 As a consequence of the wide use of ionizing radiation in medicine, patient exposure is nowadays by far the largest source of population exposure from man-made sources. It is thus very important that radiation protection as a patient is given is due consideration. Radiation protection in medicine is somewhat specific because not only too high dose can cause problems, but also too low dose is a problem. Too high dose to the patient will increase their risk either for cancer or for direct damage to the tissue. Too low dose is also harmful to the patient in a sense that it will not provide the desired result. In case of diagnostics the image quality will not be adequate for proper diagnosis and in case of treatment too low dose will lead to reduced cancer control. Radiation protection of patients is basically based on justification and optimization. Justification means that for each procedure benefit to the patient should be carefully awaited against the harmful effect of ionizing radiation. Optimization means that each procedure should be performed by the minimal dose that will still achieve the desired result. For example, they will provide adequate image quality for diagnostic purposes. The size of the image of the imaged area is also an important factor. Only the region which is really important to provide necessary information should be included in the image because this will reduce the amount of the tissue that is radiated during imaging procedure. The institute was involved in a number of technical projects through IIA. They received training, scientific visits and other ways of education and licensed support. The best known therapeutic use of ionizing radiation is cancer treatment with radiotherapy. Here the objectives of radiation protection of patients are somewhat different than in diagnostics. The main objective is to deliver high enough dose to the tumor to destroy it. At the same time, the dose to surrounding healthy tissue should be minimized so as to reduce the side effects of the treatment. A crucial element of radiation protection of patients is a treatment planning process. This is a complex multi-stage process that is tailored to each particular patient. It starts with simulation of the procedure on conventional simulators or city simulators, where the basic images of the patient and the tumor location is obtained. Those images are used by radiation oncologists to contour the tumor location as well as the critical organs that should be spared during treatment. Those information are then transferred to medical physicists that prepare a treatment plan. In this stage they decide the directions, shapes and intensities of the radiation beams that will be used during treatment. As a result of the hard work of the staff and of the support from the agency in 2011 Institute of Oncology was recognized as a center of competence. Nowadays they can not only receive support from the agency but they also support the surrounding case and center with training and expertise.