adjuvant therapy, chemotherapy and radiation (CRT), combined-modality therapy, elderly, glioblastoma, Age Factors, Aged, Aged, 80 and over, Brain Neoplasms, Chemoradiotherapy, Cohort Studies, Combined Modality Therapy, Databases, Factual, Disease-Free Survival, Female, Geriatric Assessment, Glioblastoma, Humans, Kaplan-Meier Estimate, Logistic Models, Male, Multivariate Analysis, Neoplasm Invasiveness, Neoplasm Staging, Neurosurgical Procedures, Predictive Value of Tests, Prognosis, Proportional Hazards Models, Retrospective Studies, Risk Assessment, Survival Analysis, Treatment Outcome, United States