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Gamma Knife radiosurgeryBy Mayo Clinic staff
Original Article: http://www.mayoclinic.com/health/gamma-knife-radiosurgery/MY00206
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 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. In some cases, Gamma Knife radiosurgery may have 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 and may die, and the tumor may gradually shrink.
Arteriovenous malformation (AVM). AVMs are abnormal tangles of arteries and veins in your brain. In an AVM, blood flows from your arteries to veins, bypassing smaller blood vessels (capillaries). AVMs may disrupt the normal flow of blood and lead to bleeding.
Radiosurgery destroys the AVM and causes the blood vessels to close off over time.
Trigeminal neuralgia. Trigeminal neuralgia is a disorder of one or both of the trigeminal nerves, which relay sensory information between your brain and areas of your forehead, cheek and lower jaw. This nerve disorder causes disabling facial pain that feels like an electric shock.
After treatment, many people will experience pain relief within a few days to a few months.
Acoustic neuroma. An acoustic neuroma (vestibular schwannoma), is a noncancerous (benign) tumor that develops along the main balance and hearing nerve leading from your inner ear to your brain.
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 may stop the growth or minimize the size of an acoustic neuroma with little risk of permanent nerve damage.
Pituitary tumors. Tumors of the bean-sized gland at the base of the brain (pituitary gland), can cause a variety of problems. The pituitary gland controls hormones in your body that control various functions, such as your stress response, metabolism and sexual function.
Radiosurgery can be used to shrink the tumor and lessen the disruption of pituitary hormone regulation.
Gamma Knife radiosurgery doesn't involve surgical incisions, so it's generally less risky than traditional neurosurgery. In traditional neurosurgery, you may have risks of complications 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. Your doctor may prescribe anti-inflammatory medications (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. Some people temporarily lose a small amount of hair.
Rarely, people may experience late side effects, such as other brain or neurological problems, months after Gamma Knife radiosurgery.
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:
- Contact lenses
- Nail polish
- 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 radiosurgery 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 may include computerized tomography (CT scan) or magnetic resonance imaging (MRI). In a CT scan, a series of X-rays create a detailed image of your brain. In an MRI scan, a magnetic field and radio waves create detailed images of your brain.
Doctors may inject a dye into a blood vessel to view the blood vessels in your brain and highlight blood circulation. In some cases, you may have an MRI and CT scan.
Arteriovenous malformations (AVMs). Imaging for brain AVMs may include CT scans, MRI scans, cerebral angiograms or some combination of these tests.
In a cerebral angiogram, a doctor inserts a small tube in a blood vessel in your groin and threads it to the brain using X-ray imaging. A doctor injects dye through the blood vessels to make them visible on X-rays. Your doctor may inject a dye into a blood vessel during CT or MRI scans to view the blood vessels and highlight blood circulation.
Trigeminal neuralgia. An MRI or CT scan 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 areas to treat, dosages of radiation and how to focus the radiation beams to treat the areas. 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 usually 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 procedure may take 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 headache, nausea or vomiting after the procedure, you'll receive appropriate medications.
- You'll be able to eat and drink after the procedure.
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, but the main goal of Gamma Knife radiosurgery for benign tumors is to prevent any future tumor growth.
- Malignant tumors. Cancerous (malignant) tumors may shrink more rapidly, often within a few months.
- Arteriovenous malformations (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.
- Stereotactic radiosurgery overview. International RadioSurgery Association. http://www.irsa.org/radiosurgery.html. Accessed March 18, 2013.
- Gamma Knife surgery. International RadioSurgery Association. http://www.irsa.org/gamma_knife.html. Accessed March 18, 2013.
- Stereotactic radiosurgery. American Association of Neurological Surgeons. http://www.aans.org/Patient%20Information/Conditions%20and%20Treatments/Stereotactic%20Radiosurgery.aspx. Accessed March 18, 2013.
- Chen CC, et al. Stereotactic cranial radiosurgery. http://www.uptodate.com/home. Accessed March 18, 2013.
- Stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT). Radiological Society of North America. http://www.radiologyinfo.org/en/info.cfm?PG=stereotactic. Accessed March 18, 2013.
- Arteriovenous malformations and other vascular malformations of the central nervous system fact sheet. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/avms/detail_avms.htm. Accessed March 18, 2013.
- NINDS trigeminal neuralgia information page. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/trigeminal_neuralgia/trigeminal_neuralgia.htm. Accessed March 18, 2013.
- Vestibular schwannoma (acoustic neuroma) and neurofibromatosis. National Institute on Deafness and Other Communication Disorders. http://www.nidcd.nih.gov/health/hearing/pages/acoustic_neuroma.aspx. Accessed March 19, 2013.
- Gamma Knife. Radiological Society of North America. http://www.radiologyinfo.org/en/info.cfm?pg=gamma_knife. Accessed March 19, 2013.
- NINDS pituitary tumors information page. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/pituitary_tumors/pituitary_tumors.htm. Accessed March 19, 2013.
- Kavanagh B, et al. Complications of cranial stereotactic radiosurgery. http://www.uptodate.com/home. Accessed March 18, 2013.
- A typical treatment day. International RadioSurgery Association. http://www.irsa.org/treatment.html. Accessed March 19, 2013.
- Neurological diagnostic tests and procedures. National Institute of Neurological Disorders and Stroke. http://www.ninds.nih.gov/disorders/misc/diagnostic_tests.htm. Accessed March 19, 2013.
- Link MJ (expert opinion). Mayo Clinic, Rochester, Minn. April 15, 2013.