RAYS OF LIFE
The upgraded Gamma Knife
allows surgeons to treat otherwise inoperable tumors and a range
of neurological conditions without opening the skull.
by Paul Dingsdale
In the popular comic book and a 1970s television show "The Incredible Hulk," gamma radiation was not a good thing-turning mild-mannered Dr. David Banner into the large green monster of the title.
But now the mysterious gamma rays have an altogether more benevolent use.
In June 2000, the USC University Hospital unveiled a new state-of-the-art Gamma Knife-a device described as "the new gold standard of radiosurgery" by Michael Apuzzo, M.D., the Todd-Wells Professorship in Neurosurgery and director of the Gamma Unit Facility.
It sounds more like a "Star Wars" creation than a real medical device: a knife that does not cut but attacks brain tumors and other intercranial disorders with a focused burst of radiation while the patient is awake and under only a local anesthetic.
It is the Leksell Gamma Knife, Model C, manufactured by Elekta Instrument AB of Sweden. USC University Hospital is the only facility in California, and only the fifth in the world, to own the device, which uses radiation to destroy tumors and vascular malformations with pinpoint accuracy.
The 20-ton medical device provides surgeons with a non-invasive method to treat inoperable cerebral tumors, pituitary tumors and a range of neurological conditions. It is considered one of the most powerful advances in the fight against many difficult brain disorders and diseases.
The Gamma Knife is not really a knife at all. The "cutting" is done by 201 beams of gamma rays emanating from cobalt-60 sources located in a helmet-like structure placed around the patient's head. Through narrow holes in the 400-pound suspended secondary helmet-which looks a bit like a cross between a colander and an old-fashioned beauty salon hair dryer-these beams of radiation are focused precisely on the target. Though the rays pass through many cells, they are too weak to kill any except those in the exact area they pinpoint.
The coordinates to be the focus of the radiation beam are pinpointed by high-resolution images, including MRI and CT scans. While there are other ways to deliver radiation to the brain, the difference is that the Gamma Knife gives a more powerful dose to a more specific location.
The success of the device depends on the accuracy of the targeting system. If the wrong tissue is destroyed, the consequences could be disastrous. The head is held rigid in a metal frame that is applied (under local anesthetic) to the skull, and a computerized imaging system establishes coordinates for the tissue to be destroyed.
The treatment, known as radiosurgery, is painless and allows the patient to return to work the next day. The patient is given a local anesthetic and mild sedation for the procedure, which takes around two hours. A conventional brain operation takes several hours under general anesthetic followed by intensive care and a long convalescence. During radiosurgery the skull is never opened, so many of the possible complications of brain surgery, such as infection and hemorrhage, are avoided.
"The idea is to deliver a killing dose of radiation at one single time without injuring the surrounding tissue. This is at the frontier of technology for non-invasive treatments," says Apuzzo. "Only a few years ago, the outlook was bleak for many traditional patients with these conditions. Now these patients, and others for whom surgery is not an option, can be treated with this non-invasive procedure that involves little discomfort and minimum risk.
"The Gamma Knife can tackle tumors anywhere inside the head, whereas surgery can be too hazardous" in certain areas of the brain, he explains. "It really is a substantial advance." And, says Apuzzo, "It's the most doctor-friendly and patient-friendly device available."
He adds that the new device offers several advanced features that make it by far the most sophisticated unit on the market today.
"The Model C is equipped with a Robotic Automatic Positioning System and a software program that calculates a dose-optimized treatment plan," says Apuzzo. "The neurosurgeon maintains total control and can stop the process to refine treatment strategy at any point. But the Model C eliminates manual plan data entry, shortening treatment time and minimizing potential for human error."
The Model C also maximizes patient comfort, says Apuzzo. The design of previous Gamma Knife units frequently required that the patient lay face down for extended periods, which could prove uncomfortable. The new device allows patients to lie on their backs, in relative comfort.
Nevertheless, says Apuzzo, like many of the great technological advances of our day, the new Gamma Knife is only as good as the personnel operating it.
Since 1979, the stereotactic neurosurgery team at USC University
Hospital has been a national leader in stereotactic radiosurgery.
Led by Apuzzo and Zbigniew Petrovich, M.D., chair of the Department
of Radiation Oncology, with assistance from unit coordinator Dana
MacPherson, R.N., the USC team has pioneered the use of Gamma
Knife technology in the western U.S.