Modern Warfare
The New CyberKnife at USC/NORRIS Offers People with Otherwise Untreatable Tumors a New Weapon in the Fight Against Cancer.
When President Richard Nixon declared war on cancer in 1971, few people could
have guessed how apt the analogy would someday become. Today, many tools that
were once the sole purview of the military have been adapted for cancer 
treatment
and dedicated to fighting an altogether different kind of battle.
Physicians at the Keck School of Medicine of USC have added a
weapon derived from military technology to their arsenal to bring
the war home to cancers wherever they hide in the body. The tool
is called the CyberKnife®. This stereotactic radiosurgery
system uses a three-dimensional terrain mapping and localization
technology similar to one that guides U.S. military cruise missiles
to targets smaller than tennis courts more than 900 miles away.
Michael L.J. Apuzzo, M.D., professor of radiation oncology, biology
and physics and the Edwin M. Todd-Trent H. Wells Jr. Professor
of Neurological Surgery, describes the device as essentially
a radiation gun mounted on a finely tuned robotic arm. It allows
physicians to destroy tumors with beams of radiation so precisely
controlled that they stay on target even if the patient happens
to move during treatment.
Apuzzo says this device offers patients the potential for a safe,
noninvasive treatment of tumors anywhere in the body-a major
improvement over previous systems that were restricted to treating
tumors of the head. As a result, people with otherwise untreatable
tumors may suddenly have a new weapon to fight their disease.
Zbigniew Petrovich, M.D., chair of the Department of Radiation
Oncology and the Albert Soiland Professor in Radiation Oncology,
describes the CyberKnife as "a technological marvel that
is fit for the 21st century." Petrovich is director of radiation
oncology at the USC/Norris Comprehensive Cancer Center.
Apuzzo and Petrovich, directors of the CyberKnife program at
USC/Norris Cancer Hospital, say that the concept of modern stereotactic
neurosurgery emerged at the beginning of the 20th century, with
the advent of reliable anesthesia and antisepsis and the nascent
ability to properly target specific portions of the brain.
In 1968, Swedish neurosurgeon Lars Leksell combined stereotactic
principles with a machine that could deliver pinpoint radiation
beams to targets within the head. The device, called a "Gamma
Knife," was not widely used in the U.S. until about 1990,
after two decades worth of important refinements were added and
tested-in many cases by the USC neurosurgery team, led by Apuzzo.
By 1978, Apuzzo also had begun to champion and apply a group
of crucial companion technologies-related to using computerized
imaging systems to guide surgical tools to their targets. In
the early 1990s, those technologies had evolved sufficiently
to engender the notion and development of the CyberKnife-and
John Adler Jr., M.D., a Stanford University neurosurgeon and
Apuzzo's colleague, created the device with input from his former
mentor.
"At USC, we are not simply leaders in imaging-directed surgery-we
helped create the field. Beginning with Drs. Edwin Todd and Trent
Wells during the 1960s, the Department of Neurosurgery has made
major contributions to the field through innovations and practical
applications. And this revolutionary device is a natural progression
of developments that we believe will grow to be the primary instrument
for delivering stereotactic radiosurgery during the next generations,"
Apuzzo says.
Early tests of the CyberKnife used human-like dummies packed
with radiation sensors to prove its effectiveness, clearing the
way for clinical trials to begin in 1997. Since then, more than
3,000 patients have undergone treatment. In 2001, the FDA approved
the machine for use in destroying both benign and malignant tumors
located anywhere in the body. Currently, the USC/Norris Cancer
Hospital is one of only six U.S. hospitals to have the CyberKnife.
Current radiosurgery systems such as the CyberKnife involve delivering
high doses of radiation to a specific target, whose location
is defined stereotactically-that is, in reference to a three-dimensional
map of the body prepared in advance through CT or MRI scans.
The radiation beams are relatively weak on their own and will
not harm healthy tissue. During treatment, dozens or hundreds
of them are beamed from different angles and converge on the
tumor, ideally killing it outright or causing it to shrink considerably
over time, alleviating the pain, bleeding or blockages it caused,
Petrovich says. In traditional stereotactic radiosurgery systems-which
can only be used on lesions within the cranium-patients must
stay completely still during treatment to ensure only the target
is irradiated. Patients' skulls are fitted with rigid frames
that provide crucial reference points for the machine as well
as a way to keep the patients perfectly still. They must wear
the frames for the entire treatment, often hours at a time, which
is uncomfortable in the best of circumstances and frequently
requires that patients receive pain medication, Petrovich says.
The CyberKnife, on the other hand, is the only stereotactic radiosurgery
system that uses the body's skeletal structure as a reference
point without the use of invasive restraints. Preoperative CT
images are used to define the spatial relationship between the
patient's bone structure and the lesion, creating the computerized
3-D maps that will guide the machine.
"The tracking technology was modeled after the military
technology of a cruise missile, in which the sensors continuously
compare a map with the surrounding terrain, so it always knows
where it is in relation to the target," Apuzzo says. "It's
the same here:You make a map of the patient's anatomy, and the
computer's robot drive compares that with real-time scans of
the body during treatment to ensure that the beams hit only the
target and nothing else."
Before radiation beams are delivered, the system's X-ray cameras
take images to detect any patient movement. These radiographs
will show any shifts in bony landmarks, which in turn are used
to determine changes in the target location based on the landmarks'
previous sites.
Based on the computer's analysis of the X-ray images, the highly
mobile and dexterous robotic arm automatically compensates for
changes in target position during treatment to ensure accurate
delivery of each radiation beam. The CyberKnife is the only stereotactic
radiosurgery system that can perform this correction during treatment,
and it does so within two-tenths of a second, Petrovich says.
"I observed one surgery when a patient with a lung tumor
began to cough. Immediately, the robot arm started a jerking
motion that exactly mimicked the motion of the patient. It looked
odd, but that's what it was designed to do-perfectly track the
body. It didn't affect the treatment," he says.
Because the advance tracking system eliminates the need for rigid
invasive restraints, patients undergoing CyberKnife treatment
need only lie on a table while wearing a custom-fit, flexible
mesh facemask or body stabilizer to reduce movement. Most treatments
last about one hour per lesion, and the patient returns home
the same day. Most patients require one to three sessions.
"The CyberKnife is patient-friendly," Petrovich says.
"A person comes in for treatment on an outpatient basis,
spends a few hours with us and then goes home. There's no anesthesia,
and side effects are usually minimal.
"Compare that with even the most skillful surgery, which
takes a patient out of commission for several days, plus weeks
or months for a full recovery."
Petrovich notes that rapid advances are quickly enabling the
CyberKnife to reach its full potential.
At USC, the machine already has been used to treat lesions including
malignant and benign brain tumors. Physicians are working toward
treating conditions beyond the head and spine to include certain
tumors and lesions in the lungs, liver, pancreas and prostate.
Petrovich says that the CyberKnife's mobility allows it to deliver
radiation beams to a much broader range of positions and angles,
and the ability to target any region of the body has opened up
treatment options for people who otherwise had none.
As advanced as the system is, however, Apuzzo and Petrovich emphasize
that it remains as much a physician's tool as a surgeon's scalpel-and
just as much under a physician's control during treatment.
Before they ever treat patients with the device, experienced
physicians and surgeons must undergo specialized training.
"This is a sophisticated tool that requires extensive experience
to safely and effectively employ it-it is not an instrument you
can purchase and simply apply," Apuzzo says.
He adds that USC has remained at the forefront of such radiosurgical
technologies partly because of a historically high degree of
cooperation between its radiation oncology and neurosurgery departments.
Experts in both disciplines have always been eager to try new
methods of treatment as soon as they become available-and the
CyberKnife is no exception.
"This new technology is exciting, and patients equally benefit
from the expertise of our faculty. We have been on the leading
edge of radiosurgery for more than 20 years, and we bring this
unparalleled experience to the CyberKnife," Apuzzo says.
Petrovich adds that the CyberKnife will expand the radiosurgical
therapeutic options for patients to larger tumors, tumors in
the nervous system such as spinal tumors, and tumors that are
in highly sensitive areas where it has not been practical to
treat them, such as optic nerve tumors.
While an excellent tool, Petrovich emphasizes that the CyberKnife
is an extension of a full range of treatments.
Traditional surgery is usually better for treating tumors more
than two inches across, for example. And in some instances, such
as treating solitary, small lesions within
the skull, the recently updated Leksell Gamma Knife, Model C,
which was installed at USC University Hospital in 2000, produces
superior results compared to older therapeutic methods.
Petrovich notes: "We have a Gamma Knife program that has
been very successful and we plan to keep it going. We will triage
people for the CyberKnife and treat them with it if they are
good candidates. Since we have the full line of equipment, we
can truly select the best treatment for a given patient."
He adds that with the broad range of expertise available at the
Keck School of Medicine, the CyberKnife will soon be used to
treat conditions beyond the brain.
Petrovich says he expects to treat as many as 100 patients with
the CyberKnife in the next year and believes the treatment will
quickly become popular nationwide as other centers begin acquiring
the technology.
"I always stress quality of life-and that is what this technology
offers. It is a major improvement, so in the next two to five
years, you're going to see it become available in a lot more
places.
"But for now," he says, "we're very excited that
it's available to us."
For more information about the CyberKnife Stereotactic Radiosurgery
System, or to learn more about The Doctors of USC, call 1-800-USC-CARE
(1-800-872-2273).
Jon Weiner contributed to this article.
Back Next Index