P1.05-033 Comparison of Single- and Five-Fraction Schedules of Stereotactic Body Radiation Therapy for Central Lung Tumors

Abstract

Stereotactic Body Radiation Therapy (SBRT) is a treatment option for patients with early-stage non-small cell lung cancer (NSCLC) who are medically inoperable or decline surgery. The safety of 20 Gray (Gy) x 3 fractions of SBRT within 2 cm of the proximal bronchial tree is unclear. Here we compare the clinical outcome of patients with centrally located lung tumors who underwent either single fraction (SF)- or five-fraction (FF-) SBRT at a single institution over 5 years. Between January 2009 and October 2014, 11 out of 42 patients received 26-30 Gy in 1 fraction, while the remaining 31 patients received 52.5-60 Gy (median 55 Gy) in 5 fractions. Data were retrospectively collected using an institutional review board-approved database. Kaplan-Meier method, competing risks method, and Cox regression model were used. Toxicities were graded using Common Terminology Criteria for Adverse Events version 4.0. R version 3.3.1 was used for statistical analysis. After a median follow-up of 12 months for SF-SBRT and 17 months for FF-SBRT groups (p=0.64), 1-year overall survival rates for SF- and FF-SBRT groups were 82% and 87%, respectively. There was no statistically significant difference in overall survival (p=0.061), progression-free survival (p=0.47), local failure (p=0.43), nodal failure (p=0.42), and distant failure (p=0.45) at 18 months. No primary tumor failure was seen in both groups at 18 months. Distant failure rates at 18 months were 9.1% for SF-SBRT group and 54.5% for FF-SBRT group. Among the patients with distant failure (n=4 in SF-SBRT and n=6 in FF-SBRT), median time to distant failure was 29.5 months and 8.9 months for SF- and FF-SBRT groups, respectively (p=0.0095). 3 out of 11 patients in SF-SBRT group and 2 out of 32 patients in FF-SBRT group experienced grade 3-4 toxicities. No grade 4-5 toxicities were observed in the FF-SBRT group. SF-SBRT group showed higher cumulative incidence of grade 3+ toxicity at 18 months (p=0.018). However, univariate analysis showed SF-SBRT alone was not a significant factor that increased risk for grade 3+ toxicities (HR=5.50, p=0.063). 4 out of 5 toxicities occurred at least 12 months after SBRT. SF- and FF-SBRT showed no significant difference in overall survival and local control. No grade 4-5 toxicities were observed in our FF-SBRT group. The onset of distant failure was significantly delayed in the SF-SBRT compared to the FF-SBRT group. The majority of toxicities occurred late. Having SF-SBRT itself was not significantly associated with severe toxicity.