LIGHT AND DRUG DISTRIBUTION WITH TOPICALLY ADMINISTERED PHOTOSENSITIZERS

Photodynamic therapy (PDT) based on topical application of photosensit izers is currently in clinical use for the treatment of basal cell car cinoma of the skin, and it has been evaluated in animal models for pho to-ablation of the endometrium. This paper presents a dosimetry model which indicates that a limiting factor in treating thick tumours will be the transport of the drug into the tumour rather than depletion of the optical distribution. The model predicts that an optical irradiati on of 100 mW cm(-2) at 635 nm for 20 min, ie well below the threshold for hyperthermic reaction, will give an adequate light dose to a depth of 3 mm. The time required for photosensitizers to diffuse to this de pth is in the range of 3-15 h, dependent on the diffusion properties o f the tissue.