Clinical applications of photodynamic therapy.

This is a review of photodynamic therapy, which is a classic binary system involving the use of a photosensitizer and light of very specific wavelength, consistent with the absorption characteristics of that sensitizer. As a binary system, its effects are almost entirely limited to tumour cells, but the major drawback is its limited penetration because it utilizes physical light within the visible spectrum. For Photofrin II, which is the only approved sensitizer for clinical use in this country, the effects are limited to approximately 0.5 cm or less, depending on the tissue and the amount of blood, etc. Newer sensitizers offer more penetration and the opportunity to repeat treatments, because the newer sensitizers do not have the very long (up to 10 weeks) period of enhanced skin sensitivity to sunlight. A summary of the results of photodynamic therapy by individual sites is included. The use of newer sensitizers, which represent much purer substances than Photofrin II, should give an opportunity for repeated treatments, which should eventually make this form of treatment far more important than it has been up to now.