Modification of late dermal necrosis in the pig by treatment with multi-wavelength light.

Low-level light from a multi-wavelength light source has been used to prevent late X-ray-induced dermal necrosis in the pig. Skin fields, measuring 4 cm x 4 cm on the flank, were irradiated with graded doses of X rays and the incidence of late dermal necrosis at 10-16 weeks after irradiation was scored. The control skin sites were irradiated only with 250 kV X rays but the test skin sites were subsequently exposed to low-level light. Local light exposure was from an array of gallium aluminium arsenide diodes, which produced wavelengths of 660, 820, 880 and 950 nm, pulsating at 5 kHz. Light treatment was given three times a week, from 6-16 weeks after X irradiation. Each treatment session was 1 min, which was equivalent to energy density of 1.08 Jcm-2. Light treatment increased the ED50, the dose which causes dermal necrosis in 50% of the irradiated skin fields, from 20.10 +/- 0.12 Gy to 21.94 +/- 0.30 Gy. This difference, although small, was highly significant (p < 0.001) and was equivalent to a dose modification factor (DMF) of 1.09. The effect of light treatment was minimal at incidence levels of less than the 50% but greater at higher levels of effect. These findings suggest that low-level light, when applied appropriately, may be useful in the prevention of late X-ray-induced damage to the dermis.