Cystic Brain Metastasis Outcomes After Gamma Knife Radiation Therapy

Abstract

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 cm³ (range, 0.1-39.0 cm³), and the mean edema volume was 13.9 cm³ (range, 0-165.5 cm³). 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.

Figure 1

Cumulative incidence of local progression and nonprogression mortality versus time since Gamma Knife (months). Mortality was treated as a competing risk factor for local progression using the Aalen-Johansen estimator. Abbreviation: GK = Gamma Knife.

Figure 2

Relative tumor volume change from baseline versus time since Gamma Knife (months) for tumors >2.0 cm³. Only 1 tumor per patient was included in this graph. In the 3 cases where a patient had 2 tumors >2.0 cm³, the largest was included (for a total of 24 tumors included). Abbreviation: GK = Gamma Knife.

Figure 3

Relative peritumoral edema volume change from baseline versus time since Gamma Knife (months) for tumors >2.0 cm³. Only 1 tumor per patient was included in this graph. In the 3 cases where a patient had 2 tumors >2.0 cm³, the largest was included (for a total of 24 tumors included). Abbreviation: GK = Gamma Knife.

Figure 4

Kaplan-Meier survival curve for the entire patient cohort. The shaded area represents the confidence interval at each time point. Abbreviations: GK = Gamma Kinfe; MST = median survival time.