gamma knife

Gamma Knife FAQ


What is 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 192 individual radiation sources that are positioned to precisely converge on the tumor area. By having lower doses of radiation from multiple sources converge on a single location, normal tissue in the path of each individual source receives a minimal dose, reducing the chance of radiation injury.

This 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. 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.

How common is this procedure?

Since 1991, the Gamma Knife team at UCSF has treated more than 4,400 patients with this advanced radiation treatment. Its precision in delivering a single, high dose of radiation to a tumor makes Gamma Knife radiosurgery an excellent, non-invasive treatment option for a variety of brain tumors. It may be used as a first-line treatment by itself, or used as second-line treatment following surgical removal of the tumor.

Which tumor types can be treated with Gamma Knife radiosurgery?

Gamma Knife radiosurgery most effectively treats tumors no larger than 1-2 inches in diameter. Tumor types that may be considered for Gamma Knife radiosurgery include the following:

Ultimately, the recommendation for Gamma Knife treatment depends on a number of factors, including tumor size and location, as well as the patient’s overall health and medical history.

Patients who are candidates for Gamma Knife at UCSF are reviewed at our weekly Gamma Knife conference. Important factors to consider include the patient’s general health and medical history, as well as the location and size of the tumor. Each patient's condition is evaluated by a team including neurosurgeons, radiation oncologists, physicists, neuro-radiologists, neuro-oncologists, nurses and radiation therapists.

What can I expect during the procedure?

Before the procedure starts, a nurse will start an intravenous (IV) line through which you will receive a mild sedative, along with the contrast agents necessary for the brain scans.

Next, your head is fitted to the stereotactic head frame, the device that keeps your head precisely positioned throughout the procedure to ensure accurate delivery of the radiation. This involves the injection of local anesthesia into your scalp, at the four points where the stereotactic head frame secures your head in place. Your hair will not need to be shaved.

Once your head is secured within the frame, the Gamma Knife team will take additional brain scans, using CT and MRI. This provides them with an accurate 3D “map” of the tumor within your brain, allowing them to plan treatment details, including the best positioning of your head in the machine, along with radiation dose and length. Depending on the size and location of the tumor, this planning stage may take one to several hours. During this time, you can read or watch videos in the waiting room.

After the doctors plan your treatment, you will be brought to the Gamma Knife area. For the remainder of the procedure, you will be lying on your back on a treatment bed. The stereotactic head frame will be fitted into the Gamma Knife, which precisely positions your head while up to 192 radiation beams are targeted to the tumor. During treatment, you will not feel, see, or hear anything unusual; you will not feel any pain.

Depending on the size and shape of the tumor, you may receive one or several rounds of radiation, each lasting several minutes. Between rounds of radiation, the stereotactic head frame may be re-positioned within the device to deliver radiation from different angles. Once the radiation treatment is finished, the stereotactic head frame is removed, and small adhesive bandages are applied at the contact points.

The radiation treatment time depends on your diagnosis, but the entire procedure (from application of the stereotactic head frame until treatment completion) usually takes much of the day. After treatment, you’ll be moved to the recovery room and most likely discharged within the same day.

What can I expect after the procedure?

In the recovery room, your doctors will provide follow-up instructions and monitor you before you are discharged. Some patients experience a mild headache, which is treated with medication as needed; others may experience additional discomfort from lack of food during the day. You will be monitored, including your blood pressure and pulse, but in most cases patients are discharged later the same day. Most patients resume normal activities within a day or two, and you can eat and drink as you feel able.

You will receive follow-up instructions and an informational handout before leaving, but our nurse will also call you the following day to check on your status and answer any questions.

What are the risks or side effects of Gamma Knife radiosurgery?

While Gamma Knife radiosurgery is typically a one-time treatment that delivers a precisely targeted dose of radiation to the tumor, some surrounding brain tissue may still receive small doses of radiation. This technique seeks to minimize radiation exposure in healthy brain tissue, but there may still be some adverse reaction from the effect of low radiation in normal tissue. Your doctor will discuss the full range of side effects with you, but generally side effects are mild and temporary, including nausea, fatigue, and skin irritation.

Overall, Gamma Knife radiosurgery is considered an advanced radiation technique that delivers a high dose of radiation to a tumor, while causing little or no damage to surrounding tissue.

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