Photodynamic therapy (PDT) is used to treat superficial and nodular basal cell carcinomas (BCC’s), superficial actinic keratoses (AK’s) and Bowen’s disease or intraepidermal carcinomas.
The combination of Metvix cream (Methyl aminolevulinate) applied to the lesion, oxygen in the atmosphere, and light activation creates a photochemical reaction that assists in cancer cell destruction. The process causes a localized inflammatory response and the area may become reddened, blister or crust. This is a normal response, but for some people, the procedure can cause discomfort.
Depending on what we are treating, you may require two treatments approximately two weeks apart. On each occasion, the same procedure will be followed for the prescribed treatment, and the same aftercare instructions will apply.
How does PDT work?
Photosensitising drug is applied to the lesion. The skin may be gently scraped (curettage) beforehand to increase the amount of the drug absorbed
Waiting for a period of time (usually between 3 and 6 hours) allows the drug to concentrate on the cancer cells.
Laser light or nonlaser light is shone directly on to the treated area.
Treatment usually lasts between 5 and 45 minutes.
The treated area is covered with a dressing.
Depending on the type of lesion being treated, and the photosensitising chemical used, the 2nd cycle of treatment may be given 7–10 days later.
A sunburn reaction occurs, which usually heals within 4 to 8 weeks.
What are the side effects of PDT?
During your treatment, your skin may feel hot, prickly and irritated. Afterwards, your skin may feel tender. PDT causes light sensitivity typically lasting approx. 24 hours. Side effects of this sensitivity may include:
Swelling and redness
Peeling and blisters
Due to the treatment's nature, the lesion may blister and ulcerate as the cancer cells die. This may take several weeks to heal. Scarring is generally minimal (but can be moderate). Loss of pigmentation may occur sometimes and can be permanent.
What to do after treatment
An ice pack may be applied to the area taking care not to apply directly to the skin or for any longer than 10 minutes at a time and for no longer than 24hours post-procedure.
PROTECT FROM SUNLIGHT: The treated area will remain light sensitive and should be protected from sunlight for a further 48 hours. If the treated area is in a sun-exposed area, then sunblock should be applied.
VASELINE: The treated area should not need a dressing; it is quite beneficial to leave the area uncovered. The site may be flushed with clean running water during the course of an average shower, followed by a light application of Vaseline at least twice per day while the area is healing. If a dressing is required to protect clothing from the Vaseline, then a light breathable non-adherent dressing may be used.
ELEVATE: There may be mild swelling after the procedure. Elevation of the affected part may be useful, especially if the treated area is on the lower leg/s.
Are there alternative treatments?
The best course of treatment will be discussed with your dermatologist during your consultation. The most common alternative treatment is a prescription cream such as Efudix cream. Efudix is less costly with similar efficacy, although it will need to be applied over several weeks.
When is PDT unsuitable?
Patients who are pregnant or breastfeeding
Patients who are allergic to peanuts (the Metvix cream may cause a reaction)
Patients who have porphyria (a rare disorder)
Patients are known to have had a previous adverse reaction to PDT.
Information on PDT has been taken from DermNet NZ