Intraoperative radiation of canine carotid artery, internal jugular vein, and vagus nerve. Therapeutic applications in the management of advanced head and neck cancers. As a step in the application of intraoperative radiotherapy (IORT) for treating advanced head and neck cancers, preliminary information was obtained on the radiation tolerance of the canine common carotid artery, internal jugular vein, and vagus nerve to a single, high-dose electron beam. Both sides of the neck of eight mongrel dogs were operated on to expose an 8-cm segment of common carotid artery, internal jugular vein, and vagus nerve. One side of the neck was irradiated, using escalating doses of 2500, 3500, 4500, and 5500 cGy. The contralateral side of the neck served as the unirradiated control. At 3 and 6 months after IORT, one dog at each dose level was killed. None of the dogs developed carotid bleeding at any time after IORT. Light microscopic investigations using hematoxylin-eosin staining on the common carotid artery and internal jugular vein showed no consistent changes that suggested radiation damage; however, the Masson trichrome stain and hydroxyproline concentration of irradiated common carotid artery indicated an increase in the collagen content of the tunica media. Marked changes in the irradiated vagus nerve were seen, indicating severe demyelination and loss of nerve fibers, which appeared to be radiation-dose dependent. Four patients with advanced recurrent head and neck cancer were treated with surgical resection and IORT without any acute or subacute complications. The role of IORT as a supplement to surgery, external beam irradiation, and chemotherapy in selected patients with advanced head and neck cancer needs further exploration. 