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Operating on the brain is always a delicate proposition. If a tumor or other abnormality is buried deep within the brain, neurosurgeons can sometimes damage healthy brain tissue as they make their way to the tissue to be removed.
In radiosurgery, no incisions are necessary. Doctors use the latest imaging technology to identify abnormal areas 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 damage 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.
The procedure, also referred to as stereotactic 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 neurologic 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 patients or for patients 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 lower risk of deafness or loss of facial movement, compared with conventional surgery.
- 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 controls 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.
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. You will not be allowed to wear jewelry, eyeglasses, contact lenses, makeup, nail polish, dentures or wigs during the procedure. Your doctor may give you a special shampoo to use before treatment.
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
In contrast to standard radiation therapy, which is given daily for several weeks at a time, 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. There are three main types of radiosurgery.
The gamma-knife machine was the first instrument developed for radiosurgery. The instrument precisely focuses 201 beams of gamma radiation on a precisely located area, each beam originating from a slightly different point.
Before the procedure, a box-shaped frame is attached to your head with four pins. This frame stays in place throughout the treatment. 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. The head frame is actually the key to the precision of the gamma-knife machine.
Once the frame is attached to your head, imaging scans — such as magnetic resonance imaging (MRI), computerized tomography (CT) or conventional X-rays of brain circulation taken after injection of a substance that makes the blood vessels show up (cerebral angiography) — are performed. The results are fed into the gamma knife's 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.
When it's time for the treatment, you recline on a pallet that slides into the gamma-knife machine. Your head frame is attached securely to a helmet inside the machine. Treatment times vary, depending on the size and number of targets. This procedure works best for targets less than 4 centimeters in size.
Linear accelerator (linac)
A linear accelerator produces high-energy X-rays. Linac machines are used in standard radiation therapy to treat cancer, but the machines can be modified for use in stereotactic radiosurgery. Linacs designed for radiosurgery are marketed under many trade names, including Clinac, CyberKnife, Peacock, Shaped Beam Surgery and X-Knife.
During treatment, a moveable arm, called a gantry, will rotate around you to deliver precisely targeted radiation beams from many different directions.
Some linacs have incorporated real-time imaging systems so that you don't have to wear a head frame. This procedure can also be used for tumors in other parts of your body, such as the lungs and liver, although special measures must be taken during targeting to allow for the movement of internal organs caused by your breathing.
The type of radiation used in proton beam radiosurgery has properties very different from the radiation used by gamma-knife and linac machines. Proton beams deliver almost all their radiation at a set distance from the radiation source, rather than gradually releasing the energy as the beam travels. This difference eliminates the need for multiple beams or many different directions.
When proton beam radiosurgery is used on targets within the brain, you will need to wear a head frame to improve precision. Metallic beads may be inserted under your skin to help the computer triangulate tumor volume. Some facilities use a couch that rotates you around the proton beam so that the tumor can be approached from several different angles.
Proton beam radiosurgery can also be used on targets in other places of the body, including the prostate gland. However, the process of creating and targeting proton beams is complex, and it requires a synchrocyclotron — a costly, highly specialized particle accelerator — on-site to generate the protons. Less than a dozen facilities worldwide offer proton beam radiosurgery, and most of them are outside the United States.
Before the head frame is attached, you will receive numbing shots in the four places on your scalp where the pins will be inserted. None of your hair will be shaved. When the frame is removed, those spots may be a little tender, but they typically don't scar. You may have a headache or feel nauseated for a few hours after the procedure.
The treatment itself is painless. While children are often anesthetized for the procedure, adults are typically awake. You may be given a mild sedative to help you relax.
Radiosurgery doesn't have immediate results. Weeks, months or even years may pass before the effects of the treatment become apparent. Progress is monitored through follow-up imaging studies.
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, 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 patients may need steroid medications to control persistent brain swelling.
In the past, radiosurgery could only be used on the brain, and a head frame was always necessary to keep the target perfectly still. Improved targeting techniques, already in use in some hospitals, reduce the need for head frames, allowing the procedure to be used in other parts of the body.
For example, lung tumors can be treated — despite the movements associated with breathing — by using a radiosurgery machine linked with a real-time imaging system. A gold marker inserted into the airway moves as the person breathes. The radiosurgery machine uses the marker as a reference point and can automatically stop and start radiation delivery to synchronize with breathing movements.
Future advances in targeting technology will make radiosurgery an option for more people — bringing hope to those who are poor candidates for more traditional forms of treatment.