PDT in dermatology: quantification, relevance and comparison of light sources within a few clicks

Photodynamic therapy (PDT) for dermatological conditions relies on the photoactivation of the photosensitizer protoporphyrin IX (PpIX). Many light sources have been or are being investigated. The stronger the overlap of the spectral irradiance of the light source with the absorption spectrum of PpIX is, the more powerful to photoactivate PpIX is the light source. This overlap can be quantified using the PpIX-weighted irradiance, which results from the weighting of the spectral irradiance of the light source by the normalized PpIX absorption spectrum. We have previously developed a freely available website (http://www.oncothai.fr/light-efficiency-calculator/), which aims to compute the PpIX-weighted irradiance of any uploaded spectral irradiance. Through this website, we have assessed a variety of light sources proposed for use in dermatological PDT. The spectral irradiances of these light sources were collected by either extraction from the literature or request to manufacturers. Due to the variations in position, shape, and amplitude of the spectral irradiances with regard to the PpIX normalized absorption spectrum, a wide range of PpIX-weighted irradiances has been obtained. The maximal PpIX-weighted irradiance was achieved with daylight on a clear sunny day.