This research study is studying stereotactic radiation (focused/pinpoint radiation that targets each individual tumor but not the surrounding brain) instead of whole-brain radiation (radiation targeting the entire brain) as a possible treatment for patients with small cell lung cancer and 1-10 brain metastases.

The intervention involved in this study is:

-Stereotactic (focused, pinpoint) radiation

This research study is a Phase II clinical trial. Phase II clinical trials test the safety and effectiveness of an investigational treatment, in this case stereotactic radiation, to learn whether this treatment works in treating a specific disease. "Investigational" means that the treatment is being studied.

In patients with a limited number of brain metastases (spread of a cancer that started outside of the brain to the brain itself) the standard radiation option is stereotactic radiation, which involves using a high dose of radiation that only targets the specific metastases that are visible on imaging of the brain, not the whole brain itself. However, studies evaluating the role of stereotactic radiation to treat brain metastases generally excluded patients with small cell lung cancer. Therefore, among patients with small cell lung cancer and brain metastases, the typical treatment that has been offered is whole brain radiation. However, whole brain radiation has deleterious associated side effects including significant fatigue and permanent memory/attention problems. The investigators are studying whether stereotactic radiation can be effectively utilized for patients with small cell lung cancer and brain metastases in order to avoid such side effects.

Inclusion Criteria:

• Participants must have a biopsy-proven tumor consistent with small cell lung cancer and intracranial lesions radiographically consistent with or pathologically proven to be brain metastases. Patients who have undergone prior systemic therapy are eligible. Patients who have undergone resection of one or more brain metastases but who have not yet started adjuvant radiotherapy are eligible for the study.
• 1-10 definitive intracranial lesions must be present on MRI of the brain.
• Age >=18 years at diagnosis of brain metastases.

Exclusion Criteria:

• Participants who have undergone prior radiation for brain metastases.
• Participants who have received prophylactic cranial radiation for prevention of brain metastases
• Participants who cannot receive gadolinium
• Participants with stage IV-V chronic kidney disease or end stage renal disease
• Participants with widespread, definitive leptomeningeal disease
• Participants with a maximum tumor diameter exceeding 5 cm (if not resected)
• Participants with >6 definitive lesions consistent with brain metastases
• Participants with inadequate mental capacity to complete quality of life questionnaires