What is Photodynamic Therapy?

Photodynamic therapy (PDT) is a type of treatment method that uses of light and special sensitizer to treat a variety of skin conditions.

Having become increasingly popular over the last 10 years, it is now one of the fore-running options to treat common disorders like actinic keratosis, acne vulgaris, and superficial skin cancers. The basis of photodynamic therapy is made up of three components: a photosensitizer, light of varying wavelengths (415 nm blue light, and 633 nm red light), and oxygen. The photosensitizer prepares the skin by allowing the cells to absorb the chemical, which produces free oxygen radicles once exposed to light. These free radicles trigger the cascade of intracellular reactions in target cells, eventually treating skin condition.

PDT is a non-invasive, minimally painful alternative to conventional treatment methods. In the Centre for Medical and Surgical Dermatology, we provide both conventional and daylight PDT. The difference between the two methods is the type of light and light source used to activate the photosensitizer. The Methyl Aminolevulinate (MAL), also known as Metvix, or Aminolevulinic acid HCl, known as Levulan, are our sensitizers of choice. Metvix comes in a cream form and Levulan comes as a solution form which is applied to the area that needs treatment. When sensitizer is applied to the skin, it is accumulated in the highest concentrations in inflammatory, metabolically active and/or neoplastic cells, which is why they are extremely effective in treating these types of skin conditions.

Types of PDT

Conventional PDT

Conventional PDT uses an artificial light source to activate the photosensitizer. These light sources can be lasers, red or blue lights or intense pulsed light systems. Each of these light sources emit light waves at a very specific wavelength. Other than this, the method of treatment is mostly similar to the daylight PDT.

  • Pros of Conventional PDT:
    • Allows the usage of specific wavelength which can better activate the photosensitizer.
    • There is no dependency of sunlight – can be used in places where there is a minimal presence of sunlight or during winter months
  • Cons of Conventional PDT:
    • Patients report slightly more discomfort and skin irritation after treatment from an artificial light source
    • Requires the patient’s supervision for the duration they are exposed to the light
Daylight PDT

Daylight PDT uses of sun or natural light as the source to activate the photosensitizer. Daylight PDT has been hypothesized to be a convenient alternative to conventional PDT while producing nearly similar results.

  • Pros of daylight PDT:
    • Minimal pain or almost pain-free since there is no accumulation of protoporphyrin, a sensitizing product in this treatment process which can lead to skin irritation and pain
    • Sunlight is freely available
    • It does not require a clinic space of a clinician to operate the light source
    • Produces the same results as conventional PDT
  • Cons of daylight PDT:
    • Unable to use target wavelengths
    • Difficult to accurately perform in places with very minimal sunlight or high rainfall