Influence of drug-light-interval on photodynamic therapy of port wine stains - Simulation and validation of mathematic models

Objectives: We established mathematical models of photodynamic therapy (PDT) on port wine stains (PWS) to observe the effect of drug-light-interval (DLI) and optimize tight dose. Materials and methods: The mathematical simulations included determining (1) the distribution of laser tight by Monte Carlo model, (2) the change of photosensitizer concentration in PWS vessels by a pharmacokinetics equation, (3) the change of photosensitizer distribution in tissue outside the vessels by a diffuse equation and photobleaching equation, and (4) the change of tissue oxygen concentration by the Fick's taw with a consideration of the oxygen consumption during PDT The concentration of singlet oxygen in the tissue model was calculated by the finite difference method. To validate those models, a PWS lesion of the same patient was divided into two areas and subjected to different DUs and treated with different energy density. The color of lesion was assessed 8-12 weeks later. Results: The simulation indicated the singlet oxygen concentration of the second treatment area (DLI = 40 min) was lower than that of the first treatment area (DLI = 0 min). However, it would be increased to a level similar to that of the first treatment area if the light irradiation time of the second treatment area was prolonged from 40 min to 55 min. Clinical results were consistent with the results predicted by the mathematical models. Conclusions: The mathematical models established in this study are helpful to optimize clinical protocol. (C) 2008 Elsevier B.V. All rights reserved.