Clinical Radioprotection

        In this part of the manual, practical issues regarding the author's experience in the area will be discussed. Basic atomic and radiation physics will not be addressed in this chapter. The contents are divided in the following: general concepts, the laboratory, essential equipment, rooms for hospitalization, professionals employing ionizing radiation, the patient, patient's relatives and accompanying persons and the public.

        Ionizing radiation emerging from radionuclides is the basic element used in nuclear medicine for diagnosis and therapy. Normally radioactivity amounts are small for diagnosis, but may be significant as far as treatment. Therefore, thorough care must be paid when using any quantity due to their cumulative and eventually hazardous effect. In recent scientific publications the possibility of increased cancer risk at low radiation levels has been emphasized.

General Concepts

         The type of ionizing emmissions that are used more commonly in nuclear medicine are gamma rays, x rays and beta negative particles. Radiation interacts with the body, delivering energy in a direct or indirect way.

        When doing it directly, gamma rays or particles deposit their energy to the interactive structures and molecules of the cells themselves. In the indirect way, radiations generate free radicals, by water ionization, which in turn will interact with the molecules of the cell. Free radicals are chemically intensively reactive. In both cases, damage may take place by rupture of molecules. The most important ones are proteins, RNA and DNA. The type of chromosome damage per dose level received in Gray, is variable. There may be single-stranded breaks, damage to the bases, double-stranded breaks, cross-linking of DNA and proteins. The most important is for the double-stranded breaks and is common especially after radiation with x-rays or gama rays.

        Radiations at the cellular level affect the membranes altering their permeability and the cytoplasm ionizing water with free radicals formation. As suggested before, in the nucleus they may affect the chromosomes and if they belong to germ cells, will produce potential heritable damage and mutations. Cells are more sensitive to radiation damage in the presence of oxygen and during mitosis.

        As far as the probability of radiations to produce damage to cells and human beings, the effects are divided into two. Stochastic effects (probabilistic or random) and deterministic (predictable or predetermined). The mechanism of action in stochastic ones is usually sublethal and affects a few cells. In contrast, the deterministic effects are more frequently lethal and affect a larger number of cells. In the case of stochastic effects affect mainly somatic and hereditary cells. Deterministic effects predominantly act on somatic cells. The extent of damage is independent of the dose in the case of stochastic effects and directly related to the dose in the deterministic ones. There is no threshold for the stochastic effects but so in the deterministic ones. The dose effect relationship is linear or quadratic for stochastic and often linear in the case of the deterministic. The onset is delayed for stochastic effects, immediate or delayed in the deterministic.

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