Best Practices for Photodynamic Therapy for Actinic Keratosis

Key takeaways

• Photodynamic therapy (PDT) remains a highly effective field-directed treatment for actinic keratoses, achieving lesion clearance rates exceeding 94% with both 10% ALA gel and 20% ALA solution while providing excellent cosmetic outcomes and high patient satisfaction. 
• Simultaneous PDT (immediate illumination after ALA application) significantly reduces treatment-related pain while maintaining lesion clearance comparable to conventional incubation protocols. 
• Vitamin D supplementation has shown potential to improve AK clearance. Although daylight PDT offers similar overall efficacy with fewer adverse events and greater patient comfort, reimbursement limitations currently restrict its widespread use in the US.

Photodynamic therapy (PDT) remains an effective field-directed treatment for actinic keratoses (AKs), leveraging the selective accumulation of photosensitizing protoporphyrin IX (PpIX) within dysplastic keratinocytes following topical 5-aminolevulinic acid (ALA) or methyl aminolevulinate administration. PpIX selectively absorbs visible light, generating reactive oxygen species and other reactive oxygen species, resulting in selective cytotoxicity toward atypical keratinocytes and leading to lesion destruction while preserving surrounding tissue architecture. This mechanism provides both therapeutic efficacy and favorable cosmetic outcomes compared with destructive modalities.

Current Formulations

Two formulations of ALA are currently used for PDT in the United States: ALA topical gel and a 20% ALA solution. Both agents produce intracellular PpIX accumulation within AK lesions, enabling light-induced photochemical reactions after illumination. Activation is typically achieved with either blue light or red-light sources. Blue light systems emit wavelengths centered around 417 nm, corresponding to a major absorption peak of PpIX, and are typically delivered at an energy dose of approximately 10 J/cm² with an illumination time of about 16 minutes, 40 seconds. Red light sources, with a peak wavelength around 635 nm, provide deeper tissue penetration and are delivered at higher energy doses (approximately 37 J/cm²) with illumination times of roughly 13 to 14 minutes. Selection of the light source may depend on lesion characteristics, treatment field size, and physician preference.

Standard PDT protocols generally include lesion preparation, topical photosensitizer application, incubation, and illumination. Mechanical preparation such as gentle debridement may improve penetration of ALA and enhance PpIX accumulation. In clinical practice, incubation periods commonly range from immediate illumination protocols to approximately 1 hour or longer. In a randomized, double-blind comparison of 10% ALA gel vs 20% ALA solution followed by blue light PDT for AKs of the face or scalp, two treatment sessions were performed with a 1-hour incubation period prior to illumination. Eight weeks after the second PDT treatment, lesion complete clearance rates reached 97.1% with the 10% ALA gel and 94.9% with the 20% ALA solution, demonstrating high efficacy with both formulations.¹

Pain during illumination is a common limitation of conventional PDT protocols. Alternative treatment strategies have therefore been explored to improve tolerability. One such method, termed “simultaneous PDT,” involves initiating illumination immediately after ALA solution application without a prolonged incubation period. In a split-face/scalp clinical study comparing simultaneous PDT with conventional 1-hour incubation PDT, patient-reported pain scores were significantly lower with the simultaneous protocol, while lesion clearance rates at 3 months were similar between the two approaches. These findings suggest that modified protocols may reduce treatment discomfort without compromising efficacy.²

Adjunctive Approaches

Adjunctive approaches to enhance treatment response have also been investigated. In a study evaluating the effect of vitamin D supplementation prior to PDT, patients received oral vitamin D (10,000 IU daily) for 5 or 14 days before undergoing field treatment with ALA-PDT. Mean AK clearance rates were significantly higher in the vitamin D–treated group compared with registry-based controls without supplementation, suggesting that vitamin D–mediated modulation of keratinocyte differentiation may augment PDT response.³  Another study evaluated the impact of antihistamines on adverse effects following ALA-PDT and found that while H1 antihistamines do not impair the efficacy of ALA-PDT, they also do not relieve post-treatment inflammation and discomfort.⁴

Daylight PDT represents another modification of conventional PDT protocols and has gained interest due to improved patient comfort. Meta-analytic data comparing daylight PDT with conventional lamp-based PDT demonstrated that daylight PDT was slightly less effective at three months but remained non-inferior overall. Importantly, daylight PDT was associated with fewer adverse events and higher patient satisfaction. Despite these advantages, daylight PDT currently lacks reimbursement pathways under existing PDT procedural codes in the United States, which may limit its adoption in routine practice.⁵

Overall patient satisfaction with PDT for AK is high. Clinical studies evaluating treatment outcomes in patients with AKs of the face, scalp, and upper extremities have reported satisfaction rates approaching 97%, reflecting both the effectiveness of the therapy and the favorable cosmetic outcomes typically achieved with this modality.⁶

Summary

Photodynamic therapy remains a highly effective field therapy for actinic keratosis and offers a combination of high clearance rates, excellent cosmetic outcomes, and strong patient satisfaction. Optimization of treatment protocols—including appropriate lesion preparation, selection of ALA formulation and light source, modification of incubation strategies to reduce pain, and consideration of adjunctive interventions—may further enhance therapeutic outcomes and patient tolerability.