This study investigates the effects of brain radiotherapy on cognitive function by evaluating plasma biomarkers and apolipoprotein E (APOE) genotype in patients with primary or metastatic brain tumors. Standard brain radiotherapy is known to impact cognitive outcomes, yet the underlying biological mechanisms remain unclear.

PRIMARY OBJECTIVES:

1. Assess plasma biomarkers for Aβ, GFAP, phospho Tau, and NfL pre- and post-radiotherapy.
2. Determine APOE genotype.
3. Evaluate neuropsychiatric testing aligned with standard of care brain MRIs and serum markers.
4. Measure brain morphometrics pre- and post-radiotherapy with standard of care brain MRIs.

SECONDARY OBJECTIVES:

1. Measure patient-reported quality of life changes pre- and post-radiotherapy using a standard University of California, San Francisco (UCSF) -approved questionnaire.

OUTLINE:

This is a single-arm, non-randomized, open-label pilot study. Participants will be study duration spans 12 months post-brain radiotherapy.

Inclusion Criteria:

1. >= 18 years old
2. Diagnosis of a primary brain tumor OR #3. Not both #2 and #3.
3. Diagnosis of primary solid tumor and secondary involvement of the brain
4. If the patient has brain metastases: fewer than 5 brain metastases (post-operative and definitive allowed), none > 1 cm in max diameter.
5. Candidate for standard of care / usual care (SOC) focused brain radiotherapy.
6. No prior brain radiotherapy, including whole brain radiotherapy.
7. Eastern Cooperative Oncology Group (ECOG) functional score 0 or 1.
8. Estimated life expectancy post-treatment of > 2 years.

Exclusion Criteria:

1. Diagnosis of neurodegenerative disease (Alzheimer's disease, Parkinson's disease).
2. Diagnosis of memory disorder pre-treatment.
3. Leptomeningeal disease or disease involving either hippocampus.

Adult participants with brain cancers receiving care at University of California, San Francisco (UCSF)