COMPLICATIONS OF COMBINED INTRAOPERATIVE RADIATION (IORT) AND EXTERNAL RADIATION (ERT) OF THE UPPER ABDOMEN - AN EXPERIMENTAL-MODEL

An experimental model in the rabbit is presented which is suitable for analysis of clinically relevant, early side-effects of combined upper abdominal IORT and ERT. Fractionated ERT alone given through an upper abdominal a.-p. field including the entire stomach caused gastric ulc erations within less than or equal to 58 days. Latent times decreased with increasing dose and the ED(50) for occurrence of ulcers was 39 +/ - 3.3 Gy. Single doses of IORT of 20-40 Gy alone administered through a 2-cm diameter field localized on the coeliac axis and carefully excl uding any intestinal mucosa caused neither gastric ulcerations nor oth er clinical symptoms. When ERT with 40 Gy was preceded by IORT with 20 -40 Gy or by sham IORT, 13 out of 15 animals developed ulcers after la tent times which in a life-table analysis were shown to be significant ly shorter than after ERT alone. However, a statistically significant IORT dose-dependence of latent time or incidence of ulcers could not b e demonstrated in the present experiment. The most significant histolo gical changes were observed in the areas of gastric ulcers. Already du ring ERT, the mucosal epithelium was depleted and regenerative activit y was evident in spite of ongoing fractionated irradiation. However, p rofound irregularities in glandular structure and distribution, as wel l as number of proliferating epithelial cells were still present in he aled ulcers at 80 days. In summary, IORT to the coeliac artery did pre cipitate the development of gastric ulcers induced by subsequent ERT. On the one hand, the data indicate that the surgical procedure of IORT did contribute to this effect. On the other hand, IORT to the coeliac artery could cause transient, functional alterations in blood supply to the depending organs, i.e. the stomach, and could thus precipitate the development of radiation-induced ulcers.