Radiotherapy is one of the important modalities in treating children with malignant neoplasms. It is defined as one of the ways of treating both tumors and some other diseases in which the therapeutic effect is achieved by applying ionizing radiation. The main goal of radiotherapy is the application of the maximum dose of radiation to the tumor tissue with the best possible protection of the surrounding, healthy tissue. However, a certain dose of radiation always affects healthy tissue, and as a result there are many side effects that need special attention in the radiotherapy of pediatric tumors. Radiation is most often performed with x-photons, y-photons and high-energy electrons, and it is possible to use other high-energy particles (eg protons or heavy ions). When it comes to the radiotherapy treatment planning for children, most of it is done on a CT simulator, while the radiation itself is performed on linear accelerators. The specificity of radiotherapy in the treatment of childhood tumors is that in addition to classic fixatives, which are also used to fix adult patients during radiation, general anesthesia is used in small children to make the therapy more accurate and effective.