gamma knife

Gamma Knife Radiosurgery

Gamma Knife radiosurgery is a technique that precisely focuses and delivers a high dose of radiation to a target in the brain.

As a non-surgical procedure, it does not involve an actual knife, but is called “radiosurgery” because of its precision.

With the Gamma Knife device, a finely focused, high dose of radiation is delivered from up to 192 individual radiation beams that are positioned to converge precisely on the tumor area. Since lower doses of radiation from multiple sources converge on a single location, normal tissue in the radiation path receives a minimal dose. This reduces the chance of radiation damage to healthy tissue. The size of the radiation beams can also be adjusted, so that a high radiation dose can be precisely accumulated within a tumor of almost any shape.

Using the latest version called the Icon Gamma Knife, single or multiple session treatments can be delivered. The single session technique requires precise positioning, and is performed with the aid of a device that stabilizes the patient’s head in a certain position. This device is called a stereotactic head frame, and is combined with imaging scans (like CT or MRI) to identify the tumor’s exact location and precisely focus the gamma radiation beams to converge on it.

In contrast, multiple session treatments use thermoplastic mask fixation, which involves a custom-molded plastic mask that fits the patient’s face exactly and aids in positioning. If mask treatment is used, positioning on the treatment couch is confirmed with a low dose CT scan using an imaging device attached to the Icon Gamma Knife. For multiple session techniques, both CT and MRI imaging are used for planning and cone beam xrays are used to confirm positioning on the treatment couch.

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Gamma Knife at UCSF

UCSF was one of the first centers in the United States to acquire a Gamma Knife, in 1991. We have had a very active program ever since then, upgrading to each new model of Gamma Knife. Our current model is the Icon Gamma Knife. Over 4,400 patients have been treated with Gamma Knife radiosurgery at UCSF, and we currently treat approximately 300-400 patients yearly.

Tumor Types Treated with Gamma Knife:


This content was reviewed by UCSF radiation oncologist David Raleigh MD, PhD.