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Gamma-knife radiosurgery
By Mayo Clinic staffOriginal Article: http://www.mayoclinic.com/health/gamma-knife-radiosurgery/MY00206
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Definition
Gamma-knife radiosurgery is a type of radiation therapy used to treat tumors and other abnormalities in the brain.
In gamma-knife radiosurgery, specialized equipment focuses as many as close to 200 tiny beams of radiation on a tumor or other target. Although each beam has very little effect on the brain tissue it passes through, a strong dose of radiation is delivered to the site where all the beams meet.
The precision of gamma-knife radiosurgery results in minimal damage to healthy tissues surrounding the target and, in some cases, a lower risk of side effects compared with other types of radiation therapy. Also, gamma-knife radiosurgery is often a safer option than is traditional brain surgery.
Gamma-knife radiosurgery is usually a one-time therapy completed in a single day.
Why it's done
Gamma-knife radiosurgery is often an appropriate alternative to standard brain surgery (neurosurgery), which requires incisions in the skull, membranes surrounding the brain and brain tissue. This type of radiation treatment is usually performed when:
- A tumor or other abnormality in the brain is too hard to reach with standard neurosurgery
- A person isn't healthy enough to undergo standard surgery
- A person prefers a less invasive treatment
Gamma-knife radiosurgery is most commonly used to treat the following conditions:
- Brain tumor. Radiosurgery is useful in the management of small noncancerous (benign) and cancerous (malignant) brain tumors. Radiosurgery damages the genetic material (DNA) in the tumor's cells. The cells lose their ability to reproduce, the cells die in some cases, and the tumor may gradually shrink.
- Arteriovenous malformation (AVM). AVMs are abnormal collections of arteries and veins that connect directly, instead of through a network of capillaries. These abnormalities disrupt the normal flow of blood and are prone to bleeding. Some people with brain AVMs develop signs and symptoms such as headaches or seizures. Radiosurgery causes the blood vessels to thicken and close off.
- Trigeminal neuralgia. Trigeminal neuralgia is a disorder of one or both of the trigeminal nerves, which originate at the base of the brain and control sensations of the forehead, cheek and lower jaw. This nerve disorder causes disabling facial pain that feels like an electric shock. After radiation treatment, a lesion gradually forms in the nerve and blocks the transmission of pain signals along the nerve.
- Acoustic neuroma. An acoustic neuroma, or vestibular schwannoma, is usually a benign tumor that develops along the nerve affecting balance and hearing. When the tumor puts pressure on the nerve, a person can experience hearing loss, dizziness, loss of balance and ringing in the ear (tinnitus). As the tumor grows, it can also put pressure on the nerves affecting sensations and muscle movement in the face. Radiosurgery can reduce the size or limit the growth of an acoustic neuroma with little risk of permanent nerve damage.
- Pituitary tumors. Tumors of the bean-sized "master gland" at the base of the brain can cause a variety of problems, because the pituitary helps regulate the thyroid, adrenal and reproductive glands. Radiosurgery can be used to shrink the tumor and lessen the disruption of pituitary hormone regulation.
Risks
Gamma-knife radiosurgery doesn't involve surgical incisions, so it's generally less risky than traditional neurosurgery — where you can have problems with anesthesia, bleeding and infection.
Early complications or side effects are usually temporary. They may include:
- Fatigue. Tiredness and fatigue may occur for the first few weeks after gamma-knife radiosurgery.
- Swelling. Swelling in the brain at or near the treatment site can cause symptoms such as headache, nausea and vomiting. A doctor may prescribe corticosteroid medications to prevent such problems or to treat symptoms if they appear.
- Scalp and hair problems. Your scalp may be red, irritated or sensitive at sites where a device is attached to your head during the treatment. Rarely, people experience temporary hair loss.
How you prepare
Food and medications
- Don't eat or drink anything after midnight the night before the procedure.
- Talk to your doctor about whether you can take your regular medications the night before or morning of the procedure.
Clothing and personal items
Wear comfortable, loosefitting clothing.
Avoid wearing the following items during the procedure:
- Jewelry
- Eyeglasses
- Contact lenses
- Makeup
- Nail polish
- Dentures
- Wigs or hairpieces
Precautions regarding medications and allergies
Tell your doctor if you:
- Are taking pills or injections to control diabetes
- Are allergic to shellfish or iodine, which are chemically related to special dyes that may be used during the procedure
- Have implanted medical devices in your body, such as a pacemaker, artificial heart valve, aneurysm clips, neurostimulators or stents
What you can expect
Gamma-knife surgery is usually an outpatient procedure, but the entire process will take most of a day. You may be advised to have a family member or friend who can be with you during the day and who can take you home. In some cases, an overnight stay in the hospital may be necessary.
You'll have an intravenous (IV) line, a tube that delivers fluids to your bloodstream to keep you hydrated during the day. A needle at the end of the IV is placed in a vein, most likely in your arm.
Before the procedure
Before the procedure begins, you'll have a lightweight frame attached to your head with four pins. This frame will stabilize your head during the radiation treatment and serve as a point of reference for focusing the beams of radiation. During this process:
- None of your hair will be shaved
- You'll receive numbing shots in the four places on your scalp where the pins will be inserted — two points on your forehead and two at the back of your head
After the head frame is attached, you'll undergo imaging scans of your brain that show the location of the tumor or other abnormality in relation to the head frame. The type of scan used depends on the condition being treated:
- Tumors. Imaging for tumors is done with computerized tomography (CT), a specialized X-ray that creates cross-sectional images of the brain, or magnetic resonance imaging (MRI), which uses a magnetic field and radio waves to create cross-sectional or 3-D images of the brain. In some cases, both imaging methods are used. You may receive an injection of a special dye (contrast agent) that enhances the brain tumor image.
- AVMs. Imaging for brain AVMs may include CT scans, MRI scans, cerebral angiograms, or some combination of these tests. A cerebral angiogram is an X-ray with a contrast agent. A small tube (catheter) is inserted into a blood vessel in your groin and threaded to the brain to deliver the contrast agent. A contrast agent for CT or MRI scans of AVMs is usually injected into a vein.
- Trigeminal neuralgia. MRI is used to create images of nerve fibers to select a target area for treating trigeminal neuralgia.
The results of the brain scans are fed into a computerized planning system that enables the radiosurgery team to plan the appropriate dosages of radiation and the configuration of radiation beams. This planning process may take an hour or two. During that time, you can relax in another room, but the frame must remain attached to your head.
Children are often anesthetized for the imaging tests and during the radiosurgery. Adults are typically awake, but you may be given a mild sedative to help you relax.
During the procedure
You'll lie on a bed that slides into the gamma-knife machine, and your head frame will be attached securely to a helmet inside the machine. The duration of the treatment can range from less than an hour to about four hours, depending on the size and shape of the target. During the procedure:
- You won't feel the radiation
- You won't hear any noise from the machine
- You'll be able to talk with the doctors via a microphone
After the procedure
After the procedure, you can expect the following:
- The head frame will be removed.
- You may have minor bleeding or tenderness at the pin sites.
- If you experience a headache, nausea or vomiting right after the procedure, you'll receive appropriate medications.
- You'll be able to eat and drink after the procedure.
Results
The treatment effect of gamma-knife radiosurgery occurs gradually, depending on the condition being treated:
- Benign tumors. Gamma-knife radiosurgery results in the failure of tumor cells to reproduce. The tumor may shrink over a period of 18 months to two years.
- Malignant tumors. Cancerous (malignant) tumors usually shrink more rapidly, often within a few months.
- AVMs. The radiation therapy causes the abnormal blood vessels of brain AVMs to thicken and close off. This process may take two years or more.
- Trigeminal neuralgia. Gamma-knife radiosurgery creates a lesion that blocks transmission of pain signals along the trigeminal nerve. Pain relief may take several months.
You'll receive instruction on appropriate follow-up exams to monitor your progress.
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- Trigeminal neuralgia fact sheet. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/trigeminal_neuralgia/detail_trigeminal_neuralgia.htm. Accessed Aug. 3, 2010.
- Vestibular schwannoma (acoustic neuroma) and neurofibromatosis. National Institute on Deafness and Other Communication Disorders. http://www.nidcd.nih.gov/health/hearing/acoustic_neuroma.html. Accessed Aug. 4, 2010.
- NINDS pituitary tumors information page. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/pituitary_tumors/pituitary_tumors.htm. Accessed Aug. 4, 2010.
- Kavanagh G, et al. Complications of cranial stereotactic radiosurgery. http://www.uptodate.com/home/index.html. Accessed Aug. 4, 2010.
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