Gamma Knife

(Stereotactic radiosurgery, Gamma Knife surgery)

Procedure overview

What is Gamma Knife radiosurgery?

Gamma Knife radiosurgery, also called stereotactic radiosurgery, is a very precise form of therapeutic radiology. Even though it is called surgery, a Gamma Knife procedure does not involve actual surgery, nor is the Gamma Knife really a knife at all. It uses beams of highly focused gamma rays to treat small- to medium-sized lesions, usually in the brain. Many beams of gamma radiation join to focus on the lesion under treatment, providing a very intense dose of radiation without a surgical incision or opening.

Illustration of the anatomy of the brain, adult

Gamma Knife radiosurgery is called "surgery" because the end result is very similar to physically removing the lesion with surgery. The beams of radiation are very precisely focused to reach the tumor, lesion, or other area being treated with minimal effect on surrounding healthy tissue.

Gamma Knife radiosurgery is most often used to treat small and medium tumors and other lesions in the brain. It is also used to treat certain neurological conditions, such as trigeminal neuralgia (a condition in which pressure on the trigeminal nerve causes spasms of extreme facial pain) and acoustic neuroma (a noncancerous tumor in the brain that affects the nerves that control hearing).

Gamma Knife radiosurgery may be used in situations where the brain lesion cannot be reached by conventional surgical techniques. It may also be used in people whose condition is such that they might not be able to tolerate a surgical procedure, such as craniotomy, to treat their condition.

Because the therapeutic effects of a Gamma Knife procedure occur rather slowly over time, it is not used for people whose condition requires more immediate therapy.

How does Gamma Knife radiosurgery work?

Radiosurgery works in the same manner as other types of therapeutic radiology: it distorts or destroys the DNA of tumor cells, causing them to be unable to reproduce and grow. The tumor will shrink in size over time. For blood vessel lesions such as an arteriovenous malformation (AVM), the blood vessels eventually close off after treatment.

Gamma Knife Radiosurgery

Gamma Knife treatment generally involves these steps: 

  • Head frame placement. In order to keep the head from moving during treatment, a box-shaped frame is attached to the head. Pins designed specifically for this purpose fasten the head frame to the skull. The head frame also is a guide to focus the gamma ray beams to the exact location of the lesion being treated.

  • Tumor or lesion location imaging. Once the head frame is in place, the exact location of the lesion to be treated will be determined using computed tomography (CT scan) or magnetic resonance imaging (MRI).

  • Radiation dose planning. After the CT or MRI scan has been completed, the radiation therapy team will determine the treatment plan. The results of the imaging scan, along with other information, will be used by a medical physicist to determine the best treatment.

  • Radiation treatment. After being positioned for the treatment, a type of helmet with many hundreds of holes in it is placed over the head frame. These holes help to focus the radiation beams on the target. Treatment will last a few minutes up to a few hours, depending on the type and location of the area being treated. Generally, only one treatment session is required for a lesion.

A Gamma Knife procedure involves a treatment team approach. The treatment team generally includes a radiation oncologist (a doctor specializing in radiation treatment for cancer), a neurosurgeon and/or a neuroradiologist, a radiation therapist, and a registered nurse. In addition, a medical physicist and a dosimetrist work together to calculate the precise number of exposures and beam placement necessary to obtain the radiation dose that is prescribed by the radiation oncologist. Your treatment team may include other health care professionals in addition to or in place of those listed here.

The Gamma Knife system is 1 of 3 types of radiosurgery systems. Gamma Knife systems are cobalt 60 systems, which means they use cobalt as a source for gamma rays. During Gamma Knife treatment, the equipment remains stationary (does not move).

Two other types of radiosurgery are: 

  • Linear accelerator (LINAC) systems. Linear accelerator (LINAC) systems use high-energy X-rays to treat a tumor or other lesion. Some common types of LINAC systems include CyberKnife, X-Knife, Novalis, and Peacock.
    In addition to using X-rays rather than gamma rays, LINAC systems also differ from the Gamma Knife in that the machinery moves around the patient during treatment. For this reason, LINAC systems are able to treat larger tumors and larger affected areas than the Gamma Knife. Areas other than the brain can be treated with a LINAC system.

  • Proton beam therapy or cyclotron. Proton beam therapy is a type of particle beam radiation therapy. Rather than using rays of radiation, such as gamma rays or X-rays, particle beam therapy uses particles, such as protons or neutrons. Proton beam therapy is the most widely-used type of particle beam therapy.
    Proton beam therapy may be used for radiosurgery procedures or for fractionated radiotherapy (several smaller doses of radiation over a certain period of time).

There are only a few facilities in North America that provide proton beam therapy.

Reasons for the procedure

Gamma Knife radiosurgery may be used to treat certain conditions of the brain in particular instances. Brain conditions that may be treated with a Gamma Knife procedure include, but are not limited to, the following:

  • Brain tumors

  • Arteriovenous malformations, or AVM (a type of blood vessel defect)

  • Trigeminal neuralgia

  • Acoustic neuroma

Gamma Knife radiosurgery has shown some promise for treating conditions, such as tremor and rigidity related to Parkinson disease, epilepsy, and chronic pain.

There may be other reasons for your doctor to recommend Gamma Knife radiosurgery.

Risks of the procedure

If you are pregnant or suspect that you may be pregnant, you should notify your health care provider. Radiation exposure during pregnancy may lead to birth defects.

Other risks may include, but are not limited to, the following:

  • Swelling of the brain

  • Headache

  • Nausea

  • Numbness

Some risks and side effects may be related to the location and size of the area being treated by the Gamma Knife procedure. These may include:

  • Hair loss near treated area (generally temporary)

  • Seizures

  • Weakness

  • Loss of balance

  • Vision problems

There may be other risks depending on your specific medical condition. Be sure to discuss any concerns with your doctor prior to the procedure.

Before the procedure

  • Your doctor will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure.

  • You will be asked to sign a consent form that gives your permission to do the procedure. Read the form carefully and ask questions if something is not clear.

  • In addition to a complete medical history, your doctor may perform a complete physical examination to ensure you are in good health before undergoing the procedure. You may undergo blood tests or other diagnostic tests.

  • Notify your doctor if you are sensitive to or are allergic to any medications, latex, tape, contrast dyes, iodine, or anesthetic agents (local and general).

  • Notify your doctor of all medications (prescription and over-the-counter) and supplements that you are taking.

  • Notify your doctor if you have a history of bleeding disorders or if you are taking any anticoagulant (blood-thinning) medications, aspirin, or other medications that affect blood clotting. It may be necessary for you to stop these medications prior to the procedure.

  • Notify your doctor if you have any type of implant(s), such as a pacemaker and/or implantable defibrillator, artificial heart valve, surgical clips for a brain aneurysm, implanted medications pump, chemotherapy port, nerve stimulators, eye or ear implants, stents, coils, or filters.

  • If you are pregnant or suspect that you are pregnant, you should notify your health care provider. Women of child-bearing age may be asked to give a urine specimen for pregnancy testing prior to the procedure.

  • You will be asked to fast for 8 hours before the procedure, generally after midnight.

  • You may be given a special shampoo to wash your hair with the night before or the morning before the procedure.

  • You may receive a sedative prior to the procedure to help you relax.

  • Based on your medical condition, your doctor may request other specific preparation.

During the procedure

A Gamma Knife procedure may be performed on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your doctor's practices.

Gamma Knife Machine and Helmet

Generally, a Gamma Knife procedure follows this process:

  1. You will be asked to remove any clothing, jewelry, hairpins, dentures, or other objects that may interfere with the procedure, and will be given a gown to wear.

  2. An IV line may be started in the hand or arm in order to give medications and/or fluids during the procedure.

  3. The hair at the area around the head frame insertion sites may be clipped off.

  4. The skin on your head will be cleansed at the locations where the pins for the head frame will be placed.

  5. A local anesthetic will be injected at the head frame pin insertion sites. Once the anesthetic has taken effect, the head frame will be attached to your head with pins that are inserted into your skull.

  6. You may feel some pressure during the placement of the head frame, but this sensation should go away in a few minutes.

  7. After the head frame is attached, you will undergo brain imaging so that the location of the brain tumor or lesion can be precisely identified for planning the treatment. The brain imaging procedure may be a computed tomography (CT) scan, a magnetic resonance imaging (MRI) scan, or a cerebral angiogram.

  8. After the brain imaging has been completed, you will be allowed to rest and relax while the treatment team completes your treatment plan. The images from your imaging procedure will be used by a computer in planning your specialized treatment.

  9. When your treatment plan is ready, you will be taken into the room where the Gamma Knife equipment is located. You will lie down on a sliding table. A special helmet, called a collimator helmet, will be fitted over the head frame. The collimator helmet has 201 holes in it, which allow radiation beams to pass through it into your brain in a very precise pattern that is determined by a computer.

  10. Once the helmet is in place, the table will slide into the Gamma Knife unit. You may hear a clicking sound as the collimator helmet moves into place in the machine.

  11. The treatment team will go into another room when the treatment begins. You will have an intercom available to communicate with the treatment team. They will be able to hear you at all times. You will also be observed with a video monitor.

  12. The number of treatments will depend on your specific situation. The entire treatment session may last from two to four hours, but the length of the session will depend on the treatment plan designed for you.

  13. You will not feel or hear anything from the Gamma Knife unit during the treatment session.

  14. After the treatment session is over, the treatment table will slide out of the Gamma Knife machine. You will be allowed to get up at this time, unless you had an angiogram prior to the Gamma Knife procedure.

  15. The head frame will be removed. The pin insertion sites will be cleaned and a sterile dressing will be applied.

After the procedure

After the procedure, you will be observed for a period of time. If your brain imaging prior to the Gamma Knife procedure was a cerebral angiogram, you will need to lie still with the affected leg straight for a few hours until the catheter insertion site in the groin is no longer bleeding.

Once you are able to take liquids by mouth, the IV line will be removed. You may take liquids and solid foods as tolerated.

You may feel some discomfort after the procedure, such as a headache or nausea. Let your nurse know if you are uncomfortable, so that you may be given medication and/or other treatment.

The Gamma Knife procedure is generally performed on an outpatient basis, so you most likely will be allowed to go home at the end of the day. You will need to have someone drive you home, however. If necessary, you may be admitted to the hospital for overnight observation.

Once you are home, you may resume your normal diet, medications, and activities, unless your doctor instructs you differently. You may be instructed to avoid strenuous activity, such as exercise, for a period of time.

You will most likely be allowed to gently shampoo your hair the day after the procedure. You should not scrub the pin sites on your head, however, until they have completed healed, generally within a week or so.

Call your doctor to report any of the following:

  • Severe headache that is not relieved by medication

  • Any weakness, numbness, or vision problems that are new, or have become worse than they were prior to the procedure

  • Continued bleeding or other drainage from the pin sites

  • Seizures

Your doctor may give you additional or alternate instructions after the procedure, depending on your particular situation.

Online resources

The content provided here is for informational purposes only, and was not designed to diagnose or treat a health problem or disease, or replace the professional medical advice you receive from your doctor. Please consult your health care provider with any questions or concerns you may have regarding your condition.

This page contains links to other websites with information about this procedure and related health conditions. We hope you find these sites helpful, but please remember we do not control or endorse the information presented on these websites, nor do these sites endorse the information contained here.

American Brain Tumor Association

American Cancer Society

National Brain Tumor Society

National Cancer Institute (NCI)

National Institute of Neurological Disorders and Stroke

Radiological Society of North America