Protection of the small intestine against irradiation by means of a removable prosthesis. In radiation therapy of tumors, several techniques are used to prevent injury of the intestinal loops. Their purpose is to drive the intestine out of the external beam. Understanding the disadvantages they present, a temporary prosthesis which effectively protects the small bowel, and is easy to remove, has been developed. The device is a 600 to 1,000 ml, silicone rubber, expandable balloon. When implanted in the pelvis or retroperitoneal cavity, and filled, this balloon displaces the intestinal loops out of the pelvic irradiation field. It may remain either filled or empty between each irradiation session. Due to its particular elliptical shape, once empty, the balloon can be removed through a 3 cm incision under local or peridural anesthesia at the completion of radiotherapy. Eleven patients with recurrent (8) or primary (3) cancer have been implanted. The protective effect has been evaluated on successive biologic tests, performed during treatment. No problem related to the prosthesis, no alteration of the biologic tests, nor bowel injury have been observed after several months follow-up. This device is suitable for preventing intestinal complications during therapy, allowing a higher dose of radiations in some cases. 