Simulation of Time and Frequency Domain of Photosensitizers Effect During Light Transport through Tissue as Applied to Photodynamic Therapy using a Steady State Monte Carlo Method with Simulink

Photodynamic therapy (PDT) is a treatment process that makes use of a non-ionizing light source targeted at specific section of cells (a tumor) in order to induce apoptosis, and eventually, the death of cells in such area. This is achieved using specific light sensitive photosensitizing (PS) agents (in the case of this research Metvix-Methyl Aminolevulinate (MAL)) used to saturate the treatment area for a recorded time period before irradiating with non-ionizing light source. This research was designed to observe the time and frequency domains as the PS signal decays during the PDT process. During the process, the PS agent degenerates and becomes less and less interactive with the light source. Using the Hop/drop/spin nomenclature, the source of the incident photon is simulated using A Gaussian White Noise (AGWN) on Simulink and the incident signal is allowed to attenuate through the target area while the time and frequency domain of the photosensitizer MAL is recorded as it decays. It is observed that the amplitude of the absorption coefficient of the PS agent dropped to almost 0 during a short sample time while the normalized frequency decays with a highly damped and irregular oscillatory pattern. The improvement in attenuation due to the presence of the PS agent degenerates sharply during the initial state of the treatment in order to ensure that the generation of singlet oxygen terminates just after treatment time.