The relationship between protoporphyrin IX photobleaching during real-time dermatological methyl-aminolevulinate photodynamic therapy (MAL-PDT) and subsequent clinical outcome.

BACKGROUND AND OBJECTIVE The relationship between protoporphyrin IX (PpIX) photobleaching and cellular damage during aminolevulinic (ALA) photodynamic therapy (PDT) has been studied at the cellular level. This study assessed the capability of a non-invasive fluorescence imaging system (Dyaderm, Biocam, Germany), to monitor changes in PpIX during real time methyl-aminolevulinate (MAL) PDT in dermatological lesions, and thus to act as a predictive tool in terms of observed clinical outcome post-treatment. MATERIALS AND METHODS Patients attending Royal Cornwall Hospital (Truro, UK) for MAL-PDT to licensed lesions (actinic keratosis, Bowen's disease, and basal cell carcinoma) were monitored using the pre-validated non-invasive fluorescence imaging system. Patients were imaged at three distinct time points: prior to the application of MAL, after the 3 hours of MAL application and immediately following light irradiation. The fluorescence intensity of the images were analysed with image analysis software and the percentage change in fluorescence during light irradiation was related to the clinical outcome observed 3 months following treatment. In total 100 patients underwent at least one session of MAL-PDT. RESULTS Significantly higher levels of change in PpIX fluorescence during light irradiation (P<0.005) were observed in lesions undergoing complete clearance at 3 months when compared to those patients who underwent partial or no clearance. In contrast no significant difference (P>0.500) was observed in the total levels of PpIX recorded after MAL application in patients undergoing partial and complete clearance at 3 months. CONCLUSIONS PpIX photobleaching is indicative of the level of cellular damage PDT treatment will induce and therefore the clinical outcome expected within patients. This study indicated the potential of the commercially available fluorescence imaging system investigated to predict treatment success at the time of light irradiation and in the future it may be possible to employ it to individualise treatment parameters to improve dermatological PDT efficacy/outcome.