NRG Phase III Trial of Salvage Stereotactic Radiosurgery (SRS) or SRS + Hippocampal-Avoidant Whole Brain Radiotherapy (HA-WBRT) for First or Second Distant Brain Relapse after Upfront SRS with Brain Metastasis Velocity ≥4 Brain Metastases/Year Adult CIRB - Late Phase Emphasis Active Available to Open