Survival and prognostic factors of pulmonary oligometastases treated with stereotactic body radiotherapy

Background: Stereotactic body radiotherapy (SBRT) for pulmonary oligometastatic disease achieves excellent treatment outcomes in terms of local control and toxicity. Patients treated with SBRT are often elderly and have multiple co-morbidities. This subset of patients may experience different survival as compared to young and fit patients subjected to radical metastasectomies. The purpose of this retrospective study was to evaluate OS and identify factors associated with OS for inoperable pulmonary oligometastases treated with SBRT.Material and methods: Criteria used for selection of patients with oligometastases included: metastases limited to 2 organs and in total 5 metastases at the time of treatment. Peripheral tumors were treated with 51Gy to 60Gy in three fractions or a single fraction of 30Gy. Central tumors received a dose of 45-60Gy in 5-8 fractions. Survival probabilities were estimated by means of Kaplan-Meier method and the relation between potential prognostic factors and OS was studied by means of Cox regression analyses.Results: In this study, 327 inoperable pulmonary oligometastases in 206 patients were treated with SBRT from the year 2005 to 2015. Primary sites of pulmonary oligometastases included colorectal carcinoma (n=118), lung carcinoma (n=36), melanoma (n=11), sarcoma (n=10), breast carcinoma (n=7), and other tumors sites (n=24). Median follow-up was 26months. Median survival was 33months. The 2-year and 5-year OS rates were 63% and 30%, respectively. On univariate analysis synchronous oligometastases (HR 0.59) and colorectal primary (HR 0.64) were associated with improved OS. On multivariable analysis synchronous oligometastases (HR 0.56), colorectal primary (HR 0.62) and tumor size <3cm (HR 0.68) were independently associated with OS.Conclusions: SBRT to pulmonary oligometastases was associated with a 2-year OS of 63%. Tumor size <3cm and colorectal primary tumors experienced improved OS compared to tumors >3cm and non-colorectal primary tumors.