Inclusion Criteria:  Subjects must meet all of the following criteria to be eligible for participation in this study:  Age ≥ 18 Pathological diagnosis of a non-hematopoietic malignancy Brain metastases of any size Any number of brain metastases that can all be contoured and targeted Anticipated median survival insufficient for surgery or stereotactic radiosurgery Presence of extracranial disease Estimated Glomerular Filtration Rate (eGFR) > 30 ml/min within 90 days Diagnosis-Specific Graded Prognostic Assessment (DS-GPA) ≤ 2.0 Able to complete the EuroQOL (EQ-5D-5L) questionnaire Willing and able to have regular imaging follow up Feasible to start protocol treatment within 14 days of patient enrolment Karnofsky Performance Score (KPS) ≥ 40 Willing to provide email address on the informed consent form, if unable to attend in-person follow-up assessments Signed a consent form prior to enrolment in the trial  Exclusion Criteria:  Subjects are excluded from the study if any of the following criteria apply:  Inability to have a brain MRI. Craniotomy less than 3 months prior to randomization Whole brain radiotherapy less than 6 months prior to randomization Immunotherapy, targeted therapy or hormone therapy planned after RT Disseminated leptomeningeal disease Multiple sclerosis Neurologically declining despite corticosteroids Requiring craniotomy to relieve mass effect Systemic lupus erythematosis, scleroderma, or other connective tissue disorders not in remission Active alcohol or drug abuse History of epilepsy or seizures, and not currently taking anti-epileptic medication Any other serious intercurrent illness or medical condition judged by the local investigator to compromise the patient's safety, preclude safe administration of the planned protocol treatment, or prevent the patient from being managed according to the protocol guidelines Pregnancy Potentially fertile men or women of childbearing potential who are unwilling to employ highly effective contraception