Introductory radiobiology for radiologist.pptx

An introduction for Radiographers on how to protect themselves from being exposed to radiations during their work

1. SEMINAR PRESENTATION ON INTRODUCTION TO RADIATION BIOLOGY BY RAD. MUHAMMAD ABDULKADIR USMANU DANFODIYO UNIVERSITY TEACHING HOSPITAL, SOKOTO. DEPARTMENT OF RADIOLOGY MAY,24 5/19/2024 1

2. Table Of Content Introduction Cell cycle Natural and man made radiation sources Types ionizing radiation Cell cycle and cell death Damage by ionizing radiation Effect of ionizing radiation on DNA Acute and Chronic dose Stochastic and Deterministic effect Fetal irradiation Summary References 5/19/2024 2

3. Introduction Radiobiology, in general terms, is the science that evaluates the effects of radiation in living organisms. In the field of radiography, it is defined as the science that investigates the interactions between ionizing radiation and living systems, and the consequences of these interactions. 5/19/2024 3

4. Cell structure Atoms form molecules, molecules make macromolecules, macromolecules build complex organic structures, and then cells – which are the main structural component of tissues, and reflect all features of life. However, they specialize according to the location of the tissue 5/19/2024 4

5. Cell structure Cells generally contains three parts Cell membrane Cytoplasm Nucleus 5/19/2024 5

6. Cont’ Cell membrane 1. Protects cell 2. Holds in water and nucleus 3. Allows water, nutrients, and waste products to pass into and out of the cell (it is semipermeable ) 5/19/2024 6

7. Cont’ Cytoplasm 1. Composed primarily of water 2. Conducts all cellular metabolism 3. Contains organelles a. Centrosomes : Participate in cell division b. Ribosomes : Synthesize protein c. Lysosomes : Contain enzymes for intracellular digestive processes d. Mitochondria: Produce energy e. Golgi apparatus: Combines proteins with carbohydrates f. Endoplasmic reticulum: Acts as a transportation system to move food and molecules within the cell 5/19/2024 7

8. Cont’ Nucleus 1. Contains deoxyribonucleic acid (DNA—the master molecule) and the nucleolus (with ribonucleic acid[RNA]) 2. DNA controls cell division 3. DNA controls all cellular functions 5/19/2024 8

9. Cell structure 5/19/2024 9

10. Natural and Man-Made Radiation Sources 5/19/2024 10

11. Natural Background Radiation Cosmic Radiation Terrestrial Radiation Internal Radiation 5/19/2024 11

12. Cosmic radiation The earth, and all living things on it, are constantly being bombarded by radiation from outer space (~ 80% protons and 10% alpha particles). Charged particles from the sun and stars interact with the earth’s atmosphere and magnetic field to produce a shower of radiation. The amount of cosmic radiation varies in different parts of the world due to differences in elevation and to the effects of the earth’s magnetic field. 5/19/2024 12

13. Terrestrial Radiation (Uranium, Actinium, Thorium decay series) Radioactive material is found throughout nature in soil, water, and vegetation . Important radioactive elements include uranium and thorium and their radioactive decay products which have been present since the earth was formed billions of years ago. Some radioactive material is ingested with food and water. Radon gas , a radioactive decay product of uranium is inhaled. The amount of terrestrial radiation varies in different parts of the world due to different concentrations of uranium and thorium in soil. 5/19/2024 13

14. Internal Radiation People are exposed to radiation from radioactive material inside their bodies. Besides radon , the most important internal radioactive element is naturally occurring K-40 , but uranium and thorium are also present as well as H-3 and C-14. The amount of radiation from potassium-40 does not vary much from one person to another. However, exposure from radon varies significantly from place to place depending on the amount of uranium in the soil. On average, in the United States radon contributes 55% or all radiation exposure from natural and man-made sources. Another 11% comes from the other radioactive materials inside the body. 5/19/2024 14

15. Man-Made Radiation Radioactive material is used in: Medicine - Diagnostic (X-ray, CT) Medicine - Therapeutic (Co-60, Linac) Medical - Nuclear medicine (radio-pharmaceuticals,) Exposure of selected groups of the public: Diagnostic radiology (X-rays) Nuclear medicine (radiopharmaceuticals) Radiotherapy (Co-60) ( Nias , 1998) 5/19/2024 15

16. BIOLOGICAL EFFECTS OF IONIZING RADIATION 5/19/2024 16

17. Types of ionizing radiation Divided into direct and indirect for the understanding of biological effects Particulate radiation ( α or β particle) Most are directly ionizing Individual particles with adequate kinetic energy can directly disrupt the atomic structure of the absorbing medium via which they pass Producces chemical and biological damage to molecules Electromagnetic radiations (X and γ rays) In contrast, they are indirectly ionizing They do not produce chemical and biological damage themselves but produce secondary electrons (charged particles) after energy absorption in the material. 5/19/2024 17

18. Ionizing radiation interactions with tissue When X and γ ray photons interact with living tissue, it is the absorption of radiation energy in the tissues that causes damage If it passes through the tissue without absorption, there would be no biological effects & no radiological image would be produced. Whenever radiation is absorbed, chemical changes are produced virtually immediately & subsequent molecular damage follows (within secs to mins) Biological damage becomes evident after a much longer time span of hours to decades 5/19/2024 18

19. Chain of events following exposure to ionizing radiation 5/19/2024 19

20. Cell cycle and cell death 5/19/2024 20

21. Cell cycle Interphase a. Cell growth before mitosis b. Consists of three phases: G1, S, G2 c. G1—pre-DNA synthesis d. S—DNA synthesis e. G2—post-DNA synthesis, preparation for mitosis 2. Four subphases a. Prophase—nucleus enlarges b. Metaphase—nucleus elongates c. Anaphase—two complete sets of chromosomes d. Telophase—separates the two sets of genetic material; division complete; 46 chromosomes in each new somatic cell 5/19/2024 21

22. Types of cellular damage Norma repair Interphase cell death Mitotic cell death Changes of m etabolism & function Mutation 5/19/2024 22

23. Mitotic d eath NORMAL IRRADIATED 5/19/2024 23

24. Stage of cell cycle and radiosensitivity Law of Bergonie and Tribondeau A fundamental law of radiation biology that states that the radiosensitivity of a tissue is increased the greater the number of undifferentiated cells in the tissue, the greater the mitotic activity and the greater the length of time that they are actively proliferating The stage of the cell cycle determines the extent of radiation damage. Radiation damage mostly occurs during the period of mitosis, the M phase. Least damage occurs during the DNA synthesis, the S phase. 5/19/2024 24

25. Radiosensitivity of tissues 5/19/2024 25

26. Damage by ionizing radiation Damage occurs in 2 basic ways: 1) By producing lesions in solute molecules directly ( e.g by rupturing a covalent bond) 2) By indirect action between the solute molecules and the free radicals produced during the ionization of water. Direct damage A. Occurs when radiation transfers its energy directly to the DNA (the master molecule) or RNA B. As these macromolecules are ionized, cell processes may be disrupted C. Some of this damage may be repaired D. If the DNA structure incurs sufficient damage, particularly to its nitrogenous bases, a mutation may result. ( Hall, 2000) . 5/19/2024 26

27. Cont’ Results of direct effect Results of the direct effect 1. No effect—most common result 2. Disruption of chemical bonds, causing alteration of cell structure and function 3. Cell death 4. Faulty information passed on in the next cell division possible results include mutations, cancer, and abnormal formations 5/19/2024 27

28. Indirect damage A. Because water is the largest constituent of the cell, the probability that it will be struck by radiation is greater B. Radiolysis of water: Occurs as radiation energy is deposited in the water of the cell C. The result of radiolysis is an ion pair in the cell: a positively charged water molecule (HOH+) and a free electron D. Several possibilities exist for chemical reactions at this point; most reactions create further instability in the cell E. If the two ions recombine, no damage occurs F. Positive and negative water molecules may be formed and then break into smaller molecules such as free radicals G. Some free radicals may chemically combine to form hydrogen peroxide (H2O2) H. Indirect effect results from ionization or excitation of water molecules 5/19/2024 28

29. Indirect effect Results of indirect effect 1. No effect—most common response 2. Formation of free radicals 3. Formation of H2O2( hydrogenperoxide ) Most damage to the body occurs as a result of the indirect effect because most of the body is water, and free radicals are readily mobile in water. 5/19/2024 29

30. Direct and indirect effect 5/19/2024 30

31. Indirect damage (Steel, 2002) 5/19/2024 31

32. Effects of Ionizing Radiation on DNA Single strand break Double-Strand Break Double-Strand Break in Same Rung of DNA Mutation 5/19/2024 32

33. Single-Strand Break Single-Strand Break If ionizing radiation interacts with a DNA macromolecule, the energy transferred can rupture one of its chemical bonds, possibly severing one of the sugar-phosphate chain side rails or strands of the ladderlike molecular structure (single-strand break). This type of injury to DNA is called a point mutation. Gene mutations may result from a single alteration along the sequence of nitrogenous bases. Point mutations commonly occur with low-LET radiations. Repair enzymes, however, are capable of reversing this damage. 5/19/2024 33

34. Single Strand Break 5/19/2024 34

35. Double-Strand Break Further exposure of the affected DNA macromolecule to ionizing radiation may result in additional breaks in the sugar-phosphate molecular chain(s). These breaks might also be repaired, but double-strand breaks (one or more breaks in each of the two sugar-phosphate chains) are not repaired as easily as single-strand breaks. If repair does not take place, further separation may occur in the DNA chains, threatening the life of the cell. Double-strand breaks occur more 5/19/2024 35

36. Double Strand Break ( sherer et al., 2014) 5/19/2024 36

37. Double-Strand Break in Same Rung of DNA When two interactions (hits), one on each of the two sugar-phosphate chains, occur within the same rung of the DNA ladder like configuration, the result is a cleaved or broken chromosome, with each new portion containing an unequal amount of genetic material. If this damaged chromosome divides, each new daughter cell will receive an incorrect amount of genetic material. This will culminate in the death or impaired functioning of the new daughter cell. 5/19/2024 37

38. Double Strand Break In Same Rung Of DNA 5/19/2024 38

39. Mutation ( sherer et al., 2014) 5/19/2024 39

40. Acute Dose An organ or tissue expresses response to radiation damage either as an acute effect or as late (chronic) effect. Acute effects manifest themselves soon after exposure to radiation. Acute radiation dose is defined as a large dose (10 rad or greater, to the whole body)delivered during a short period of time If large enough, it may result in effects which are observable within a period of hours to weeks Acute doses can cause a pattern of clearly identifiable symptoms (syndrome) These conditions are referred to in general as Acute radiation syndrome (Hall, 2000) 5/19/2024 40

41. Chronic Dose Chronic effects are delayed effects Relatively small amount of radiation received over a long period of time The body has time to repair damage because a smaller percentage of the cells need repair at any given time The body also has time to replace dead or non-functioning cells with new, healthy cells This is the type of dose received as occupational dose Since the probability for cancer at higher doses increases with increasing dose, this relationship is assumed to hold true with lower doses. This type of risk model is called stochastic effect 5/19/2024 41

42. Stochastic Vs Deterministic effects Stochastic effect is one in which the probability of occurrence increases with increasing dose but the severity in affected individuals does not depend on the dose (induction of cancer, i.e., radiation carcinogenesis, genetic effects). There is no threshold dose for effects that are truly stochastic. D eterministic (non-stochastic) effect is one which increases in severity with increasing dose, usually above a threshold dose, in affected individuals (organ atrophy, fibrosis, lens opacification, blood changes, decrease in sperm count). ( sherer et al., 2014) 5/19/2024 42

43. Stochastic Vs Deterministic effects Stochastic effect No minimum dose (threshold) Cannot predict occurrence or severity in individual Probability of occurrence increases with dose Subdivided into somatic and genetic effect Somatic effect Somatic effects appear in the exposed person. Can be further divided into 2 classes based on the rate at which the dose was received Prompt somatic effects (PSE) Occurs soon after an acute dose (typically 10 rads or greater to the whole body in a short period of time) Typical example of PSE is temporary hair loss that occur about 3 wks after dose of 400 rad to the scalp 5/19/2024 43

44. Stochastic Vs Deterministic effects 2) Delayed somatic effect (DSE) Occurs years after radiation doses are received Examples of DSE are increased potential for the development of cancer and cataracts Genetic or heritable effects Appears in the future generations of the exposed person as a result of radiation damage to the reproductive cells Genetic effects are abnormalities that occur in the future generations of the exposed individual. ( sherer et al., 2014) 5/19/2024 44

45. Stochastic effects: somatic (Steel, 2002) 5/19/2024 45

46. Deterministic effects 5/19/2024 46

47. Deterministic effects (Steel, 2002) 5/19/2024 47

48. Fetal irradiation Between conception and birth the fetus passes through three basic stages of development: - pre-implantation (day: 1 to 10) organogenesis (day: 11 to 42) - growth stage (day: 43 to birth). Radiation is a known teratogen. The effects of radiation on the fetus depend on two factors: dose and stage of development at the time of exposure. An abortion, to avoid a possibility of radiation-induced congenital abnormalities should be considered only when the fetal dose has exceeded 10 cGy . For doses exceeding 25 cGy an abortion is recommended. (Hall, 2000) 5/19/2024 48

49. Foetal radiation risk (Steel,2002) 5/19/2024 49

50. Foetal radiation risk Potential effects associated with prenatal radiation doses include: Growth retardation Small head brain size Mental retardation Childhood cancer (Hall, 2000) 5/19/2024 50

51. SUMMARY When cells are exposed to ionizing radiation the standard physical effects between radiation and atoms or molecules of the cells occur first and the possible biological damage to cell functions follows later. The biological effects of radiation result mainly from damage to the DNA which is the most critical target within the cell; however, there are also other sites in the cell which, when damaged, may lead to cell death. When directly ionizing radiation is absorbed in biological material, the damage to the cell may occur in one of two ways: direct or indirect action. 5/19/2024 51

52. References Coia,L.M , Moylan D.J., (2004) Introduction to clinical radiation oncology Hall, E. J.,(2000)“Radiobiology for the radiologist”, Lippincot , Philadelphia, Pennsylvania,U.S.A . Nias , A.W.(1998),“An introduction to radiobiology”, Wiley, New York, New York, U.S.A. Steel, GG., (2002)“Basic clinical radiobiology”, Arnold, London, United Kingdom Sherer M, Visconti P, Ritenour E, Haynes K (2014) Radiation protection in medical radiography , ed 7, St. Louis, Elsevier. 5/19/2024 52

53. THANK YOU 5/19/2024 53

54. We Live (And Have Always Lived) in a “Sea of Radiation” THANK YOU 5/19/2024 54