The Gamma Knife uses a precisely focused intersecting dose of radiation from 201 Cobalt60 sources to treat abnormal tissue with a degree of accuracy (less than 1mm) not achievable with any other type of radiosurgery system. This spares the adjacent healthy brain because each of the 201 beams arhe dose not strong enough to damage the normal tissue, but at the target the beams combine to destroy the lesion.
Although the name implies a surgical incision, Gamma Knife radiosurgery is actually a non-invasive outpatient procedure. Stereotactic radiosurgery combines the precise localization and treatment approach of neurosurgery with the technical aspects of radiation therapy. Once a patient is thought to be a candidate for Gamma Knife surgery, the case is reviewed by a multidisciplinary team of physicians including neurosurgeons, radiation oncologists, and neuroradiologists at a biweekly Radiosurgery Case Conference. When appropriate, medical oncology input is also sought.
The day of the procedure, the stereotactic headframe is applied using local anesthesia and mild sedation. The discomfort is brief and usually consists of a pressure sensation lasting only 10-15 minutes. This frame provides the basis.for accurate target localization and is used to immobilize and position the patient's head with the Gamma Knife helmet.
Once the headframe is in place, measurements are taken and the patient is imaged by MRI, CT, angiography or some combination of these modalities. After target localization and imaging have been completed, the patient waits comfortably in the holding area with their family while the neurosurgeon, radiation oncologist and physicist carry out the complex treatment phase of the procedure.
With the help of a high-powered computer workstation, the team of physicians and physicists can develop three-dimensional models of the lesion to be treated and nearby important normal structures using images from MRI, CT and/or angiography. These images are used to develop the treatment plan and it is during this phase of the procedure that the appropriate dosage and treatment time is determined.
When the study is completed, the patient is brought to the treatment room and the first of (usually) several targets coordinates is entered into the frame. The patient's head (with the frame in place) is then suspended from the inside of the collimator helmet. The collimator helmet is supported by the couch and has 201 holes, each of which are anywhere from 4 to 18 millimeters in diameter. It is through these holes that the radiation is focused on the target. Some of these holes may be plugged to avoid radiation to the eye or other important structures. The patient is now ready to undergo the "surgical" part of the procedure. Depending on the complexity of the treatment plan, there can be one or many radiation cycles or "shots", each of which can last from one to ten or more minutes.
In contrast to an being in an MRI machine, only the upper body enters the Gamma Knife treatment unit. The patient can very easily see out of the unit and the body is not enclosed, thereby eliminating any fear of claustrophobia. Patients are encouraged to bring their own selection of music, especially for longer treatments (e.g., pituitary tumors, multiple metastatic tumors, larger tumors).
Indications for radiosurgery would be one or more of the following:
See the our Links Page for further information on the Gamma Knife. Elekta's site (the manufacurer) is also helpful, as is the Florida Hospital Gamma Knife Center's Web Page.
Information comparing Gamma Knife radiosurgery to microsurgical removal of acoustic neuromas is also available elsewhere on this site.
