Preoperative X-Ray Therapy in a Simulated Colon Carcinoma in the Rat

X-ray treatment may be of some value in slowing, at least temporarily, the cancerous invasion of a fast-growing tumor so that its total removal by surgery is greatly facilitated. The experiment to be described was designed to determine the effect of preoperative x-ray therapy on a simulated colon carcinoma in the rat (1). Methods and Materials For this experiment 2-mm. bits of Walker 256 carcinosarcoma were implanted in the cecal appendix in 200 female Wistar rats (Charles River Farms) having an average weight of 200 gm., by a method previously reported (1). The tumors of 100 of the rats were irradiated with an exposure dose of 200 r for four successive days, starting two weeks after implantation. The remaining 100 rats were kept as controls. The radiation source was a General Electric Maxitron operated at 250 kevp and 30 ma, emitting a beam having a half-value layer of 1 mm. Cu (0.38 mm. Cu filtration added). The target-source distance was 100 cm. During irradiation the rats were restrained in dorsal recumbency, their bodies being protected with a lead shield 0.5 cm. thick, except for a hole 2 cm. square which permitted exposure of the tumor. Twenty-four hours following the x-ray treatment, all 200 rats were operated upon. Following Nembutal anesthesia, the abdomen was opened and the animals scored as to operability. All cases with local extension of the primary tumor and distant metastasis were considered inoperable. In the operable animals a cecal appendectomy was performed 1 cm. distal to the tumor. The remaining portion of the intestine was then replaced in the peritoneal cavity and the laparotomy incision was closed in the conventional manner. Following surgery, records were kept on survival. At death the animals were autopsied and the visual extent of the disease scored. Nine weeks after surgery surviving animals were sacrificed and autopsied; the extent of the disease in these animals was also scored. Results The results are shown in Figures 1 and 2, and are summarized in Table I. The number of operable animals was increased significantly by the preoperative irradiation (90 per cent versus 79 per cent). Two weeks before surgery all of the animals were palpated and those with large tumors were scored as “doubtful.” Almost all of those in the unirradiated group thus scored were found to be inoperable at surgery, while most of the animals scored as “doubtful” in the irradiated group proved to be operable. Unfortunately, this difference was not significant, possibly because there were so few “doubtful” animals (unirradiated N = 13, and irradiated N = 16). The number of rats surviving nine weeks was significantly greater in the irradiated (49 per cent) than in the unirradiated (33 per cent) group.