Gamma Knife surgery is unique in that no surgical incision is made to expose the inside of the brain, thereby reducing the risk of surgical complications and eliminating the side effects and dangers of general anesthesia. The “blades” of the Gamma Knife are the beams of gamma radiation programmed to target the lesion at the point where they intersect. In a single treatment session, 201 beams of gamma radiation focus precisely on the lesion. Over time, most lesions slowly decrease in size and dissolve. Exposure to radiation is brief and only the tissue being treated receives a significant dose of radiation, while the surrounding tissue remains unharmed.
It works by a process called stereotactic radiosurgery, which uses multiple beams of radiation converging in three dimensions to focus precisely on a small volume, such as a tumor or vascular malformation.
The patient is placed under local anesthesia and a special head frame with three-dimensional coordinates built into it is attached to the skull with four screws. Then, magnetic resonance imaging (MRI) and/or a cerebral angiogram are obtained and the results are sent to the gamma knife’s planning computer system. Physicians use the planning computer to determine the exact relationship between the target lesions and the frame and calculate how to set the controls of the gamma knife to treat the targets optimally. Targets often are best treated by combinations of several aimings, commonly known as “shots.” The physicians and physicists routinely consider numerous fine-tuning adjustments until an optimal plan is created. Simultaneously, an optimal dose is selected depending on the size, location, and type of lesion to be treated.
Using the three-dimensional coordinates determined in the planning process, the frame is then precisely attached to the gamma knife unit to guarantee that when the unit is activated, the target is placed exactly in the center of 201 precision-aimed, converging beams of (Cobalt-60 generated) gamma radiation. Treatment takes anywhere from several minutes to a few hours to complete depending on the shape of the target and the dose required. Patients do not feel the radiation. Following treatment the head frame is removed. The treatment generally requires only one session.
With the Gamma Knife, a surgical incision is not required; the attendant risks of open neurosurgical procedures (hemorrhage, infection, cerebrospinal fluid leakage, etc.) are therefore avoided.
Published reports indicate that the Gamma Knife may be used as an alternative to standard neurosurgical operations or as an adjunctive therapy in the treatment of residual or recurrent lesions left unresected by conventional surgery.
Conditions for which the Gamma Knife is considered most effective are:
- Intracranial tumors such as acoustic neuromas, pituitary adenomas, pinealomas, craniopharyngiomas, meningiomas, chordomas, chondrosarcomas, metastases and glial tumors.
- Vascular malformations including arteriovenous malformations.
- Functional disorders such as trigeminal neuralgia and obsessive-compulsive disorder.
In addition to the above mentioned indications, functional disorders such as intractable pain, Parkinson’s disease, essential tremors, and epilepsy are often treated with Gamma Knife.
