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.