This study builds on the results of prior studies (UNITED and UNITED-3). The goal of UNITED-4 is to test whether an adaptive radiation therapy (RT) therapy approach ('dose painting'), with reduced margins, impacts approach in participants with glioblastoma impacts local control compared to standard non-adaptive RT approach. The main questions of the study are to see how this adaptive RT approach with reduced margins compares to standard RT in terms of:
* Local control
* Overall and progression-free survival
* Patterns of failure
* Toxicity, Neurological Function, and Quality of Life
* Longitudinal imaging features