Daylight-mediated PDT: More than an alternative

Using daylight instead of artificial light makes PDT treatment of actinic keratosis simple, less painful – and cheaper

Photodynamic therapy (PDT) has been adapted as an attractive therapy for non-melanoma skin cancer and actinic keratosis. It is very suitable for treatment of large areas with field cancerization.

The cosmesis of PDT is normally excellent, but the treatment is time-consuming and, for many patients, associated with pain during illumination, especially when face and scalp are treated.

The conventional PDT treatment consists of skin pre-treatment with superficial curettage, followed by application of methylaminolevulinat (MAL) cream, occlusion to avoid light penetration to the area for 3 hours, and, hereafter, illumination with red diode light for 8-9 minutes. The pain during illumination is often very severe and sometimes intolerable for the patient.

Simplifying the method

To simplify the method and to avoid pain we have revised the treatment to include only superficial curettage and application of MAL cream in the clinic. After 30 minutes the patient must stay outdoors for 2 hours, to expose the treated area(s) to daylight. On sunny days the treatment procedure must be preceded by use of sunscreen.

Light destroys the cancer cells

When MAL penetrates into the skin cells PPIX (protoporphyrine IX) is formed, making the cells sensitive to light. In the conventional PDT treatment a high concentration of PPIX is formed within the 3 hours of cover and then burned away by high intensity red light illumination. As PPIX is primarily formed in abnormal cells, these are destroyed in the process. In daylight-mediated PDT, the skin is continuously illuminated during the formation of PPIX. The PPIX will thus be burned away by low intensity daylight, as fast as it is formed, and this process is not associated with pain (pain level about 1 – 1.5). Illumination can be done in the patient’s own garden, and patients do not have to return to the clinic after treatment.

Cheaper treatment

About 25% more patients can be treated with this simplified method, by the same staff. Patients that have tried daylight PDT do not accept the conventional PDT treatment any more. If the weather is too cold or too windy we have a greenhouse in the hospital garden where patients can sit comfortably during treatment. Additionally we have established a daylight PDT room, where light sources simulate natural daylight to provide the treatment indoors.

One session of PDT can cure about 80% of actinic keratosis, which is comparable to or better than the result of conventional treatment.

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