In vivo fluorescence kinetics and photodynamic therapy efficacy of delta-aminolevulinic acid-induced porphyrins in basal cell carcinomas and actinic keratoses; implications for optimization of photodynamic therapy

Photodynamic therapy (PDT) with topical delta-aminolevulinic acid (ALA) has become a therapeutic option of growing interest for superficial non-melano ma precancerous and malignant lesions. After application of ALA, in situ co nversion to endogenous porphyrins is accomplished in a gradual manner. Ther efore, the determination of fluorescence kinetics and spatial distribution in vivo versus time is a crucial point for the success of ALA-PDT. Seventeen basal cell carcinomas (BCC) and 20 actinic keratoses (AK) were en rolled in this study. In 5 BCC and 4 AK, in vivo fluorescence kinetics were performed over 24 hrs and for the remaining lesions between 2 and 7 hrs af ter ALA application. In vivo spatial and quantitative detection of the fluo rescence intensity versus time showed considerable variations among tumors of the same type, so light irradiation was performed according to patient i ndividualities. Both BCC and AK showed maximal median fluorescence intensit y at 4-6.5 hrs post-application. In the present study, a high cure rate was proven after topical ALA-PDT (70 .6% in BCC and 85% in AK). The results of fluorescence studies suggest that optimum irradiation time f or BCC is approximately 3.5-5 hrs and for AK 5 hrs after ALA application, w hen relative maximal fluorescence intensity in correlation with fluorescenc e selectivity on the lesion, is obtained.