THE EFFECT OF PHOTODYNAMIC THERAPY ON THE MECHANICAL INTEGRITY OF NORMAL RABBIT CAROTID ARTERIES

Photodynamic therapy (PDT) for tumor ablation is effective in the trea tment of superficial cancers. Adjunctive intraoperative PDT has been p roposed for the ''sterilization'' of tumor beds after the resection of malignancies. Arteries in photosensitized animal models exposed to ap propriate light receive characteristic injury. This study was conducte d to determine whether photodynamic injury to the rabbit carotid arter y results in thrombotic occlusion or weakening of the vessel wall. PDT of the carotid arteries of New Zealand white rabbits, using either di sulphonated aluminum phthalocyanine or 5-aminolevulinic-acid-induced p rotoporphyrin IX as the photosensitizer, was performed with a light do se of 100 J/cm(2). 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 inf iltrate was evident. Elastin van Gieson staining showed preservation o f 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 s egments were subjected to intraluminal hydrostatic distention until th e vessels burst. No reduction in the pressure required to burst the ve ssels was evident in the treated vessels as compared with the control vessels. The authors of the study concluded that despite full-thicknes s cell death. PDT-treated arteries are not at risk for thrombotic occl usion or hemorrhage.