Fluorescence monitoring of a photosensitizer and prediction of the therapeutic effect of photodynamic therapy for port wine stains

In this study, a fluorescence method was established to obtain the local concentration of a photosensitizer (PS) based on the realtime fluorescence measurement of skin with port wine stain (PWS) during photodynamic therapy (PDT). This algorithm corrected for the distortions of PS fluorescence spectra imposed by the absorption of melanin and hemoglobin in skin and other factors, which yields a semi-quantitative measurement of PS concentration. Based on this information, a therapeutic effect correlation index (TECI) was proposed as the area under the PS concentration-time curve during PDT. The correlation between TECI and PDT treatment outcome was analyzed from 31 PWS patients. The measured PS fluorescence spectra showed that under the same PS dose, there were clear variations in the concentrations of the PS during PDT. Statistical analysis showed that TECI has a positive correlation with PDT outcome. Patients with a higher TECI value had a better treatment outcome. These results suggest that fluorescence spectroscopy can be used in situ to monitor skin PS concentration during PDT and to provide a valuable diagnostic tool to predict PDT outcome.