Stereotactic Brain-directed Radiation With or Without Aguix Gadolinium-Based Nanoparticles in Brain Metastases

This study tests whether adding tiny gadolinium nanoparticles (called AGuIX) to targeted brain radiation (stereotactic radiosurgery) improves outcomes for people with cancer that has spread to the brain. The nanoparticles are designed to make radiation more effective right where it's needed. **You may be eligible if...** - You have a solid cancer with at least one confirmed or suspected tumor that has spread to the brain - Your brain tumor is at least 5mm in size - You have one of the following: melanoma that progressed despite immunotherapy, a GI cancer, HER2-positive breast cancer, cystic brain metastases, a large brain tumor (at least 2cm), or a tumor that has come back after prior brain radiation - You are 18 or older **You may NOT be eligible if...** - You have widespread cancer spreading rapidly in the brain - You have had allergic reactions to gadolinium contrast agents - Your overall health status is too poor to tolerate the treatment - You are pregnant Talk to your doctor to see if this trial is right for you.