A Comparison of White-light and Daylight Topical Methyl 5-aminolaevulinic Acid Photodynamic Therapy for Actinic Keratoses

Photodynamic therapy (PDT) uses visible light to treat a premalignant condition, called actinic keratosis, which results on chronically sun exposed skin such as on a balding scalp. A cream is applied containing aminolaevulinic acid or methyl aminolaevulinate and this is converted in the cells to the photodegradable product protoporphyrin IX (PpIX). Visible light causes the degradation of PpIX resulting in the production of reactive oxygen species and then cell death in the actinic keratosis. In conventional PDT a lamp is used to supply the visible light. The main draw back to treatment is pain. Recent studies have shown that daylight can be used as the source of visible light and is as effective as conventional PDT. Patients find this form of treatment less painful and therefore preferable. The reduction in pain seen in daylight PDT appears to be related to the fact that no significant quantity of PpIX accumulates prior to exposure to the light source and small quantities of PpIX are activated continuously during daylight exposure. The drawback of performing daylight PDT in Ireland is the climate, both in terms of cloud cover and temperature. The typical daylight treatment times is 2 hours and it would be difficult for patients to stay outside in winter, spring and autumn. This study investigates the use of an artificial white light source, a Maquet PWD 50SF theatre-light, as an alternative.