Proton beam irradiation and hyperthermia. Effects on experimental choroidal melanoma
K. G. Riedel, P. P. Svitra, J. M. Seddon, D. M. Albert, E. S. Gragoudas, A. M. Koehler, D. J. Coleman, J. Torpey, F. L. Lizzi and J. Driller
Ultrasonically induced hyperthermia (4.75 MHz) and proton irradiation (160
meV) were evaluated alone and combined to treat experimental choroidal
melanoma in 58 rabbit eyes. Threshold tumoricidal doses were established
for each modality. Therapy was performed combining subthreshold doses of
heat and radiation. Focused ultrasonic energy via an external beam was
found to deliver well-localized heat to an intraocular tumor. Ectopic
temperature elevations due to soft-tissue-bone interfaces were alleviated
by modifying beam alignment. The results indicate that hyperthermia (43
degrees C for one hour) potentiated the tumoricidal effects of radiation,
while sparing normal ocular structures. Therefore, we believe that
experimental hyperthermia is suitable as an adjuvant treatment modality.
This shows that ultrasound hyperthermia has the potential to increase the
efficacy of proton irradiation by lowering radiation doses and thus
decreasing posttreatment ocular morbidity in human intraocular
malignancies.
