Topical 5-aminolevulinic acid–based photodynamic therapy (ALA-PDT) has been established in recent years as an effective treatment for disseminated actinic keratosis (AK). As yet, however, data are lacking to define the optimal light dose for activation of ALA-induced protoporphyrin IX in AK.

In the present study our purpose was to compare the efficacy and tolerability of 3 different doses of red light for ALA-PDT of AK.

Twenty-seven patients with at least 3 clearly definable, mild or moderate AKs on the scalp or face entered the study. After occlusion for 4 hours with 20% ALA, one AK each was irradiated at random with a single dose of 70, 100, or 140 J/cm². PDT-induced pain was assessed by the patients by means of a visual analog scale that graded pain intensity between 0 and 10. Follow-up examinations were performed 1 and 3 months after PDT.

One month after PDT, the rate of complete remission (CR) was 89% for 70 J/cm², 92% for 100 J/cm², and 81% for 140 J/cm². The CR rates at 3 months were 81% for 70 J/cm², 77% for 100 J/cm², and 69% for 140 J/cm². No significant difference in therapeutic efficacy was found among the 3 light doses at either 1 month (P = .36) or 3 months (P = .96) after PDT. The degree of PDT-induced pain during irradiation was substantial and not statistically different (P = .06) for all 3 light doses.

The conclusions from this study are limited by the small sample size and only apply to topical ALA-PDT.

Our results indicate that a red light dose of 70 J/cm² may be sufficient for effective topical ALA-PDT of disseminated, mild to moderate AK on the face and scalp.