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.