Abstract

Photodynamic Therapy, PDT, promises to be an effective and minimally invasive modality for the treatment of this early stage disease. Typically PDT of solid tumours is performed using an array of interstitial fibreoptic light sources implanted in the tumour, illuminated continuously with light from a single laser until the required lethal dose of light is delivered. The literature teaches that PDT is dose rate independent so that the illumination intensity of the sources will not influence the therapeutic outcome. Recent work, however, suggests that this teaching should be qualified. PDT will saturate when the cellular oxygen is depleted, consumed by the photo-oxidation of the photosensitizer. This implies that time fractionated light delivery should increase the lethality of treatment. In this paper we describe a computer controlled time fractionated fibre optic light delivery/detection system that may be used to synchronize treatment and tissue perfusion. Two laser diodes are each coupled to a computer controlled fibreoptic switch. The switch couples the laser sequentially to an array of interstitial fibre optic light sources. The dose delivered to each source is time moderated so that a non-uniform dose distribution may be delivered across the tumour. We describe preliminary results of this light delivery system and the photo-toxin QLT0074 for the treatment of rats with AT an –H flank tumours. We also compare tissue response to both time-fractionated and continuous light delivery.

© 2003 SPIE