Numerical simulation of singlet oxygen generation by a porphyrin-based photosensitizer

Photodynamic therapy is a new, minimally invasive method of treating cancer. It is based on the light activation of a photosensitizer, which can be administered in several forms (e.g. as an injection or an ointment) and accumulates selectively in the tumour. The activated photosensitizer in turn generates singlet oxygen in the malignant tissue, the action of which leads to tumor necrosis or apoptosis. In the present paper, we have developed and implemented a simulation model by using the main processes that the photosensitizer undergoes in the presence of irradiating light and molecular oxygen. We have carried out the simulation for the commercially available photosensitizer porfimer sodium (commercial name Photofrin), which is also currently used in clinical practice, regarding its ability to generate singlet oxygen. The model allows predictive statements to be made regarding the efficiency of photodynamic treatments at various initial conditions, including photosensitizer concentration and tissue oxygen concentration.