Background: The optimal radiation treatment (RT) length (6 weeks of 60 Gy in 30 fractions versus 3 weeks of 40 Gy in 15 fractions) for older adults with glioblastoma is debatable, with Level 1 evidence (PMID 15051755) revealing no difference in survival between RT regimens. However, there remains a paucity of evidence describing the role of insurance on out-of-pocket (OOP) costs for patients undergoing varying lengths of RT. This project aims to quantify expenses by insurance plans, enhancing transparency in treatment cost understanding. Methods: We utilized the National Comprehensive Cancer Network guidelines to determine the standard treatment protocol, including 30-fraction or 15-fraction RT with concurrent and post-radiation temozolomide for 12 cycles. The model assumes a Medicare- and/or Medicaid-eligible patient ≥ 65 years of age with glioblastoma. The total aggregate out-of-pocket (OOP) costs were determined from the sum of treatment costs, deductibles, and copays/coinsurance based on Medicaid, Original Medicare, Medigap Plan G, and Medicare Part D Rx plan over a two-year time horizon (not adjusted for inflation). All procedures were assumed to take place within the premises of an Ohio hospital. Results: Treatment charges include neurosurgery, neuro-oncology, and radiation oncology initial consultation, follow-up visits, diagnostic head CT, MRI, craniotomy with maximum safe resection, surveillance brain MRI, temozolomide, antiemetics, prophylactic TMP-SMX, weekly CBC, and tumor treating fields. RT-specific treatment charges include treatment planning, simulation and verification, RT delivery, and on-treatment visits. Original Medicare beneficiaries face an OOP cost of 20% for Medicare Part B claims with no cost cap for approved procedures after the deductible. Medications are covered under Medicare Part D with copays. This results in a total OOP treatment charge of $4,454.01 for 30 fractions and $3,913.86 for 15 fractions. Medigap Plan G beneficiaries face a total OOP charge of $2,387.22 for 30 fractions and $2,369.61 for 15 fractions. For Medicaid beneficiaries (assuming all treatments are approved by Medicaid), all expenses are covered without limit, resulting in no OOP expense for either treatment plan. Conclusions: Three-week versus six-week RT for GBM reduces OOP costs facing patients by 10%. By understanding the financial implications, healthcare providers, policymakers, and patients can make informed decisions about treatment options, and healthcare systems can develop strategies to mitigate the economic burden associated with GBM care.