Experimental ruthenium plaque therapy of amelanotic and melanotic melanomas in the hamster eye

The effects of beta-radiation on melanoma implanted into the hamster's eye were investigated. Two Bomirski hamster melanomas (BHMs), differing in thei r melanin content, were compared with regard to their radiosensitivity to r uthenium-106 (Ru-106) radiation. Tumours growing in the iris were irradiate d with 3, 6 or 10 Gy of Ru-106 given as a single dose or in four fractions at 24 h intervals. Tumour growth kinetics and distant metastases were studi ed, and the eyeballs were examined histologically. Dose-dependent delay of tumour growth was observed in both melanomas. After treatment with a dose o f 6 Gy, the Ab amelanotic tumours grew 2.6 times slower, and the Ma melanot ic tumours 1.4 times slower than untreated ones. The location of metastases differed in the two tested lines - pigmented metastases were found mainly in the lungs, while unpigmented metastases were found mainly in the kidneys . Histopathological analysis showed signs of blood vessel damage such as en dothelial cells swelling, erythrocyte extravasation and tumour necrosis. Th is last finding increased with the rising dose of beta-radiation, Pigmented tumours were found to be two times more resistant to beta-radiation than a melanotic ones. The pattern of metastases of BHMs is determined by the type of melanoma (Ab or Ma). Exposure to beta-radiation from Ru-106 did not sig nificantly affect either the number or size of metastases except at a dose of 10 Gy. This dose caused a statistically significant decrease in the numb er of metastases in the Ma melanotic subline. (C) 2000 Lippincott Williams & Wilkins.