Ferromagnetic hyperthermia and iodine 125 brachytherapy in the treatment of choroidal melanoma in a rabbit model
W. F. Mieler, G. J. Jaffe and R. A. Steeves
Department of Ophthalmology, Medical College of Wisconsin, Milwaukee 53226.
Hyperthermia has been combined with conventional radiation methods to
achieve enhanced tumor destruction. We combined iodine 125 seeds with
ferromagnetic thermoseeds in a single plaque to simultaneously deliver
radiation and heat in a rabbit model of choroidal melanoma. Initially, six
ferromagnetic thermoseeds were placed in parallel on a 14-mm episcleral
plaque. The plaques were placed on normal rabbit eyes and on eyes
containing transvitreally implanted choroidal melanoma. The heating
response was assessed in both normal and tumor-containing eyes. Rigid
copper-constantan and flexible Baily thermocouples were used to monitor
temperature responses. The animals were subjected to an electromagnetic
field of 100 kHz, with power of 1100 to 1500 W. The thermoseeds
autoregulated at 48.2 degrees C. Scleral temperatures stabilized at 45.8
degrees C +/- 0.4 degrees C (SD), while temperatures at the base of the
tumor stabilized at 43.6 degrees C +/- 0.1 degrees C. Ferromagnetic
thermoseeds were then combined with iodine 125 seeds. Similar temperature
responses were recorded, and autoradiographic findings confirmed a uniform
radiation distribution. Varying the amount or type of ferromagnetic
material in the thermoseeds allows the delivery of heat at virtually any
temperature. Ferromagnetic hyperthermia may provide a more simplified
approach over currently available methods of heat delivery.
