Ablative dose stereotactic body radiation therapy for oligometastatic disease: a prospective single institution study.

Localized, metastasis-directed stereotactic body radiation therapy (SBRT) of oligometastatic disease (OD) is currently rapidly evolving standard of care in many institutions. Further reports of outcomes are needed to strengthen the level of evidence in the absence of comparative trials evaluating different practical procedures. The aim of this prospective single institutional study is to analyse, in unselected cohort of patients from real-world clinical practice, the long-term survival, tumor control outcomes and safety of SBRT (radical ablative radiotherapy with biological equivalent dose BED10 > 100 Gy) for OD. In addition to the standard toxicity and survival parameters, we report unique outcomes as FFWD - Freedom from widespread dissemination, FFNT - Freedom from the need of subsequent treatment and lastly functional survival with Karnofsky performance status higher than 70 %. Total of 110 patients were prospectively evaluated, 60% and 40% were treated for lung and liver oligometastatic disease, respectively. No grade 3 or 4 acute toxicities (CTCAE) were reported. With median follow up of 22.2 months and 2-year overall survival of 88.3 %, four patients (6.1 %) experienced local progression in the lung SBRT cohort. In liver SBRT cohort, median follow up was 33 months, 2-year overall survival 68.5 % with 11 patients (25.0 %) experiencing local and 36 (81.8 %) distal progression. Higher BED10 (150-170 Gy comparing 100-150 Gy) was independent positive prognostic factor for local progression-free survival for all patients with hazard ratio 0.25, confirming ablative radiobiology effects of SBRT which are independent of primary histology or location of OD. The best outcomes in terms of FFNT were observed on the multivariable analysis in patient with 1-2 lung OD comparing to liver OD or comparing to patients with more than 2 lung metastases. For liver SBRT cohort, better FFNT was in patients with 1-2 liver metastases or in patients whose liver OD were irradiated by higher BED10. In conclusion, SBRT is a suitable option for patients who are not surgical candidates, given approximately 30 % of patients did not require subsequent treatment 2 years after SBRT in our study. We believe, this treatment represents a safe and effective treatment options for oligometastatic involvement in patients of various primary tumors.