COMPARATIVE-STUDY BETWEEN PULSED AND CONTINUOUS-WAVE LASERS FOR PHOTOFRIN(R) PHOTODYNAMIC THERAPY

A study was conducted in the normal canine esophagus to compare contin uous wave (CW) and pulsed laser light for photodynamic therapy with Ph otofrin(R) (4 mg/kg). Forty-eight hours postinjection, 630 nm laser li ght (CW light from an argon-pumped dye-laser and pulsed light from a K TP/532-pumped dye-laser) was delivered using a 24 mm diameter cylindri cal esophageal PDT balloon positioned at either distal or proximal eso phagus. A 1.0 cm cylindrical diffuser placed in the center of the ball oon delivered 300 J/cm of light at an intensity of 400 mW/cm. Three do gs received CW light proximally and pulsed light distally. Four dogs r eceived CW light distally and pulsed light proximally. The light dose delivered to the esophageal mucosa was measured using three isotropic probes placed on the balloon wall. Laser-induced fluorescence techniqu e was used to compare photosensitizer fluorescence intensities at dist al and proximal locations. Similar mucosal light doses and drug fluore scence intensities were verified for sites receiving pulsed or CW lase r light. Two days after light delivery, the dogs were endoscoped to ev aluate the severity of the lesions. While some response variability wa s observed among different animals, endoscopic examination of the lesi ons revealed comparable injury from CW and pulsed light in each subjec t. The animals were then euthanized and necropsies were performed. Bas ed on the gross and histological examination of the lesions, the CW an d pulsed laser-induced injuries could not be distinguished.