To evaluate the effect of a new infrared laser in the destruction of pigmented choroidal melanomas.
B16F10 melanomas were implanted in the subchoroidal space of 64 rabbits(tumor height, 2.0-4.0 mm). Laser radiation from an Nd:yttrium-lanthanum-fluoride laser (1047 nm) was delivered as a focused (beam waist, 25 µm; irradiance, 100 kW/cm2) raster-scanned transpupillary beam. To investigate melanin heating, treatment with focused light was compared with collimated light (beam waist, 2 mm; irradiance, 16 W/cm2). Fine-wire thermocouples were implanted at the base of 3 tumors for in vivo temperature measurements. Untreated animals were used as controls.
Of 64 animals, 27 received a single treatment with focused 1047-nm light. The rate of complete tumor eradication was 91% (10 of 11 animals) at a dosage of 125 J/cm2 and 75% (9/12) at 63 J/cm2 to 87 J/cm2. The eradication rate dropped to 25% (1 of 4) at 38 J/cm2 or less (P<.001). Continuous tumor growth was observed in all animals treated with collimated radiation and in untreated controls. Temperature measurements indicated that tissue heating at the tumor base was more rapid at 1047 nm than at 805 nm.
These data suggest that a single treatment with a focused, raster-scanned beam at 1047 nm may play a role in the destruction of pigmented choroidal melanoma. Focused irradiation at 1047 nm may provide more effective submillisecond heating of melanin than collimated irradiation, resulting in immediate photothermal disruption of tumor cells.