Radt-55. Treatment Outcomes After Gamma Knife Stereostatic Radiosurgery for Intracranial Ependymoma: A Single Institution Experience

PURPOSE To evaluate the treatment outcomes after adjuvant Gamma Knife stereostatic radiosurgery (GK SRS) in patients with intracranial ependymoma METHODS Eight patients with pathologically confirmed diagnosis of ependymoma were treated with Gamma Knife SRS at our institution from December 2012 to June 2023. All patients underwent previous surgical resection. One patient was treated three times for recurrent disease. Grade 2 ependymoma was present in 4 patients and grade 3 (anaplastic) ependymoma was present in 4 patients. The median tumor volume was 5.18 cc (0.87-5.49) but we were unable to retrieve records of the treatment volumes for four patients in this study. Median prescription dose was 13.25 Gy (range 10-16) to the 50% isodose line. Overall survival was assessed using Kaplan-Meier survival curves from time of gamma knife to last known follow up, or date of death. RESULTS Median follow-up was 3.23 years (range 0.66-4.75). Out of the eight patients treated with SRS, seven (87.5%) were deceased from recurrent widespread disease and one (12.5%) was alive as of the time of data collection. Median survival was 3.28 years (1.2-6.25). Mantel-Cox test showed no statistically significant difference in overall probability of survival when comparing tumor grade (grade 2 vs grade 3), sex (male vs female) or prescription dose (<14 Gy vs >14 Gy). CONCLUSION GK SRS is a viable treatment modality for patients with intracranial ependymomas after initial surgical resection that can yield reasonable survival times. This study also shows that there is a need for further investigation on how specific GK SRS planning metrics could affect patient outcomes in a larger patient cohort. Such data could help to better optimise personalised treatment planning for GK SRS in patients with intracranial ependymoma.