Novel After‐loading Interstitial Photodynamic Therapy of Canine Transmissible Sarcoma with Photofrin II and Excimer Dye Laser

Novel after‐loading interstitial photodynamic therapy was performed in a canine transmissible sarcoma (CTS) model, utilizing photofrin II and an excimer dye laser. First, photofrin II was injected intravenously at a dose of 5 mg/kg, then 48 h later, laser‐proof plastic tubing was inserted into the CTS, followed by photoradiation of the tumor from the inside. The mean diameter of tumor necrosis rapidly increased in parallel with increase in total irradiation energy below 240 J/cm; the mean diameter of tumor necrosis was 20.7 mm at an energy of 120 J/cm, and 24.5 mm at 240 J/cm. Beyond 240 J/cm, the diameter gradually increased to 26 mm at 960 J/cm. As a side effect, cutaneous tissue showed a deep open ulcer at 240 J/cm, a shallow open ulcer at 180 J/cm, and a scar healing at 120 J/cm. The thermal effect of laser light is considered negligible below 480 J/cm.