Irradiation of choroidal melanoma with iodine 125 ophthalmic plaque.

Radioactive iodine 125 is a low-energy gamma isotope with physical characteristics suitable for irradiation of intraocular tumors. Metal ophthalmic applicators have been designed to shield vital ocular structures while allowing irradiation of the tumor. We compared the radiation effects of iodine 125 and cobalt 60. The Greene melanoma was transplanted into the suprachoroidal space of rabbits. The tumor then grew as an intraocular mass, was irradiated, and was followed up for two months before enucleation. Histopathologic examination defined the extent of the radiation damage to the tumor and other ocular structures from the iodine 125 and from the cobalt 60. The eye irradiated with iodine 125 suffered minimal radiation damage, whereas the tumor was sterilized. The eye irradiated with cobalt 60 showed substantial radiation damage, and the melanoma was incompletely treated. Our results support the use of iodine 125 in treating intraocular tumors. More research is needed as to optimum total dose and dose rate.