FAQ About Gamma Knife® Radiosurgery

What is a Gamma Knife?
How does radiosurgery work?
Which patients can be treated with GammaKnife radiosurgery?

What is a Gamma Knife?

The Gamma Knife® actually is not a knife at all. It is radiation therapy device that delivers a single, very finely focused, high dose of radiation precisely to the target abnormality, while causing little or no radiation damage to the surrounding normal tissue. Abnormalities measuring 1.5 inches in maximum diameter or smaller-even abnormalities no larger than a small pebble-are often very responsive to treatment with Gamma Knife® radiosurgery.


How does radiosurgery work?
The technique that permits the precise identification and localization of such a small abnormality within the brain is called stereotaxy. Stereotactic radiosurgery is performed with the aid of a stereotactic head frame applied to the skull under local anesthesia with intravenous sedation, imaging techniques called computerized tomography (CT) scanning, magnetic resonance (MR) imaging, and angiography, which are used together with special computer-assisted instruments to provide three-dimensional views of the abnormality and the surrounding brain structures. By studying these images, the doctor is able to localize the abnormality within the brain with great accuracy and then precisely focus the gamma radiation beams emitted by the Gamma Knife® upon the abnormality. Patients who have Gamma Knife® radiosurgery are asked to lie on a treatment couch of the new Perfexion unit and the couch moves between each isocenter of treatment, not the patient. Through each of these 192 apertures of 4, 8 and 16 mm., radioactive cobalt-60 sources are focused simultaneously at the target abnormality. The size of the apertures can be adjusted to deliver a high radiation dose precisely to a target of almost any shape.


Which patients can be treated with Gamma Knife® radiosurgery?

 Abnormalities that can be treated effectively with Gamma Knife® radiosurgery include:

. Benign brain tumors that grow slowly and do not tend to invade surrounding normal brain tissues, such as meningiomas, acoustic neuromas, pituitary adenomas, craniopharyngiomas, and low-grade astrocytomas


. Primary or recurrent malignant brain tumors, including glioblastoma and anaplastic astrocytoma


. Solitary and multiple brain metastases


. Arteriovenous malformations (AVMs), dural AV fistulas


. Recurrent trigeminal neuralgia


. Some cases of epilepsy


Patients who are considered candidates for Gamma Knife® radiosurgery have their case reviewed by a multidisciplinary team of specialists, which may include adult or pediatric neurosurgeons, radiation oncologists, radiologists, biophysicists, nurses, and radiation technologists. Important factors that distinguish whether a patient may benefit from radiosurgery are the patient's age and general medical condition, the location and size of the abnormality, and what treatment the patient may have had previously for the abnormality. For patients who are treated with Gamma Knife® radiosurgery at UCSF, their referring physician plays an important part in their therapy. When the patient is being considered for this therapy, the referring physician is consulted to be certain that all the variables affecting the patient's potential responsiveness to therapy are taken into consideration. During the patient's stay at UCSF, the referring physician is kept informed about their patient's progress as an integral, synergetic member of the Gamma Knife® team, assuring continuity and coordination of the patient's care.