Abstract

Diode lasers have long been viewed as the future technology for clinical light sources for use in Photodynamic Therapy (PDT). This has been based on their small size, high efficiency, potential reliability and potential low cost. The requirement for a laser source in PDT is based on their ability to deliver light efficiently through small single optical fibers. This in turns allows for endoscopic and interstitial use. The wavelength of the diode source must match that of the absorption of the photosensitizer used, which are chosen to provide good tissue penetration. Due to the high tissue penetration requirements wavelengths in the red and near infrared are used. At present the photosensitizers in clinical testing and commercial development have peak absorptions in the 630nm to 695nm range, while preclinical testing includes photosensitizers with absorption extending up to 800nm. Above 800nm the photophysics of the compounds tend to make them less desirable for use in PDT. The accuracy and stability of the center wavelength of the light source, and its bandwidth, must match to the action spectrum of the photosensitizer in-vivo. For example the first generation photosensitzer Photofrin® activation is specified as 630+/-3nm while for the second generation photosensitizer SnET2 it is 664+/-7nm.

© 1995 Optical Society of America