The most frequent use of Gamma Knife radiosurgery is in the treatment of intracranial metastatic brain disease.
Metastatic brain tumors arise from systemic neoplasms that spread to the brain from other parts of the body. Autopsy studies reveal brain metastases in approximately 25% of cancer patients. The incidence of metastatic brain tumors is greater in patients with lung or breast cancer given the high incidence of these tumors. The frequency that certain neoplasms metastasize to the brain is greater in patients with certain tumors such as melanoma.
Metastatic tumors may occur anywhere in the brain. They may be single or multiple. The tumors may present with a number of symptoms or signs such as seizures, headaches, confusion, gait instability, or weakness among others. Tumors are diagnosed with CT or MR imaging.
Treatment options depend on the specifics of the individual patient. These options include no aggressive treatment but supportive care, surgical resection, or radiation treatment. Radiation treatment options include conventional fractionated radiation to the whole brain or stereotactic radiosusrgery.
For example, patients with advanced widespread systemic cancer and a low quality of life may not benefit from aggressive intervention. Patients with single lesions located in a surgically respectable location may be chosen to be treated primarily with surgery.
Small or moderated sized tumors located in area that are not well-suited for surgery may be good candidates for Gamma Knife radiosurgery. Gamma Knife radiosurgery may also be the selected treatment for patients with recurrent metastatic tumors after surgery.
Gamma Knife may be used to "boost" local radiation at the site of residual disease after treatment with whole brain radiation treatment.
Complications and Outcomes
In general, treatment with Gamma Knife radiosurgery controls the growth of metastatic tumors in greater than 80% of patients. Often the tumors decrease in size. If patients are dependent on steroids to control edema or swelling around metastatic tumors, Gamma Knife radiosurgery may decrease their steroid dependence. In a minority of patients, the brain swelling may increase after treatment with radiation.
Radiation necrosis after Gamma Knife may be difficult to distinguish from recurrent tumor growth on subsequent MR imaging. The prognosis for survival after treatment with Gamma Knife radiosurgery often depends on the success of treating the systemic cancer.