[5.07] Recovery fluorescence after 5-ALA-induced PpIX-photodynamic therapy

Objective Loss of fluorescence is used to determine the endpoint of irradiation in PDT with 5-ALA of non-melanoma skin cancers (NMSC) as actinic keratosis (AK) and superficial basal cell carcinomas (sBCC). Based on earlier research, we investigated the appearance of recovery fluorescence (recurrence of any fluorescence after initial therapeutic irradiation) with regard to the type of lesion. As penetration of any applicable drug into skin is time-related and the production of PpIX from 5-ALA depends on the transformation of the externally applied precursor (5-ALA) by the diseased cells, thicker lesions should behave different from smaller lesions with regard to the time frame. Material and methods In 20 patients with AK, Bowen's disease (MB) or BCC-lesions 5-ALA/Tylose-gel (20%) was applied under occlusion and light shielding dressings for 2 h. Then the remaining gel was removed and incubation with light shielding was continued for another two hours. After a total of four hours fluorescence detection with a D-light-system (Storz) was performed and signal wavelength, relative intensity and the contrast to surrounding tissues were measured (AVASpec). Irradiation with 635 nm up to a dose of 37–74 J/cm 2 with LED (Aktilite) in AK and 70–125 J/cm 2 with diode laser (Biolitec) in BCC was performed under protective (non-bleaching) yellow ambient light. Irradiation was maintained until intermittent fluorescence monitoring showed the complete loss of signal. The lesions were covered again with light shielding dressings for 24 h and fluorescence was re-evaluated. If fluorescence re-occurred, another irradiation was performed until no recurrent fluorescence could be detected each 24 h. Anesthesia was maintained by cooled air stream and if requested, either by regionally or locally applied xylocain. Results AK displayed less frequent recovery fluorescence than deeper lesions (MB, BCC) at day two and none at day three. In most patients with MB or BCC a significant recovery-fluorescence was found. All patients with recovery-fluorescence received further irradiation with 635 nm-light until PpIX-specific fluorescence was eliminated. Local necrosis was more pronounced in patients who had received repeated irradiations; nevertheless some recurrences were seen during a follow-up of at least six months than in patients who were treated conventionally with one irradiation (e.g. in BCC). Conclusion The finding of a recovery-fluorescence suggests: (a) excess amount of 5-ALA in the lesions, (b) deeper penetration of 5-ALA with extended incubation times, (c) local persistence of viable cells being able to produce PpIX after first irradiation, (d) a need for an individualized light and drug dosimetry including prolonged incubation times, repeated irradiation and fluorescence control during topically ALA-induced PpIX-PDT.