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Researchers investigate magnetic
treatment for prostate cancer
IOWA CITY, IA -- Feb. 12, 2001 (Cancer Digest)--
A new approach using heat generated from implanted magnetic rods
to treat prostate cancer is showing promise in early clinical
trials say researchers. The hope is that the new technique will
be as successful as surgery and radiation therapy in treating
the disease, but will spare patients the side effects of those
standard treatments.
The treatment involves implanting small magnetic
alloy rods into the prostate using methods similar to those used
in brachytherapy to implant radioactive seeds. When the patient
with implanted rods is placed in an external, alternating magnetic
field, the rods heat up and transfer the heat to the surrounding
tissue. The heat from the rods delivers a one-two punch to tumor
cells. The heat causes proteins in the cells to denature or unravel,
and it coagulates the blood supply, causing tumor cells to die.
"Our results, and those of our international
collaborators, suggest that these rods could be extremely effective
in treating the cancer with potentially fewer side effects,"
said lead investigator Dr. Robert D. Tucker, in a prepared statement.
Tucker, who is associate professor of pathology
at the University of Iowa, says his collaborators at the Charité
Hospital in Berlin, Germany, and the University of Chile in Santiago
have produced promising results in early clinical trials.
"Another advantage of these permanent
rods is that, unlike radiation treatment, thermal therapy can
be repeated non-invasively if the patient's serum PSA values
start to rise again," he says. "We think that this
approach could also prove useful against other localized tumors."
The U.S. Food and Drug Administration recently
approved a clinical study, now under way at University of California
San Francisco, aimed at treating prostate cancer patients who
have failed radiation treatment.
Tucker's team uses rods made of cobalt and
palladium developed by Ablation Technologies of San Diego, Calif.
to be biocompatible, which has not been true of materials tested
for this purpose in the past. Each cylindrical rod is 1.4 centimeters
(1/2 in.) long and 1 millimeter (.04 in.) in diameter.
Using a long hollow needle the physician places
the rods in a pattern surrounding the tumor in a relatively simple
procedure that takes about 45 minutes The patient receives only
a spinal anesthetic and can undergo an initial treatment in the
magnetic field the same day and go home.
Scientists have known for decades that certain
alloys (mixtures of metals) heat up in a magnetic field to a
specific temperature, determined by the composition of the alloy,
and maintain that temperature while they remain in the magnetic
field.
"Different alloys have different Curie
temperatures, which is the temperature at which the alloy goes
from being magnetic to nonmagnetic," says Tucker, who also
serves on Ablation Technology's board of directors.
"When the rod is magnetic, it heats up
in a magnetic field. At the Curie temperature, the rod becomes
nonmagnetic and ceases to heat up and it simply maintains the
Curie temperature as long as it remains in the magnetic field."
The research team has conducted a series of
laboratory experiments to test the properties of the rods and
have confirmed the rods are capable of producing enough heat
to achieve a uniform temperature increase throughout the tumor
and destroy tissue. Each rod has a power output of half a watt,
so an array of 60 rods, as might be used in the prostate, would
generate as much heat as a 30-watt light bulb.
"Our experiments have shown that when
the rods are arranged in arrays, the heat or power is concentrated
between the rods. The heating only extends a few millimeters
beyond the outside edge of the array," Tucker said. "This
means you can place the rods close to the edge of the prostate
and minimize the risk of damaging tissue beyond the gland."
The magnetic field used to activate the rods
is low and not commonly found in everyday life, thus the risk
of inadvertent heating of these permanent implants is very small.
Also, the strength of the magnetic field used drops off sharply
with increased distance from the coil generating the field. This
means that magnetic objects in a patient's body that are more
than about 8 in. away will not heat up. A metal hip replacement
however, is an example of a magnetic implant that would present
a problem for using this treatment.
Last year more than 180,000 men in the United
States were diagnosed with prostate cancer. When the cancer is
confined to the prostate gland, surgical removal of the prostate,
or radiation therapy are the two most commonly recommended treatment
options. Although both these methods offer good odds for success,
they each entail risks of damage to the tissue around the prostate,
which in turn can cause incontinence and impotence.
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