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Analysis: Gamma Knife Zaps Epilepsy

Posted on: Tuesday, 5 December 2006, 18:02 CST

By ED SUSMAN

So-called Gamma Knife surgery -- focusing radiation to one point in the brain -- offers an alternative to open surgery for one of the most common forms of epilepsy.

We had a 67 percent overall success rate in giving patients freedom from seizures after two years following Gamma Knife surgery, said Mark Quigg, associate professor of neurology at the University of Virginia in Charlottesville.

Quigg recruited 30 patients diagnosed with mesial temporal lobe epilepsy, usually caused by abnormalities in the part of the brain known as the hippocampus. While the disabling seizures associated with mesial temporal lobe epilepsy are often resistant to anti-epileptic drugs, they can be abolished in most patients by surgical treatment.

Quigg acknowledged that the open-surgery treatment is successful, but open surgery has its risks, he said in presenting his pilot study as part of a highlights session at the first North American Regional Epilepsy Congress in San Diego, jointly sponsored by the American Epilepsy Society and organizations in Canada and Jamaica, which concluded Tuesday.

After imaging techniques determine the exact location of the anomaly in the brain, patients are fitted with a type of helmet that allows gamma radiation to be focused at that certain spot in the brain. The Gamma Knife radiation then eliminates the area causing the seizures.

Gamma Knife surgery, sometimes referred to as stereotactic radiosurgery, is a non-invasive method for treating brain disorders. The precision of the Gamma Knife makes it possible to administer a high radiation dose to the diseased area, minimizing the risk of damaging healthy tissue.

The radiation passes harmlessly through the skull to be delivered to a small and critically located point inside the skull. The risk of complications, as compared to open surgery, is less. Gamma Knife surgery can normally be performed in a day, and the convalescence time is extremely short.

In the study to determine the safety and efficacy of Gamma Knife surgery for epilepsy, Quigg divided his patients into two groups with varying levels of radiation. He assigned 13 patients to receive a high dose consisting of 24 Gray units of radiation; while the other 17 patients were assigned to receive the low dose of 20 Gray.

The patients receiving the low dose of radiation had about a 55 percent success rate of being seizure-free after two years, while those receiving the higher dose had about an 80 percent rate. Because of the small number of patients in the trial, the difference between the groups did not reach statistical significance, although it appears that the higher dose was more effective at two years, Quigg said.

He noted that, at each visit after the procedure, more of the patients were able to report being seizure-free. Patients were counted as seizure-free if no seizures occurred between the 18-month and 24-month visit. Overall, three patients dropped out of the study: One patient was non-complaint with the protocol; the other two were not effectively treated and underwent open surgery.

The patients in the study will continue to be followed for another year to determine long-term efficacy and if there are adverse side effects, Quigg said. The study is being funded by the National Institutes of Health and by Elekta AB of Stockholm, Sweden, manufacturer of the Gamma Knife.

The question that a patient and a doctor have to discuss is whether the open brain surgery which results in immediate freedom of seizures is a better option than non-surgical treatment with a delay in freedom of seizures, Quigg said.

He said the success rate he reported for the Gamma Knife appears to be similar to what is achieved in published literature for open surgery.

Source: United Press International

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