PHOTODYNAMIC THERAPY (PDT) OF GASTROINTESTINAL TUMORS - A NEW LIGHT DELIVERY SYSTEM

The Paterson lamp is a convenient, low cost, portable, alternative lig ht source to lasers for photodynamic therapy (PDT). A multiwavelength capability enables the clinician to vary the photosensitiser used. The Paterson lamp has been applied in the field of dermatology using a li quid light guide with distal optics for surface application. We now de scribe distal optics suitable for use with this light guide for intral uminal applications in the oesophagus and colorectum. The geometry of the site (oesophagus and colorectum) requires distal optics such as a cylindrical diffuser or a side-fire diffuser. We have designed new pro bes that diffuse light radially from the guide axis (cylindrical diffu sion). The tips have a frosted glass surface that scatters and effecti vely couples light radially into the tissue. An acrylic spacer is plac ed over the diffuser to position the tissue at a constant diameter fro m the probe. This is held in position by a silicone sheath placed over the distal one metre. For use in the oesophagus, a channel, to facili tate intubation over a guide wire, is included. The diameter of the en tire probe is 8.4 mm and the power output can be adjusted from 0-500 m W. Pilot PDT of tubulovillous adenomas of the rectum and Barrett's oes ophagus using this light delivery system is currently underway and has shown good early response in the treated area.