Stereotactic Body Radiation Therapy (SBRT) Using CyberKnife in Oligometastatic Cancer Patients; Retrospective Evaluation, Single Institution Experience

Objectives We retrospectively evaluate local control rate at 6 months and 1 year in oligometastatic cancer patients treated with SBRT using CyberKnife. Methods Total of 21 patients with 24 treatment sites from February 2014 till June 2017 who were treated with SBRT in our institution were included in this study. Results Eleven patients were males, 10 patients were females, median age at diagnosis was 63 years, and colorectal cancer is the most commonly diagnosed cancer in 18 patients. The abdomino-pelvic lymph nodes were the commonest treatment site in 11 (45.8%), average PTV volume of 46.4 cc. All the patients received SBRT with average (BED) of 97 GY, 7 treatment sites received BED of < 100GYgroup 1, and 17 received BED >= 100GY group 2. No reported G3 or G4 acute or chronic toxicity. The 6 months and 1 year local control (LC) were 95.8 and 88.2%, respectively. After a median follow-up of 16.8 months, 19(90.5%) patients were alive; among them, local progression was observed in 1 (4.1%) treatment site, while systemic progression in 4 (16.6%), and two (9.5%) patients died; they had both local and systemic failures. The 1-year local PFS rate was 82%. In univariate analysis, PTV volume was significantly correlated with LC rate at 6 months (p = 0.001), while the site of metastasis appeared to significantly correlate with PFS (p = 0.03). Conclusion SBRT using CyberKnife is feasible, safe, and effective treatment for oligometastatic sites. Six months and 1 year local control rate is 95.8 and 88.2% respectively in our patients cohort, treatment regimens with higher BED resulting in better 1-year local PFS, although it was not statistically significant. A larger cohort of patients and longer follow up is required for better evaluation.