Feasibility of daylight-mediated photodynamic therapy for actinic keratosis throughout the year in Central and South America: a meteorological study

Background Daylight-mediated photodynamic therapy (DL-PDT) is an efficacious treatment option for thin actinic keratosis (AK) that offers advantages over conventional PDT in terms of tolerability, treatment duration, and cost. A clinical study conducted in Australia determined the mean irradiance during a 2-hour exposure to be 305.8 W/m(2) (range: 40-585 W/m(2)). The protoporphyrin IX light dose is influenced by latitude, weather conditions, and time of year. A recent study of meteorological data concluded that DL-PDT can be performed effectively throughout the year in Australia. Objectives Based on the same hypothesis and applying the same methodology, the present study investigated the suitability of daylight to perform DL-PDT in Central and South America. Methods Solar radiation and weather data were gathered and analyzed to assess daylight irradiance (light intensity) throughout a full year across 32 geographical locations in Central and South America. Results The minimum average daily solar irradiance reported was above 305.8 W/m(2) in all locations investigated throughout the year. Annual averages of daily irradiance ranged from 578 W/m(2) in Chihuahua, Mexico, to 321 W/m(2) in Puerto Montt, Chile. Conclusions Daylight-mediated PDT for AK can be performed effectively throughout the year in Central and South America given that weather conditions permit a comfortable 2-hour direct exposure to daylight.