Researchers at the University of Iowa are utilising heat generated by implanted magnetic rods to destroy cancer in the prostate.
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.
The treatment under development at the UI involves 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 centimetres long and 1 millimetre 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 then causes proteins to denature or unravel, which kills cells, and it coagulates the blood supply, which starves the cells and causes them to die.
Scientists have known for many years that certain alloys 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,’ said Tucker. ‘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.
The UI research team has conducted a series of experiments to test the properties of the rods and 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 millimetres beyond the outside edge of the array,’ said Tucker. ‘This means you can place the rods close to the edge of the prostate and minimise the risk of damaging tissue beyond the gland.’
The magnetic field used to activate the rods is low and the risk of inadvertent heating of these permanent implants is said to be 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.