THE OPTICAL-PROPERTIES OF SKIN TUMORS MEASURED DURING SUPERFICIAL PHOTODYNAMIC THERAPY

Accurate measurement of light distribution in tissue can improve the k nowledge of in vivo tissue optical properties, which is essential for precise dosimetry calculations during photodynamic therapy (PDT). In o ur application of PDT, superficial skin lesions are treated by topical administration of 5-aminolaevulinic acid followed by surface illumina tion using 630 nm laser light. Several small detector probes inserted under the skin surface prior to illumination record the light intensit y at different depths throughout the treatment. Results from 11 patien ts are presented. These results indicate light distributions described by the diffusion theory for light transport in tissue. The accumulate d data do not imply one specific set of optical parameters for the ski n, but indicate that although the depth of light penetration is consta nt for all patients, the variation in skin colour is significant when performing dosimetry calculations. The average value of effective atte nuation coefficient was found to be 0.359 mm(-1) (+/-9.5%) and the coe fficient k that is used to quantify the build-up of subsurface fluence rate varies between 0.12 and 8.23.