Parameter Optimization for FEM Based Modeling of Singlet Oxygen During PDT Using COMSOL

T.C. Zhu, and X. Liang
University of Pennsylvania, Philadelphia, PA, USA
Published in 2010

Singlet oxygen (1O2) is the major cytotoxic agent in photodynamic therapy (PDT). The reaction between 1O2 and tumor cells defines the treatment efficacy. Based on 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, the distance-dependent reacted 1O2 is numerically calculated using finite-element method (FEM) on COMSOL. The formula of reacted 1O2 concentration involves 5 photophysiological parameters which need to be determined explicitly to predict the generation of 1O2. We have developed an algorithm to iteratively calculate the singlet oxygen concentration profile and compare with the measurements to obtain an optimal set of parameters. The optimization is performed using Matlab and dynamically linked with COMSOL for the forward calculation. The sensitivity of the model parameters to the necrosis depths and treatment conditions are examined. Our algorithm is capable of robustically determining the parameters with a total calculation time of less than 30 seconds.

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