Health Risks of Ionizing Radiation: - Clark University

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Radiotherapy for childhood cancer. Tucker et al. (1987), investigating leukemia after childhood cancer therapy, found an excess associated with alkylating agents but not radiation therapy. Garwitz et al. (2000), on the other hand, concluded that radiation was the most important treatment-related risk factor for the development of a second malignant neoplasm in children who were exposed under the age of 20 for a first malignant neoplasm. The irradiated group had a RR of 4.3. Chemotherapy appeared to play only an accessory role of potentiating the effects of radiotherapy. Loning et al. (2000) found that children that received cranial radiation for the treatment of acute lymphoblastic leukemia had a higher risk for developing secondary neoplasms. The risk of thyroid cancer was specifically investigated by de Vathaire et al. (1999b). Cases where the first cancer had been thyroid cancer were excluded from this cohort of French and English children. The mean thyroid dose was quite high (7 Gy), and although the estimated risk was unusually high, suggesting a predisposition to cancer, the dose-response relationship within the cohort was consistent with radiation-induced thyroid cancer patterns in other cohorts 31 . Acharya et al. (2003) looked at 33 cases of thyroid neoplasms in cancer survivors who had been treated with radiation. Thirteen of these neoplasms were malignant, more than would be expected based on a 5% malignancy rate in the general population. Again, doses had been quite high (10-42 Gy) and these patients were possibly predisposed to cancer. Wong et al. (1997) examined retinoblastoma 32 patients; these patients are expected to have a strong genetic predisposition to cancer. The authors demonstrated a much higher risk in patients whose primary cancer was hereditary, as expected, but also demonstrated a dose-response trend for sarcomas of bone and soft tissue 33 . The OR for any second cancer Medical Exposures 29 among nonhereditary retinoblastoma patients was 1.6 (0.7-3.1). 3.5 In utero exposures Studies of prenatal exposure to radiation, mainly through obstetric x-rays, have clearly demonstrated risks at relatively low doses. Alice Stewart and others published results linking prenatal exposure and childhood cancer in the 1950s (Stewart et al 1956, 1958), and this study grew into the Oxford Survey of Childhood Cancers (OSCC). Although the OSCC contains the majority of the data pertaining to this association, other studies have generated consistent results. One of the challenges in analyzing these data is the lack of good dose information; the average dose of an x-ray exam has declined over the years and precise estimates of dose per exam are not available 34 . The studies discussed below have attempted to make reasonable inferences about dose and apply them to observed childhood cancer outcomes. The OSCC grew to include all childhood cancers in Great Britain and in 1981 consisted of 15,276 casecontrol pairs. Initial observations found increased risks of childhood leukemia (RR 1.92, 1.12-3.28) and other childhood cancers (RR 2.28, 1.31-3.97) after prenatal x-rays of the mother’s abdominal area (Stewart et al. 1956, Doll and Wakeford 1997). As prenatal exposure has decreased, so has the estimated risk. Knox et al. (1987) estimated an average relative risk of 1.94 over the period 1953-79. This analysis also suggested that the relative risk was highest for cancers at age 4-7. Gilman et al (1988) also looked at the OSCC and argued that the timing of the exposure in the pregnancy was more important than the dose in increasing cancer risk. Specifically, these authors found that x-rays taken in the first trimester 31 With a dose of 0.5 Gy the SIR was 35 (90% CI 10-87). The ERR was stated to be between 4 and 8 per Gy; this can be compared to the estimate from Ron et al. (1995) of 7.7/Gy 32 Retinoblastoma is a cancer of the eye that typically affects young children and is largely hereditary. 33 The odds ratios for sarcomas (1.9, 3.7, 4.5, 10.7) increased with median dose (7, 20, 40, 98 Gy) compared to the 0-5 Gy dose group. 34 Knox et al. (1987) cite the National Radiological Protection Board estimate that the mean fetal gonadal dose per exposure in 1977 was 3.5 mGy. The United Nations Scientific Committee on the Effects of Atomic Radiation estimated that the mean fetal dose per film was 18.0 mGy between 1947 and 1950 and 5.0 mGy between 1958 and 1960. Mole (1990) used an estimated mean dose of 6 mGy for the period 1958-61.
30 Medical Exposures posed 2.69 times more risk than those taken in the third trimester. Mole (1990) demonstrated that the association seen in the OSCC was similar in both singleton and twin pregnancies. This finding was confirmed in the US by Harvey et al. (1985). Bithell (1993) combined the OSCC data with estimates of in utero dose to generate an estimated ERR of 51/Gy (28-76). Studies in the US have produced similar results to those seen in the OSCC. MacMahon (1962) and Monson and MacMahon (1984) looked at children born and discharged alive from maternity hospitals in the northeastern states and found a RR of 1.47 (1.22-1.77) with prenatal x-rays. It was found that excess cancer mortality was most marked in the ages of 5-7, where the relative risk was closer to 2. With adjustments made for confounding factors, MacMahon determined a relative risk value for prenatal x-ray exposure of 1.52 for all cancers. Harvey et al. (1985), mentioned above, estimated the childhood cancer incidence RR to be 2.4 (1.0- 5.9) with an average dose of 10 mGy. Bithell (1993) made a meta-analysis of all available data, including the studies mentioned above and several others. The overall RR was 1.38 (1.31-1.47) and the studies were remarkably consistent 35 . Several reviews of these data provide much more insight into the issue than we cover here 36 , but comments regarding the compatibility of atomic bomb survivor data bear repeating. Boice and Miller (1999) provide a skeptical voice, noting that the estimated risks from prenatal x-rays and in utero atomic bomb exposure are apparently not compatible (among other concerns 37 ). Wakeford and Little (2002, 2003), however, decided that the atomic bomb ERR estimate for childhood cancer mortality was in fact compatible with the ERR estimate of 51/Gy (28- 76) from the OSCC 38 . The atomic bomb data might not be a useful comparison for several reasons. The at-risk subgroup of the atomic bomb survivors was small (~1,200) and the expected number of childhood cancer deaths in exposed children was less than one. This statistical uncertainty is responsible for the wide confidence intervals noted above. It might also be the case that a few childhood cancer deaths occurred in the few years between the bombings and the onset of the studies; given the small numbers of cancers observed any additional cases would change the risk estimates appreciably. It is also important to consider that atomic bomb exposures were over a wide range of doses. Effects such as cell sterilization or fetal death might have reduced the observed childhood cancer risk at higher doses. Wakeford and Little (2003) conclude that the atomic bomb survivor data are compatible with the prenatal x-ray exposure data and that the evidence supports a cause and effect relationship. The preferred risk estimate is an ERR of 51/Gy, equivalent to an EAR of 8%/Gy. Most importantly, these authors conclude that there is evidence of significant risk to doses as low as 10 mGy. 3.6 Parental exposures Boice et al. (2003) analyzed the genetic effects of radiotherapy. Specifically, they examined whether there was evidence that children of patients who received radiotherapy for cancer had an increased risk of cancer themselves. The authors found that children of radiotherapy patients did have elevated cancer risks but found that the risk was concentrated in the diseases known to have a strong hereditary component (retinoblastoma). This study is very different from other preconceptional exposure studies in that the exposures in this case occurred during childhood. Other human and animal studies suggest that risk is associated with paternal exposures that occur within a few months of conception; these childhood cancer survivors do not fit that description and may therefore be uninformative on the issue. 35 The OSCC estimate was 1.39 (1.30-1.49) and the combined estimate from all other studies was 1.37 (1.22-1.53). 36 Good sources of further reading include Doll and Wakeford (1997) and Wakeford and Little (2003). 37 Boice and Miller (1999) also suggest that the in utero risks should not be greater than risks following exposures in infancy, that some cohort studies have been inconclusive, and that leukemia and solid cancer risks should not be so similar on biological grounds. 38 The atomic bomb survivors exposed in utero produced only one childhood cancer death. An ERR of 7/Gy (-3-45) was estimated based on Japanese background rates and an estimate of 23/Gy (2-88) was based on rates among LSS subjects with little or no exposure (Delongchamp et al. 1997).
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 and 20: 8 Introduction In epidemiological s
Page 21 and 22: 10 Introduction precision to detect
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: 28 Medical Exposures (2.1-28.7). Th
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
Page 71 and 72: 60 Nuclear Weapons Testing by disti
Page 73 and 74: 62 Nuclear Weapons Testing Figure 5
Page 75 and 76: 64 Nuclear Weapons Testing near the
Page 77 and 78: 66 Nuclear Weapons Testing
Page 79 and 80: 68 Nuclear Weapons Testing
Page 81 and 82: 6 RADIATION WORKERS Introduction Th
Page 83 and 84: 72 Radiation Workers • 50 rem (0.
Page 85 and 86: 74 Radiation Workers work, reports
Page 87 and 88: 76 Radiation Workers Figure 6-5. A
Page 89 and 90: 78 Radiation Workers Figure 6-8. To
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80 Radiation Workers Figure 6-10. A
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82 Radiation Workers Feed Material
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84 Radiation Workers by Beral et al
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86 Radiation Workers Figure 6-14. A
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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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Page 174 and 175:
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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
Page 238 and 239:
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
Page 262 and 263:
(RERF), 43 Radiation Exposure Compe
Page 264:
Viruses, 118, 154, 193 West Germany
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