LATE EFFECTS OF INTRAOPERATIVE RADIATION-THERAPY ON RETROPERITONEAL TISSUES, INTESTINE, AND BILE-DUCT IN A LARGE ANIMAL-MODEL

Purpose: The late histopathological effects of intraoperative radiothe rapy (IORT) on retroperitoneal tissues, intestine, and bile duct were investigated in dogs. Methods and Materials: Fourteen adult foxhounds were subjected to laparotomy and varying doses (0-45 Gy) of IORT (11 M eV electrons) delivered to retroperitoneal tissues including the great vessels and ureters, to a loop of defunctionalized small bowel, or to the extrahepatic bile duct. One control animal received an aortic tra nsection and reanastomosis at the time of laparotomy; another control received laparotomy alone. This paper describes the late effects of si ngle-fraction IORT occurring 3-5 years following treatment. Results an d Conclusion: Dogs receiving IORT to the retroperitoneum through a 4 X 15 cm portal showed few gross or histologic abnormalities at 20 Gy. A t doses ranging from 30-45 Gy, radiation changes in normal tissues wer e consistently observed. Retroperitoneal fibrosis with encasement of t he ureters and great vessels developed at doses greater than or equal to 30 Gy. Radiation changes were present in the aorta and vena sava at doses greater than or equal to 40 Gy. A 30 Gy dog developed an in-fie ld malignant osteosarcoma at 3 years which invaded the vertebral colum n and compressed the spinal cord. A 40 Gy animal developed obstruction of the right ureter with fatal septic hydronephrosis at 4 years. Anim als receiving IORT through a 5 cm IORT portal to an upper abdominal fi eld which included a defunctionalized loop of small bowel, showed few gross or histologic abnormalities at a dose of 20 Gy. At 30 Gy, hyalin e degeneration of the intestinal muscularis layer of the bowel occurre d. At a dose of 45 Gy, internal intestinal fistulae developed. One 30 Gy animal developed right ureteral obstruction and hydronephrosis at 5 years. A dog receiving 30 Gy IORT through a 5 cm portal to the extrah epatic bile duct showed diffuse fibrosis through the gastroduodenal li gament. These canine studies contribute to the area of late tissue tol erance to IORT.