Microvascular effects of Photofrin^®-induced photodynamic therapy

Background and objective: The object of our study is to evaluate the feasibility of photodynamic therapy (PDT) for complicated hemangiomas. The photosensitizing activities of Photofrin^® have been used in vivo models for our goal of evaluation. Study design/materials and methods: The in vivo biological activities of Photofrin^® exposed to the total laser energy density of 100 J/cm² with the power density of 100 or 120 mW/cm² at 630 nm wavelength was studied. The amount of vascular damage produced in the chick chorioallantoic membrane (CAM) was evaluated. At 630 nm wavelength, those individual vessels with a diameter of 40 μm or less and those with a diameter between 40 and 100 μm were treated with Photofrin^® at a concentration of about 2.5 mg/mL, and injected intraperitoneally at 2.5 mg/kg, illuminated at 100 and 120 mW/cm², respectively. Both exhibited coagulation. Results: There were no statistically significant differences between the two groups (100 and 120 mW/cm²) on vessel damage grade 1. With vessel damage grades 2 and 3, the differences were statistically significant between two groups. Vessel damages between arterioles and venules also demonstrated differences in the 100 mW/cm² treated group but not in the 120 mW/cm² group. Statistically significant differences were also shown in arteriole and venules damage between 100 and 120 mW/cm² treated groups. The severity of vessel damage between grades 1 and 2, 1 and 3, and 2 and 3, were compared. The differences were statistically significant in 100 mW/cm² treated group. There was no statistically significant difference in 120 mW/cm² treated group. Conclusion: Photofrin^® has the capabilities for destruction of microvascular vessels of CAM. Extension of this study to the second-generation photosensitizers is underway. The most important treatment variables seem to be the power density.