The goal of this observational study is to learn about the effects of the timing of radiation therapy and immunotherapy in adults with non-small cell lung cancer (NSCLC) that has spread to the brain. The main questions it aims to answer are:
1. Does the timing of the two treatments change how long the brain tumor stays stable and how long participants live?
2. What medical problems do participants have when receiving these treatments at different times?
3. How does the timing of treatments affect the body's immune system?
Researchers will compare participants who receive radiation and immunotherapy 30 days or less apart to those who receive them more than 30 days apart to see if the timing affects the treatment's success and safety.
Participants already receiving radiation and immunotherapy as part of their regular medical care will:
1. Allow researchers to collect information about their treatment, health, and medical imaging during regular checkups.
2. Give a small blood sample during their routine blood draws.
3. Have standard magnetic resonance imaging (MRI) scans of their brain.