Photochemical approach of photodynamic therapy applied to skin

Photodynamic Therapy (PDT) is a recent treatment modality that allows malignant tissue destruction. The technique provides a localized effect and good cosmetic results. The application of PDT is based on the inoculation of a photosensitizer and the posterior irradiation by an optical source. This radiation chemically activates the drug and provokes reactions that lead to tissue necrosis. Nowadays there are fixed clinical PDT protocols that make use of a particular optical dose and photosensitizer amount. These parameters are independent of the patient and the lesion. In this work we present a PDT model that tries to predict the effect of the treatment on the tissue. The 3D optical propagation of radiation is calculated by means of the Radiation Transport Theory (RTT) model, solved via a Monte Carlo numerical model. Once the optical energy is obtained, a complex photochemical model is employed. This model takes into account the electronic transitions between molecular levels and particles concentrations. The data obtained allow us to estimate the destroyed area. The optical power of the source, the exposition time and the optochemical characteristics of the tissue can be varied. This implies that these parameters could be adjusted to the particular pathology we are dealing with. As a consequence, the treatment would be more efficient. We apply the model to the skin, due to the fact that PDT is commonly applied on it.