Continuous ultra-low-intensity artificial daylight is not as effective as red LED light in photodynamic therapy of multiple actinic keratoses

Background/Purpose: Daylight-mediated photodynamic therapy (PDT) is a simple and tolerable treatment of nonmelanoma skin cancer. It is of interest which light intensity is sufficient to prevent accumulation of protoporphyrin IX (PpIX) and effectively treat actinic keratoses (AKs). We compared the efficacy of PDT with light-emitting diode (LED) to daylight-mediated PDT with very low-intensity artificial daylight ('daylight') in the treatment of multiple AKs in the face or scalp. Methods: Twenty patients were treated with conventional methyl aminolevulinate (MAL) PDT in one area. Another area was, after half an hour of occlusive treatment with MAL, illuminated for 2.5 h with low-intensity 'daylight' (0.5 mW/cm(2)-3.7 mW/cm(2)) that corresponds to midday outdoor intensity in the Scandinavian winter. Results: After 3 months, with a response rate of 52%, low-dose artificial daylight was less effective than conventional LED-PDT (63%) (P = 0.0017). The mean PpIX light dose during 'daylight' exposure was 2.23 J/cm(2) and the lower the PpIX light intensity, the higher the accumulation of PpIX (P = 0.003). Conclusions: Even very low-intensity/dose artificial daylight-mediated PDT of multiple AKs resulted in a response rate of more than 50%. However, to ensure efficacies equivalent to conventional LED-PDT, the treatment should not be conducted on very overcast days.