Cystic Brain Metastasis Outcomes After Gamma Knife Radiation Therapy.

Purpose: The response of cystic brain metastases (BMets) to radiation therapy is poorly understood, with conflicting results regarding local control, overall survival, and treatment-related toxicity. This study aims to examine the role of Gamma Knife (GK) in managing cystic BMets.
Methods and Materials: Volumetric analysis was conducted to measure tumor and edema volume at the time of GK and follow-up magnetic resonance imaging studies. Survival was described using the Kaplan-Meier method, and the cumulative incidence of progression was described using the Aalen-Johansen estimator. We evaluated the association of 4 variables with survival using Cox regression analysis.
Results: Between 2016 and 2021, 54 patients with 83 cystic BMets were treated with GK at our institution. Lung cancer was the most common pathology (51.9%), followed by breast cancer (13.0%). The mean target volume was 2.7 cm ³ (range, 0.1-39.0 cm ³ ), and the mean edema volume was 13.9 cm ³ (range, 0-165.5 cm ³ ). The median prescription dose of single-fraction and fractionated GK was 20 Gy (range, 14-27.5 Gy). With a median follow-up of 8.9 months, the median survival time (MST) was 11.1 months, and the 1-year local control rate was 75.9%. Gamma Knife was associated with decreased tumor and edema volumes over time, although 68.5% of patients required steroids after GK. Patients whose tumors grew beyond baseline after GK received significantly more whole-brain radiation therapy (WBRT) before GK than those whose tumors declined after GK. Higher age at diagnosis of BMets and pre-GK systemic therapy were associated with worse survival, with an MST of 7.8 months in patients who received it compared with 23.3 months in those who did not.
Conclusions: Pre-GK WBRT may select for BMets with increased radioresistance. This study highlights the ability of GK to control cystic BMets with the cost of high posttreatment steroid use.
Competing Interests: Joseph A. Bovi reports a relationship with Imaging Biometrics that includes consulting or advising. Christopher J. Schultz reports a relationship with Elekta AB that includes funding grants and travel reimbursement; a relationship with Siemens Healthineers that includes board membership and funding grants; and relationships with Accuray Inc and Mantia Medical Imaging that include funding grants. Lindsay Puckett reports a relationship with Accuray Inc that includes speaking and lecture fees. The other authors declare no personal, financial, or institutional interests in any of the drugs, materials, or devices described in this article.
(© 2023 The Author(s).)