The Gamma Knife targets a cancer tumor with hundreds of invisible rays of radiation. The machine may also be useful against epilepsy.

On the cutting edge

New technology focuses radiation rays on cancer without need for invasive surgery

Web posted July 9, 1998

By Tom Corwin
Staff Writer

The tiny holes that line the helmet are actually bombsights, guiding invisible rays of radiation that pass harmlessly through the brain until all 201 beams intersect on the tumor and deliver a devastating dose.

It is brain surgery without opening the skull, brain surgery in which the patient is up and on the way home hours later. The machine that performs this remarkable procedure is called a gamma knife, and the Medical College of Georgia is going to be the second hospital in Georgia to get one. Only about 38 centers in the country have the nearly $3 million machine, which can be used to treat not only tumors but epileptic seizures, chronic pain, malformed blood vessels and other problems inside the skull, said neurosurgeon Joseph Smith, director of stereotactic and functional neurosurgery at MCG.

For centers seeing a large number of these patients, ``this is really essential to a comprehensive treatment program,'' Dr. Smith said.

The machine works by delivering small beams of radiation from a constant cobalt 60 source through 201 ports in a helmet worn by the patient into one carefully targeted area in the head. Those numerous pathways are the advantage over standard radiation therapy, said W. Chris Sheils, chief of radiation oncology at MCG.

Gamma Knife

VIDEO

•Gamma Knife Surgery

ON THE WEB

•Dr. Duma's Proceedure •Univ. of Alabama •Elekta Inc. Homepage •Elekta Gamma Knife

``What it does is allow you to deliver a high dose to a smaller area,'' Dr. Sheils said.

Traditional radiation therapy uses a limited number of ports, and larger doses of radiation pass through the surrounding tissue, Dr. Smith said.

``If for instance you use three ports, that means all the tissue from the surface to the tumor in each of those ports will receive a third of the (radiation),'' Dr. Smith said. ``In the case of the gamma knife, where you have 201 sources, then along each pathway from the cobalt source down to the tumor, it's only receiving roughly 1/200th of the dose; and (the brain tissue) can readily tolerate that; and it allows you to deliver a higher dose.''

And because a smaller, more focused area is receiving the full dose in a single sitting, it should cut down on the typical side effects of nausea, headaches and hair loss, Dr. Sheils said.

Between 5 percent and 10 percent of the patients now seen in neurosurgery would be candidates for the gamma knife, and it will not be a replacement for those whose tumors can more easily be treated by traditional surgery and radiation therapy, Dr. Smith said. But for tumors in hard to reach places or near areas where surgeons fear to cut, and for patients who might not be able to withstand an operation, the gamma knife should prove ideal, Dr. Smith said.

The machine should also prove useful for some epilepsies and pain surgery, Dr. Smith said. The machine's manufacturer, Elekta, has agreed to provide $240,000 for a three-year program to treat some epilepsies with the device, Dr. Smith said.

With temporal lobe epilepsy, for instance, the area causing the seizures often shows up on MRI and other imaging scans as a shrunken area on the lobe. In the past, surgery required opening the skull and carefully removing the area.

``It's a major open operation with all the potential risks that go along with that,'' Dr. Smith said. With the gamma knife, there is no need to open the skull, he said. And that can be a major advantage for the patient, and the insurance company, because most of the gamma knife procedures will likely be done on an outpatient basis, Dr. Smith said.

``There's no question it saves money,'' Dr. Smith said. ``In our own institution, the surgical costs alone will be cut in half, not to mention the bypassing of the inpatient bills. That's usually the bulk of the expense.''

The thought of drive-through brain surgery may seem chilling, but because it takes weeks and months for the radiation to stunt cell growth and shrink the tumor, there is little immediate effect. So there is actually no danger in releasing the patient, Dr. Smith said.

Though the procedure has only recently been approved by the State Health Planning Agency, it can take 12 to 18 months to build and deliver the devices, Dr. Smith said. Although there is a chance MCG can get one set to be ready in November, it would be early next year before any patients could go under the gamma knife, and it may take almost a year.

``I would be very happy if we got started by the summer of 1999,'' Dr. Smith said.