The study addresses at relevant laws that guide and regulate the use of ionizing radiation in radiotherapy services inside a public hospital (INCA - National Cancer Institute, HC 1), situated in Rio de Janeiro, Brazil. Radioactivity is a phenomenon of natural origin easily found in the environment or artificially generated. It has beneficial applications being applied in agriculture, energy production, industry and medicine in health treatments. It brings harmful effects when used inappropriately, as it has physical peculiarities that, despite of advantages, in high-level doses can cause severe damage to the body (PERUZZO, 2012). During radiotherapy treatments, it is essential to maintain safe shielding conditions, including protective equipment and constant supervision so that professionals working in these areas do not suffer excessive exposure. Radiotherapy assists in the treatment of diseases using diagnostic and therapy techniques employing radioactive substances such as Cesium, Cobalt, Iodine, Technetium among others. These substances are present in radiopharmaceuticals, applied directly to patients through brachytherapy techniques or into the capsules installed in the pieces of equipment used in teletherapy. Currently, regulation of activities involving radioprotection and nuclear safety in Brazil is under the responsibility of the CNEN (National Nuclear Energy Commission), an autarchy of the Ministry of Science, Technology and Innovations. It is a government agency responsible for licensing and controlling all practices involving ionizing radiation.