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The Gamma Knife

Posted Jun 05 2009 5:07pm

Gamma Knife for the Treatment of Epilepsy.

I recently attended the 62nd Annual meeting of the Eastern Association of Electroencephalographers. One of the very interesting talks was given on the use of the gamma knife for the treatment of seizures. "Gamma knife", sounds futuristic, right? Well, this technology was actually developed by Lars Leksell (Sweden) in 1967. The technology is pretty expensive and not many centers have a unit. Canada currently has 3 gamma knives country-wide and the USA has about 90.

What is the Gamma Knife?
The gamma knife does not actually involve a knife. In fact, it is a non-invasive form of surgery insofar as there is no cutting or removal of skull. It is a form of “radiosurgery”. Radiosurgery is basically the use of radioactivity to kill tissue.

The gamma knife contains 201 radioactive cobalt sources. Cobalt gives off gamma rays, and these rays are focused toward a common, intersecting point. This point is called the “active zone”, where a very small lesion is created by the radiation (see picture).

How is the Gamma Knife Used in Epilepsy?
The gamma knife is normally used to treat vascular malformations in the brain, or to "blast" small tumors. The rationale for using it in epilepsy is to destroy a small group of cells that are thought to be causing the seizure activity. This means that the use of the gamma knife surgery is limited to focal seizures.

Advantages
- Discharged same/next day (no hospitalization required)
- Non invasive (no craniotomy – ie, opening of the skull)
- Can access the deep structures of the brain that are hard to reach surgically (each of the 201 ray beams is not damaging alone, but the aggregate of them in a single focus is. Therefore, you can pass rays through the skull, but it's only where they intersect that a lesion can be created - allowing deep structures to be lesioned without opening the skull)
- Effective against lesions in eloquent cortex

Disadvantages
- Often takes 2-30 months before the effects become apparent (the gamma rays don't immediate destroy the tissue. Rather, they seem to set-into-motion a series of events that lead to the tissue's death)
- Only effective at making small lesions
- Doesn’t give you a specimen (tissue sample) to study and analyze for pathology
- Can cause transient edema (swelling)

Possible Complications
Nausea 2-10%,
Seizures 2-8%
Edema (swelling) 2-8%
Development of tumors from radiation (this has happened, but very very rarely - about 3/200,000)

Conclusions
Irradiating the brain seems a bit scary, but the beams are very focused to the active zone and aren't thought to cause any harm to other brain/body areas. Of course, the alternative to gamma knife surgery is open brain surgery, which has its own risks and tends to make people very uncomfortable. That said, brain surgery remains the gold-standard for the removal of an "epileptic focus". This use of the gamma knife in the treatment of epilepsy is not well established and is only an option for patients with focal seizures that stand to be improved by destroying a small brain region.

It is "Family Day" here in Ontario - it's a new provincial holiday.
Happy Family Day everyone.

Kirk.

Photo credit: www.karmanos.org
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