Influence of Photobleaching in Photodynamic Treatment on Port Wine Stains by Mathematical Simulation

Objective Through establishing mathematical model of the distribution of laser,photosensitizer, oxygen and their interaction relationship, simulating the generation of singlet oxygen in blood vessel, epidermis and dermis, analyzing the effects of various factors relating with photobleaching on the generation of singlet oxygen,to explore the action and value of photobleaching in photodynamic therapy on port wine stains. Methods The distribution of laser was formulated by Monte Carlo model.The distribution of photosensitizer in vessels by pharmacokinetics. The diffuseness of photosensitizer and oxygen in tissues was formulated by the Fick's law.The photobleaching was described by second order kinetic reaction including the content of oxygen in tissues. The generation of singlet oxygen in every tissue was calculated by the law of Lambert-Beer and quantum yields of singlet oxygen. Results The increase in singlet oxygen in vessel's wall was more than that in other normal tissues by the reason of photobleaching when the dose of laser or photosensitizer was increased. The change in photosensitizer bleaching characteristic had great effect on generation of singlet oxygen in epidermis and dermis, but no use in vessel. Conclusions Mathematical simulation could show whole aspects of photobleaching's action and value in photodynamic therapy on port wine stains.