3505 - Long Term Proton Therapy Outcomes in the Reirradiation Setting for Recurrent Pediatric Ependymoma

G. S. Gill¹, K. W. Allison², B. Bajaj², S. Gallotto², M. P. Lawell², B. Patteson³, S. Baliga⁴, L. Wiltsie⁵, D. H. Ebb⁵, N. J. Tarbell², S. M. MacDonald², and T. I. Yock²; ¹Department of Radiation Oncology and Applied Sciences, Dartmouth Cancer Center, Dartmouth Health, Lebanon, NH, ²Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, ³Department of Pediatric Hematology & Oncology, Childrens Healthcare of Atlanta, Atlanta, GA, ⁴Department of Radiation Oncology, The Ohio State University, Columbus, OH, ⁵Department of Pediatric Hematology & Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA

Purpose/Objective(s): The objective of this study was to update a previously reported retrospective series with long-term outcomes on the efficacy and safety of re-irradiation with proton therapy for recurrent ependymoma. Materials/

Methods: With IRB approval, we searched our pediatric database to identify children with a diagnosis of ependymoma who received at least two courses of radiation therapy. Only patients who received proton therapy for their re-irradiation were included in our analysis. Progression free survival (PFS) and overall survival (OS) were calculated using the Kaplan-Meier method from the start date of the second radiation.
Results: The median age at re-irradiation was 8.5 years (n=35). The majority of patients were female (57%) with anaplastic histology (71%), infratentorial tumors (69%), and received a median of 54.0 Gy (52.2-59.4) with proton radiation therapy (86%) for their initial treatment. The median time to first failure was 2.39 years from the initial treatment. The most common site of first failure was local (77%) followed by distant (14%) and both (9%). Salvage therapy typically included re-resection (83%), chemotherapy (57%), and proton radiation therapy (100%) to a median dose of 52.2 GyE (14.0 – 58.0). The median time to second failure was 1.16 years from the second treatment. The most common site of second failure was local (64%) followed by distant (32%) and both (4%). The median follow up was 5.22 years (0.9-14.0). Six-year OS and PFS are 55.5% (39.9-76.2) and 25.5% (13.5-45.1). An improved OS was associated with patients who did not receive chemotherapy as part of the treatment for their first recurrence (HR 3.17, p = 0.014). Four of 30 patients (13.3%) locally re-treated experienced grade 2 radiation-associated treatment change and 1 patient (3.3%) experienced a grade 3 radiation-associated treatment change.
Conclusion: Among a cohort of patients with long-term follow up, proton therapy remains a safe and effective option for re-irradiation in the treatment of recurrent ependymoma and can be an effective salvage strategy for patients with recurrent disease.