Abstract B073: Radiotherapy dosing in intracranial ependymoma using the National Cancer Database

Purpose: To determine the dose-dependent effect of adjuvant radiotherapy on survival for pediatric intracranial ependymomas and explore patient/disease characteristics that may benefit from higher doses using survival data. Methods: Data was accessed from the National Cancer Database and included patient data from 2004-2021. Inclusion criteria was comprised of a diagnosis of non-metastatic intracranial ependymoma, World Health Organization (WHO) grade I or II, surgical resection, adjuvant radiotherapy between 4500-6300cGy, and had survivorship data. Patients were included up to the age of 22 years. Crude and adjusted Cox proportional hazard ratios (HRs) were calculated to estimate the associations of patient, tumor, and treatment characteristics with overall survival (OS). Kaplan-Meier (KM) curves were used to visualize survival data for dosing for the general cohort and by subgroups (age, resection extent, and grade). Statistical significance was defined as p<0.05. Results: Our study included 1154 patients who met inclusion criteria, of whom 405 (35%) received ≤5400cGy and 749 (65%) received >5400cGy. Those who received <5400cGy tended to be younger, and were more likely to have tumors that were WHO grade II and/or located in the infratentorial area. We found no difference in crude (0.95, 95% CI 0.72-1.06, p=0.69) or adjusted (0.88, 0.46-1.69, p=0.71) OS HR for those receiving ≤5400cGy compared to >5400cGy. Likewise, there was no statistical difference in crude or adjusted OS HR for age ≤3years (1.09, 95% CI 0.84-1.41, and 1.17, 95% CI 0.62-2.18, respectively) or surgical resection extent (1.07, 95% CI 0.68-1.67, and 0.94, 95% CI 0.47-1.86, respectively). Crude OS HR for WHO grade III was 1.95 (95% CI 1.43-2.65, p<0.001) and adjusted was 3.12 (95% CI 1.49-6.52, p=0.002), compared to WHO grade II. On KM curves there was no difference in OS for radiotherapy for the general cohort based on dose alone, dose by age ≤3years, dose by surgical extent, or dose by grade. However, we did find better OS in those with grade II tumors compared to III regardless of radiotherapy dose received. Conclusions: There was no difference in OS between patients who received ≤5400cGy compared to >5400cGy. We found improved OS in those with grade II tumors compared to grade III, however there was no difference in survival based on dose received by tumor grade, age, or resection extent. Limitations in data available prevented exploring local control, event free survival, or toxicity. Future research should focus on identifying tumor or patient characteristics that would benefit from higher radiotherapy doses. Citation Format: Melanie L. Rose, Erika L. Moen, Bryan Ager, Benjamin V.M. Bajaj, Matthew Poppe, Gregory A. Russo, Torunn I. Yock. Radiotherapy dosing in intracranial ependymoma using the National Cancer Database [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pediatric Cancer Research; 2024 Sep 5-8; Toronto, Ontario, Canada. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl):Abstract nr B073.