Efficacy and safety of stereotactic radiosurgery for large cystic brain metastases: a comparison with and without cyst aspiration via Ommaya reservoir

To evaluate the therapeutic efficacy and safety of stereotactic radiosurgery (SRS) in the management of large cystic brain metastases. A retrospective analysis was conducted. Large cystic brain metastases were defined as cyst volume ≥ 5 mL. Tumors that received SRS as adjuvant therapy following surgery were excluded. The cohort was stratified into two groups: (1) SRS group (upfront hypofractionated SRS without Ommaya reservoir [OR]), (2) OR-SRS group (cyst aspiration via OR before SRS). Local tumor control rate (LCR), progression-free survival (PFS), overall survival (OS), and radiation-induced adverse events (RAEs) were evaluated. Thirty-one metastases in 28 patients met the inclusion criteria: SRS (14 metastases) and OR-SRS (17 metastases). Most baseline characteristics, including cyst diameter (P = 0.15), cyst volume (P = 0.06), and tumor volume (P = 0.95), were not significantly different between the groups. The cyst volume just before SRS in the OR-SRS group was significantly smaller compared to the SRS group (P < 0.01; Mann-Whitney U test). The LCR was 86% in the SRS group and 82% OR-SRS group (P = 1.00). Other outcomes, including PFS, RAEs, and OS, were not significantly different between the groups. Kaplan-Meier analysis revealed no statistically significant differences in PFS or OS among the groups (P = 0.28 and P = 0.20, respectively; log-rank test). This study demonstrates that both SRS and OR-SRS are effective and safe treatment modalities for large cystic brain metastases. The treatment outcomes were comparable, and these approaches may be equally viable options in the management of this challenging subset.