EARLY INFLAMMATORY REACTION OF THE RABBIT CELIAC ARTERY WALL AFTER COMBINED INTRAOPERATIVE (IORT) AND EXTERNAL (ERT) IRRADIATION

The present immunohistochemical study of radiation-induced damage in m ajor blood vessels is based on a multidisciplinary study (Schultz-Hect or et al., Radiother. Oncol., 38:205-214, 1996) investigating the comb ined effect of IORT of the coeliac axis and upper abdominal ERT. The p aper describes the sequential changes occurring in the coeliac artery after IORT with 30 Gy, i.e. during and after combined IORT and fractio nated ERT (total dose 40 Gy). Within 24 h after IORT, the arterial wal l was found to be invaded by TNF-alpha positive macrophages, which lat er on disappeared within 7-14 days. At 2 days post-IORT, the medial sm ooth muscle cells were strongly positive for TNF-alpha and remained po sitive throughout the observation period of 63 days. At 80 days, a com parison of different IORT dose groups showed that TNF-alpha expression after 20 and 30 Gy IORT plus 40 Gy ERT had subsided, while it was sti ll strongly evident after 40 Gy IORT. Negative reactions in sham irrad iated animals or animals treated with ERT alone indicate that TNF-alph a expression was caused by IORT. After >30 days post-IORT, there was i ncreased collagen type I deposition in the adventitia. In two animals receiving the full ERT course, intimal proliferations involving mainly smooth muscle cells were observed. Our findings indicate that some fe atures typical of radiation induced arteriosclerosis such as periarter ial fibrosis and intimal proliferations can occur as early as <60 days postirradiation. Macrophage invasion as well as TNF-alpha expression in medial smooth muscle cells are known to be important steps in the d evelopment of spontaneous atherosclerotic lesions. Therefore, early TN F-alpha induction in the arterial wall by a high local dose of X-irrad iation may be regarded as one initiating factor of chronic radiation-i nduced arteriosclerosis.