The irradiation of the rectum cancer occurs in many institutes by using a rectum balloon in order to reduce the mobility of the target organ and to distance the rectum from the target organ. The objective is to reduce side effects quantitatively as well as qualitatively. On the basis of two hospitals using identical techniques for the prostate irradiation with the sole difference of the rectum balloon the toxicity has been evaluated with the result of no significant difference between the cohorts concerning diarrhea, rectal pain symptoms and rectal bleedings. Therefore the authors consider the use of the rectum balloon prior to each irradiation not necessary for the reduction of toxicity particularly due to the fact that the application is often very painful, especially for patients with hemorrhoids. The rectum balloon as a tool for the reduction of the prostate mobility was not objective of this study.