Light distribution and calibration of commercial PDT LED arrays.

Commercial photodynamic therapy (PDT) light sources are supplied with no evidence of traceability to national measurements standards to validate indicated delivered dose. Also, the spatial distribution of the radiant energy is not disclosed. This means that there is no way for the user to be able to verify that the required dose is being delivered to the appropriate area of the lesion. To this end, a simple method, traceable to national standards, is described and applied to an investigation of two commercial LED arrays. In one case, the dose fell to 38% of that received at the central area at a distance of only 2 cm. In the other, the output was more uniform over a larger area but the maximum irradiance was not at the centre of the field. All of these inhomogenieties were taken into account when the actual light dose delivered to the patient was calculated in the method described. This ensured transparent traceability in PDT dosimetry.