Stereotactic radiosurgery is the use of a precise beam of radiation to destroy tissue in the brain.
This procedure is used to treat brain tumors, arteriovenous malformations in the brain, and in some cases, benign eye tumors or other disorders within the brain.
Stereotactic radiosurgery is used to treat a variety of disorders with widely differing demographic profiles.
"Radiosurgery" refers to the use of a high-energy beam of radiation. "Stereotactic" refers to the three-dimensional targeting system used to deliver the beam to the precise location desired. Stereotactic radiosurgery is primarily confined to the head and neck, because the patient must be kept completely still during the delivery of the radiation in order to prevent damage to surrounding tissue. The motion of the patient's head and neck are restricted by a stereotactic frame that holds them in place. It is difficult to immobilize other body regions in this way.
The high energy of the radiation beam disrupts the DNA of the targeted cells, killing them. Multiple weak beams are focused on the target area, delivering maximum energy to it while keeping surrounding tissue safe. Since the radiation passes through the skull to its target, there is no need to cut open the skull to perform the surgery. The beam can be focused on any structure in the brain, allowing access to tumors or malformed blood vessels that cannot be reached by open-skull surgery.
Two major forms of stereotactic radiosurgery are in use as of 2003. The Gamma Knife ® is a stationary machine that is most useful for small tumors, blood vessels, or similar targets. Because it does not move, it can deliver a small, highly localized and precise beam of radiation. Gamma knife treatment is done all at once in a single hospital stay. The second type of radiosurgery uses a movable linear accelerator-based machine that is preferred for larger tumors. This treatment is delivered in several small doses given over several weeks. Radiosurgery that is performed with divided doses is known as fractionated radiosurgery. The total dose of radiation is higher with a linear accelerator-based machine than with gamma knife treatment.
Disorders treated by stereotactic radiosurgery include:
A patient requiring radiosurgery has already been diagnosed with a specific disorder that affects the brain. As preparation for radiosurgery, he or she will undergo neuroimaging studies to determine the precise location of the target area in the brain. These studies may include CT scans , MRI scans, and others. Imaging of the blood vessels ( angiography ) or the brain's ventricles (ventriculography) may be done as well. These require the injection of either a harmless radioactive substance or a contrast dye.
Prior to the procedure, the patient will be fitted with a stereotactic frame or rigid mask to immobilize the head. This part of the treatment may be uncomfortable. The patient may receive a simulation scan to establish the precise relationship of the mask or frame to the head to help plan the treatment.
The patient may be given a sedative and an antinausea agent prior to the simulation scan or treatment.
Stereotactic radiosurgery does not produce some of the side effects commonly associated with radiation treatment, such as reddening of the skin or hair loss. Most patients can return to their usual daily activities following treatment without any special precautions.
The risks of stereotactic radiosurgery include mild headache, tiredness, nausea and vomiting, and recurrence of the tumor. Questions have been raised as to whether radiosurgery can cause secondary tumors, but as of 2003, there is little detailed information about this potential risk.
Stereotactic radiosurgery does not cause pain; and because the skull is not opened, there is no long hospital stay or risk of infection. Recovery is very rapid; most patients go home the same day they are treated, although follow-up imaging and retreatment may be necessary in some cases. This form of surgery appears to be quite successful in extending the length of survival in cancer patients; one study found that gamma knife radiosurgery controlled tumor growth in 96% of patients with kidney cancer that had spread to the brain, and added an average of 15 months to the patients' survival.
Stereotactic radiosurgery has a low reported rate of serious complications with minimal mortality. One German study reported a 4.8% rate of temporary morbidity in patients under treatment for brain tumors, with no permanent morbidity and no mortality. An American group of researchers found that less than 2% of patients who had eye tumors treated with radiosurgery suffered damage to the optic nerve from the dose of radiation.
Mild side effects following gamma knife radiosurgery are not uncommon, however. One group of British researchers found that 47 out of a group of 65 patients treated with gamma knife surgery had mild or moderate side effects within two weeks of treatment. Of these patients, more than half suffered headaches and a fifth reported unusual tiredness or nausea and vomiting.
With certain types of brain tumors, whole-brain radiation treatment (WBRT) is an option; however, it has a number of severe side effects. Surgical removal of the tumor is another option, but it carries a higher risk of tumor recurrence. For other tumors, gamma knife radiosurgery is the only treatment available as of 2003.
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International Radiosurgery Support Association (IRSA). 3005 Hoffman Street, Harrisburg, PA 17110. (717) 260-9808. http://www.irsa.org .
Johns Hopkins Radiosurgery. Weinberg 1469, 600 North Wolfe Street, Baltimore, MD 21287. (410) 614-2886. http://www.hopkinsmedicine.org/radiosurgery/treatmentoptions/stereotacticradiosurgery.cfm .
Richard Robinson
Stereotactic radiosurgery is performed by a radiosurgeon, who is a neurosurgeon with advanced training in the use of a gamma knife or linear accelerator-based machine. The radiosurgeon's dose plan is checked by a physicist before the treatment is administered to the patient. Stereotactic radiosurgery is done in a hospital that has the necessary specialized equipment.
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Tom Gregory
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