Photodynamic Therapy
Photodynamic therapy (PDT) is a special treatment used for facial rejuvenation and acne treatment (mild to moderate stages). It is also widely used for the superficial types of skin cancer and pre-cancers. It is effective in treating actinic keratosis and superficial basal cell carcinoma.
PDT involves usage of photosensitising agents, oxygen, and light to create a photochemical reaction that specifically targets only cancer cells and destroys them. Photosensitising agents refer to the type of drugs that have to be administrated into the body through topical, oral or intravenous ways. Once they get into the body, they concentrate in cancer cells and only become activated when the light of a certain wavelength is directed onto the affected site. The photodynamic reaction between the light, photosensitising agent, and oxygen results in the destruction of cancer cells.
Some examples of photosensitising agents include methyl aminolaevulinic acid cream, aminolaevulinic acid hydrochloride topical solution, and BF-200 ALA gel. Methyl aminolaevulinic acid cream is used with red light or daylight. The cutaneous photosensitivity usually resolves within the 24 hours after its application on affected areas. The aminolaevulinic acid hydrochloride topical solution is used with blue light. The BF-200 ALA gel is used with red light, BF-RhodoLED. The nanoemulsion formulation contains the 10% aminolaevulinic acid hydrochloride.
The light sources that are used in PDT include laser or non-laser light. The laser light has a few advantages due to being monochromatic, coherent, and intense. Monochromatic means that only one colour/wavelength would correspond with the peak absorption of the photosensitising agent. The coherent property enables the focus of lightwaves into a specific site. The intense property refers to the high irradiance which allows treatment times to be shorter.
The laser light is usually suitable for small skin lesions, while the nonlaser light is more suitable for larger skin lesions due to having a larger field of illumination.
Natural daylight is used as a light source for tearing patients diagnosed with actinic keratosis.
PDT is used for various skin conditions like actinic keratosis on face and scalp, squamous cell carcinoma, basal cell carcinoma, and acne.
The first stage of PDT treatment involves applying the photosensitising drug onto the lesion. Prior to application, skin can be gently scraped via curettage or needled in order to increase the amount of drug’s absorbance. The waiting time may take 3 to 6 hours so that the drug can get fully absorbed into cancer cells.
The second stage involves using the laser or nonlaser light shone directly onto the treated area. This stage lasts from 5 to 45 minutes. The treated area is covered with a dressing. Depending on the type of lesion that requires treatment and photosensitising chemical used, the second procedure can be repeated after 7-10 days.
The third stage involves the occurrence of sunburn reaction, which usually takes 1-3 weeks to heal.
The post-procedure side effects are caused due to the treated area being sensitive to light. The photosensitivity lasts about 24 hours. Some side effects may include swelling, redness, burning/stinging sensation, itchiness, crusting, peeling, blisters, and skin infections.
The treated area should be protected from any light exposure. The dressing is recommended to be applied to the affected area. A local anaesthetic (lignocaine spray) should be applied to a treated area before or during the second stage of the procedure in order to numb the pain.
The treated skin lesion may blister and ulcerate as cancer cells start to die off. It may take a few weeks to heal. The scarring is usually very minimal. There can be a loss of pigmentation which can be either temporary or permanent in rare cases.
Even though the photosensitising agents are targeted at cancer cells, they can also affect the normal cells by making them more sensitive to light. This can be avoided by using photosensitising creams that are directed only on the treatment site. If photosensitising drugs are given through mouth or injected intravenously then there may be an issue and normal cells will get affected as well. These patients may experience sensitivity to light in all parts of their bodies. Thus, they have to take some precautions to protect themselves from light for a few days-weeks.
Centre for Medical and Surgical Dermatology offers unique and personalized photodynamic therapy treatment options for each patient to treat various skin conditions like acne and actinic keratosis.
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For more information about basal cell carcinoma, visit the following link:
2 Comments
Love your blog!
Very informative post!