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

Purpose: To compare concurrent vs. sequential ferromagnetic thermoradi otherapy in vivo. Methods and Materials: Greene melanomas were implant ed subretinally in rabbits and observed until they were 3-5 mm in diam eter. 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 o ver the intraocular melanoma, After a given dose of radiation had been delivered, the plaque was removed and a nonradioactive plaque contain ing FM thermoseeds was inserted into the same extrascleral space, One hour later, hyperthermia (46-47 degrees C at the plaque-scleral interf ace) was initiated and continued for a period of 1 h by placing the ra bbits in a magnetic induction coil powered to 1200 W. Tumor size was d etermined at 1-to 2-week intervals by indirect ophthalmoscopy and by u ltrasound. 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 f or I-125 followed by FM hyperthermia. The thermal enhancement ratio wa s 1.4. Conclusion: Comparison with a previously published thermal enha ncement 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 d uring, rather than after, the irradiation process.