by Steven Seung, M.D., Ph.D. When cancer spreads beyond the original tumor site to another part of the body (or "metastasizes"), doctors turn to whole-body (or "systemic") treatments like chemotherapy to fight the disease. Localized treatments like Gamma Knife radiosurgery can also play a role in fighting cancer growth and improving quality of life. This is especially true when cancer spreads to the brain. Brain metastases are the most common type of brain tumors with about 140,000 cases diagnoses per year. The most common source of brain metastases is lung cancer in men and breast cancer in women. In these cases, cancer cells travel from the original tumor through arterial blood into the brain. Roughly speaking, areas of the brain with the highest blood flow are most vulnerable to brain metastasis. The cerebrum is involved in 80 to 85% of all brain metastases, the cerebellum in 10 to 15% and the brainstem in 3 to 5%. Metastatic brain tumors present with signs and symptoms of any expanding intracranial mass lesion, such as headaches, focal weakness, mental status changes, seizures, ataxia and sensory and visual changes. Symptomatic brain metastases are extremely dangerous. If left untreated (or treated only with corticosteroids to reduce brain swelling), only half of cancer patients with brain metastases will survive more than one or two months. To help these patients, whole brain radiation therapy is most commonly recommended. Acute side effects of whole brain radiation therapy include hair loss (alopecia), nausea, vomiting, lethargy, otitis media and severe cerebral edema. Chronic effects include atrophy, leukoencephalopathy, radiation necrosis, neurological deterioration and dementia. In many cases, Gamma Knife radiosurgery can treat metastatic brain tumors effectively with marked reduced acute and chronic effects. The Gamma Knife allows numerous beams of radiation to converge on a target site, resulting in a high dose of radiation delivered to the target site. A recent report by Somaza, et. al., revealed that even in patients with radioresistant tumors (such as melanoma), local control for small tumors was achieved in 97% of lesions and neurological improvement occurred in 53% of affected patients. Despite such results, radiosurgery has not been considered a primary therapy in many centers. For solitary lesions, radiosurgery should be considered as an alternative to surgery provided no significant mass effect exists. Multiple metastases raise another important concern, because the number of lesions has been thought to be a limiting factor in single session Gamma Knife treatment, although most centers prescribe radiosurgery for one to four metastases. Multiple metastases may be more of an issue in terms of the equipment itself not allowing multiple lesions to be treated in a single sitting. At the new Cancer Center at Providence due to open in early 2008, we will be showcasing the new Gamma Knife Perfexion which essentially eliminates the technical limitations of treating multiple lesions that we face today.
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