Photodynamic therapy: response of normal canine urethra using a cylindrical fiber

Normal urethral response to photodynamic therapy (PDT) utilizing a cylindrical fiber was assessed in ten study and two control NIH fox-hounds. The canine urethras were treated 48 hours after intravenous injection of 3 mg/kg dihematoporphyrin ether (Photofrin II). A 1-mm fused silica optical fiber, with the distal 2-3 cm modified for cylindrical light distribution (660-microns diameter), was placed in the pendulous urethra. An argon-pumped dye laser delivered 100 mW of 630-nm light for 7 minutes (42 J) to the treatment area. Urethroscopy using either a 2.5-mm or a 2.8-mm flexible pediatric bronchoscope with video recording capability was performed immediately after PDT (12 animals) and 6 weeks later (nine animals); intravenous urography was performed 3 days and 6 weeks after PDT. There was no evidence of either urethral damage or stricture formation in any animal. Histopathology of the first three study specimens, obtained at 6 weeks, confirmed the absence of any pathology. Flexible instrumentation facilitates post-treatment assessment. This study demonstrates for the first time that, when a cylindrical fiber is used, photodynamic therapy may be applied to the urethra without damage to the normal urethral mucosa. This result has implications for potential treatment of initial or recurrent carcinoma in situ of the urethra using PDT.