ORIGINAL ARTICLES - LASER ENERGY THRESHOLD FOR THERMAL VASCULAR INJURY IN A PORT-WINE STAIN SKIN MODEL

Monte Carlo simulation of laser energy deposition in a port-wine stain (PWS) skin model and numerical solution of the thermal diffusion equa tion have been used to calculate threshold energies for thermal injury of PWS blood vessels for different vessel sizes and laser pulse durat ions. It has been assumed that an average vessel temperature rise of 6 5 degrees C causes thermal injury to the blood vessel. The result is t hat for a certain combination of wavelength, pulse duration and incide nt energy density, only a limited range of blood vessel sizes can be i njured optimally. Higher energy densities are required to injure small er vessels with the same pulse duration, spot size and wavelength. Thi s gives support to the mechanisms of selective photothermolysis sugges ted previously by Anderson and Parrish, although their model was based on the cooling behaviour of instantaneously heated vessels. The autho rs hypothesize that different laser parameter settings that match the individual PWS vessel anatomy during treatment will be used in the fut ure, instead of many treatments with the same laser parameters. This c ould lead to less treatment sessions and to an improved predictability of clinical results.