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Gamma-knife radiosurgery
By Mayo Clinic staffMayo Clinic Health Manager
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Definition
Gamma-knife radiosurgery treats a variety of structural abnormalities inside the brain by applying intersecting beams of radiation to the abnormal area. Gamma-knife radiosurgery is often a safer option than traditional neurosurgery because no incisions are involved.
In gamma-knife radiosurgery, doctors use advanced imaging technology to localize tumors and vascular abnormalities in the brain with pinpoint accuracy, so an array of radiation beams can be focused precisely on the target from many different directions.
Each individual radiation beam is too weak to harm the brain tissue it passes through. The effect of gamma-knife radiosurgery occurs only at the spot in the brain where all the beams meet. With the help of a computer, this spot can be accurately plotted to within a fraction of a millimeter.
Why it's done
Operating on the brain is always a delicate proposition. If a tumor or other abnormality is buried deep within the brain, traditional neurosurgery can sometimes damage healthy brain tissue as surgeons cut their way to the tissue to be removed. Because gamma-knife radiosurgery requires no incisions, it's less likely to damage healthy brain tissue.
Gamma-knife radiosurgery is most commonly used for:
- Brain tumors. Radiosurgery is useful in the management of both benign and malignant brain tumors, especially tumors originating elsewhere in the body that have metastasized to the brain. Radiosurgery often can treat tumors that may have been termed inoperable because of their location in hard-to-access areas of the brain.
- Arteriovenous malformations (AVMs). AVMs are abnormal collections of arteries and veins that connect directly, instead of through a network of capillaries. When located in the brain, these abnormalities can cause severe bleeding, headaches or seizures. While many AVMs can be removed with conventional microsurgery, radiosurgery may offer a much less invasive option with less risk of neurological injury.
- Trigeminal neuralgia. This nerve disorder causes disabling facial pain that feels like an electric shock. Radiosurgery can create a lesion on the nerve, blocking its pain signals. This procedure is typically reserved for older adults or for people with recurrent pain after other operations for trigeminal neuralgia.
- Acoustic neuromas. These noncancerous tumors, also called schwannomas, develop on the nerve that affects balance and hearing. Radiosurgery can effectively control the growth of small tumors in the majority of cases, with a low risk of deafness or loss of facial movement.
- Pituitary tumors. Tumors of the pea-sized "master gland," which is located deep within the brain, can cause a variety of problems because the pituitary helps regulate the thyroid, adrenal and reproductive glands. Radiosurgery may be employed to stop the growth of the tumor and halt the abnormal hormone secretion that can occur from these tumors.
Risks
Gamma-knife radiosurgery doesn't involve surgical incisions, so it's less risky than traditional neurosurgery — where you can have problems with anesthesia, bleeding and infection.
In some cases, gamma-knife radiosurgery can cause radiation injury to brain tissue surrounding the target. This can cause swelling, which may develop months after the procedure. In most cases, this swelling is temporary and resolves without treatment. Some people may need corticosteroid medications to control persistent brain swelling.
The risk of radiation injury increases with the amount of brain tissue receiving treatment. Gamma-knife radiosurgery, as a general rule, is best suited to target areas measuring no more than 3 centimeters (1.2 inches) at their widest points.
How you prepare
Don't eat or drink anything after midnight the night before the procedure. Ask your doctor if it's OK to take your regular medications with a sip of water.
Items not allowed during the procedure include:
- Jewelry
- Eyeglasses
- Contact lenses
- Makeup
- Nail polish
- Dentures
- Wigs
Be sure to tell your doctor if you:
- Are taking pills or injections to control diabetes
- Are allergic to shellfish or iodine
- Have implanted medical devices in your body — such as a pacemaker, artificial heart valve, aneurysm clips, neurostimulators or stents
What you can expect
Unlike standard radiation therapy, which is given daily for several weeks at a time, gamma-knife radiosurgery usually happens all in one day. Most of these procedures are done on an outpatient basis and don't require a stay in the hospital.
Before the procedure
Before the procedure begins, you'll need to have a lightweight frame attached to your head with four pins. 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
In addition to holding your head perfectly still, the head frame serves as a reference point in determining exactly where the beams of radiation should converge.
After the head frame is attached, you'll undergo imaging scans of your brain. The results are fed into a computerized planning system. This planning process may take several hours. During that time, you can relax in another room, but the head frame must remain attached to your head.
While children are often anesthetized for the procedure, adults are typically awake. 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 length of time the treatment will take can range from a few minutes to a few 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
Aftereffects of the procedure are rare but may include:
- Tender spots on your scalp where the frame was attached
- Headache
- Nausea
Results
Gamma-knife radiosurgery works by damaging the cells inside the target area so that they can't reproduce. Results aren't immediate. Weeks, months or even years may pass before the effects of the treatment become apparent. Progress is monitored through follow-up imaging studies.
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