Consequences of changing illumination procedures in photodynamic therapy

Conventional photodynamic therapy (PDT) for actinic keratoses (AK) involves a three-hour accumulation of protoporphyin IX (PpIX) after methyl aminolevulinate (MAL) or 5-aminolevulinic acid (ALA) application, followed by 7-12 minutes of illumination which may elicit severe pain. Daylight-mediated PDT greatly reduces pain by activating PpIX while it forms. Various visible light sources can be used to replicate daylight PDT indoors, with either prolonged incubation time before illumination, or a fixed incubation of 30 min. before illumination. Extended incubation before illumination causes more pain, whereas shortening the illumination duration reduces the amount of activated PpIX which may impair treatment efficacy.