Use the metastatic pattern and lesion size to decide between focal therapy and whole-brain treatment, and keep leptomeningeal spread in mind when systemic disease is diffuse. The bedside question is whether the disease is focal enough for radiosurgery or too widespread for it.

Lung cancer is the most common source of brain metastases; Stereotactic radiosurgery is best for a solitary lesion under three centimeters; Whole-brain radiation is used when metastases are widespread; Leukemias and lymphomas commonly seed the leptomeninges; CSF in leptomeningeal disease often shows elevated white cells, low glucose, and high protein