Comparative study between pulsed and continuous wave lasers for Photofrin photodynamic therapy

A study was conducted in the normal canine esophagus to compare continuous wave (CW) and pulsed laser light for photodynamic therapy with Photofrin (4 mg/kg). Forty-eight hours post-injection, 630 nm laser light (CW light from an argon-pumped dye-laser and pulsed light from a KTP/532-pumped dye-laser) was delivered using a 24 mm diameter cylindrical esophageal PDT balloon positioned at either distal or proximal esophagus. A 1.0 cm cylindrical diffuser placed in the center of the balloon delivered 300 J/cm of light at an intensity of 400 mW/cm. Three dogs received CW light proximally and pulsed light distally. Four dogs received 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 technique was used to compare photosensitizer fluorescence intensities at distal and proximal locations. Similar mucosal light doses and drug fluorescence intensities were verified for sites receiving pulsed or CW laser light. Two days after light delivery, the dogs were endoscoped to evaluate the severity of the lesions. While some response variability was observed among different animals, endoscopic examination of the lesions revealed comparable injury from CW and pulsed light in each subject. The animals were then euthanized and necropsies were performed. Based on the gross and histological examination of the lesions, the CW and pulsed laser-induced injuries could not be distinguished.