Arginine and Whole Brain Radiation Therapy for Brain Metastases is a study to see how safe it is to give arginine, an essential amino acid, with whole brain radiation therapy (WBRT) for people whose cancer has spread to the brain. Arginine can help brain tumors respond better to radiation. This study tests different ways to take arginine, either by mouth or through an IV, and checks how much gets into the blood.

Participants will be randomly chosen to be in one of two groups. In one group, patients receive arginine by IV, followed by WBRT for 10 days over two weeks. The other group takes arginine by mouth before WBRT for the same period. Patients will have tests, like CT scans and MRIs, to check their progress, and researchers will follow up for a year.

• This study runs for 10 days over 2 weeks, plus follow-up visits.
• Participants must be 18 or older and able to consent.
• Patients must not be taking other cancer treatments during the study.

Participation includes risks, like side effects from arginine or radiation. The study helps find the best way to use arginine with WBRT for better treatment outcomes.