Improved light delivery for chromophore-enhanced laser-induced hyperthermia in a murine breast cancer model

The effects of heat on malignant tumors are well known. Laser-induced hyperthermia is an alternative to microwave or radio wave tissue heating for cancer treatment. In situ injection of a chromophore that converts light into heat allows selective tissue heating. Our attempts to reproduce published results, using the chromophore ICG to enhance tissue heating, produced unacceptable skin damage. This was likely a function of light delivery methods or ICG diffusion into the skin from the tumor. We therefore set about to investigate the effects of ICG on normal and tumor tissue heating, and to develop methods of light delivery and skin cooling to minimize damage to normal tissues. ICG significantly increased tissue heating during 810 nm laser irradiation. Both argon gas and argon gas with water mist cooled the skin; only the addition of water mist maintained normal skin temperatures during laser treatments. In situ injection of ICG, combined with active cooling of the skin produced selective heating of the tumor. Laser light delivery through a microlens produced lower energy densities in the skin while sufficiently heating ICG-containing tumors. Selective laser-induced hyperthermia may become a useful cancer therapy with refinements in laser energy delivery, chromophore localization, and active cooling methods.