Outcomes following SRS for small- to medium-sized brain metastases are exceptionally dependent upon tumor size and prescribed dose

Abstract

Background

At our institution, we have historically treated brain metastasis (BM) ≤2cm in eloquent brain with a radiosurgery (SRS) lower prescription dose (PD) to reduce the risk of radionecrosis (RN). We sought to evaluate the impact of this practice on outcomes.

Methods

We analyzed a prospective registry of BM patients treated with SRS between 2008 and 2017. Incidences of local failure (LF) and RN were determined and Cox regression was performed for univariate and multivariable analyses (MVA).

Results

1,533 BM ≤2cm were evaluated. Median radiographic follow-up post SRS was 12.7 months (1.4-100). Overall, the 2year incidence of LF was lower for BM treated with PD≥21Gy (9.3%) compared with PD≤15Gy (19.5%);(subHR 2.3; 95CI 1.4-3.7;p=0.0006). The 2-year incidence of RN was not significantly higher for the group treated with PD ≥21Gy (9.5%) compared to the PD ≤15Gy group (7.5%) (p=0.16). MVA demonstrated that PD (≤15 Gy) and tumor size (>1cm) were significantly correlated (p<0.05) with higher rates of LF, and RN, respectively. For tumors ≤1 cm, when comparing PD ≤15Gy to ≥21Gy, the risks of LF and RN are equivalent. However, for lesions >1cm, PD ≥21Gy is associated with a lower incidence of LF without significantly increasing the risk of RN.

Conclusion

Our results indicate that rates of LF or RN following SRS for BM are strongly correlated to size and PD. Based on our results, we now, depending upon the clinical context, consider increasing PD to 21 Gy for BM in eloquent brain, excluding the brain stem.