Gamma Knife Radiosurgery

Gamma Knife radiosurgery is a very precise form of radiation therapy that focuses intense beams of gamma rays with pinpoint accuracy to treat lesions in the brain.

Despite its name, Gamma Knife surgery involves neither traditional surgery nor an actual knife. Gamma Knife radiosurgery is called “surgery” because its outcome is similar to that of a surgical procedure.

Gamma Knife radiosurgery can be effective in treating tumors, blood vessel malformations, and nerve conditions. In each instance, surgeons and radiation oncologists use the Gamma Knife system somewhat differently:

  • Radiosurgery for tumor treatment works by damaging or destroying the DNA of tumor cells so that these cells cannot reproduce or grow. Over time, the brain tumor shrinks.
  • For blood vessel malformations, such as an arteriovenous malformation, Gamma Knife treatment causes the malformed blood vessels gradually to close off.
  • When nerves are the target for treatment, as in the case of the pain disorder trigeminal neuralgia, radiosurgery diminishes the function of improperly acting nerves, which provides relief.

Our Gamma Knife Center is home to the Leksell Gamma Knife Icon, the latest Gamma Knife system. This stationary unit delivers beams of highly focused gamma rays. It enables our neurosurgeons and radiation oncologists to provide world-class care.

Many beams of gamma radiation, each emitted from a different location outside the head, join to focus on the lesion—without a surgical incision. On its own, each beam carries a very low dose of radiation and has minimal effect on the healthy tissue through which it passes, but when they converge on the lesion, the beams combine to provide a precise, intense dose of radiation. Your medical team will program the Gamma Knife system with extreme precision to deliver the radiation necessary for your individual situation—the strength of the beams, the angles from which they arrive, the number of times they are discharged, and the exact location that is their destination.

Although other radiosurgery systems are available, our neurosurgeons and radiation oncologists use the Leksell Gamma Knife Icon because it is designed specifically for treating lesions in the brain and has the greatest precision and accuracy of any radiosurgery system to date.

Another advantage of the Leksell Gamma Knife Icon is its superior ability to spare healthy brain tissue, as compared with other systems. Other radiosurgery systems must deliver high doses of radiation to a specified margin of healthy tissue around the lesion to ensure complete destruction of the lesion. Because the Leksell Gamma Knife Icon has such high accuracy and precision, this added margin is reduced to 1mm, which is approximately the thickness of one sheet of paper.

Avoiding unnecessary radiation is particularly important for children, who may be more at risk than adults for late effects from radiation. Children treated with the Leksell Gamma Knife Icon may have a much lower likelihood of developing late effects than do those treated by other systems.

The Gamma Knife system has improved with each new model; among other notable advantages over earlier models, the latest Leksell Gamma Knife Icon:

  • Uses either a head frame or a frameless face mask to secure the head during treatment
  • Treats both small and large tumors
  • Treats lesions near critical structures

Earlier models used only a head frame, which is not necessary for certain conditions. The face mask is often more comfortable for patients than the head frame, so having both the head frame and face mask as options allows our neurosurgeons to recommend the option best for your unique condition.

When is Gamma Knife Radiosurgery performed?

Gamma Knife radiosurgery is used to treat certain conditions of the brain, many of which could only be treated by open surgery had this option not become available. At the Gamma Knife Center, our expert neurosurgeons and radiation oncologists most often use the Leksell Gamma Knife Icon to treat the following brain conditions:

Primary brain tumors, in particular:

  • Acoustic neuroma/Vestibular Schwannoma
  • Pituitary tumor
  • Craniopharyngioma
  • Glioma
  • Meningioma
  • Hemangioblastoma
  • Glomus jugulare tumor


  • Chordoma
  • Pediatric brain tumors
  • Arteriovenous malformation
  • Trigeminal neuralgia
  • Essential tremor
  • Epilepsy
  • Obsessive-compulsive disorder

Other conditions may also respond to Gamma Knife radiosurgery. This may be the procedure of choice when a brain lesion cannot be reached by conventional surgical techniques. Gamma Knife may also be used in lieu of operations that require craniotomy for those patients who must avoid open surgery.

Because the therapeutic effects of a Gamma Knife procedure occur over time, it may not be suitable for individuals whose condition requires more immediate therapy.

Gamma Knife radiosurgery can be used to treat children and adults.

How should I prepare for Gamma Knife Radiosurgery?

At Columbia University Irving Medical Center/NewYork-Presbyterian Hospital’s Gamma Knife Center, over five thousand patients have been successfully treated with the Gamma Knife procedure by a specialized, multidisciplinary team.

The treatment team typically includes a neurosurgeon, a radiation oncologist, a radiation therapist, and a registered nurse. In addition, a medical physicist calculates the precise beam placement and number of exposures necessary to obtain the radiation dose that is prescribed by the radiation oncologist. (Your treatment team may include other healthcare professionals in addition to, or in place of, those listed here.)

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

Before the procedure begins, you may be asked to remove any clothing, jewelry, hairpins, dentures, or other objects that may interfere, and you will be given a gown to wear. An intravenous (IV) line may be started in your hand or arm in order to supply you with medications and/or fluids.

Next, the head is prepared for placement of a box-shaped head frame or custom-made face mask. No shaving is required for either method. Which method is used depends on the individual condition and diagnosis of the patient. Frames confer maximum precision, necessary for working with trigeminal neuralgia, essential tremor, epilepsy, and obsessive-compulsive disorder. Face masks, which may be more comfortable, also ensure an extremely high degree of accuracy. The frameless face mask also enables treatment of larger tumors over a series of days usually on an outpatient basis. The frequency and amount of treatments required will be determined by the Gamma Knife team.

If a head frame is used the head frame is attached to the head and will prevent the head from moving during the procedure. This technique is also called frame-based radiosurgery.

If a face mask is used, a thermoplastic mask will be placed and then molded over your face for a customized fit. The mask has an opening for your nose and you will be able to breathe comfortably while wearing it. The mask is then contoured to fit your face perfectly and will have a snug, tight fit, minimizing head movement during the procedure. It will take about 10 minutes or less for the mask to harden, forming a custom face mask. Although tight, the face mask is comfortable to wear throughout the procedure. This technique is also called frameless radiosurgery.

You may receive a mild sedative to help you relax prior to a frame or frameless procedure.

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

After the brain imaging has been completed, you will be allowed to rest and relax while the treatment team completes your treatment plan. Determining your treatment plan can take between 30 and 90 minutes. To make your treatment plan, the team will combine the results of the imaging scan with other information to determine the optimal dosage and number of exposures. The team will input specific instructions to the computer system on where to focus the gamma rays, ensuring pinpoint precision and accuracy.

When your treatment plan is ready, you will be taken into the room where the Leksell Gamma Knife Icon is located. You will lie down on a sliding table, with your head pointing toward the machine. The table will then slowly slide you into the wide opening of the Gamma Knife unit.

During the entire treatment, you will be monitored by the Gamma Knife team via live video feed. You will have an intercom available to communicate with the team. They will be able to hear and communicate with you at all times.

The Icon machine is silent and you will not feel or hear anything during the procedure. The team will continuously monitor your head placement and radiation dosage. The head frame or face mask will keep your head in alignment. The Leskell Gamma Knife Icon has a safety feature that blocks radiation if movement occurs.

The number of treatment sessions will depend on your specific diagnosis. You may be inside the Gamma Knife unit as briefly as 15 minutes, or up to a few hours; the duration will depend on the treatment plan designed for you.

After the treatment session is over, the treatment table will slide out of the Gamma Knife machine.

The head frame or face mask will be removed. You will then be briefly monitored by the nursing team prior to discharge.

What are the risks for this procedure?

Although Gamma Knife radiosurgery is less invasive than traditional open surgery, there are some possible side effects and risks.

Radiation therapy is not recommended to women who are pregnant. Women of childbearing age may need to provide a urine sample prior to Gamma Knife treatment to ensure they are not pregnant.

Other side effects may include cerebral edema, headache, nausea, numbness or weakness in the face, loss of balance, vision problems, hair loss near the treated area (the hair loss is usually temporary), and seizures. Medication can be used for many of these side effects. Your physician will explain possible side effects before the procedure and manage any side effects after the procedure, should they occur.

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

How is Gamma Knife Radiosurgery performed?

Your physician will explain the procedure to you and offer you the opportunity to ask questions. You will be asked to sign a consent form to give your medical team permission to undertake the procedure. Please read the form carefully and ask questions if anything is not clear.

Be sure to tell your physician if you are sensitive or allergic to any medications, latex, tape, contrast dyes, or iodine. Also inform your physician of all medications, both prescription and over-the-counter, and all supplements, including herbs or vitamins, that you are taking.

If you are taking any anticoagulant medications, aspirin, or other medications that affect blood clotting, it may be necessary for you to stop these medications temporarily before undergoing the procedure.

Tell your physician if you have any 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, and shunts.

The morning of the procedure, eat a light breakfast at home and wear loose, comfortable clothing when you arrive. Do not wear jewelry or makeup.

Be sure to arrange transportation because you will not be permitted to drive yourself home after the procedure.

What can I expect after Gamma Knife Radiosurgery?

How long will I stay in the hospital?

The Gamma Knife procedure is generally performed on an outpatient basis, so you will go home at the end of the day.

Will I need to take any special medications?

No, you will not need to take any special medications for the procedure. If you feel some discomfort after the procedure, such as a headache or nausea, you will be given medication for relief.

When can I resume exercise?

Once you are home, you can resume most of your normal activities. You can resume exercise and other forms of strenuous activity about 18 to 24 hours after the procedure unless your physician instructs you differently.

What follow-up will I receive?

After the procedure, you will receive a follow-up call from the Gamma Knife nursing team. Follow-up appointments will be discussed with your neurosurgeon and possibly other team members. During these appointments, imaging studies may be ordered to monitor the treated lesion and determine the effect radiation had on it. Gamma Knife radiosurgery may take weeks, months, or years to work.

If you experience any of the following, call your physician or 911 emergency depending on the severity of symptoms:

  • Severe headache that is not relieved by medication
  • Any weakness, numbness, or vision problems that are new or have become worse than they were before the procedure
  • Seizures
  • Unable to tolerate liquids and persistent vomiting
  • Temperature greater than 100.4 degrees Fahrenheit over a 24 hour period unrelieved by medications.

Will I have any long-term limitations due to Gamma Knife radiosurgery?

Usually, patients do not have any long-term limitations as a result of Gamma Knife radiosurgery. Some possibility of long-term limitations may exist as a result of the underlying condition treated. Please ask your doctor about your own situation.