stage I SCLC patients over SBRT alone.