The diploma thesis dealt with the theme of "Assessment of the average radiation exposure from medical diagnostics" is divided into two main parts. The first one is concerned with the various measurement of radiation dose during diagnostic medical radiation. The second one is focused on radiation dose optimization during diagnostic medical radiation. With increasing of the collective effective dose in population, we should consider the importance of radiation protection during diagnostic medical radiation and accuracy of effective dose estimate that is used during individual medical examinations. On the basis of these estimates, it is necessary to determine the medical theory of radiation protection and to gain control over radiation dose and optimization of diagnostic medical radiation somehow. The theoretical part describes the kinds of ionizing radiation and their biological effects on organism. This part follows the chapter devoted to radiation protection and legal framework of the Czech Republic that is related to the topic: the application of ionizing radiation, mainly the Act No. 18 /1997 Coll. on Peaceful Utilisation of Nuclear Energy and Decree of the SÚJB No. 307 /2002 Coll., on Radiation Protection. There are discussed also the particular principles of protection against radiation. Afterwards, in the theoretical part, the quantities and the units used by radiodiagnostics and nuclear medicine are described. They are needed to know for the following determination and the estimate of dose amount absorbed by human organism. The conclusion of the theoretical part treats the methods used for estimate of dose received during medical examination and new trends in radiation management of individual patients. In the diploma thesis, there are set up two research questions. The thesis has been looking for the answers by its own research. The first research question is, if the current way of measurement of radiation dose is sufficient. The second one has been asking for manners of access allowed the decreasing of dose for patients regarding to registered effective dose. On the basis of these defined research questions, the basic aims have been set up to consider the application of individual methods of dose evaluation during medical radiation, to determine, from the registered values, probably the most exact method for evaluation of radiation dose and to deduce the probability of stochastic effects formation conditioned by radiation. The research was performed with two groups of patients that were undergone skiagraphic examination of lungs and examination of stomach by computed tomography (CT). The research devoted to skiagraphic examination of lungs was dealt with women suffering by similar body constitution. The results of measured effective dose of these patients were compared, and the manner of measurement and influencing of final absorb dose in the mammary gland were presented. The relation of individual projections towards probability of cancer birth conditioned by radiation was demonstrated. For comparison and setting up the most exact method, the first group was measured by the most available and the most common way used in clinical practice. PCXMC and ImPACT CT software are the most applying methods in clinical practice. As the most available method, standardize values and the procedure from the Bulletin of the Ministry of Health for Radiation Physics were applied. The final effective doses were compared with the local and national diagnostic referential levels in order to set up the correct procedure of radiation protection. The second researched group of patients undergone stomach examination performed by computed tomography (CT). The final effective doses of these patients were compared according to ICRP 60 and ICRP 103. Just as in the first group, there were compared two methods of measurement, the most available and the most applying in the practice.

During X-ray examinations a large part of the radiation is scattered from the patient, contributing to larger radiation doses to medical staff operating inside the examination room. Ionizing radiation contributes to the risk of developing cancer and hereditary diseases but also to the risk of developing cataract.   The aim of this thesis was to investigate the radiation environment and construct three-dimensional maps of the dose distribution, in a Computed Tomography (CT) room during examinations.    Air kerma was measured with real time dosimeters while irradiating an anthropomorphic phantom, using the X-ray tube voltages 100, 120 and 140 kV. The effective dose received by protected and unprotected medical staff inside the CT room during radiation exposure was estimated by using spectra from scattered X-ray radiation, a simulation of X-ray spectra and the dose evaluation program PCXMC. The equivalent dose to the eye lens was estimated by using spectra from scattered X-ray radiation and tabulated conversion factors from air kerma to the personal dose equivalent at 0.07 mm depth, Hp(0.07). From the estimated values of the effective dose and equivalent eye lens dose received by medical staff inside the room, three-dimensional dose distribution maps were constructed. The shielding effectiveness of a lead apron regularly used in the room was examined using tube voltages of 100, 120 and 140 kV.   The radiation dose distributions have a maximum closest to the irradiated phantom for most heights except at eye level where the maximum is shifted outwards along the patient table due to strong shielding by the gantry at eye level. The strong shielding of the gantry is noticed for all energy levels and at all heights but is exceptionally noticeable at eye level. The shielding of the patient table is strongest for the lower heights but is also noticeable at eye level which may seem surprising since there were no objects between the phantom and that point. The dose distribution along directions with minimal shielding seems to follow the inverse square law well. The lead apron is effective but its efficiency decreases for higher photon energies which is expected.   From information about the frequency and durations of CT-guided procedures, the estimated annual effective dose is 1.6-2.3 mSv for protected and 14.3-19.8 mSv for unprotected personnel at the operator position. The estimated annual equivalent eye lens dose is 4.7-7.8 mSv at the operator position. All annual doses at the operator position are below the annual threshold values of 20 mSv set by the ICRP.