2/14/2016 L10,L11 and L12 1 PRINCE SATTAM BIN ABDUL AZIZ UNIVERSITY COLLEGE OF PHARMACY Nuclear...
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2/14/2016 L10,L11 and L12 1 PRINCE SATTAM BIN ABDUL AZIZ UNIVERSITY COLLEGE OF PHARMACY Nuclear Pharmacy (PHT 433 ) Dr. Shahid Jamil The roentgen is the amount of x or radiation that produces ionization of one electrostatic unit of either positive or negative charge per cubic centimeter of air at 0C and 760 mmHg (STP). Since 1 cm3 air weighs g at STP and a charge of either sign carries 1.6 Coulomb (C) or 4.8 electrostatic units, it can be shown that 1R = 2.58 C/Kg It should be noted that the roentgen applies only to air and to x or radiations. Due to practical limitations of the measuring instruments, the R unit is applicable only to photons of less than 3 MeV energy 1. The exposure dose(rontgen). 1. The exposure dose (rontgen). 2/14/20162 L5,L6 and L7 b- Dose units The unit of absorption dose. The absorbed dose of any ionizing radiation is the energy imparted to matter per unit mass of irradiated material. 1 rad is that quantity of radiation which delivers 100 ergs per gm of matter. Absorbed dose (rads) = Exposure dose (Roentgens) X (C.F.) C.F. = Conversion factor depending on the density of the absorbing body and type of radiation. 2- The Radiation Absorbed Dose (RAD) C.F. in MevEnergy MuscleBoneWater Soft X rays Medium X rays rays (from Co 60 ) The unit of absorption dose. The absorbed dose of any ionizing radiation is the energy imparted to matter per unit mass of irradiated material. 1 rad is that quantity of radiation which delivers 100 ergs per gm of matter. Absorbed dose (rads) = Exposure dose (Roentgens) X (C.F.) C.F. = Conversion factor depending on the density of the absorbing body and type of radiation. 2/14/20163 L5,L6 and L7 The Rem is used to express human biological doses as a result of exposure to one or several types of ionizing radiations. Thus it is defined as: That dose of radiation which produces in man the effects of 1 rad. 3. The Roentgen Equivalent Man (REM) Dose equivalent H (rems) = absorbed dose (rads) X (Q.F.) X (D.F.) Q.F. = Quality Factor. D.F. = Distribution factor depends on the energy produced and angle of incidence. and angle of incidence. Both Q.F. and D.F. could be replaced by RBE (Relative Biological Effectiveness) = 1 for , X and radiation and equal to 10 for particles, protons and fast neutrons. 2/14/20164 L5,L6 and L7 The primary event producing injury in a cell is the production of ionization. Excitation plays a small part, since radiations which cause excitation without ionization, as UV, are less effective in cell damage. The dose of radiation which kills a cell may cause ionization in only one molecule in 108. THE BIOLOGICAL EFFECTS OF RADIATION Mechanism of Injury 2/14/20165 L10,L11 and L12 Direct radiation effects Result from an ionization or excitation within a biologically functional molecule. The occurrence of an ion cluster within such a molecule releases sufficient energy that terminate biological function of the cell. There are several theories concerning the mechanism by which damage arises. but the damage results from a mixture of direct and indirect effects. 2/14/20166 L10,L11 and L12 All nuclear disintegrations result directly or indirectly in production of fast-moving, charged particles. As these charged particles pass through matter they collide with atoms in their path and share their energies with the planetary electrons. Some of the latter may acquire sufficient energy to tear themselves away from the atom. Thus, a track of negative electrons and positively charged molecule together with its separated electron is called an ion pair and the "tearing-away" process is known as ionization. 1. Ionization 2/14/20167 L10,L11 and L12 Sometimes, when radiations react with matter, ionization does not take place. Instead, the atoms simply acquire extra energy from the particles and assume an excited state, a process known as excitation. This excess energy may be discharged in several ways, one which is the emission of light. Alpha and beta particles cause ionization and excitation directly. 2. Excitation 2/14/20168 L10,L11 and L12 Gamma radiation, because it is without mass or charge, reacts much less strongly with matter. However, it does interact with some of the planetary electrons and these escape, often with high energy, causing the above effects. 2/14/20169 L10,L11 and L12 Ionization and excitation of molecules in the body cause abnormal chemical reactions. For example, essential enzymes are inactivated, proteins are coagulated, nucleic acids in the genetic apparatus are damaged, and histamine- like substances are produced. These primary effects lead to the familiar signs of radiation damage. Biological Effects: 2/14/ L10,L11 and L12 Indirect radiation Effects It result from the radiolysis of intracellular water (80 %) of most cells, and of any extracellular water which may be present. The principal effects are oxidative that oxidations may result from reactions with the hydroxyl, hydroperoxy free radicals, hydrogen peroxide and the hydrogen radicals, which is responsible for destructive effects of radiation. As oxygen enhances radiation damage thus substances which protect against radiation are reducing agents (e.g. cysteamine, cysteine, glutathione). 2/14/ L10,L11 and L12 Reactions in the radiolysis of water (free radicals underlined) 2/14/ L10,L11 and L12 The free radicals OH and H may reacts OH + OH H 2 O 2 H + H H 2 2/14/ L10,L11 and L12 Radiation Effects on the Human Body The effects of radiation on the entire organism depends on the proportion irradiated, Most severe with whole body exposure and least if only a small mass of insensitive tissue such as the hands is exposed. The degree of damage is influenced by the radiation intensity and the exposure time. In general, a number of small doses spread over several week does less damage than the same amount of radiation in one dose. However, this does not apply to the reproductive cells of the testes and ovaries, that the effect on which is cumulative. 2/14/ L10,L11 and L12 Short term effects.(prompt effect) Immediately appeared effect Whole body doses of about 25 rem would produce a transient change in the leucocyte count. Increasing the dose would result in increasing severity, 100 rem causing moderate illness (diarrhea, vomiting) in about 10 per cent of subjects, and severe illness in about 1 per cent, the syndrome is known as radiation sickness. The median lethal dose (LD 50 ) for death in 30 days is about 400 rem and with a dose of 600 rem there would be few survivors. Death from doses of this magnitude is usually the result of gut damage and a loss of resistance to disease. So that infections due to the intestinal microflors proceed. 2/14/ L10,L11 and L12 Some degree of protection against radiation sickness is afforded by the presence of reducing chemicals (cysteamine, glutathione) and by shielding certain important tissues such as the spleen and the bone marrow. 2/14/ L10,L11 and L12 Long term effects. The results of long term exposure include permanent skin damage, bone necrosis and increased incidence of anemia, leukaemia, cataract and carcinomata. The human embryo is very sensitive and doses as small as 25 rem may lead to sever abnormalities. 2/14/ L10,L11 and L12 This was observed in early workers with X-rays who received very large doses over a prolonged period. A short exposure to intense radiation produces erythema. Longer exposure can cause brittleness and dryness (due to destruction of the sebaceous glands), loss of hair (due to damage to the hair follicle) and, if the dose is very large, burns. The latter heal very slowly and occasionally become malignant. 1- Skin Damage 2/14/ L10,L11 and L12 2. Somatic effects This may become evident from about two months to many years after exposure. They include cataract, severe anaemias, leukaemia, and cancer. Cancer tends to occur in tissues severely damaged by radiation. The latent period is very long and often exceeds twenty years. 2/14/ L10,L11 and L12 3. Genetic effects Radiation has two effects on reproductive cells. It can damage the chromosomes and increase the frequency of gene mutation. The former is not very important because it is caused only by long exposure to low intensity X- and gamma - rays. Because damage to genetic material is cumulative and irreversible, long exposure at low intensity effects the mutation rate as much as an equivalent dose of high intensity, i.e. there is no safe threshold dose. 2/14/ L10,L11 and L12 The mutations will be hereditary by future generations and most are harmful. Consequently, it is not the exposed person who is at special risk but, rather, future generations and, through these, the whole population. Thus it is important that radiation exposure should be minimized during the early years. 2/14/ L10,L11 and L12 4- The effect on the rate of cell division All cells are susceptible to radiation damage depends on the rate of cell division. Thus tissues increase in resistance in the following order: lymphocytes, erythrocytes, germinal epithelium, intestinal epithelium, skin, internal organs, brain, muscle, nerve. This indicates that an important part of the damage must be to the nuclear apparatus due to interference with nucleic acid synthesis with the production of abnormal chromosomes. 2/14/ L10,L11 and L12 Since any defect would result in imperfect replication, that the effect of which would be multiplied at each cell division, thus the greater the rate of cell division the greater being the observed damage. The effects in radiosensitive tissues (gonads, gut) commence at doses of about 10 rem and are severe at 100 rem. In liver and muscle, which are relatively radioresistant, doses greater than 1000 rem are needed to produce effects. 2/14/ L10,L11 and L12 Man is continually exposed to external and internal radiations of natural origin (background radiation) Exposure to Radiation Radiation from natural sources. 2/14/ L10,L11 and L12 (a) The earth's crust contains radioactive miner