Influence of laser wavelength on the damage of comb’s vasculature by photodynamic therapy—simulation and validation of mathematical models

Lasers of different wavelengths have been used as a photodynamic therapy (PDT) light source in the treatment of port-wine stains. This study attempts to investigate the influence of wavelength on depth of vascular damage using a cock comb model and mathematical modeling/simulation. Monte Carlo simulation was used to calculate the distribution of laser light in skin tissue. A series of equations including the diffusion equation for modeling the distribution of photosensitizers and oxygen, and the photobleaching equation were established to calculate the singlet oxygen generation in PDT. The singlet oxygen generation in comb tissue model with vasculature was simulated with 532- and 627.8-nm laser, respectively. In the animal experiment, the comb was treated using hematoporphyrin monomethyl ether (HMME) (10 mg/kg dose) as a photosensitizer and lasers of two different wavelengths (532 and 627.8 nm) at an identical power density (100 mW/cm², fluence 120 J/cm²). The simulation results showed that the 627.8-nm laser was more effective in generating singlet oxygen in blood vessels at deep dermis. The animal experiments showed that the average depth of thrombosis was 1,012.5 ± 647.06 μm with the 532-nm laser, and 2,204.2 ± 410.35 μm with the 627.8-nm laser. The results showed that the laser wavelength had a strong effect on the depth of thrombosis in PDT treatment for the comb model. The simulation results were consistent with the animal experimental results.