Physiological considerations acting on triplet oxygen for explicit dosimetry in photodynamic therapy

The aims of this study were to determine the spatial and temporal theoretical distribution of the concentrations of Protoporphyrin IX, ³O₂ and doses of ¹O₂. The type II mechanism and explicit dosimetry in photodynamic therapy were used. Furthermore, the mechanism of respiration and cellular metabolism acting on ³O₂ were taken into account. The dermis was considered as an absorbing and a scattering medium. An analytical solution was used for light diffusion in the skin. The photophysical, photochemical and biological effects caused by PDT with the initial irradiances of 20, 60 and 150mW/cm² were studied for a time of exposure of 20min and a maximum depth of 0.5cm. We found that the initial irradiance triples its value in 0.02cm and that almost 100% of PpIX is part of the dynamics of reactions in photodynamic therapy. Additionally, with about 40μMof ³O₂ there is a balance between the consumed and supplied oxygen. Finally, we determined that with 60mW/cm², the highest dose of ¹O₂ is obtained.