Gamma Knife: A Subspecialized Approach to Precision
| Disorders
Treatable with a Gamma Knife
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Increasingly neurosurgeons across the country are recognizing
the value of adding SRS capabilities to their procedural
armamentarium. Today, patients benefit from neurosurgeons
that have subspecialty expertise in the treatment of
brain tumors, seizures, vascular anomalies and functional
disorders as well as are proficient in the use of SRS
as an effective tool against these neurological conditions.
Using this subspecialized approach to the use of SRS
ensures that individual cases are reviewed and handled
by neurosurgeons thoroughly versed in the various treatment
options available and their level of appropriateness
with regard to a particular condition’s nuances.
Additionally, because leading centers have a comprehensive
portfolio of neurosurgical tools and expertise, their
Gamma Knife-operating neurosurgeons are not limited
or biased in their treatment decisions by anything other
than that which is in the best interest of the patient.
Gamma Knife and SRS Advancements
The Gamma Knife is a specialized radiation delivery
mechanism used to supply the extreme radiation concentration
and steep volume edge radiation fall-off involved in
stereotactic radiosurgery (SRS).ii It allows a completely
noninvasive approach to treating malformations with
the greatest of precision. CINN’s experience with
the remarkable tool began in 1988, when it was only
the third organization in the country to install one—just
behind the University of Pittsburgh and the University
of Virginia.
Since its introduction, SRS technology advancements,
refined imaging and physician experience with dose volume
relationships have allowed for an expanded list of indications
and lower complication rates. Today the Gamma Knife
is used for larger and irregular shaped lesions, requiring
multiple isocenters. The ability of the technology to
precisely conform with the tumor geometry allows for
less morbidity, even with such anatomic challenges.
Now, with approximately 2,000 Gamma Knife procedures
completed and a new, updated Gamma Knife system being
housed at The Neurologic & Orthopedic Institute
of Chicago, CINN neurosurgeons are treating an increasing
range of conditions.
Brain Metastases
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| One
month post Gamma Knife. |
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| Female,
40 years old, metastatic tumors of breast cancer
origin. Pre-Gamma Knife. |
Once used almost exclusively to treat arteriovenous
malformations (AVMs), acoustic neuromas and benign tumors,
the Gamma Knife’s true worth as an agent against
brain tumor metastases has only recently become more
fully realized. “I saw that it could be used for
metastatic disease,” says Dr. Cerullo. “Now
Gamma Knife is the preferred approach for treating multiple
metastases.”
Brain metastases arise from various primary systematic
cancers outside the brain and can spread to the brain
parenchyma or dura.iii According to Contemporary Neurosurgery,
about 175,000 central nervous system (CNS) metastases
are diagnosed in the United States per year and the
number is only increasing.iv The once popular procedure
of whole brain radiotherapy (WBRT) in treating these
metastases has become outdated with the rise of the
Gamma Knife. No longer is it advocated that the whole
brain be subject to radiation as part of protocol, but
rather that every measure be taken to target tumors
as precisely as possible to ensure maximum protection
of cognitive ability.
Gamma Knife advances, along with improved intraoperative
image guidance and microsurgery techniques, are helping
to increase the proportion of patients considered eligible
for multimodality treatment of metastases.v Of the various
modalities available, in recent studies SRS has emerged
as the recommended initial treatment option over WBRTvi
and the preferred option to open surgeryvii for several
prominent categories of cancer patients, and most clearly
among those with multiple metastases. Approximately
60% to 68% of patients newly diagnosed with CNS metastases
would fall into such categories and be considered ideal
candidates for SRS.viii
Recent studies have also concluded that the key to
maximizing patient life expectancy and quality of life
lies in maximizing local CNS tumor control.x CINN neurosurgeon
Dr. Gail L. Rosseau agrees: “Gamma Knife is a revolution
in the way we think about tumors. Until now, we thought
the only way to deal with tumors was to completely remove
them. What we’ve learned is that we need to control
the tumor, not necessarily remove it.” Rosseau
explains the paradigm by relating it to the treatment
of high blood pressure and diabetes—two conditions
approached in terms of control rather than cure. “Now
we are starting to realize that same approach is effective
with some tumors,” she says. “We also understand
it can be complimentary to microsurgery. Used in combination,
microsurgery can make radiation treatment safer.”
Recent findings suggest that if local CNS tumor control
is optimized in such a manner, then the rate-limiting
step for ultimate patient survival becomes the extent
of the systemic disease and the availability and effectiveness
of multiple therapies for controlling that systemic
disease.xi
AVMs
The Gamma Knife’s usage in the treatment of arteriovenous
malformations (AVMs) has also been the subject of refinement
in recent years. Believed to affect approximately 300,000
Americans,xii AVMs are complex lesions of the brain
that can develop in people of any age, sex or ethnicity.
The nest of abnormal blood vessels can be asymptomatic,
cause headaches, or if they hemorrhage, may lead to
weakness, loss of consciousness, seizures and death.
There are three forms of accepted AVM treatment: open
surgery; embolization; and radiosurgery. CINN has one
of the few programs in the country with a fellowship-trained
endovascular neurosurgeon holding expertise in all three
modalities.
As that neurosurgeon, Dr. Demetrius Klee Lopes, believes
that the patients he serves benefit from an extraordinarily
consistent treatment process. “We can offer timely
evaluation, individualized treatment plans and the ease
of communication that comes from talking to one doc
as opposed to three,” Lopes remarks. Such one-on-one
interaction is especially valuable for assessing AVMs,
as recommended treatments can vary quite considerably
with a patient’s age and lifestyle. At times, it
can even be assessed that the best course of treatment—being
the one least impacting quality of life—is no treatment
at all.
When appropriate, however, Gamma Knife radiosurgery
can offer a substantial advantage over other options.
“The patient suffers minimal downtime, has an easy
recovery and avoids major discomfort,” claims Lopes.
“…and the psychological impact is less than
that of open surgery.” Additionally, a Gamma Knife
can easily target lesions that are positioned too deep
in the brain for other techniques to reach. But if the
patient should suffer a hemorrhage during the two-year
period it takes for an AVM to completely disappear with
Gamma Knife treatment, immediate open surgery would
be required as an adjuvant to the radiosurgery. Open
surgery and embolization might actually be better initial
therapies in the case of younger patients, for whom
the long-term effects of radiation are yet questionable;
older patients tend to outlive any radiation damage
that might occur. Taking this into account, all three
modalities should be considered either on their own
or in tandem as possible treatments. Embolization and
Gamma Knife, for instance, has recently been praised
as a very efficient combination against larger AVMs.
Epilepsy
A recent study suggests that SRS might also be a viable
treatment option for some cases of epilepsy. Mesial
temporal lobe epilepsy is traditionally treatable with
open surgery, but the Gamma Knife would provide a noninvasive
alternative, averting the risks of bleeding, infection
and severe headaches. CINN neurosurgeon Dr. Richard
W. Byrne is on the leading edge of such possibilities.
“Stereotactic radiosurgery is a clear alternative
to open surgery…a great option for patients who
are afraid of surgery,” he says. “However,
because open surgery has such a low morbidity and we
see its effects instantly, it’s hard to beat it
with Gamma Knife.”
Though only in trial phase, Byrne predicts other limitations
in epileptic Gamma Knife usage that would necessitate
a continued working knowledge of conventional approaches.
In neurosurgical programs dependent on a sole Gamma
Knife operator for conducting all SRS procedures, that
operator would not likely have sufficient expertise
in the nuances of epilepsy to render the procedure.
“You have to know where the amygdala is and be
able to define the borders of the hippocampus,”
says Byrne.
The possibilities for the Gamma Knife in epilepsy treatment
are only beginning to emerge. The National Institute
of Health (NIH) is pleased with the recent study results
and is expected to approve a larger, multi-centered
trial in 2004, in which Dr. Byrne will participate.
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