RTHP-39. SURVIVAL OUTCOME OF LONG-TERM RESPONDERS TO FRACTIONATED VERSUS SINGLE-DOSE STEREOTACTIC RADIOSURGERY (SRS)

Abstract

Treatment of brain metastases with fractionated stereotactic radiosurgery (F-SRS) is predicated on intent to reduce radiation toxicity without compromising local control. In patients with large brain metastases, F-SRS has been suggested to have improved local control compared to single-fraction stereotactic radiosurgery (S-SRS) with acceptable toxicity. The differences, though, between patients who undergo S-SRS and F-SRS that survive well beyond the one-year time frame are still unclear. Here we present a retrospective review of brain-metastatic lung and breast cancer patients that survived at least one year from initial SRS. A total of 91 patients, 58 lung- and 33 breast-primary, were treated between September 2006 and October 2014 with a median overall survival from initial SRS (SRS-mOS) of 24.9 months (range, 12.1-84.9 months). 203 lesions were irradiated in 86 patients (range, 1 to 9). The S-SRS group included 34 patients (26 lung, 8 breast) and the F-SRS group had 57 patients (32 lung, 25 breast). The S-SRS group received total doses ranging from 15-20 Gy (median, 17 Gy) and the F-SRS group received total doses ranging from 20-25 Gy in 3-5 fractions (median, 21 Gy). The median age was 59.6 yo (range, 31.2-85.1 yo). Kaplan-Meier analyses revealed no significant difference between single-dose and fractionation (S-SRS, 28.3 mo; and F-SRS,31.8 mo; p=0.5735) even when adjusted for primary cancer site. No differences were seen between primary site (p=0.3284) or 1-4 vs. 5 or more brain metastases (p=0.8364). The similarity in survival between S-SRS and F-SRS suggests that fractionation may be used without compromising survival, although it remains to be seen how other prognostic factors influence outcomes in this cohort.