SUMMARY Thirty-five rabbit eyes were implanted subchoroidally with Greene's hamster melanoma. When the tumours reached a base diameter of 5 mm, they were treated with ultrasonically induced hyperthermia with a range of temperatures and exposure durations (43-67°C and 75 s to 60 min). Of the 23 treated eyes examined two months after treatment eight showed complete regression of the tumour. Seven showed initial tumour regression, but there was subsequent regrowth of tumour round the margins of the original mass. In eight eyes the tumour continued to grow, though in some cases the rate of growth appeared to be slower than in the controls. In contrast, in all untreated animals the tumour grew to fill the vitreous cavity. These preliminary findings indicate that ultrasonically induced hyperthermia can be an effective local treatment of this intraocular tumour model.The tumoricidal effect of hyperthermia either alone or in conjunction with radiotherapy is well known.' Heat treatment of tumours has ranged from the use of hot waterbaths2 to regional perfusion with warmed blood.3 Modern methods of inducing selective heating of tissues has involved radiofrequency electromagnetic waves,4 microwaves,56 and ultrasound techniques.78 This paper describes local, ultrasonically induced hyperthermia (UIH) in the treatment of experimental choroidal melanoma. We describe the model and define temperature and exposure duration relationships required to kill Greene's hamster melanoma growing in the choroid of rabbits. Material and methodsThirty-five eyes of 26 rabbits (New Zealand White and Dutchbelt strains weighing between 2 and 3 kg) were studied.An experimental model of choroidal melanoma was prepared by a modification of Krohn and colleagues' technique.9 The tumour stock used was a strain of amelanotic Greene's melanoma"' maintained by serial transplantation into the anterior Correspondence to

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He report on the use of a 5.8 GHz microwave applicator to treat choroidal melanoma (Greene) in rabbits. The physical requirements needed to treat these intraocular tumors are quite different from those encountered elsewhere in the body. From a trans-acleral approach the penetration needed is minimal (5-10 ma.). The fibrous aclera is the only structure between the heat source and the tumor. The sclera has a relatively low water content when compared to tumor.This fact in addition to the frequency dependent interactions of tissue and electromagnetic radiation, results in an advantage to the use of the 5.8 GHz microwave device in treating intraocular malignancies.

Proton beam irradiation was used to treat human retinoblastoma (Y-79 cell line) grown subcutaneously in the athymic "nude" mouse. Thirty-four tumors were included in the experimental groups, of which twenty-three were irradiated and eleven served as controls. Tumors were irradiated with protons produced at the 160 megavolts Harvard cyclotron. The dose delivered to the tumor ranged from 7.5 to 27.5 proton gray in a single treatment, and 25.0 proton gray delivered in two fractions separated by 24 hours. Reduction of tumor growth was significantly greater than controls (p less than 0.001) with treatment doses greater than or equal to 17.5 proton gray. Histologic examination revealed a marked decrease of mitotic activity in all specimens examined 48 hours after treatment at these higher doses. Total regression without evidence of remaining malignant cells was noted in three tumors treated at 17.5 proton gray or above. Our results indicate that human retinoblastoma in a murine host, with a tumor mass similar to that seen in a clinical setting, is sensitive to radiation by high energy protons.