Daylight Photodynamc Therapy: Back to the Future?

P.Lehmann

Photodynamic therapy (PDT) has gained a central role in the treatment of precancerous lesions (actinic keratosis, field cancerization), superficial basal cell carcinomas and bowen’s disease. The main drawback of this procedure is the associated pain during the light treatment.

The first publication on daylight PDT, which described this procedure to be almost painless and at the same time leading to similar results, achieved, therefore, great interest.

The authors (Riegell D., et al.) postulated, that  the continuous building of PPIX in the cell during the daylight illumination leads  to a significant reduction of pain, whereas in conventional PDT the irradiation at three hours, when the PPIX reaches its highest concentration in the cell, causes the painful sensation.

Therefore, most patients prefer daylight PDT when compared to conventional PDT. However, a few problems remain to be solved, in order for daylight PDT to become a standard procedure. In international consensus recommendations the following requirements for the outdoor weather were defined:

The temperature should be over 10 degree Celsius, at the same time not too hot, because excessive sweating may interfere with the desired effect.

No rain, no direct sun illumination. Best would be diffuse shadow during a sunny day. Strong wind should be avoided (“wind chill factor”), as well as pauses over 5 minutes.

It is debatable, how in a busy praxis these defined conditions can  always be guaranteed, as well as the requirement of an excellent patient’s compliance. In consequence, comparing to conventional PDT, this procedure goes along with a significant loss of control on the treatment procedure, thus leading to inconsistent results in the daily practice. Furthermore, the introduction of LUX as the decisive parameter for required light intensity is very unusual and differs from all previous parameters defining the physical properties in photodermatology, as J/cm2, Watt, Hertz, etc.

A possible solution would be the development of lamps emitting the daylight spectrum, with well defined photobiologic dosage parameters. First prototypes are on the market making daylight PDT independent of weather conditions. However, further clinical studies has to be conducted in order to demonstrate the equal efficacy of these new devices.