The correct treatment for choroidal melanoma is under debate, but radiation therapy (scleral plaques or external beam charged particles) is being used as the primary therapy in an increasing number of patients. Secondary effects of ocular radiation therapy are observed several years after treatment and can result in a significant decrease in visual acuity. Adjunctive use of ocular hyperthermia could reduce the dose of ionizing radiation needed to sterilize choroidal melanomas. If the production of ocular hyperthermia can be limited only to the tumor, then a reduction in the dose of ocular radiation could in turn reduce the severity of secondary complications to normal ocular structures. Our goal is to document the efficacy of using a low power, continuous wave (c.w.) Neodymium YAG laser as a source of precise and efficient ocullar tumor hyperthermia. The low power, c.w. YAG laser will not be used in an ablative, cutting or photocoagulation procedure. Rather, we will exploit the tissue transmission properties as well as efficient heating characteristics of the c.w. YAG laser. Trans-corneal delivery of a diverging beam of low power infra-red light generated from the YAG laser should provide extremely well localized and controlled hyperthermia originating at the apex off a choroidal melanoma. Pigmented rabbits with transplanted choroidal Greene's melanoma will be used in research projects. Tumor temperature profiles will be determined as a function of laser light power density and tumor tissue depth. Ocular toxicity (both in and out of the treatment field) induced by YAG laser hyperthermia will be examined and quantitative normal tissue dose response curves will be generated. Acute and chronic toxicity will be documented by ophthalmoscopic observation, fundus photography, fluorescein angiography and histopathological examination. Quantitative dose response experiments will also be performed to compare the effectiveness of scleral plaque (I-125) radiation therapy to a combination of radiation plus hyperthermia. The effectiveness of various treatments and doses will be determined from tumor regrowth and tumor cure parameters.
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