INTRAOPERATIVE RADIATION (IORT) INJURY TO SCIATIC-NERVE IN A LARGE ANIMAL-MODEL

Peripheral nerve appears to be a dose-limiting normal tissue in the cl inical application of intraoperative radiation therapy (IORT). To asse ss IORT injury to peripheral nerve, three groups of five beagle dogs r eceived doses of 12, 20 or 28 Gy to the surgically exposed and isolate d right sciatic nerve in the mid-femoral region using 6 MeV electrons. The left sciatic nerve of each dog served as its own control. As a su rgical control five dogs received surgical exposure of the nerve only. Monthly neurologic exams, electromyogram and nerve conduction studies were performed following treatment for 12 months. After that dogs wer e euthanatized and histologic studies of nerves were done to define th e degree of axon and myelin loss as well as presence of fibrosis and v ascular lesions for different doses of IORT. Results showed that the t hreshold dose most likely related to expression of severe radiation da mage to the nerve in this model is between 20 and 25 Gy. Radiation inj ury to peripheral nerve appears to be the result of direct radiation e ffects on Schwann cells and nerve vasculature and secondary effects re sulting from damage to regional muscle and vasculature. A theoretical mechanism of radiation injury to peripheral nerve is proposed.