Photodynamic therapy (PDT)

Photodynamic PDT therapy

A method that enables a quick, bloodless and painless treatment.

Photodynamic therapy (PDT) is becoming a useful tool in medical and cosmetic dermatology. The aim is to restore skin that has been damaged by the sun and other environmental effects.  These actinic keratoses (AK) are precursors of skin cancer, which deteriorates the texture and appearance of the skin.

The procedure removes 90 to 100 per cent of AKs (actinic keratoses) and rejuvenates the treated skin for a significant cosmetic improvement.

PDT is a combination of a photosensitising drug, most commonly aminolevulinic acid (5-aminolevulinic acid ALA), and exposure to light energy. Light energy on sensitised skin generates oxygen free radicals that target dysplastic proliferating cells and malignant epidermal derived cells and immune cells, while sparing mesenchymal tissue, including the dermis. Because the sensitizer is applied to broad areas such as the exposed skin of the entire face and scalp, PDT can treat the entire field rather than targeting individual lesions.

How does photodynamic therapy (PDT) work?

PDT acts directly on cells by generating singlet oxygen and free radicals, resulting in changes in membranes and swelling and autolysis of cells.

A variety of light sources can be used, including lasers, filtered xenon arcs, metal halide or fluorescent lamps, LEDs, intense pulsed light and natural sunlight. Blue light is most effective for surface lesions, while red light penetrates deeper into the dermis and is more effective for deeper treatments.

PDT essentially consists of three steps. First, a light-sensitising liquid, cream or intravenous drug (photosensitizer) is applied or administered. Occasionally, a photosensitising molecule can be activated that is already part of the body.

Secondly, there is an incubation period of minutes to days. Finally, the target tissue is exposed to a specific wavelength of light, which then activates the photosensitising drug.

The mechanism by which tissue is destroyed seems to depend on the presence of activated oxygen molecules.

Steps:

  • Application of photosensitizer
  • Incubation time
  • Light activation

PDT works by directly injuring the target cells and tissues. This involves the production of an activated oxygen molecule that can injure or destroy nearby cells. Since the normal skin barrier is not present at the sites of actinic keratoses, the photosensitising molecule is preferentially absorbed there and then activated by light. The activated oxygen destroys the adjacent abnormal tissue. Once the areas have healed after PDT, the areas are re-examined to determine if additional treatments or biopsies are needed.

Applications of PDT

PDT can be used on all skin types and is particularly helpful in organ transplant patients who have an increased rate of skin cancer.

Immunosuppressed patients require dermatological examinations every two to six months, depending on the degree of skin carcinogenesis. PDT is a convenient and cost-effective method of treating field cancer.

Photodynamic therapy (PDT) is becoming increasingly popular for the treatment of acne. PDT can be very effective alone or in combination with other traditional medications and is an excellent alternative for those who are resistant to traditional acne medications, as well as for those who do not want to use isotretinoin (Accutane).

In addition to treating acne, PDT is an effective treatment for a pre-cancerous form of sun damage known as actinic keratosis. As it helps to improve discolouration as well as overall texture and tone, it is a popular and effective option for those who wish to improve the overall appearance of their skin.

Although PDT was first used in the early 1900s, it is a new and evolving science in the modern sense. Current PDT involves a variety of incubation times for different light-sensitising drugs and a variety of light sources, depending on the target tissue. The basic premise of PDT is selective tissue destruction.

Currently, the main limitation of available PDT technology for the skin is the penetration depth of the light and the ability to target cells within 1/3 inch (approximately 1 cm) of the light source. Therefore, tumours or atypical growths must be close to the skin surface for PDT to work.

PDT is currently used in a number of medical fields including oncology ( cancer ), dermatology (skin), cosmetic surgery , ophthalmology and oral medicine.

What light sources are available and how are they applied?

PDT light sources include laser light, intense pulsed light, light-emitting diodes (LEDs), blue light, red light and many other visible lights (including natural sunlight). Photosensitizers can be activated by one or more types of light. The optimal light source depends on the ideal wavelength for the particular drug used and the target tissue.

The light source must be applied directly to the target tissue for an appropriate amount of time. For surface skin treatments, the light is applied directly to the area of skin to which the photosensitising agent has been applied (e.g. face, scalp, arms, etc.).

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