Photodynamic therapy (PDT) is a method of treating sun damage and certain types of skin cancer and pre-cancerous lesions, as well as augmenting the effect of some other light-based treatments. A substance is used which is taken up into dividing cells. As cancerous and pre-cancerous lesions are growing, they will take up more of this substance than normal skin. This applies also to inflamed areas such as acne lesions. The substance is a photosensitizing agent, so areas that have taken it up become more sensitive to light.
When bright light is shone on such lesions, they are selectively affected more than the normal surrounding areas. As the normal surrounding area will also take up some of the substance, but more slowly, bright light must be avoided afterwards for 48 hours. This means one must stay indoors, or wear covering clothing, or a dressing for 2 days afterwards, otherwise blistering or swelling may occur.
PDT can be done in one of two ways.
The more-comfortable way is “ambient light PDT”. Once the skin is prepared and the special solution has been on for half and hour, the patient will go outside for 2 hours with the solution still on. There is enough light in Australia, even in the shade, to activate the solution to perform its work. After this 2 hours, the patient returns inside and washes off the solution.
The second way is for the solution to be on for 1-2 hours in the Centre, then to be washed off and a a red light is applied to the area for 20 minutes. This light is much more intense and the treatment can be quite painful, despite chilled air blowers and anaesthetic being used. This is usually now reserved for small or difficult-to-reach areas.
PDT does not help all types of skin cancer (eg. melanoma), so it does not replace all other forms of therapy such as excision. It is very useful for actinic/solar keratoses and many forms of basal cell carcinoma, and can treat large areas of sun damage where it is sometimes difficult to see where one lesion starts and another finishes. It can also be useful in treating lesions before they become visible to the naked eye.