Survival impact of prolonged postoperative radiation therapy for patients with glioblastoma treated with combined-modality therapy

Abstract

Though conventionally fractionated chemoradiation (CRT) is well tolerated by selected patients with newly diagnosed glioblastoma (GBM), adverse health-related and nonhealth-related factors can lead to unplanned interruptions in treatment. The effects of prolonged time to completion (TTC) of radiation therapy (RT) on overall survival (OS) for these patients are unclear. The National Cancer Database (NCDB) was queried for all adult patients with newly diagnosed GBM undergoing surgical resection followed by adjuvant CRT with conventionally fractionated RT (6000-6600 cGy in 30-33 fractions) from 2005 to 2012. TTC was defined as the interval from first to last fraction of RT. Recursive partitioning analysis (RPA) was used to determine a threshold for TTC of adjuvant RT. Cox proportional hazards modeling was used to identify covariates associated with OS. A total of 13489 patients were included in our cohort. Patients who completed adjuvant RT within the RPA-defined threshold of 46 days from initiation of RT (median OS: 14.0 months, 95% confidence interval (CI) 13.7 to 14.3 months) had significantly improved OS compared to patients with TTC of 47 days or greater (median OS: 12.0 months, 95% CI 11.4 to 12.6 months, P < .001). Delays in completing adjuvant RT were relatively common, with 15.0% of patients in our cohort having a TTC of RT of 47 days or greater. Delays in completing adjuvant RT were associated with a worse survival outcome. Any unnecessary delays in completing adjuvant RT should be minimized while ensuring the safe delivery of therapy.