Tolerance of Retroperitoneal Structures to Intraoperative Radiation

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Abstract
In conjunction with the clinical development of intraoperative cancer radiotherapy, a study was undertaken in dogs to define the tolerance of normal anatomic structures in the retroperitoneum to radiation delivered during operation. Twenty adult dogs were subjected to laparotomy and intraoperative 11 MeV electron irradiation in single doses ranging from 0 to 5000 rad. Animals were followed regularly with clinical observation, blood count, serum chemistries, pyelography and angiography. Animals were sacrificed and autopsied at regular intervals up to 12 mo. following treatment to assess radiation-induced complications or tissue damage. Irradiation field in all dogs consisted of a 4 .times. 15 cm rectangle extending in the retroperitoneum from the level of the renal vessels to the bifurcation of aorta and vena cava. The field included aorta, vena cava, inferior portion of the left kidney and the distal portion of the left ureter. No complications or histologic changes occurred in any animal given doses of 2000 rad, with a follow-up in excess of 18 mo. A dose of 3000 rad was well tolerated, except for left ureteral occlusion in 1 animal. Mild vascular fibrosis was present in the aorta and vena cava, and significant ureteral fibrosis developed by 6 mo. after doses of 4000 or 5000 rad. All animals that received 5000 rad died of radiation-related complications, including ureteral obstruction and rectal perforation. Major vessels tolerate intraoperative irradiation well up to and including 3000 rad and no clinically significant vascular problems develop after 4000 and 5000 rad, although some fibrosis does occur. The ureter and kidney appear to be the most radiosensitive structures in the retroperitoneum, showing progressive changes at 3000 rad or greater and showing the potential for serious complications after doses of 4000 rad or more.