Photochemical effects in laser-tissue interactions: photodynamic therapy, an overview

Abstract

Photodynamic Therapy (PDT) is the best-known biomedical application of photochemical approaches to therapeutics. Although regulatory approvals for this modality have been obtained only over the last decade, the concept and indeed clinical studies of PDT are over a century old. During the first part of the last quarter century the focus of PDT applications had been on the treatment of cancer. However in recent years this has been broadened to a variety of non-cancer and diagnostic applications. This may be considered a return to the “roots” of PDT where one of the initial observations that form the basis of this approach was the inactivation of paramecium when exposed to acridine orange and light and the fluorescence of tumors when treated with porphyrins and light. Currently the most successful application of PDT is non-oncologic in the treatment of age-related macular degeneration (AMD) with Visudyne; so far this is the only first line use of PDT. At the present time, other diseases are being explored as targets for PDT in laboratories worldwide with a variety of strategies and PDT may now be considered a platform technology where photochemistry may be directed to specific anatomical sites and molecular targets with potentially a large number of applications.