THERMORADIOTHERAPY OF INTRAOCULAR TUMORS IN AN ANIMAL-MODEL - CONCURRENT VS SEQUENTIAL BRACHYTHERAPY AND FERROMAGNETIC HYPERTHERMIA

Purpose: To compare concurrent vs. sequential ferromagnetic thermoradiotherapy in vivo. Methods and Materials: Greene melanomas were implanted subretinally in rabbits and observed until they were 3-5 mm in diameter. Episcleral plaques were assembled with I-125 seeds for radiation therapy, or with ferromagnetic (FM) thermoseeds and nonradioactive I seeds for hyperthermia. Rabbits were implanted by centering a plaque over the intraocular melanoma, After a given dose of radiation had been delivered, the plaque was removed and a nonradioactive plaque containing FM thermoseeds was inserted into the same extrascleral space, One hour later, hyperthermia (46-47 degrees C at the plaque-scleral interface) was initiated and continued for a period of 1 h by placing the rabbits in a magnetic induction coil powered to 1200 W. Tumor size was determined at 1-to 2-week intervals by indirect ophthalmoscopy and by ultrasound. Results: Dose-response analysis of 27 treated eye melanomas showed 50% local tumor control at 43 Gy for I-125 alone and 29.4 Gy for I-125 followed by FM hyperthermia. The thermal enhancement ratio was 1.4. Conclusion: Comparison with a previously published thermal enhancement ratio of 4.4 (for concurrent I-125 and FM hyperthermia) leads us to conclude that thermal enhancement of I-125 brachytherapy is more efficient in this tumor model system when hyperthermia is delivered during, rather than after, the irradiation process.