FEL reaches brain tumors
too risky for traditional surgery
The prognosis is good that within 18 months Vanderbilt neurosurgeons
could use the University's 
free-electron laser
to remove tiny brain tumors near vital nerves and arteries too risky to
pursue with conventional medical lasers or by traditional brain surgery.
Lasers have been used for nearly three decades in some forms of surgery,
but their use in neurosurgery has been limited. A lack of control and the
likelihood of damage to areas surrounding diseased tissue have caused fewer
than 20 percent of neurosurgeons to adopt it as a surgical tool.
Most laser surgery is now performed using either the CO2 or YAG laser.
Unlike either of these, the FEL can be precisely tuned to destroy even very
small tumors while leaving surrounding tissue virtually undamaged, says
neurosurgeon Michael Copeland, who joined scientists at the FEL Center
in 1993 while still a resident at Vanderbilt University Medical Center.
The laser's tunability has important implications for deep-seated infiltrating
tumors previously considered inoperable. Currently, surgeons are restricted
to lasing whatever is in the beam path. The FEL, however, can be tuned to
such a wavelength that minimizes the heat generated and, thus, the collateral
injury to normal tissue.
"Three to 5 millimeters of dead tissue around a laser incision can
make a huge difference in neurosurgery," says Copeland, an assistant
professor in the Department of Neurological Surgery who also has a Ph.D.
in neuroanatomy.
Researchers also believe the FEL will allow them to excise hard-to-reach
tumors without significant damage. "Near the optic nerve or motor regions
of the brain, that amount of collateral damage could lead to blindness
or paralysis.
"If we have to pass through normal tissue to approach a deep-seated
tumor, we can minimize the injury to normal tissue on the way in. It also
will allow us to remove a tumor growing off of a nerve coming off of the
brain stem. You should be able to dissect off that tumor while inflicting
minimal injury to the nerve."
At its inception a decade ago, the Vanderbilt FEL, one of only four university-based
FELs in the United States and the most powerful in the world, was intended
to be both a research laser and a medical tool.
"We have demonstrated that the free-electron laser is not just better
than other lasers, it has the best possible characteristics for neural tissue,"
says Copeland, who hopes experiments this fall will lead to approval for
human surgery by Vanderbilt's Institutional Review Board and the Food and
Drug Administration.
Two spacious, state-of-the-art surgical suites and a treatment room on
the FEL Center's fourth floor await patients. Adjoining the surgical suites
and treatment room is the laser contingency room, which houses an optical
system to distribute the infrared FEL beam and other conventional medical
lasers.
In addition to its ability to be tuned to a specific wavelength, the free-electron
laser can also be adjusted to the appropriate power level and pulse sequences,
which are unique features of the FEL, says Copeland, who is principal investigator
for a series of studies on the laser's applications in neurosurgery and
that department's FEL liaison.
A seminal event in 1994 at the FEL Center led to optimizing the laser for
neurosurgery. A Vanderbilt team of physicists and physicians discovered
how to put the laser's tunability to use by developing a new way of destroying
surplus tissue. In the past, researchers ablated tissue with short blasts
from infrared lasers at a wavelength of 3 microns (three-thousandths of
a millimeter). At this wavelength, water molecules in tissue are heated
and vaporized, causing a mini-explosion. However, the heat and explosion
cause damage to the adjacent tissue.
The team, led by biophysicist Glenn Edwards, tried a wavelength of infrared
light at about 6.4 microns, which caused the proteins that make up tissue
to melt. At the same time, water molecules were warmed by absorbing the
radiation, but not by the same route as at 3 microns. By melting protein
in the target at the same time as it vaporizes the water, the laser causes
a gentler explosion - one with very little collateral damage.
Copeland's interest in precision neurosurgery led him to the work of Vanderbilt
cell biologists Jim McKanna and Vivien Casagrande. The two researchers,
also using the FEL, had been investigating how damaged brain cells recover.
"Along those lines, I began to think about how to judge brain injury,
which is in no way precise. I wondered if we couldn't come up with a microscopic
scale for brain injury," he says.
McKanna and Casagrande examine the response of glial cells to damage in
the form of laser cuts in rat brains. Glial cells provide nutritive support
to nerve cells and their circuits and they outnumber neurons 10 to 1. The
researchers are using cell response data to determine which laser parameters
might prove of most use in human neurosurgery.
Copeland also was summarizing his progress in tissue ablation and his work
began to fit into a larger pattern [Edwards' tissue ablation research].
"In essence, we crunched all the numbers and it worked. The longer
wavelength works wonderfully with neural tissue, which has shown the greatest
agreement with a predicted pattern," he says.
The synergy at Vanderbilt's FEL Center points to its continued and future
success. "There are some spectacular researchers here-the physicists,
biophysicists, biologists -and the facilities you can't downplay either,"
says Copeland.
"At the international FEL conferences, everyone is waiting for Vanderbilt
to show researchers worldwide the success of the free-electron laser as
a surgical tool. And we are very nearly there."
-Brenda Ellis
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This document created November 18, 1996