PHOTODYNAMIC THERAPY (PDT)
Photodynamic therapy (PDT) is an advanced technique for treating some types of skin cancer and skin conditions that have the potential to become cancerous. It does not involve surgery and can usually be done as an out patient appointment taking less than four hours in total.
The principle of photodynamic therapy
PDT works by applying a photosensitive cream to the skin and stimulating it with a precise wavelength of light to create a chemical reaction that kills cancerous and pre-cancerous cells. Since the photosensitive cream is attracted to cancerous or pre-cancerous cells, there is little damage to the surrounding healthy tissue
Both the cream, typically 5-aminolaevulinic acid (5-ALA) or methylaminolaevulinate (MAL), and the light, usually in the red end of the spectrum, are harmless on their own. However, when they are combined, they create a reaction in the cells that excites the oxygen molecules and kills the cell.
What skin conditions can PDT treat?
PDT is primarily used for thin cancers or skin lesions with the potential to turn cancerous (pre-cancers). These include basal cell carcinomas, Bowen’s disease and actinic keratoses (skin lesions caused by sun damage).
Photodynamic therapy is not suitable for deeper basal cell carcinomas or squamous cell skin cancers, as the light cannot penetrate the skin far enough to be effective.
Photodynamic therapy step by step
PDT takes place in two stages, approximately 3 hours apart. In the first stage the cream is applied and in the second stage the light is used. The period of time between the stages is to allow the cream to be absorbed by the cancer or pre-cancerous cells.
Stage one – applying the cream
- Before the photosensitive cream can be applied, the area of skin to be treated is cleaned and any scabs or crusting removed. The area may also be gently abraded (scratched lightly) to help the cream penetrate the skin
- The cream is then placed on the skin and a dressing placed over the treated area. You will be asked to wait for around three hours for it to be absorbed. You may wait at The Devonshire Clinic in our comfortable waiting area or leave and return later
- Once the cream has had time to be absorbed, the dressing is removed and the skin is cleaned again before a laser light of a very specific frequency is shone directly onto the treatment area for around ten to fifteen minutes. This may produce a mild burning or tingling sensation, but is usually not painful. Cooling the skin is usually all that is required, although a local anaesthetic can be applied if you find it uncomfortable
- Once the treatment is complete, the area will be dressed. It is important that this dressing is kept in place for 24-48 hours as the skin will remain sensitive to light
Stage two – applying the light
- It may be necessary to repeat PDT treatment after any swelling or inflammation has subsided, particularly if the treatment area is large or complex
- It is possible to introduce the light sensitive drug into the body by injection, but it is more usual for surface skin cancers lesions to be treated using cream in conjunction with light therapy
What are the advantages of PDT?
PDT is the preferred treatment for thin skin cancers as it does not involve surgery and therefore there is far less risk of scarring. It is particularly useful for larger areas of skin cancer or in cases where there is a close grouping of cancerous or pre-cancerous cells.
Photodynamic therapy is also less stressful for the patient as there is no surgery involved and the procedure can be done as an outpatient without the need for a general anaesthetic or an overnight stay.
What are the side effects of PDT?
Photodynamic therapy may cause mild pain at the site of the treatment, but this can be dealt with using standard painkillers or by cooling the area. Occasionally, local anaesthetic may be required to reduce the pain if you are particularly sensitive to the treatment.
The treated area may remain sore and look swollen and inflamed for a couple of days and may even blister or scab, but this will heal quickly and should not cause a scar if the treatment site is left undisturbed.
Occasionally, skin that has been treated with PDT will have a slightly lighter or darker appearance than before.