BIOLOGICAL HAZARDS & RADIOLOGICAL SAFETY

1. PRINCE SATTAM BIN ABDUL AZIZ UNIVERSITY COLLEGE OF PHARMACY BIOLOGICAL HAZARDS & RADIOLOGICAL SAFETY Nuclear Pharmacy (PHT 433 ) • Dr. ShahidJamil L10,L11 and L12

2. b- Dose units 1. The exposure dose(rontgen). The roentgen is the amount of x or γ 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 0.001293 g at STP and a charge of either sign carries 1.6 × 10-19Coulomb (C) or 4.8 × 10-10 electrostatic units, it can be shown that 1R = 2.58 × 10-4 C/Kg It should be noted that the roentgen applies only to air and to x or γ radiations. Due to practical limitations of the measuring instruments, the R unit is applicable only to photons of less than 3 MeV energy L5,L6 and L7

3. 2- The Radiation Absorbed Dose (RAD) 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. 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. L5,L6 and L7

4. 3. The Roentgen Equivalent Man (REM) 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. 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. Both Q.F. and D.F. could be replaced by RBE (Relative Biological Effectiveness) = 1 for γ, X and β radiation and equal to 10 for α particles, protons and fast neutrons. L5,L6 and L7

5. THE BIOLOGICAL EFFECTS OF RADIATION Mechanism of Injury 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. L10,L11 and L12

6. There are several theories concerning the mechanism by which damage arises. but the damage results from a mixture of direct and indirect effects. 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. L10,L11 and L12

7. 1. Ionization • 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. L10,L11 and L12

8. 2. Excitation 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. L10,L11 and L12

9. 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. L10,L11 and L12

10. Biological Effects: 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. L10,L11 and L12

11. 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). L10,L11 and L12

12. Reactions in the radiolysis of water (free radicals underlined) L10,L11 and L12

13. The free radicals •OH and •H may reacts •OH + •OH H2O2 •H + •H H2 L10,L11 and L12

14. 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. L10,L11 and L12

15. 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 (LD50) 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. L10,L11 and L12

16. 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. L10,L11 and L12

17. 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. L10,L11 and L12

18. 1- Skin Damage 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. L10,L11 and L12

19. 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. L10,L11 and L12

20. 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. L10,L11 and L12

21. 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. L10,L11 and L12

22. 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. L10,L11 and L12

23. 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. L10,L11 and L12

24. Exposure to Radiation Radiation from natural sources. Man is continually exposed to external and internal radiations of natural origin (background radiation) L10,L11 and L12

25. (a) The earth's crust contains radioactive minerals and therefore, man made structures of brick and material expose to measurable amounts of radiation. (b) Cosmic (outer space) rays from outer space (c) The atmosphere contains minute amounts of radon and thorn, gaseous decay products of radium and thorium. (d) Radioactive constituents of the human body, e.g.: 40K, 14C, and 226 Ra. L10,L11 and L12

26. The Gonads Dose Of Radiation From Natural Sources L10,L11 and L12

27. Radiation from other sources Man also receives radiation from the accessories of civilization. Sources of such radiation include natural background, X-ray examination, Fall-out from test explosions and industrial exposure. L10,L11 and L12

28. THE CONTROL OF RADIATION EXPOSURE Maximum Permissible Doses (MPD) One maximum permissible dose is that dose which, received in a certain defined period and repeated regularly and is not expected to cause appreciable bodily harm. Doses resulting from medical procedures are excluded since they are regarded as necessary and beneficial. L10,L11 and L12

29. The relationship governing the total permissible cumulative dose results • in an average dose rate of 5 rems per year for persons engaged in radiation work from the age of 18 years. • It is assumed that there is no occupational exposure to radiation permitted at age less 18 years. • Lower limits of permissible dose are set for the general population, amounting to an addition equal to the natural background dose, and for groups exposed occasionally, such as laboratory maintenance workers. L10,L11 and L12

30. Maximum Permissible Dose For Radiation Workers L10,L11 and L12

31. This is an average dose rate. The total permissible cumulative dose is given by: Where N is the age in years, and not More than 60 rem may be accumulated by 30 age of years. 5(N- 18) rems L10,L11 and L12

32. Radioprotection Dose rates at working positions should always be measured. The effect of distance γ-dose rates β-dose rates. L10,L11 and L12

33. The effect of distance Radiations are emitted from a source in all directions so with a point source in a non-absorbing medium where dis the distance from the source. For γ-radiation air is almost a non-absorbing medium. With β--particles there is considerable air absorption and external dose rates are not usually a problem. dose rate α 1 /d2 L10,L11 and L12

34. γ-dose rates The specific γ-ray constant (k-factor) is the dose rate produced by the γ-radiation from a radionuclide at a distance of 1 cm from a 1 mCi point source of that nuclide and have units of rongtens per millicurie hour at 1 cm. This is the most accurate basis for calculating the dose at any distance from γ-emitting source L10,L11 and L12

35. β-dose rates. The whole body dose rates due to β--particles is not considered since the particles have a limited finite range and can be stopped completely by simple shielding. But some parts of the body, as the hands and forearms, may be exposed. For a point source of β—emitter, the exposure dose is given by : where C is the source strength in curies. Dose rate at 10 cm = 3100 C rads per hour in tissue L10,L11 and L12

36. The effect of β--energy is negligible. It should be noted that β--particle doses to the hands may be very large, and the handling of an unshielded 1 mCi source of 32P would give a dose to the hands of about 3 rems per hour, assuming an average distance of 10 cm. This would result in the accumulation of one year's maximum permissible dose in 25 h. L10,L11 and L12

37. Shielding From the inverse square law and the appreciable air absorption of β--particles, that doses may be reduced by working at a sufficient distance from a source with small amounts of radioactivity. With larger amounts of activity shielding is necessary. Shielding materials may consist of lead, iron or concrete L10,L11 and L12

38. Shielding against β--particles. The maximum range of 2 MeV β--particles in air is about 7.5 m. But in denser materials the ranges are much less, the range in Perspex is about 8.5 mm, thus 1 cm of Perspex will give effective protection against β—particles that a Perspexscreencan be used as the simplest method of shielding. L10,L11 and L12

39. Shielding against γ-particles. The extent to which the intensity of a beam of γ-radiation is reduced by a barrier depends on the radiation energy and the atomic number and thickness of the barrier material. The tenth thicknessof an absorber is that thickness required to reduce the intensity of radiation to one-tenth of its initial value. A greater thicknesses are required to reduce doses by the first factor of 10 than are needed for subsequent factors of 10. e.g. for 60Co (mean γ-energy 1.25 MeV) the thickness of lead required to attenuate the dose by a factor of 1000 is approximately (4.4+3.6+3.6) cm = 11.6 cm. L10,L11 and L12

40. Estimation of Internal Dose Rates The calculation of the dose rates, which arise due to the presence of radionuclides in the tissues (internal radiation), is required only for patients receiving diagnostic or therapeutic doses of radionuclides or in the case of accidental ingestion by radiation workers. L10,L11 and L12

41. Factors influence such calculations are: • The rate of turnover of the element in the body. The effective half life (Teff) is derived from the actual half-life of the radionuclide (T½) and the biological half- life (Tb), which defines the turnover rate Teff = T1/2 x Tb / (T1/2+Tb) L10,L11 and L12

42. (2) The degree of absorption by the body and of selective localization within particular organs and the nature of the organ. (3) The energy and quality of the radiation, the energy of α - and β- particles being absorbed wholly within a small volume; whereas only a part of the emitted γ-radiation is absorbed within the body. L10,L11 and L12

43. RADIATION CONTROLS • A. Basic Control Methods for External Radiation ALARA (As low as reasonable attainable) principles • Decrease Time • Increase Distance • Increase Shielding B. Monitoring • Personnel monitoring • Laboratory monitoring • Biological monitoring

44. . Basic Control Methods for External Radiation(ALARA) • Time: Minimize time of exposure to minimize total dose. Rotate employees to restrict individual dose. • Distance: Maximize distance to source to maximize attenuation in air. The effect of distance can be estimated from equations. • Shielding: Minimize exposure by placing absorbing shield between worker and source.

45. Thank You