Salvage radiosurgery for brain metastases: prognostic factors to consider in patient selection

Stereotactic radiosurgery (SRS) is offered to patients for recurrent brain metastases after prior brain radiation therapy (RT), but few studies have evaluated the efficacy of salvage SRS or factors to consider in selecting patients for this treatment. This study reports overall survival (OS), intracranial progression-free survival (PFS), and local control (LC) after salvage SRS, and factors associated with outcomes.

This is a retrospective review of patients treated from 2009 to 2011 with salvage SRS after prior brain RT for brain metastases. Survival from salvage SRS and from initial brain metastases diagnosis (IBMD) was calculated. Univariate and multivariable (MVA) analyses included age, performance status, recursive partitioning analysis (RPA) class, extracranial disease control, and time from initial RT to salvage SRS.

There were 106 patients included in the analysis with a median age of 56.9 years (range 32.5-82 years). A median of 2 metastases were treated per patient (range, 1-12) with a median dose of 21 Gy (range, 12-24) prescribed to the 50% isodose. With a median follow-up of 10.5 months (range, 0.1-68.2), LC was 82.8%, 60.1%, and 46.8% at 6 months, 1 year, and 3 years, respectively. Median PFS was 6.2 months (95% confidence interval [CI]=4.9-7.6). Median OS was 11.7 months (95% CI=8.1-13) from salvage SRS, and 22.1 months from IBMD (95% CI=18.4-26.8). On MVA, age (P=.01; hazard ratio [HR]=1.04; 95% CI=1.01-1.07), extracranial disease control (P=.004; HR=0.46; 95% CI=0.27-0.78), and interval from initial RT to salvage SRS of at least 265 days (P=.001; HR=2.46; 95% CI=1.47-4.09) were predictive of OS.

This study demonstrates that patients can have durable local control and survival after salvage SRS for recurrent brain metastases. In particular, younger patients with controlled extracranial disease and a durable response to initial brain RT are likely to benefit from salvage SRS.