10/31/97
CONTACT: Tim Stephens, (650) 725-8047 or 723-6911; e-mail [email protected]
FOR PATIENTS WITH BRAIN TUMORS, RADIATION TECHNIQUE OFFERS ALTERNATIVE TO SURGERY
STANFORD -- There is certainly no good place to get a brain tumor, but one of the worst is in the lower portion of the brain along the base of the skull. Skull-base tumors are often intimately entwined with critical arteries and cranial nerves that emerge from the base of the brain, making surgical removal challenging and risky.
Now, neurosurgeons at the Stanford University School of Medicine have shown that they can cure a relatively common type of brain tumor, called a meningioma, without performing open surgery in this extremely vulnerable area.
In a paper published in the November issue of the journal Neurosurgery, the researchers report that stereotactic radiosurgery -- which kills tumor cells with a carefully targeted, highly focused blast of radiation -- can effectively treat skull-base meningiomas without the risks of conventional surgery.
"The results appear to be excellent in terms of tumor control and resolution of symptoms, with a minimum of morbidity and complications," said the study's lead author, Dr. Steven Chang, a neurosurgery resident at Stanford.
In their journal paper, Chang and Dr. John Adler, an associate professor of neurosurgery, review the outcomes of 55 patients who underwent stereotactic radiosurgery for the treatment of skull-base meningiomas at Stanford between 1989 and 1996. This is the largest group of such patients to be described in a published report.
Meningiomas are tumors, usually benign, that arise from the membranes covering the brain. They can cause seizures and a variety of other neurologic symptoms by putting pressure on adjacent brain structures and by irritating the surrounding brain tissue.
In many cases, meningiomas are located on the surface of the brain and are easily removed through surgery. For meningiomas along the skull base, however, surgery poses the risk of damaging cranial nerves or arteries carrying blood to the brain. A nerve injury could cause facial paralysis, facial numbness or loss of eye movements, while damage to an artery could cause a major, life-threatening stroke.
In studies previously published by others, complete surgical removal of skull-base meningiomas damaged patients' cranial nerves in as many as 30 percent of the cases. While some surgeons continue to advocate complete resection, others now choose to avoid the risks by leaving some of the tumor behind.
"We get a lot of patients who have undergone surgery for skull-base meningiomas and whose surgeons were able to resect [remove] 50 to 90 percent of the tumor but were unwilling to go for a complete resection for fear of jeopardizing the nerves and arteries," Chang said.
In those cases, radiosurgery can be used to treat the remaining tumor and eliminate the possibility that it will grow back, he said. For patients with small meningiomas (less than 3 centimeters in diameter), radiosurgery can be used as the initial treatment, avoiding the surgical procedure altogether.
Radiosurgery differs from conventional "fractionated" radiation therapy in the size of the area treated and in the intensity of the radiation dose. Radiosurgery takes advantage of advanced imaging techniques to locate the tumor and uses computerized targeting to focus a single large dose of radiation entirely on the tumor.
Conventional radiotherapy, in contrast, would involve a series of much smaller doses of radiation applied to a wider region. A larger field of coverage is necessary with the conventional technique because of the lower accuracy of radiation delivery. The total radiation dose is delivered in small fractions separated by 24-hour periods to allow normal tissues adjacent to the tumor to recover between treatments.
"With radiosurgery, because you're treating just the tumor, with minimal radiation to the adjacent structures, you're able to deliver a single high dose of radiation," Chang said.
Cranial nerves near the tumor often receive some of the radiation dose, but they tend to resist the effects of radiation, Chang said. He and Adler report that 12 of the patients in their study experienced transient cranial-nerve deficits, such as numbness in the face, which went away within six months after treatment. Only two of the 55 patients suffered permanent damage to cranial nerves.
The Stanford neurosurgeons used a technique called LINAC radiosurgery, in which radiation is generated by a linear accelerator that rotates around the patient's head, delivering the radiation dose in a series of precisely computed arcs converging on the target. A linear accelerator is typically used for radiation therapy to treat tumors throughout the body, but can be modified for neurosurgical applications.
An alternative radiosurgery device, called the gamma knife, uses radioactive cobalt as the radiation source and is designed for use as a dedicated neurosurgical tool. A gamma knife, however, can cost as much as $7 million, whereas a linear accelerator can be adapted for neurosurgical use for under $500,000, Chang said. He estimates that the gamma knife is available at around 50 to 60 medical centers in the United States, while there are probably about 100 U.S. centers that can perform LINAC radiosurgery.
###
RSS