Optimization of energy parameters for laser-induced PDT of cervical tissues using numerical simulation and fluorescent monitoring

The main problem in the photodynamic therapy (PDT) of tumors is insufficient light exposure to tissue or the appearance of undesirable surface effects. The reason is the irregular distribution of the absorbed light dose by depth. The influence of the spot diameter on the relative fluence rate in the near-surface layer of the cervical tissue was studied by Monte Carlo simulation. Photodynamic exposure with chlorine-type photosensitizer (PS) was carried out on the tissue model with laser 660 nm at the same power density with a change in spot diameter from 5 to 15 mm and radiation energy density from 100 to 300 J cm(-2). The distributions of the fluorescence indices of the PS and the hemoglobin oxygenation degree by depth were obtained. The dependence of PS photobleaching on the energy density was established at the same power density and different spot diameters. The developed method increased the efficiency of PDT by delivering a sufficient energy density of laser radiation to the entire tumor tissue by depth without thermal damage, that allowed minimizing side effects and prevent possible growth and recurrence of the disease.