According to the following study, SBRT favors long-term overall survival in patients with lung metastases:
http://www.cmj.org/Periodical/PDF/2011121939260730.pdf
There were 8 patients with sarcoma in this study but it doesn't say what type of sarcoma.
Another study shows SBRT provides excellent control and minimal toxicity for lung metastases from high grade sarcoma:
http://www.ncbi.nlm.nih.gov/pubmed/24198717
Another study showing positive outcomes with SBRT for lung metastases (a lot of synovial sarcoma patients in this study):
http://www.ncbi.nlm.nih.gov/pubmed/25686482