Restenosis Reduced
with Brachytherapy
November / December 2002
 In
the United States more than one million angioplasties are
performed each year. "Intracoronary stents, by virtue of
their ability to prevent elastic recoil and constrictive
remodeling,
reduce the frequency of angiographic restenosis to approximately
20 percent.
As a result, routine stenting has become the
preferred
approach of many cardiologists for the prevention of restenosis
and is used in more than 80 percent of current coronary
interventions,"
says Daniel
M. Kolansky, MD, interventional cardiologist and director
of the Cardiac Care Unit at the Hospital of the University
of Pennsylvania. "But restenosis remains a barrier to the
long-term durability of this treatment modality, occurring
in 15 to
20 percent of patients."
 The
FDA approved coronary vascular brachytherapy in the fall
of
2000. The team of interventional cardiologists and radiation
oncologists at Penn Cardiac Care at the Hospital of the University
of Pennsylvania and Penn Presbyterian Medical Center have now
performed
coronary vascular brachytherapy on more than 150 patients.
"Previously, the alternatives for patients with restenosis
were another angioplasty, continued angina or bypass surgery,"
says Howard
C. Herrmann, MD, director of Interventional Cardiology
at the Hospital of the University of Pennsylvania. "Brachytherapy
has become an important modality in the armamentarium of interventional
cardiologists. It can help us avoid the need for multiple
angioplasties and open-heart surgery and allows us to treat
restenosis more effectively."
Coronary vascular brachytherapy entails administering radiation
to the blocked area of the blood vessel. It inhibits cellular
proliferation and reduces in-stent restenosis by up to 40
to 60 percent.
Immediately following angioplasty, an interventional cardiologist
places a specially designed catheter at the site of the treated
stenosis. Radioactive seeds are then advanced into the treatment
segment by the radiation oncologist. The seeds are sent out
through the catheter hydraulically and remain in the vessel
for 2.5 to 4.5 minutes depending on the length of the treated
segment, the diameter of the stenotic region, the number of
radioactive seeds used, and the planned radiation dose. Brachytherapy
also requires the expertise of a radiation physicist in addition
to an interventional cardiologist and the cardiac catheterization
laboratory staff. The procedure is not available at most hospitals.
Administering the correct dosage of radiation during therapy
and placing the patient on prolonged anti-platelet therapy,
has been effective in reducing late thrombosis and restenosis
from occurring for up to two to five years from angioplasty.
"An excessive radiation dose could prohibit proper healing
following angioplasty, which requires a small amount of normal
tissue growth. Without this tissue growth, the bare metal
becomes a prime location for blood clots and other problems,"
explains Gene
Chang, MD, interventional cardiologist at Penn Cardiac
Care at Penn Presbyterian Medical Center.
To help adequately measure the distribution of the radiation
dose, Peter Bloch, PhD, radiological physicist in Penn's
Department
of Radiation Oncology has developed an innovative software
program in which data can be directly input into a laptop
during vascular brachytherapy. "This is ideal for our patients.
It allows us to treat much longer segments of blood vessel
and make adjustments to the radiation dose distribution during
the procedure so we can avoid under and over doses of radiation,"
says Paul E. Wallner, DO, FACR, radiation oncologist at the
Hospital of the University of Pennsylvania.
Although all patients who undergo angioplasty are at risk
for in-stent restenosis, patients who are diabetic, have smaller
caliber arteries, have extensive blockage or have a long lesion
have up to a 40 to 50 percent chance of developing restenosis
within six months.
"Pharmaceutical agents and mechanical devices such as cutting,
balloons, atherectomy devices and lasers used to treat recurrent
plaque build-up from inside the artery wall continue to be
an area of intense research. So far, these methods have
not
proven to be any more effective than redilating and reopening
the blocked section of the artery through balloon angioplasty,"
says Dr. Chang. "Unfortunately, once restenosis occurs it
is likely to continue to reoccur." In fact, investigators
at Penn recently published a study that found when in-stent
restenosis returns very aggressively within three months,
the patient is at a much higher risk of having the artery
narrow again no matter what treatment is administered.
In the near future, drug-eluting stents (stents coated with
an immunosuppressant agent that blocks cell growth) will be
available. In ongoing clinical trials in the United States,
interim analysis has shown that renarrowing has been reduced
to about five percent or lower when a drug-coated stent is
utilized.
"Cardiologists will then be faced with determining the best
treatment for patients who present with in-stent restenosis
after having a drug-coated stent deployed during their initial
angioplasty," says Dr. Chang. "Researchers are looking at
radiation therapy versus placing another stent. Vascular brachytherapy
may still remain the best therapy for these patients."
In general, the risks of the procedure are similar to those
of angioplasty. At present, the diameter of the radiation
sources and delivery catheter may prevent treatment of very
narrow distal vessels, but thinner sources and catheters
will be available shortly.
Another question is the unknown
effects that radiation may have in later years. "Although
a small percentage of patients could develop a problem 10,
15, or 20 years later, patients undergoing coronary vascular
brachytherapy are faced with the absolute risk of myocardial
infarction or needing cardiac surgery in the near term," says
Dr. Wallner.
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