Protection of normal tissues with 2-aminoethylisothiouronium during local pelvic radiation in monkeys.

Intestinal and bladder injury are the main limiting factors to radiation therapy in patients with pelvic neoplasms. 2-Amino-ethylisothiouronium (AET) is a radiation-protective agent when given systemically but absorbs poorly from the intestines. Accordingly, it was explored for the local protection of the bowel and bladder during radiation to the pelvis. Radiation localized to the pelvis in various high fractionated doses and various schedules was applied to pairs of stumptailed monkeys (Macaca arctoides): one was always a control; and the other was treated with AET. AET was applied to the bladder through a catheter and to the rectum with a cotton tampon during the time of radiation. After radiation, AET was removed by repeated washings. Control animals developed hemorrhage, diarrhea, and emaciation and died at various times after completion of the radiation course; biopsy of rectal mucosa showed severe radiation damage. AET-treated animals had only occult blood in the stools and suffered slight weight loss; rectal biopsies showed normal tissues 2 weeks after radiation.