Abstract: Nuclear engineer is one among a team of specialists enrolled in radiotherapy and radiosurgery. Survey of the types of radiotherapy, properties of the radioactive sources and machines used in radiotherapy, conformal therapy as well as stereotactic radiosurgery will be presented. The article will focus on the role of nuclear engineer during the design stage of the shelter room where the radiotherapeutic machine will be located, choice of concrete shield ingredients during constructing the shelter room, area monitoring around and above the shelter room, machine calibration and testing and finally during radiotherapy and radiosurgery.