摘要： Background: Blue light photodynamic therapy (PDT) is effective for actinic keratosis (AK), but many patients experience stinging pain during illumination. Objective: Compare a conventional regimen (1 h ALA preincubation, followed by blue light), to a new modified regimen in which blue light is started immediately after ALA application. Methods: A clinical trial with a bilaterally controlled, intrapatient study design was conducted in 23 patients. Topical 20% ALA was applied to the entire face and/or scalp. On one side of the body, blue light was started immediately and continued for either 30, 45, or 60 min (“simultaneous PDT”). On the contralateral side, blue light began 1 h after ALA application and lasted 1000 sec (“conventional PDT”). Pain was evaluated on a 0-10 scale. AK lesion counts were determined by clinical exam and photography. Results: All patients experienced significantly less pain during simultaneous illumination than during the conventional regimen. At 3 months post-treatment, lesion clearance was nearly identical on the two sides, as determined by statistical testing of non-inferiority ± 15% margin. Limitations: Although bilaterally controlled, the study was relatively small. Additional studies are recommended. Conclusion: The modified PDT regimen is essentially painless, yet provides treatment efficacy similar to a conventional regimen.