August 2, 2001
The patient, a woman in her 50s, has a metal frame resembling scaffolding attached to her skull. As she lies on a table, the frame is secured to a helmet that resembles a huge, heavy kitchen colander. Then she is drawn head-first into a large white machine that resembles something out of a science fiction movie. The procedure doesn't seem like a lot of fun, but then it depends on what you compare it to.
For the patient, the alternative to this technologically sophisticated treatment at the New Orleans Regional Gamma Knife Center would be brain surgery to remove the tumor that has grown near the auditory canal of her ear. Instead, after an hour of virtually painless treatment, the frame will be removed and she will sleep off the light sedation before going home with her husband. If she wants, she can go back to work tomorrow.
The gamma knife is a machine that precisely focuses 201 beams of weak radiation on one tiny spot. It's non-invasive, making it ideal for patients for whom surgery would be too risky. The elderly, for example, are prime candidates for this treatment--the first patient treated in New Orleans was 98 years old.
"You can deliver a whole six-week course of radiation in one day. That's how strong it is," said John Walsh, professor of neurosurgery and medical director of the gamma knife center, which opened in March. "The dose is very high right where the beams converge," Walsh said. "But it falls off so steeply that three millimeters away you can't detect any changes in the tissue."
The real work of using the gamma knife happens before the patient is exposed to any radiation. After the frame is attached to the patient's head, an MRI is performed. Using a three-dimensional map generated from the MRI images, doctors carefully plot a series of radiation shots on a computer. It's time-consuming and painstaking work, because the area of treatment must be carefully shaped to fit the tumor.
In this case, the doctors must be sure to avoid the patient's auditory nerve, which could be damaged by the radiation. The gamma knife can be used to treat small brain tumors as well as Parkinson's disease and a handful of other disorders. It can also be used to control pain in patients with disseminated cancer. The machines are relatively scarce. There are approximately 60 of them in the United States.
Walsh, who had worked with gamma knives in Houston and at the University of Kentucky, had been lobbying for one in New Orleans since he arrived at Tulane four years ago. But the multi-million-dollar price tag was far too expensive. Eventually, New Orleans' gamma knife was purchased by a consortium of investors for the use of doctors at Tulane, Louisiana State University and Touro Hospital.
Located in a building in the Touro complex uptown, the machine is made of cast iron and weighs a hefty 18 tons. Deep inside is a capsule of cobalt 60 radioisotopes. Although it occupies a space once occupied by a bank vault, extra pilings had to be driven into the floor to support its weight.
The gamma knife opened in conjunction with a PET (positive emission tomography) scanner, a whole-body imaging system that can show doctors things that an MRI cannot. The PET also is available for research work, said Walsh.
Tulane University, New Orleans, LA 70118 504-865-5000 firstname.lastname@example.org