Brain metastases are cancer cells that spread to the brain from tumors in other organs in the body, which happens in 10% – 35% of adult cancer patients. Estimating prognosis in brain metastasis is clinically relevant, as it allows clinicians to recommend treatments that balance durability of intracranial tumor control with quality of life and side effects of treatment. We develop and use mathematical models to understand the response of these secondary tumors to radiotherapy and provide image-based biomarkers of survival and response as well as designing optimized treatments.