CONTACT: JENNIFER BROWN
Iowa City IA 52242
(319) 335-9917; fax(319) 384-4638
Release: Feb. 12, 2001
UI researchers investigate the use of magnetic rods to treat prostate
IOWA CITY, Iowa -- University of Iowa researchers are developing a new approach
to treat prostate cancer. The treatment uses heat generated by implanted magnetic
rods to destroy the cancer. The UI scientists hope the new technique will
be as successful as surgery and radiation therapy in treating the disease,
but will avoid the difficult and unpleasant side effects often associated
with those standard treatments.
"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 Robert D. Tucker, M.D., Ph.D., UI associate
professor of pathology and adjunct associate professor of biomedical engineering.
"And we think that this approach could also prove useful against other
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.
The treatment under development at the UI will involve implanting small
magnetic alloy rods into the prostate using methods similar to those employed
to place radioactive brachytherapy seeds. Each cylindrical rod is 1.4 centimeters
long and 1 millimeter in diameter. 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 does two things:
it causes proteins to denature or unravel, which kills cells, and it coagulates
the blood supply, which starves the cells and causes them to die.
Scientist 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
"Different alloys have different Curie temperatures, which is the temperature
at which the alloy goes from being magnetic to nonmagnetic," Tucker explained.
"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 rods used by Tucker's team are made of cobalt and palladium and are
biocompatible, which has not been true of other materials tested for this
purpose. This technology is being developed by Ablation Technologies of San
Diego, Calif. Tucker serves on the company's board of directors.
The UI research team has conducted a series of experiments to test the properties
of the rods. The investigators have confirmed that at temperatures necessary
to destroy the tissue, the rods are capable of producing enough heat to achieve
a uniform temperature increase throughout the targeted 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
inches away will not heat up. Unfortunately, a hip replacement device containing
metal would present a problem for using this technique.
In addition to the promising laboratory studies conducted by Tucker and
his colleagues at the UI, clinical trials conducted by Tucker's international
collaborators at the Charité Hospital in Berlin, Germany, and the University
of Chile in Santiago have started to yield exciting results.
The results of these trials were so compelling that the U.S. Food and Drug
Administration approved a clinical study now being conducted at University
of California San Francisco to treat patients who have undergone radiation
treatment, but whose cancers have returned.
Implanting the rods using a long hollow needle takes about 45 minutes. The
patient receives only a spinal anesthetic. The patient undergoes a single
treatment in the magnetic field and is able to go home on the same day.
"In patients treated so far, the results have been encouraging,"
Tucker said. "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."
University of Iowa Health Care describes the partnership between
the UI College of Medicine and the UI Hospitals and Clinics and the patient
care, medical education and research programs and services they provide.