This study aims to see which type of radiation treatment is better for cancer patients with brain metastasis who are also receiving immunotherapy. Brain metastasis is when cancer spreads to the brain from other parts of the body. The two treatments being compared are **Single Fraction Stereotactic Radiosurgery (SSRS)** and **Fractionated Stereotactic Radiosurgery (FSRS)**. SSRS is a single, high dose of radiation, while FSRS is a lower dose spread over several days. The study will focus on whether FSRS reduces side effects better than SSRS. Key Points:

• Participants will be randomly assigned to either SSRS or FSRS treatment.
• Participants must have specific types of cancer and be 18 or older.
• Study participation requires several visits and tests like MRI scans.

Participants must be able to understand and consent to the study, and those who have had certain previous treatments or conditions may not be eligible. The study hopes to improve the quality of life for patients by finding the best treatment option with fewer side effects.