The purpose of radiation protection is to protect workers, patients and members of the general public against any excessive impact of exposure to ionizing radiation, and to control the radioactive contamination of the environment in accordance with the strict regulatory standards. In order to adopt any measures to regulate the exposure from various sources, it is necessary to introduce a reliable and consistent system of the quantification of radiation exposure due to external and internal sources. Only very low doses (comparable with the natural radiation background) are encountered under normal circumstances. Such exposures may result in stochastic (delayed) effects, where the probability of their occurrence is proportional to the magnitude of the effective dose expressed in Sv (sievert). While for the stochastic effects only the unit of Sv can be used, for the quantification of deterministic effects (tissue reaction), which occur at rather higher doses, other quantities and units are more appropriate. In this case, one relies on a new quantity, namely RBE-weighted dose with a unit of Eq-Gy (equivalent gray). The paper offers some original illustrations of the system of quantities for assessing both stochastic and deterministic harmful effects of ionizing radiation.

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