SINGLE HIGH-DOSE IRRADIATION FOR SELECTED CANINE RECTAL CARCINOMAS

Single high-dose radiotherapy was evaluated as a treatment for seven adenocarcinomas of the distal half of the rectum and anal canal in six dogs. A single dose of radiation ranging from 15–25 Gy was given to the tumor by the use of a well-collimated, low-energy orthovoltage x-ray beam. Six tumors had complete response to treatment. Minimal acute radiation reaction was observed in all dogs. The tumor control and survival rates at 1 year were estimated to be 46% and 67%, respectively. Median and mean tumor-free times were 6.0 and 9.7 months, respectively; and median and mean survival times were 7.0 and 11.3 months, respectively. No long-term side effects were noted. Proper patient selection was critical because of the physical limitations of the procedure. Tumors should be less than 3 cm in diameter, confined to the rectal wall, and be located in the distal half of the rectum and anal canal. This preliminary study documented the fasibility, efficacy, and lack of toxicity of single high-dose radiotherapy for selected rectal carcinomas.