Gamma radiation and MC540 photosensitization of melanoma in the hamster's eye

The purpose of this study was to evaluate the effects of cobalt-60 gamma-ra diation and argon laser irradiation using injected merocyanine (MC540) as a photosensitizer on pigmented and non-pigmented Bomirski hamster melanomas growing in the eye. The animals were treated with one of four regimens, rec eiving gamma-irradiation only, photosensitization only, a combination of ga mma-irradiation and photosensitization, or a combined time-fractionated tre atment. Tumours were exposed to laser light 24 h after injection, when the photosensitizing dye concentration was highest. The degree of tissue damage was evaluated by observation of the area for necrosis, interruption of blo od circulation, and the shape and dissemination of the tumour cells. Additi onally, tumour growth was monitored through the measurement of tumour volum e and also calculated from histological cross sections on the assumption th at the tumour morphology is hemi-ellipsoidal. A single treatment of tumours by a combination of photodynamic therapy and ionizing radiation resulted i n an additive effect, inhibiting tumour growth for 2-4 days. A time-fractio nated treatment, given four times every 24 h, markedly delayed tumour growt h for up to 6 weeks. The results indicate that MC540-mediated photodynamic treatment in combination with gamma-radiation exerts a significant therapeu tic effect on a rapidly growing melanoma. (C) 1999 Lippincott Williams & Wi lkins.