The effect of photodynamic therapy on the mechanical integrity of normal rabbit carotid arteries.

Photodynamic therapy (PDT) for tumor ablation is effective in the treatment of superficial cancers. Adjunctive intraoperative PDT has been proposed for the "sterilization" of tumor beds after the resection of malignancies. Arteries in photosensitized animal models exposed to appropriate light receive characteristic injury. This study was conducted to determine whether photodynamic injury to the rabbit carotid artery results in thrombotic occlusion or weakening of the vessel wall. PDT of the carotid arteries of New Zealand white rabbits, using either disulphonated aluminum phthalocyanine or 5-aminolevulinic-acid-induced protoporphyrin IX as the photosensitizer, was performed with a light dose of 100 J/cm2. Histologic examination of the carotids treated with either agent demonstrated typical full-thickness loss of cellularity 3 days after PDT. All vessels remained patent, and no inflammatory infiltrate was evident. Elastin van Gieson staining showed preservation of inner and medial elastic laminae and medial and adventitial collagen. Additional rabbits were similarly treated with PDT to 1-cm segments of both common carotid arteries. The animals were sacrificed at 3, 7, and 21 days. The carotids were exposed, and both control and treated segments were subjected to intraluminal hydrostatic distention until the vessels burst. No reduction in the pressure required to burst the vessels was evident in the treated vessels as compared with the control vessels. The authors of the study concluded that despite full-thickness cell death, PDT-treated arteries are not at risk for thrombotic occlusion or hemorrhage.