This trial is a pilot, Phase 2, sequential two-cohort study designed to test two de-escalated whole brain radiation therapy (WBRT) dose levels and assess their ability to maintain acceptable in-brain distant control. The WBRT dose would decrease as the study moves forward, both in terms of absolute value and equivalent dose in 2 Gray fractions (EQD2) (as determined by the linear quadratic radiobiological model). The absolute value of the simultaneous integrated boost (SIB) dose will change with each dose level because the number of fractions delivered will depend on the WBRT dose. As such, the SIB dose will be manipulated such that the EQD2 will remain essentially equivalent despite the difference in the number of fractions delivered. This design will ensure that the only variable is the change in WBRT dose.