Thermodynamical and biological aspects of laser-induced heat treatment in medicine

Abstract: Heat has for long been utilised as a therapeutic tool in medicine. Tumour diseases and vascular malformations can be treated by elevating the temperature to cytotoxic levels. Laser-induced heat treatment relies on the conversion into heat of light absorbed in the tissue. Mathematical models were used to calculate the light absorption distribution and the subsequent temperature distribution in laser-irradiated tissues. The influence of various boundary conditions was investigated and, using the mathematical model, blood perfusion rates in irradiated experimental tumours were estimated. A new treatment strategy for improving the treatment result after laser treatment of port wine stains was proposed based on theoretical considerations. The importance of a number of treatment parameters was investigated by modelling laser-induced thermo-therapy of benign prostatic hyperplasia. A prototype to an internally water-cooled applicator including a diffusing optical fibre was constructed. A new tissue temperature estimation method was elaborated based on the temperature rise of the circulating cooling water. The effectiveness of the method was confirmed by in vitro experiments. Vessel damage resulting from hyperthermia alone and in conjunction with photodynamic therapy was investigated by scanning electron microscopy. It was shown that the combined treatment resulted in extensive damage to tumour vessels, which might be responsible for secondary tumour cell death.