Radiotherapy is a way of treating malignant tumors with ionizing radiation whose goal is to maximally irradiate the tumor and to spare the surrounding healthy tissue. Depending on the type and stage of the cancer, various radiotherapy techniques are used, including external beam therapy or brachytherapy. Endometrial cancer is the most common cancer affecting the female reproductive organs in highly developed countries. In the treatment of this type of cancer, adjuvant radiotherapy is used after primary surgery, and other modalities such as chemotherapy are often used in addition to it. The goal of adjuvant radiotherapy is to destroy the residual microscopic foci of tumor tissue after surgery and to reduce the rate of locoregional recurrence of the disease. It is important to emphasize the importance of proper radiotherapy planning which includes determining the appropriate margins of all radiation volumes and marking organs at risk.