Singlet Oxygen Modeling of BPD Mediated-PDT Using COMSOL

Singlet oxygen ( 1 O2) is the major cytotoxic agent during photodynamic therapy (PDT). A previously developed model that incorporates the diffusion equation for the light transport in tissue and the macroscopic kinetic equations for the generation of the singlet oxygen, can be used to numerically calculate the distance-dependent reacted 1 O2 using finiteelement method (FEM). The formula of reacted 1 O2 concentration involves 5 photophysiological parameters which can be determined explicitly to predict the generation of reacted 1 O2. We have improved an algorithm developed previously to solve the inverse problem to determine the 5 parameters. The optimization is performed using Matlab and dynamically linked with the COMSOL for the forward calculation. The sensitivity of the model parameters to the necrosis depths and treatment conditions are examined. We have shown the results of applying this algorithm on a new photosensitizer drug, BPD, which does not have any published results for these parameters in-vivo. The results are compared with in-vivo experiments performed in mice. In conclusion, our method can successfully extrapolate critical photochemical parameters in vivo for singlet oxygen based dosimetry of PDT.