Colorectal cancer is the second most common type of cancer in Europe, and rectal cancer is the third leading in colorectal cancers. It is therefore necessary to bring optimal treatment plan to extend survival. In modern radiotherapy, the emphasis is on reducing the volume of tissue exposed to high doses of radiotherapy, improving accuracy and reducing the exposure of normal tissue to radiation. In the last two decades, the treatment of rectal cancer is of purely surgical approach, took on multidisciplinary approach. Although surgery is still crucial, neoadjuvant treatment is all the more important. Patient positioning is extremely important to accurately deliver doses. Reproducibility can be affected by several factors such as the physical condition of the patient, body mass index (BMI), use of the immobilization means, positioning the patient in prone or supine position. The consequences of missing a target volume, even in part, have the effect of reducing the probability of tumor control and increase the likelihood of complications by healthy tissue. Small intestine, colon and bladder are the most important organs of the risk (OAR) in the radiation of the pelvis. The small intestine is the most radiosensitive and dose-limiting normal structure; and therefore, the diarrhea is the most common acute side effects of radiation therapy in the pelvis. The incidence of acute and chronic complications by the small intestine in pelvic radiotherapy dose of 50 Gy is between 2 - 9%. Studies of the NTCP (normal tissue complication probability) have found that the volume of small bowel receiving 15 Gy (V15) and 45 Gy (V45) are the most important parameters for gastrointestinal toxicity. It is common for patients during CT simulation and implementation of radiotherapy lying prone with full bladder, regardless of whether the radiation therapy is before or after surgery. In some centers they are using the belly boardto move the intestines, so they can reduce the volume of the intestines in the field of high dose pelvic radiation. Prone position is often unpleasant for patients, and it is difficult to maintain the same position for a long time. This is especially true for older patients and the patients who come to radiotherapy after surgery with colostomy. As a result we have unstable position of the patient who is not constantly reproducible and subject to systematic and random mistake in the positioning. Achieved a remarkable improvement of the reduction of error ratio and the positioning of the patient indicates the importance of quality assurance in the process of adjustment of the patient and the goal of this review article is to get the information how to improve the accuracy of radiotherapy of rectum and thus reduce the exposure of healthy tissue to high doses of radiation which might result in the reduction of unwanted effects of radiotherapy. Keywords: radiotherapy of rectum, supine position,prone position, the side effects of radiotherapy, belly board