One autumn day in October 2014, Elliott Hermann of North Wilkesboro, NC, began having trouble with his balance. He also couldn't see properly out of his right eye and became confused. At the hospital he was diagnosed with an arteriovenous malformation—an abnormal tangle of arteries and veins in the brain—which had caused a brain bleed. During an operation to repair the bleeding, the surgeons discovered two meningiomas (tumors called meninges in the lining of the brain) near his brain stem that appeared to be growing and could cause problems. In September 2015, the tumors were removed by a technique known as stereotactic radiosurgery, which uses three-dimensional computerized imaging to deliver gamma rays precisely to a target.
This type of procedure, which doesn't involve a knife or incisions, is an alternative to traditional brain surgery and can treat tumors, vascular malformations, some forms of epilepsy, essential tremor, and other neurologic disorders.
Hermann, now 72 and a retired advertising photographer and community college teacher, had a second stereotactic radiosurgery—on an outpatient basis—in February 2023 to remove a third meningioma, which had been revealed on an MRI scan.
William Patrey, 75, a retired data processor in Boonsboro, MD, underwent stereotactic radiosurgery in 1997 for an acoustic neuroma, a tumor in nerves that lead to the inner ear, that was compromising his hearing and balance. He had a second stereotactic radiosurgery in April 2022 to treat trigeminal neuralgia, a chronic disorder that caused “pain like an electric shock to my face,” says Patrey. His doctor recommended the procedure after several different medications didn't relieve the sudden bouts of severe facial pain. The pain was eliminated by stereotactic radiosurgery.
When using this procedure for trigeminal neuralgia, doctors deliver a dose of radiation to the trigeminal nerve in a precise manner to injure the part of the nerve that causes the widespread pain, says Glen Stevens, DO, PhD, FAAN, section head of neuro-oncology at the Cleveland Clinic. A study in World Neurosurgery published in March 2023 found that 85 of 103 study participants with trigeminal neuralgia who were treated with stereotactic radiosurgery initially experienced a cessation of pain, and 60 participants remained pain-free after 10 years. In some cases, however, people may feel facial numbness after treatment, says Neil C. Porter, MD, assistant professor of neurology at the University of Maryland School of Medicine in Baltimore.
The concept behind stereotactic radiosurgery—whose brand names include Gamma Knife, CyberKnife, Edge, Novalis, and View Ray—originated in 1951 when Swedish researchers investigated combining proton beams with devices that could pinpoint targets inside the brain. The initial approach was abandoned because it was too complex and expensive. In 1967, the same researchers created the first device, which used cobalt-60 as its gamma radiation source, and called the procedure “stereotactic radiosurgery.” It was initially done on people with intractable pain and movement disorders. Over subsequent decades, the unit's design and applications have evolved.
“The theory behind stereotactic radiosurgery has remained unchanged since it was developed,” says Dr. Stevens. “It's a way of treating something in the brain without opening the cranium. It allows several radiation beams to converge on a single lesion to remove tissue from that area.”
Equipment Differences
For the procedure, the patient's head is immobilized by either a stereotactic frame or a thermoplastic mask. The patient is given mild sedatives to relieve any pain from the frame pressing into the skull. Despite the sedatives, Hermann says, the frame felt “like getting stung four times by a hornet.” Most people do not experience this level of discomfort; Hermann's pain subsided by the end of the day.
Once the frame is in place, doctors use imaging technology—such as computed tomography, MRI, or angiography—in conjunction with special computer-assisted instruments to get three-dimensional views of the targeted area and the surrounding brain structures and to focus the radiation beams. “The machine looks like a giant hair dryer at a salon,” says Lilyana Angelov, MD, a neurosurgeon and the director of the Gamma Knife Center at the Cleveland Clinic. The patient lies on a bed that slides into the machine. “It's silent, and patients can listen to music or whatever they want” during the procedure, says Dr. Angelov.
With the frameless approach to radiosurgery, a thermoplastic material is warmed and molded to the front and back of the patient's head to create a rigid mask that keeps the head still during treatment. “It looks like a hockey mask,” says Dr. Angelov. A small study published in the Journal of Medical Imaging and Radiation Sciences in 2020 compared the experiences of patients who had stereotactic radiosurgery using both the frame and the mask and found “overwhelming agreement that the mask was the preferred choice.” Another benefit: With the mask, the amount of radiation overall and per dose can be decreased, with treatment being delivered over several days, which reduces the risk of side effects, Dr. Stevens says.
Stereotactic radiosurgery allows a medical team to reach areas that it couldn't surgically or that would be very high risk, says Dr. Stevens. How long the procedure takes depends on the condition. “It can be as short as 15 minutes or as long as three hours,” Dr. Angelov says. “You don't need to fast beforehand, and after treatment patients can go home and proceed with the rest of their day,” she adds.
Eligibility for this type of surgery is determined by a patient's diagnosis, explains David Schiff, MD, FAAN, endowed professor of neurology, neurological surgery, and medicine at the University of Virginia in Charlottesville. It is good for a localized tumor that has sharp borders and is no larger than three centimeters in diameter but is not recommended for a tumor with lots of microscopic tentacles that infiltrate the surrounding brain tissue, because the tentacles create a risk for tumor regrowth, says Dr. Schiff.
“Stereotactic radiosurgery treats most metastases [cancer that has spread to the brain from another body part, such as a breast or lung] very effectively without requiring whole-brain radiation, which can lead to cognitive changes,” says Patrick Wen, MD, FAAN, director of the division of neuro-oncology at the Dana-Farber Cancer Institute and Brigham and Women's Hospital in Boston.
Treating Epilepsy
The technique may sometimes be appropriate for treating epilepsy. For people who have seizures due to a vascular malformation or tumor, treating the underlying condition with stereotactic radiosurgery may reduce the frequency of their seizures, says Paul A. Garcia, MD, professor of neurology at the University of California, San Francisco. If no identifiable condition is causing the seizures, he says, the benefits of the procedure are less clear.
For people who do undergo the procedure, the impact is not immediate, Dr. Garcia says. “Initially there is no change. A few months later, patients have more frequent but milder seizures. Then the seizures happen less often.”
In a study published in Epilepsia in 2018, researchers compared the effects of stereotactic radiosurgery and open surgery in people with drug-resistant mesial temporal lobe epilepsy, the most common form of focal epilepsy. They found that open surgery resulted in higher rates of seizure relief. Each procedure, however, had side effects. Those who underwent stereotactic radiosurgery had more swelling in the brain, headaches, and a temporary worsening of their seizures, says Dr. Garcia, one of the study authors. People who had open surgery had complications directly related to the surgery such as infections, bleeding, or deep vein thrombosis.
Swelling (edema) in the brain is “the main potential side effect” of stereotactic radiosurgery, says Dr. Schiff. Depending on where the swelling is, you could experience headache, nausea, cognitive changes, or sensory loss. Rarely, cranial nerves are temporarily or permanently damaged. Edema is treated with a short course of corticosteroids, which also helps with accompanying side effects, Dr. Stevens says.
“To some extent, the amount of radiation determines the extent of edema,” says Michael Sperling, MD, FAAN, endowed professor of neurology at the Sidney Kimmel Medical College at Thomas Jefferson University in Philadelphia. “To mitigate the risk, we try to use as low a dose of radiation as possible and still have it remain effective.”
Another concern is the potential for radiation necrosis, or irreversible damage to brain tissue. “We're giving a big dose of radiation with these approaches, so it could cause damage to the surrounding areas,” Dr. Wen says. This is another reason doctors use the lowest level of radiation possible, or break it up into multiple doses. When the radiation is spread out over multiple doses (typically over a period of days or weeks), the risk of side effects such as edema are lower than if the radiation is given in one big dose.
Physicians continue to fine-tune the amount and frequency of radiation doses for stereotactic radiosurgery and are trying to identify other conditions for which the procedure might work and how it could provide more lasting control of symptoms, says Dr. Angelov.
A study published in the Journal of Neurosurgery in 2018 involving 426 people with acoustic neuromas who were followed for at least two years found that the tumor was controlled—the size stayed the same or shrank, and no additional procedure or surgery was needed—in 98 percent of them. A small study in the April 2023 issue of Neurologia found that stereotactic radiosurgery significantly improved essential and parkinsonian tremors in nearly two-thirds of patients who had contraindications or declined more commonly recommended surgical treatments such as deep brain stimulation (DBS) surgery. Tremor and other movement disorders are more commonly treated with focused ultrasound, a similar process that uses sound waves instead of radiation, as an alternative to DBS or stereotactic radiosurgery.
“There's also interest in using radiosurgery for treating cluster headache, but the ideal target and treatment parameters remain unclear,” says Dr. Stevens. And some researchers are investigating whether it can be used to treat pain or mood disorders effectively, he adds.
Additional Questions About Stereotactic Radiosurgery
At what point are people eligible for this procedure?
It depends on their conditions. If they have trigeminal neuralgia, for example, they need to show that medication does not work, says Neil Porter, MD, assistant professor of neurology at the University of Maryland School of Medicine. With other conditions, timing will vary. If you have temporal lobe epilepsy that doesn't respond to medication, you may be a candidate if traditional surgery isn't safe because you have a bleeding disorder or other high-risk circumstances, says Paul A. Garcia, MD, professor of neurology at the University California, San Francisco.
What is the follow-up protocol?
Generally, it involves periodic visits to your neurologist—“commonly [every] three months for metastatic tumors and yearly for noncancerous tumors,” says David Schiff, MD, FAAN, endowed professor of neurology at the University of Virginia. The neurologist will assess how you're feeling and do follow-up imaging, such as MRI scans. With noncancerous conditions such as trigeminal neuralgia and acoustic neuroma, postprocedure appointments depend on symptoms that remain or recur or emerge after the treatment, but typically those appointments are annual.
What happens if the procedure doesn't work?
Before undergoing the procedure, talk to your team about possible alternative procedures if it doesn't work, advises Michael Sperling, MD, FAAN, endowed professor of neurology at Sidney Kimmel Medical College at Thomas Jefferson University in Philadelphia. Ask if the procedure could be repeated or whether other noninvasive or surgical procedures are an option if stereotactic radiosurgery doesn't sufficiently treat the condition.
