CC BY
17B-O-1
Modeling of a photosensitizer fluorescence response during accumulation and photobleaching in biotissue
E. Sergeeva1, D. Kurakina1, A. Khilov1, M. Kirillin1
institute of Applied Physics RAS, Laboratory of Biophotonics, Nizhny Novgorod, Russian Federation
Photosensitizer (PS) fluorescence registration upon its excitation in the course of a photodynamic therapy (PDT) procedure is a novel approach which allows for monitoring the PS distribution in biotissue and to predict the efficiency of PDT. The process of PS penetration and accumulation in biotissue as well as its photobleaching during PDT is accompanied by changes of its fluorescence response. To understand the PS fluorescence dynamics a proper analytical description of light penetration in tissue is required. Most analytical approaches are based on diffusion approximation (DA) of radiative transfer theory while it is not applicable within units of mm from the biotissue boundary. At the same time, this superficial region is the most important in PDT action. We have developed a novel hybrid analytical model of light penetration in biotissues which is valid both at small and large depths. The model is verified by the comparison with the results of Monte Carlo simulations. We have analytically evaluated the dynamics of a PS fluorescence in biotissue during its penetration after topical application. For a specific class of PSs with the two pronounced peaks of absorption spectrum in the red and blue ranges (e.g., chlorin-based PSs) it was demonstrated that due to dispersion of biotissue optical properties the PS penetration depth can be estimated from the ratio of fluorescence signals excited at the two absorption peaks. In the modeling of PS photobleaching during PDT procedure it was shown that red light exposure results in faster decay of fluorescence compared to the exposure in the blue region due to more uniform in-depth distribution of red light compared to blue light. The rate of photobleaching can be estimated by the dynamics of a ratio of fluorescence signals excited at the red peak versus blue peak. Simulated dynamics of the fluorescence signal ratio is in qualitative agreement with the dependencies observed in the course of clinical PDT procedures. The results of the proposed model can assist in understanding the experimentally observed PDT effects.
The study is supported by Russian Science Foundation (project 17-15-01264).
