Health Risks of Ionizing Radiation: - Clark University

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and controls are matched according to potentially confounding variables (age, smoking, gender, etc.). The cases and controls are assessed to determine if a certain risk factor like radiation is more prominent among the cases. Cohort studies look at things the other way around, comparing populations based on known exposures rather than known disease outcomes. In a typical cohort study design an exposed population is followed through time to see if they develop diseases more than a non-exposed population. Cohort studies can either be done retrospectively (looking back in time) or prospectively (following a population into the future). The result of any of these epidemiological designs is an expression of the rate of a disease in the study population compared to some reference value, and this could be matched controls from within the study, national disease rates, or some other standard. This is discussed more below. 1.7 Risk terminology Researchers use different terms when quantifying risk depending on study design and their own goals and preferences. Some of these concepts can be applied to either disease incidence or disease mortality. The following list scratches the surface of an epidemiologist’s glossary but should be sufficient for our purposes: Relative Risk (RR). The relative risk is a ratio of disease rates in exposed and unexposed groups without units of dimension. If, for example, the cancer rate in an exposed population is 5 out of 10,000, and in the unexposed population the rate is 2 out of 10,000, the relative risk would be 5 divided by 2, or 2.5. Relative risks are sometimes given in percentages. An author may explain the above example by saying that the RR equals 250%, meaning that the risk in the study population is 250% of the risk in the unexposed population. A Rate Ratio is typically equivalent to a relative risk, particularly at low disease rates. Both incidence and mortality can be described with a relative risk. Excess Relative Risk (ERR) is simply the relative risk minus 1. This number refers to the additional risk of a disease that can be associated with an exposure. In the example given above the ERR would be equal to the RR (2.5) minus one, or Introduction 9 1.5. This unit becomes more important in describing dose-response relationships, described below. Odds Ratio (OR). An odds ratio compares the odds of a disease among an exposed population to the odds of a disease among an unexposed population. “The odds” in this case means the number of times an event happens versus the number of times it does not happen. In the example given above the odds of an exposed person getting cancer are 5/9,995 = 0.00050025, because 5 out of the 10,000 had cancer and 9,995 did not. The odds of an unexposed person getting cancer are 2/9,998, or 0.00020004. In order to find the odds ratio, you would divide the odds of the exposed person by the odds of the unexposed person. The odds ratio in this example would be 2.50075. For rare outcomes like cancer the odds ratio is very similar to the relative risk. Odds ratios can sometimes be difficult to interpret intuitively although they can be mathematically beneficial. Odds ratios are often used in case-control studies where disease prevalence is unknown among the general population. Excess Absolute Risk (EAR). The excess absolute risk describes the exact number of cases of a disease that we should expect, without reference to the background rate. In our example we have 5 cancer deaths, which are two more than we expected. The EAR in this case is 2/10,000 or 0.0002. EAR, like ERR, is often used to describe dose-response relationships (discussed below). Standardized Incidence Ratio (SIR) is a ratio of the number of cases of a disease observed in the study population to the number of cases that would be expected in the study population. The expected number is calculated by recreating a hypothetical study population out of a standard reference group. This standardization helps to eliminate differences between the study population and the reference group. For example, if our study population were comprised of 70 children and 8 adults we would not want to base our expected number on the average US. Instead we would calculate the US incidence among children and the US incidence among adults and combine these rates in proportions that are appropriate for our study group. Standardized Mortality Ratio (SMR) is similar to SIR but measures mortality rather than incidence. Studies using SMRs and SIRs are usually ecologic studies and are rarely done with enough
10 Introduction precision to detect low-dose effects. P-value. As we discussed above, there is considerable uncertainty in any study of low-dose radiation and in epidemiologic studies generally. To deal with this problem there are statistical ways of describing how well we know what we know. The simplest way is to say whether a result is significant or not. This is accomplished with the p-value, which gives an estimate of the probability that the result occurred by chance. A p-value of 0.01, for example, indicates that the result could have happened by chance only 1 out of 100 times. The results of a study are often given with an indirect reference to the p-value by saying that the p-value is less than some threshold (0.1, 0.01, 0.05, etc.). This is done to demonstrate that the result passes the significance test. The threshold for significance, as we mentioned above, is usually a 5% probability of the result occurring by chance, and so a p-value less than 0.05 is generally indicative of a significant result. Confidence interval. A confidence interval gives a range of possible results, and for some purposes this is more informative than the ‘best guess’. This range of possibilities could theoretically extend into infinity and so it is usually truncated at some predetermined level of certainty. A 95% confidence interval, for example, will include the range within which we are 95% sure the true answer lies. The confidence interval typically follows a risk estimate in the following manner: RR 2.13 (95% CI 2.00-2.26). This means that the true relative risk is probably between 2.00 and 2.26, the author is 95% sure that it is, and the most likely estimate is 2.13. The confidence interval gives us a shortcut to assessing the significance of a result. Consider a relative risk. A relative risk of 1 signifies that an exposed group has the same risk as a control group and there is thus no evidence of an additional risk. If we have a relative risk of 1.01, and a 95% confidence interval of 0.98-1.08, then we have a positive result but not a significantly positive result. This is because our range of possibilities, indicated by our confidence interval, includes the possibility that there is no additional risk (RR=1) and even the possibility that the exposure decreased our risk (RR
Page 1 and 2: Health Risks of Ionizing Radiation:
Page 3 and 4: Contents List of Tables ...........
Page 5 and 6: Contents iii Rocky Flats ..........
Page 7 and 8: Contents v APPENDIX A .............
Page 9 and 10: List of Figures Figure 1-1 Average
Page 11 and 12: We are indeed grateful to those who
Page 13 and 14: 2 Introduction 1.2 A brief history
Page 15 and 16: 4 Introduction Figure 1-2. The evol
Page 17 and 18: 6 Introduction Figure 1-5(a). Alpha
Page 19: 8 Introduction In epidemiological s
Page 23 and 24: 12 Introduction available informati
Page 25 and 26: 14 Background Radiation Figure 2-1.
Page 27 and 28: 16 Background Radiation Figure 2-3.
Page 29 and 30: 18 Background Radiation
Page 31 and 32: 20 Medical Exposures Fi
Page 33 and 34: 22 Medical Exposures
Page 35 and 36: 24 Medical Exposures with national
Page 37 and 38: 26 Medical Exposures localized expo
Page 39 and 40: 28 Medical Exposures (2.1-28.7). Th
Page 41 and 42: 30 Medical Exposures posed 2.69 tim
Page 43 and 44: 32 Medical Exposures with diagnosti
Page 45 and 46: 34 Medical Exposures Table 3-1. Stu
Page 55 and 56: 44 Atomic Bomb Survivors Figure 4-2
Page 57 and 58: 46 Atomic Bomb Survivors
Page 59 and 60: 48 Atomic Bomb Survivors approximat
Page 61 and 62: 50 Atomic Bomb Survivors (ALL), acu
Page 63 and 64: 52 Atomic Bomb Survivors of the 8 t
Page 69 and 70: 5 Nuclear Weapons Testing Over 500
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60 Nuclear Weapons Testing by disti
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62 Nuclear Weapons Testing Figure 5
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64 Nuclear Weapons Testing near the
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66 Nuclear Weapons Testing
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68 Nuclear Weapons Testing
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6 RADIATION WORKERS Introduction Th
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72 Radiation Workers • 50 rem (0.
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74 Radiation Workers work, reports
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76 Radiation Workers Figure 6-5. A
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78 Radiation Workers Figure 6-8. To
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82 Radiation Workers Feed Material
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84 Radiation Workers by Beral et al
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88 Radiation Workers Table 6-1. Leu
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90 Radiation Workers No
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92 Radiation Workers N
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94 Radiation Workers S
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96 Radiation Workers ERR estim
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98 Mayak Workers Table 1. Dose (Gy)
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100 Mayak Workers workers at the ra
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102 Mayak Workers
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104 Uranium Miners enrichment facil
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106 Uranium Miners Samet et al. (19
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108 Uranium Miners were selected 12
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Uranium Miners 111
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9 RADIATION EXPOSURE IN FLIGHT The
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DNA damage (a chemical change in DN
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10 PRECONCEPTION EXPOSURES Several
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of risk in the lowest dose groups,
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found elevated solid cancer risk wi
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preconception doses between 2.5 and
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Table 10-1. Preconception irradiati
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Preconception Exposures 127
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Tracheoesophageal fistula and conge
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cancer were both associated with th
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0.10-4.71) while respiratory system
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elationship was not significant for
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times higher than in less-contamina
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Nuclear Power Accidents 139
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12 COMMUNITIES NEAR NUCLEAR FACILIT
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levels (this could not in itself be
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Figure 12-3. Native Americans from
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of leukemia was measured over a lar
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(RR 1.06; 1.00-1.11) and risks of s
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more that we can say about this app
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Communities Near Nuclear Facilities
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54 observed vs. 46.1 expected death
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13 DISCUSSION Our intention in crea
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myeloid leukemia) was significantly
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0.1-3.5 WLM; this is roughly equiva
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adon (Lubin et al. 1997). These res
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Leukemia Leukemia, a general term t
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vical cancer. The doses to these pa
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England have found it convenient to
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Thyroid disease Thyroid cancer is a
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1986 through 1995. These workers sh
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dence of this disease includes elev
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Analysis of preconception exposure
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Paternal age, education, drinking O
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Gardner et al. 1990 Employed at Sel
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we consider this group of a few hun
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Leukemia risk (excluding CLL) among
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Glossary of Terms for Epidemiology
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Glossary 199 Beta radiation: Stream
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Dosimetry: Measurement or estimatio
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Glossary 203 Hypothyroidism: The cl
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Glossary 205 Metastasis: 1. Movemen
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Glossary 207 waves, ultra violet (U
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Glossary 209 Thyroid Disease: disea
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Bibliography ATSDR. Public Health A
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Bhatia S, Sklar C. Second cancers i
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Bibliography 215 Cavallo D, Tomao P
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Bibliography 217 Department of Ener
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Bibliography 219 Gardner MJ, Hall A
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Haldorsen T, Reitan JB, Tveten U. C
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Bibliography 223 Howe GR, Nair R, N
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of Mayak, A comparison of numerical
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Bibliography 227 Laird NM. Thyroid
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control population. International J
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Bibliography 231 Neel JV, Schull WJ
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2003.160:381-407. Bibliography 233
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Bibliography 235 Saccomanno G, Auer
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Bibliography 237 analysis of cancer
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Bibliography 239 Tokarskaya ZB, Sco
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Journal of Epidemiology 1987.125(2)
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Actinium, 84 Acute lymphocytic leuk
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and Nevada Test Site, 60-61, 62 nuc
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Hashimoto’s thyroiditis, 185 Heal
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studies, 101-2 Medical exposure, 19
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(RERF), 43 Radiation Exposure Compe
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Viruses, 118, 154, 193 West Germany
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