Introduction
Harvey Lui and Sunil Kalia Photodynamic Therapy 135
Chapter Contents
Photodynamic Therapy (PDT) – Photochemistry,
Synonym: Photoradiation therapy
Key features
Photodynamic therapy (PDT) is an established, light-based thera- peutic option for actinic keratoses (AKs) and superficial keratinocyte cancers, with an expanding range of applications including acne, photoaging, cutaneous infections, and vascular anomalies
The photodynamic effect is due to photochemical reactions that generate singlet oxygen and it requires three components: photosensitizing molecules, photoactivating wavelengths of light, and tissue oxygen
Singlet oxygen is highly reactive and initiates a series of cellular and tissue reactions that culminate in necrosis, apoptosis, and/ or antimicrobial effects; host immunologic responses to singlet oxygen-altered tissue may also contribute to the overall clinical effect
For cutaneous indications, the current standard technique is topical application of pro-photosensitizers (e.g. aminolevulinic acid and its derivatives) that are metabolized in situ, i.e. within the skin, to photoactive protoporphyrin IX
Non-coherent artificial light (blue or red), daylight, or other light sources can be used to illuminate the skin and energize the photosensitizer