Factors affecting local control of pulmonary oligometastases treated with stereotactic body radiotherapy

Background: Oligometastases refers to a state of limited metastatic disease. The use of local ablative therapies to patients with oligometastases can result in durable state of remission or long-term cure. Stereotactic body radiotherapy (SBRT) is a highly conformal radiation technique that delivers ablative doses to the target. The study aimed to evaluate local control (LC) and identify factors associated with poor LC in patients with pulmonary oligometastases treated with SBRT. Primary endpoint of the study was to assess LC; secondary endpoint was to determine factors associated with LC.Material and methods: Criteria used for selection of patients with oligometastases included: metastatic disease limited to a maximum of two organs and no more than five metastatic lesions at time of treatment. Peripheral tumors were treated with 51-60Gy in three fractions or a single fraction of 30Gy. Central tumors received a dose of 45-60Gy in 5-8 fractions.Results: In 206 patients, 327 pulmonary oligometastases were treated with SBRT. Median follow-up was 22 months (range 2-100). LC at 2 and 3 years was 85% and 83%, respectively. On univariate analysis, biological equivalent dose assuming an / ratio of 10 (BED10)<100Gy (HR 3.09), single-fraction SBRT (HR 2.83), synchronous metastasis (HR 1.99), and pre-SBRT chemotherapy (HR 2.79) were significantly associated with inferior LC. In the multivariable analysis BED10 <100Gy (HR 3.59), pre-SBRT chemotherapy (HR 2.61) and presence of synchronous metastasis (HR 2.21) remained independently associated with poor LC.Conclusions: SBRT achieved an excellent LC of 85% at 2 years. Although retrospective in nature, our study identified three factors associated with inferior LC. These factors may help to refine SBRT practice for pulmonary oligometastases in the future.