INAYA MEDICAL COLLEGE (IMC) NMT 232 RADIATION PHYSICS DR. MOHAMMED MOSTAFA EMAM

Transcription

1 INAYA MEDICAL COLLEGE (IMC) NMT 232 RADIATION PHYSICS DR. MOHAMMED MOSTAFA EMAM 1

2 Radiation: It is defined as the process by which energy is emitted from a source and propagated through the surrounding medium. 2

3 NUCLEUS CHARACTERISTICS This appear is a nucleus; the red ones are going to be the protons and the blue ones are going to be the neutrons. 3

4 NUCLEUS CHARACTERISTICS If we look at the periodic table, we can see neon has same number of proton and neutron, similar way calcium also has same no. of neutrons and protons. Stable atoms 4

5 NUCLEUS CHARACTERISTICS Uranium have 92P and 146N. Why is that??? Nucleus is held together by a strong nuclear force; All these nucleons are held together by this force (came from neutrons) which hold the nucleus together. 5

6 Radioactivity : It is the act of emitting radiation spontaneously from the unstable atoms. Unstable atoms differ from stable atoms because they have an excess of energy or mass or both. Unstable atoms are known as radioactive atoms. E.g. Carbon 14, Uranium 238 6

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8 CLASSIFICATION OF RADIATION Radiation Non-ionizing Ionizing Directly ionizing; (charged particles) electrons, protons, etc Indirectly ionizing 8

9 NON-IONIZING RADIATION Non-ionizing radiation refers to any type of electromagnetic radiation that does not carry enough energy to ionize an atom or molecule. Examples: Near ultraviolet radiation infrared radiation, microwave, radio waves, etc 9

10 IONIZING RADIATION Ionizing radiation has sufficient energy to ionize an atom or molecule. Ionization is a process in which a charged portion of a molecule (usually electron) is given enough energy to break away from the atom. Ionization results in the formation of charged particles or ions; the molecule with net positive charge and the free electron with a net negative charge. All ionizing radiation is capable, directly and indirectly of removing electrons from most of the molecules. Ionizing radiation has enough energy to damage DNA in cells which in turn may lead to cancer. 10

11 ALPHA RADIATION 11

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13 Characteristics of alpha radiation: Alpha radiation is not able to penetrate skin. Alpha emitting materials can be harmful to humans if the materials are inhaled, swallowed or absorbed through open wounds. 13

14 Characteristics of alpha radiation: Alpha radiation is not able to penetrate skin. Alpha radiation is the least penetrating. It can be stopped (or absorbed) by a sheet of paper. 14

15 Characteristics of alpha radiation: When alpha particles are emitted outside our bodies, virtually all of their ionizing radiation is harmlessly absorbed by the nonliving outer layer of our skin. This means that alpha radiation doesn t have much effect on our health unless radioactive isotopes get inside our bodies and emit radiation internally. 15

16 Alpha radiation travels a very short distance through air. A variety of instruments have been designed to measure alpha radiation. Instruments can not detect alpha radiation even a thin layer of water, blood, dust, paper or other material, because alpha radiation is not penetrating 16

17 USES OF ALPHA RADIATIONS Alpha particles are most commonly used in smoke alarms (smoke detectors). The alpha particles ionize air between a small gap. A small current is pass through the ionized air. Smoke particles from fire that enter the air gap reduces the current flow, sounding the alarm. Alpha decay can produce safe power sources for radioisotope thermoelectric generators used for space probes and artificial heart pacemakers. 17

18 BETA RADIATION Beta radiation is a stream of electrons called beta particles. When a beta particle is ejected, a neutron in the nucleus is converted to a proton, so the mass number of nucleus is unchanged, but the atomic number increases by one unit. 18

19 Thorium undergoes radioactive decay to form Protactinium and beta particle. 19

20 Characteristics of beta radiation: Beta radiation is more hazardous because it can also cause ionization of living cells. If the particles hits a molecule of DNA it can cause spontaneous mutation and cancer. 20

21 Characteristics of beta radiation: Beta emitting contaminants may be harmful if deposited internally. Beta radiation may travel meters in air and is moderately penetrating, so It can penetrate human skin to germinal layer where new cells are produced. 21

22 Characteristics of beta radiation: Beta radiation is more hazardous because it can also cause ionization of living cells. If the particles hits a molecule of DNA it can cause spontaneous mutation and cancer. 22

23 Characteristics of beta radiation: Beta radiation is more hazardous because it can also cause ionization of living cells. If the particles hits a molecule of DNA it can cause spontaneous mutation and cancer. 23

24 Beta radiation cannot be detected with an ionization chamber such as a CD V-715. Clothing and turnout gear provide some protection against most beta radiation. Turnout gear and dry clothing can keep beta emitters off of the skin. 24

25 USES OF BETA RADIATIONS Beta radiation are widely used in medicine. In brachytherapy, beta radioisotopes can be used to irradiate areas inside a patient to prevent the growth of certain tissues. Beta particles are also used in some forms of therapy to kill cancer cells. 25

26 USES OF BETA RADIATIONS Brachytherapy is a procedure that involves placing radioactive material inside your body. Brachytherapy is one type of radiation therapy that's used to treat cancer. 26

27 USES OF BETA RADIATIONS Brachytherapy is sometimes called internal radiation. Brachytherapy allows doctors to deliver higher doses of radiation to more-specific areas of the body, compared with the conventional form of radiation therapy (external beam radiation) that projects radiation from a machine outside of your body. 27

28 USES OF BETA RADIATIONS Brachytherapy may cause fewer side effects than does external beam radiation, and the overall treatment time is usually shorter with brachytherapy. 28

29 USES OF BETA RADIATIONS Beta radiation is used in leak detection in the pipeline. This is achieved by adding small amount of beta radiation to the fluid. The area above the ground where high intensity of beta radiation is detected will pin point the leak sources in the pipeline. 29

30 USES OF BETA RADIATIONS Carbon-14 is used as tracers in chemical and biological research. The age of the ancient organic materials can also be found by measuring the amount of Carbon-14 that is left. 30

31 GAMMA RADIATION Gamma radiation is electromagnetic radiation of high frequency and therefore high photons with a very short wavelength. 31

32 GAMMA RADIATION The emission of gamma radiation results from an energy change within the atomic nucleus. 32

33 GAMMA RADIATION It should be noted that the emission of gamma rays does not change the mass number or atomic number of the nucleus. 33

34 GAMMA RADIATION Alpha and beta emission are often accompanied by gamma emission, as an excited nucleus drops to a lower and more stable energy change. 34

35 X-RAYS X-ray photons carry enough energy to ionize atoms and disrupt molecular bond. This makes it a type of ionizing radiation and thereby harmful to living tissues. X-ray machine sends individual x-ray particles through the body. The image is recorded on a computer or film. 35

36 Characteristics of gamma radiation and x-rays: Gamma radiation and X-rays are electromagnetic radiation like visible light, radio waves, and ultraviolet light. These electromagnetic radiations differ only in the amount of energy they have. Gamma rays and X-rays are the most energetic of these. X-rays are like gamma rays. They, too, are penetrating radiation. 36

37 Gamma radiation is able to travel many meters in air and many centimeters in human tissue. Radioactive materials that emit gamma radiation and X-rays constitute both an external and internal hazard to humans Gamma radiation or X-rays frequently accompany the emission of alpha and beta radiation 37

38 Gamma radiation is detected with survey instruments, including civil defense instruments. Low levels can be measured with a standard Geiger counter, such as the CD V-700. High levels can be measured with an ionization chamber, such as a CD V-715. Instruments designed solely for alpha detection will not detect gamma radiation Pocket chamber (pencil) dosimeters, film badges, thermo luminescent, and other types of dosimeters can be used to measure accumulated exposure to gamma radiation. 38

39 USES OF GAMMA RADIATIONS Even after it has been packaged, gamma rays can be used to kill bacteria, mould and insects in food. This process prolongs the shelf-life of the food, but sometimes changes the taste. Gamma rays are also used to sterilise hospital equipment, especially plastic syringes that would be damaged if heated. 39

40 The most common tracer is called Technetium-99 and is very safe because it only emits gamma rays and doesn't cause much ionization. Radioisotopes can be used for medical purposes, such as checking for a blocked kidney. To do this a small amount of Iodine-123 is injected into the patient, after 5 minutes 2 Geiger counters are placed over the kidneys. Also radioisotopes are used in industry, to detect leaking pipes. To do this, a small amount is injected into the pipe. It is then detected with a GM counter above ground. 40

41 Checking welds. If a gamma source is placed on one side of the welded metal, and a photographic film on the other side, weak points or air bubbles will show up on the film, like an X-ray. Because Gamma rays can kill living cells, they are used to kill cancer cells without having to resort to difficult surgery. This is called "Radiotherapy", and works because cancer cells can't repair themselves when damaged by gamma rays, as healthy cells can 41

42 USES OF X-RAYS X-rays are used in medicine for medical analysis. Dentists use them to find complications, cavities and impacted teeth. Soft body tissue are transparent to the waves. Bones also block the rays. X-rays are used in industry to inspect products made by various kinds of materials. X-ray machines are used in airports to check luggage etc. 42

43 In Science x-rays are used to analyze the arrangement of atoms in many kinds of substances, particularly crystals. Archaeologists used X-rays to examine ancient objects covered by a crust of dirt. X-rays are also used in consumer goods the manufactures treat certain kinds of plastic to check the quality of many mass produced products. 43

44 How does radiation injure people? - High energy radiation breaks chemical bonds or DNA molecules. This creates free radicals, like those produced by other insults as well as by normal cellular processes in the body. The free radicals can change chemicals in the body. These changes can disrupt cell function and may kill cells. + 44

45 DNA is the most important molecule that can be changed by radiation Effects of DNA Damage Gene Expression A gene may respond to the radiation by changing its signal to produce protein. Gene Mutation Sometimes a specific gene is changed so that it is unable to make its corresponding protein properly Chromosome Aberrations Sometimes the damage effects the entire chromosome, causing it to break or recombine in an abnormal way. Sometimes parts of two different chromosomes may be combined Genomic Instability Sometimes DNA damage produces later changes which may contribute to cancer. Cell Killing Damaged DNA may trigger apoptosis, or programmed cell death. If only a few cells are affected, this prevents reproduction of damaged DNA and protects the tissue. Studies have shown that most radiation-induced DNA damage is normally repaired by the body 45

46 How does this damage from ionizing radiation effect our bodies? Sufficient Cell Killing Sufficient Genetic Alterations Radiation Sickness Cancer 46

47 Radiation Dose 47

48 Radiation Dose One of the most confusing things about understanding radiation effects is visualizing how much radiation is involved. It is very difficult to keep the units which measure radiation straight. A number describing the amount of radiation means nothing without evaluating the units, but this is not easy. For example... 48

49 ...try to match the letter with the amount of radiation involved in each example Amount of potassium 40 in the body Dose to Atomic bomb survivors You can safety hold this amount of alpha radiation One coast to coast flight A diagnostic X-ray A. Billions of becquerels B. About 250 picocuries C millirem D. 0-5 Gy E. 2 millirads 49

50 Commonly Used Radiation Units Each of these units has a different technical meaning. All are used by experts to talk about radiation. With so many terms, you can see why it is important to know what the unit means when you are evaluating radiation information. RAD Sievert Becquerel Absorbed dose (Gray or rad) Average dose Organ dose Dose commitment Collective dose Effective dose (Sievert or rem) Committed effective dose Equivalent dose Collective equivalent dose Committed equivalent dose Uniform equivalent dose Dose equivalent Collective dose equivalent Ambient dose equivalent Directional dose equivalent Individual dose equivalent Individual dose equivalent, penetrating Individual dose equivalent, superficial Dose and dose-rate effectiveness factor Man-gray Man-sievert Tissue weighting factor Relative biological effectiveness (RBE) Quality factor (Q) Fatality probability coefficient Nominal fatality probability coefficient Radiation weighting factor (w R ) Linear energy transfer (LET) Radioactivity (Becquerel or curie) 50

51 Understanding Radiation Units Activity The number of times, each second, a radioactive material decays and releases radiation. Exposure Amount of ionization per mass of air due to x and gamma rays. Dose (Absorbed) The amount of radiation energy absorbed into a given mass of tissue. Dose (Equivalent) H & Effective dose equivalent (HE ) Measures the energy per unit mass times adjustments for the type of radiation; Involved Radiation (quality factor) and the biological response in the tissue (a weighting factor). * Equivalent dose converts dose into a measure of risk. 51

52 Understanding Radiation Units Activity Disintegration/sec=1 Becquerel (Bq) 37 billion Bq = 1 curie Exposure Roentgen Dose (Absorbed) 1 joule/kg=1 Gray(Gy) 1Gray=100 rad =100,000 mrad Dose (Equivalent) Gray x quality factors= Sievert (Sv) 1 Sievert =100 rem =100,000 mrem Standard Units S.I. Units 52

53 What is the meaning of activity? This is the expectation rate of spontaneous nuclear transitions in a source. Becquerel = 1 disintegration/second. This is the SI unit for measuring radioactivity. Curie. ACTIVITY Defined as 3.7 x disintegrations per second= 3.7 x Bq. The Rutherford. 1 Rd = 10 6 Bq. This is the activity of 1 gram of radium in equilibrium with its decay products 53

54 More curies = a greater amount of radioactivity. A large amount of material can have a very small amount of radioactivity; a very small amount of material can have a lot of radioactivity. 54

55 ACTIVITY How much is a Becquerel (Bq)? The natural 40 K activity in the body of an adult human of normal weight is Bq. There is an average of about 50 Bq per cubic meter of air inside a home from radon. Even though a 60 Co source of strong gamma radiation containing billions of Bq can kill you if you are standing 5 meters from it, it is harmless at a distance of 100 meters. A Bq has 27 times more disintegrations than a pci, but is still a very small amount of radiation. 55

56 ACTIVITY How much is a picocurie (pci)? Many times the media reports excess radiation in picocuries. It takes 1,000,000,000,000 pci to make 1 Curie. A Becquerel is 1 disintegration/second. It takes 27 pci to make one Bq, so a pci represents less radioactivity that a Bq and results in very, very little dose. 56

57 Exposure What is the meaning of exposure? The quantity of X- or gamma-radiation to which an object is exposed. This electromagnetic radiation produces ionization within the object. Amount of ionization per mass of air due to x and gamma rays. This is the amount of ionization produced by photons in air. Since it is impossible to directly measure the absorbed dose in tissue, the measurement of radiation is performed in air. It is measured in roentgen (R) and Sieverts (Sv). 57

58 Exposure What is the meaning of exposure? Roentgen. Röntgen or Roentgen may refer to: Roentgen (unit), unit of measurement for ionizing radiation, named after Wilhelm Röntgen Wilhelm Röntgen ( ), German physicist, discoverer of X- rays 58

59 Exposure What is the meaning of exposure? Roentgen. This is defined as the amount of gamma radiation that produces 1 cm 3 of air ionization equal to 1 electrostatic unit (esu). 1 esu = 3.3 x coulombs = 2 x 10 9 ion pairs/cm 3 of air. Equivalent to 2.58 x 10-4 C/kg air ( J/kg of air). 1R is approximately 10-2 Sv. 59

60 ROENTGEN Roentgen was defined as 1R=1 electrostatic unit (esu)/cm 3 air at standard temp and pressure(stp) = Δ Q by Δ m; Where: Δ Q is the absolute value of total charge of ions of one sign produced in air when all the electrons liberated by photons in air of mass (Δ m). X = Δ Q/ Δ m Conventional units is Roentgen SI unit : c/kg 1R=2.58*10-4 c/kg 60

61 ABSORBED DOSE What is the meaning of absorbed dose? This is the energy imparted/ given to matter by charged or uncharged ionizing particles. 61

62 ABSORBED DOSE What is the meaning of absorbed dose? Gray 1Gy = 1 J/kg. This is the SI unit for absorbed dose of ionizing radiation. The Rad. 1 rad = 10-2 Gy (= 10-2 J/kg). This is defined as the amount of radiation that deposits 100 ergs (10-5 J) in each gram of tissue it traverses. Two different types of radiation may, however, produce different degrees of biological damage even though they are both rated as 1 rad. 62

63 ABSORBED DOSE How much radiation is an X-ray? 1Gray=100 rad =100,000 mrad So, the average chest X-ray may give a dose; 10 millirads = 0.01 rads = Gray. A millirad is comparatively small. Average normal background level of radiation is 370 mrad/year. One Gray is a relatively large amount of radiation. If 3-4 Gray are delivered over a short time to the whole body, they can be deadly. 63

64 EQUIVALENT DOSE What is the meaning of equivalent dose? This is the quantity used to express on a common scale the risk to exposed persons from all ionizing radiations. 64

65 Dose Equivalent Different radiations have different harmful effects on human tissues. Dose Equivalent is measured in Sieverts (Sv). H = D Q.F. H = equivalent dose (Sv) D = dose (Gy) 1 Sv = 1 J/kg = 100 rem Q.F. = radiation quality factor for the particular type of ionizing radiation (no unit); 65

66 EQUIVALENT DOSE What is Radiation Quality Factor? Different types of radiation behave in different ways. In order to compare the amount of risk or biological change that occurs, quality factors are introduced. Biologic effects of radiation depend not only on dose but also on the type of radiation. 66

67 EQUIVALENT DOSE What is Radiation Quality factor? For example: The damage produced by 1 Gy of x-radiation is equal to that produced by 1 Gy of gamma radiation. Thus, Gamma radiation has a quality factor of 1 or 1 Gy gamma rays x 1 =1 Sv. The damage produced by 20 Gy of x-radiation is equal to that from 1 Gy of alpha radiation. Thus, Alpha radiation has a quality factor of 20 or 1 Gy of alpha radiation x 20 = 20 Sv. Quality factors for other types of radiation are between 1 &

68 Dose Equivalent Conventional unit is Roentgen equivalent in man (rem) RADIATION Q.F. X-rays & gamma rays 1.0 Electron (incld. β-rays) of energy >30kv Thermal ( slow) neutron Fast neutrons 20 68

69 EQUIVALENT DOSE Radiation Q. Factors Illustration Type and Energy Range Q. Factor X and γ rays, electrons, positrons and muons 1 Neutrons <10 kev 5 Neutrons 10 kev to 100 kev 10 Neutrons >10 kev to 2 MeV 20 Neutrons > 2 MeV to 20 MeV 10 Neutrons >20 MeV 5 Protons, other than recoil protons and energy >2 MeV 2 Alpha particles, fission fragments, nonrelativistic heavy nuclei 20 69

70 EQUIVALENT DOSE What is the meaning of equivalent dose? Sievert (Sv) 1 Sv = 1 J/kg. The Sievert is equal to the absorbed dose in tissue (Gy) multiplied by the 'quality factor' for the particular type of ionizing radiation. The quality factor is a dimensionless number representing the relative effect produced by the same absorbed doses of different types of radiation. Rem (Roentgen Equivalent Man): 1 rem = 10-2 Sv (= 10-2 J/kg). This is defined as the amount of radiation which when absorbed by a person, will produce the same biological effects as the absorption of 1 roentgen of x-ray or gamma-ray radiation. In older terminology the quality factor was referred to as the Relative Biological Effectiveness. number of rem = number of rad x RBE; 70

71 EQUIVAENT DOSE How much is a Sievert (Sv)? Radiation induced cancers have been seen in the atomic bomb survivors exposed to as low as 0.2 Sieverts. A Sievert is a relatively large amount of radiation. The annual background radiation exposure for a typical American is Sv, 3.7 msv or 370 millirem. 1 Sv = 100 rem 1000 msv = 100,000 mrem 71

72 EQUIVAENT DOSE How much is a millirem (mrem)? The annual background radiation exposure for a typical American 370 mrems. The average dose from watching color TV is 2 mrem each year. The granite from Grand Central Station exposes its employees to 120 mrem of radiation each year. People in Denver receive 50 mrem more each year than those in LA because of the altitude. The nuclear industry contributes to less than 1 mrem /year to an individual s background radiation. A millimrem is a small unit of measure. 72

73 EQUIVALENT DOSE What is the meaning of equivalent dose? In older terminology the quality factor was referred to as the Relative Biological Effectiveness. number of rem = number of rad x RBE; 73

74 EQUIVALENT DOSE What is the meaning of equivalent dose? To define the rem quantitatively, a Relative Biological Effectiveness (RBE) has been established (number of rem) = (number of rad) x RBE. The following table gives RBE for the usual types of radiation. RELATIVE BIOLOGICAL EFFECTIVENESS Type of radiation rad x RBE = rem x-rays and gamma-rays Beta radiation Protons Alpha particles Fast Neutrons Slow Neutrons

75 EQUIVALENT DOSE EFFECTIVE (H E ) Whole body exposures are rarely uniform. Tissues vary in sensitivity to radiation induced effects Effective dose is a measure of radiation and organ system specific damage in man The effective dose equivalent H E =Sum of H t x W t H t = mean dose equivalent received by the tissue t W t =weighing factor of tissue t 75

76 EQUIVALENT DOSE EFFECTIVE (H E ) Tissue Weighting Factors Illustration Bone surface Bladder Bone Marrow Gonads Skin Breast Colon Liver Lung Esophagus Stomach Thyroid Remainder 76

77 Dose-rate The effectiveness of the dose is dependent on the dose-rate Dose 1 bottle of Aspirin or 250,000 mrem of Radiation Dose -Rate Over 50 seconds?? Or over 50 years?? Over 50 seconds?? Or over 50 years?? Death Minimal health risk Death Minimal health risk 77

78 Biological Effects of Ionizing Radiation DR. MOHAMMED MOSTAFA EMAM 78

79 Objective To become familiar with the mechanisms of different types of biological effects following exposure to ionizing radiation. To be aware of the models used to derive risk coefficients for estimating the damage. 79

80 Contents Basic concepts, cellular effects Deterministic effects Stochastic effects Effects on embryo and fetus Risk estimates 80

81 Biological Effects 81

82 Early Observations of the Effects of Ionizing Radiation 1895 X-rays discovered by Roentgen 1896 First skin burns reported 1896 First use of x-rays in the treatment of cancer 1896 Becquerel: Discovery of radioactivity 1897 First cases of skin damage reported 1902 First report of x-ray induced cancer 1911 First report of leukaemia in humans and lung cancer from occupational exposure cases of tumour reported in Germany (50 being radiologists) 82

83 Effects of Radiation Exposure Information comes from: studies of diseases propagation (epidemiology) Experimental Radiobiology (studies of animals and plants) Fundamental studies of cells and their components (cellular and molecular biology) The key to understanding the health effects of radiation is the interaction between these sources of information. 83

84 Radiation exposure affects Chromosomes the center of life: the cell 84

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86 Exposure of the Cell No change radiation hit cell nucleus! DNA mutation 86

87 Outcomes after cell exposure Mutation repaired Viable Cell Unviable Cell Cell death DNA Mutation Cell survives but mutated Cancer? 87

88 Repair The human body contains about cells. An absorbed dose of 1 mgy per year (natural sources) will produce about ionizations, which means 100 per cell in the body. If we assume that the mass of DNA is 1% of the mass of the cell, the result will be one ionization in the DNA-molecule in every cell in the body each year. 88

89 order of magnitudes 999 of 1000 harms are repaired 999 of 1000 damaged cells die (not a major problem as millions of cells die every day in every person) many cells may live with damage (could be mutated) 89

90 Cell killing Radio-Sensitivity RS = Probability of a cell, tissue or organ of suffering an effect per unit of dose. Bergonie and Tribondeau (1906): RS LAWS : RS will be greater if the cell: Is highly mitotic. Is undifferentiated. 90

91 RADIOSENSITIVITY High RS Medium RS Low RS Bone Marrow Spleen Thymus Lymphatic nodes Eye lens Lymphocytes Skin Mesoderm organs (liver, heart, lungs ) Muscle Bones Nervous system 91

92 Biological Effects at Cellular Level % survival cells (semi logarithmic) Cellular effects of ionizing radiation are studied by cell survival curves 100% D q (threshold) Hereditary Possible mechanisms of cell death: Physical death Functional death Death during interphase Mitotic delay Reproductive failure D 0 (radiosensitivity) Dose 92

93 Linear Energy Transfer (LET) (Term used in Dosimetry) - LET (Linear Energy Transfer) is the amount of energy (MeV) a particle will lose in traversing a certain distance (m) of a material. - It describe the action upon matter. 93

94 Linear Energy Transfer (LET) (Term used in Dosimetry) - It is identical to the retarding force acting on a charged particle travelling through the matter by unit distance. - LET is a positive quantity and depends on the nature of the radiation as well as on the material traversed. 94 EXTRACT

95 Schematic of the cell cycle (Mitosis) outer ring: I = Interphase, M = Mitosis; inner ring: M = Mitosis, G 1 = Gap 1, G 2 Gap 2, S = Synthesis; not in ring: G 0 = Gap 0/Resting. 95

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97 Stages of Mitosis 97

98 Meiosis Meiosis occurs during the formation of gametes. Gametes are haploid reproductive cells, the egg and sperm cells. Meiosis reduces the chromosome number by ½. Ex = 46 2n = diploid, 1n = haploid 98

99 In cells without a nucleus (prokaryotic), the cell cycle occurs via a process termed binary fission. In cells with a nucleus (eukaryotes), the cell cycle can be divided into three periods: interphase, the mitotic (M) phase, and cytokinesis. 99

100 Factors Affecting Radio-Sensitivity Physical LET (linear energy transfer): RS Dose rate: RS Temperature: RS Chemical OXYGEN, cytotoxic drugs: RS SULFURE (cys, cysteamine ): RS Biological Cycle status: G2, M: RS S: RS G2 M G0 G1 S 100 EXTRACT

101 Cell Survival Radiation Quality Surviving fraction Låg low LET high LET low LET high Hög LET Absorbed dose LET (linear energy transfer) is the amount of energy (MeV) a particle will loose in traversing a certain distance (m) of a material. 101

102 Biological Effects Direct effects Indirect effects Primary damage Repair Cell death Modified cell Damage to organ Somatic cells Germ cells Death of organism Deterministic effects Cancer Leukemia Stochastic effects Hereditary effects 102

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111 Definition A free radical is a molecule or atom, which is not combined to anything (free) and carries an unpaired electron in its outer shell. It is in a state associated with a high degree of chemical reactivity. 111

112 Indirect Action of free radical In indirect action the radiation interacts with other molecules and atoms (mainly water, since about 80% of a cell is composed of water) within the cell to produce free radicals, which can, through diffusion in the cell, damage the critical target within the cell. 112

113 Indirect Action In indirect action the radiation interacts with other molecules and atoms (mainly water, since about 80% of a cell is composed of water) within the cell to produce free radicals, which can, through diffusion in the cell, damage the critical target within the cell. 113

114 Indirect Action In interactions of radiation with water, short lived yet extremely reactive free radicals such as H 2 O + (water ion) and OH * (hydroxyl radical) are produced. The free radicals in turn can cause damage to the target within the cell. 114

115 If the water molecule is ionized H 2 O = H 2 O + + e - (H 2 O is the water molecule ; H 2 O + is an ion radical ) Ion meaning it is electrically charged, because it has lost an electron and a radical because it has an unpaired electron in the outer shell, making it very 115

116 Ion radicals have a short life, usually no more than s, before they decay to form free radicals Free radicals are not charged, but do have an unpaired electron in the outer shell. 116

117 The water ion radical can, for example, do the following: H 2 O + + H 2 O = H 3 O + + OH* (H 2 O +, H 3 O + are the ion radicals H 2 O is a water molecule) OH* is a highly reactive hydroxyl radical, with 9 electrons, therefore one is unpaired. 117

118 Hydroxyl radicals (OH*), are highly reactive and can go on to react with DNA; It is estimated that 2/3 of the x-ray damage to mammalian DNA is by hydroxyl radicals. 118

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