Gamma knife surgery is a technique in which multiple beams of gamma rays are focused on a section of the brain. Each beam of radiation is harmless on its own, but where the rays intersect, tissue is burned away. This technique can therefore reach tissue deep in the brain, without having to cut through the upper layers of the brain or even open the skull. Patients undergoing this bloodless surgery feel no discomfort and only need to stay in hospital for a day. However it can take a year or more for the effect of the procedure to become apparent.

The technique was first developed in the 1960s in Stockholm, Sweden, to treat tumours and some types of blood vessel malformation. Surgery using beams of radiation (radiosurgery) relies on having high-quality three-dimentional imaging available to be successful. As imaging methods, especially magnetic resonance imaging (MRI), improved, and the limitations of drug treatments for epilepsy became more apparent, gamma knife surgery was pioneered for the treatment of epilespy in Marseilles, France.

Promising new results for this technique were reported at the 131st Annual Meeting of the American Neurological Association (Abstract S-95) in Chicago. Dr Nicholas Barbaro from the University of California in San Francisco and Dr Mark Quigg from the University of Virginia in Charlottesville described small study of 30 patients with mesial temporal lobe epilepsy, one of the types of epilepsy most commonly not controllable with anti-epileptic drugs. All patients had a very clearly localisable seizure focus, and were selected to receive either low-dose or high-dose radiation gamma knife surgery to the affected areas of the temporal lobe.

At follow-up two years later, 67% of patients were in remission, having had no seizures in the previous six months. But there was a difference between the dose groups: 85% of patients in the high-dose range were in remission, compared with 56% in the low-dose group.

The study found that patients who became seizure-free showed an improvement in their quality of life. The authors were also interested in any changes in verbal memory (ability to remember and use words correctly) after surgery, as the temporal lobe is very important for processing language and speech. A previous large study had found 60% of patients showed a decrease in verbal memory after open surgery. In this study of gamma knife surgery, 42% of patients showed a decrease, but 25% showed an increase.

Previous studies of gamma knife surgery have not been encouraging. However they all used lower doses of gamma rays than were used in the high dose group in this study. The good outcomes in this group indicate that this dose might be better.

While this is an encouraging result, we must be careful about interpreting the results. Thirty patients is a very small number, and larger trials are needed to confirm the benefit of this technique. The results may also be due in part to the careful selection of patients with a very specific type of epilepsy. What about people with less clearly defined seizure focuses - will gamma knife surgery work as well for them? The authors hope that the prospect of a non-invasive surgical technique will encourage more patients with suitable types of surgery to opt for the operation.

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