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Appendix F: Ionizing Radiation Exposure to the U.S. Population, with a Focus on Radiation from Medical Imaging
Pages 409-444

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From page 409...
... Ionizing Radiation Radiation with enough energy to remove tightly bound electrons from their orbits (and enough energy to break chemical bonds) is called ionizing radiation (reflected by wave lengths to the right in Figure F-1, shown for electromagnetic radiation, including ultraviolet waves, X-rays and gamma rays)
From page 410...
... Ionizing Radiation Used in Medical Imaging Ionizing radiation used in medical imaging includes gamma rays and X-rays. Gamma rays are delivered through nuclear medicine examinations, when a small amount of radioactive material is inhaled, injected, or swallowed by a patient, and the resulting gamma waves that are emitted by the radio-pharmaceutical from within the patient are detected.
From page 411...
... FIGURE F-2 Sample doses of and exposures to ionizing radiation. 411 Figure F-2.eps bitmap, landscape
From page 412...
... The types of effects included in this group are carcinogenesis and birth defects. Mechanism of Carcinogenesis The mechanism through which radiation exposure can lead to cancer is outside the scope of this review.
From page 413...
... Radiation in tissue REM / Sievert (=100 rem) Radiation in tissue, accounting for biologic sensitivity of tissue Effective dose Full body equivalent dose equal to a partial anatomic area radiation EUS Average effective dose per individual in the U.S.
From page 414...
... Because of the ease of comparison, effective dose is an extremely useful measure of radiation exposure and will be the primary metric used in this summary. The measurement of radiation emitted by radioisotopes used in nuclear medicine and positron emission tomography (PET)
From page 415...
... Metrics of Population Exposure The most useful metric to compare the population's radiation exposure from different sources is the average exposure, measured in effective dose, per individual in the entire population. It is calculated by dividing the cumulative dose to the population by the number of individuals in the population (EUS)
From page 416...
... Evidence of radiation-induced cancer is strongest for leukemia, but an increased risk of all solid cancer types (e.g., breast, lung, colon) has been associated with exposure to doses of ionizing radiation in the same range as that delivered by medical imaging.
From page 417...
... SOURCES OF IONIZING RADIATION EXPOSURE TO THE U.S. POPULATION The National Council on Radiation Protection and Measurements (NCRP, 2011)
From page 418...
... I have led several analyses that describe medical imaging and associated radiation exposure within a large cohort of patients (approximately 2.5 million) enrolled across six integrated health plans in the United States (Burger et al., 2010a,b)
From page 419...
... and from our research of radiation exposure across six integrated health care systems that participate in the NCI funded Cancer Research Network (calculations of EExp, medical imaging) (Burger et al., 2010a,b)
From page 420...
... In our work describing the radiation exposure to enrollees of six large integrated health plans, we had detailed information about imaging utilization and doses for individual patients. We were also able to calculate the average effective dose limited to those who underwent medical imaging that delivers ionizing radiation.
From page 421...
... . As a proportion of all radiation exposure, medical imaging con
From page 422...
... . The absolute radiation exposure from other sources did not change, and thus the population's total exposure increased due to the increase in radiation from medical imaging.
From page 423...
... TABLE F-3 Typical Effective Doses of Radiation for Common Conventional X-ray and CT Procedures Average Effective Examination Dose (mSv) Adult Effective Doses for Various Diagnostic Radiology Procedures Skull 0.1 Cervical spine 0.2 Thoracic spine 1.0 Lumbar spine 1.5 Posteroanterior and lateral study of chest 0.1 Posteroanterior study of chest 0.02 Mammography 0.4 Abdomen 0.7 Pelvis 0.6 Hip 0.7 Shoulder 0.01 Knee 0.005 Other extremities 0.001 Adult Effective Doses for Various CT Procedures Head 2 Neck 3 Chest 7 Chest for pulmonary embolism 15 Abdomen 8 Pelvis 6 Three-phase liver study 15 Spine 6 Coronary angiography 16 Calcium scoring 3 Virtual colonoscopy 10 SOURCE: Adapted from Mettler et al.
From page 424...
... . Our work assessing patterns of imaging across the CRN allowed us to assess average radiation exposure among only those who underwent medical imaging, and to assess change in these exposures over time.
From page 425...
... to characterize the radiation doses patients receive from various medical imaging tests. Each year the Nationwide Evaluation of X-ray Trends (NEXT)
From page 426...
... . Our study aimed to estimate the amount of radiation exposure associated with the types of CT examinations performed most commonly in the United States; to estimate variation across study types, patients, and institutions; and to use these data to estimate the lifetime attributable risk of cancer associated with these tests.
From page 427...
... 2009. Radiation dose associated with common computed tomography examinations and the associated lifetime attributable risk of cancer.
From page 428...
... The following broad categories are typically used to characterize occupational exposures: medical, aviation, commercial nuclear power, industry and commerce, education and research, and governmental/ Department of Energy/ military. The average annual occupational radiation exposure across all industries is 1.1 mSv per year, with considerable variation across industries (Table F-4)
From page 429...
... Annual occupational radiation exposure limits established by the Nuclear Regulatory Commission are found in Title 10, part 20 of the Code of Federal Regulations (http://www.nrc.gov/reading-rm/doc-collections/cfr/ part020/)
From page 430...
... There are several ongoing studies, sponsored by the NCI, to assess cancer risks among physicians who are exposed to high levels of radiation associated with medical imaging, including interventional cardiologists and interventional radiologists. The results of these studies are expected to be published during 2012.
From page 431...
... reported that the between 2005 and 2007, among a fee-for-service insured population aged 18–65, high and very high radiation doses were incurred by approximately 2 percent and 0.2 percent of adult enrollees per year, respectively. In our recent study across the six integrated health plans, we found that nearly twice as many enrollees had high exposures, and five times as many enrollees had very high radiation exposures that exceeded the annual occupational exposure limits (Burger et al., 2010a,b)
From page 432...
... Risk from an Individual Nuclear Medicine Scan Nuclear cardiac perfusion tests are used in the assessment of coronary artery disease, and they represent the second largest source of medical radiation exposure in the United States. The risks tend to be lower than for CT, as the patients imaged tend to be older.
From page 433...
... 2009. Radiation dose associated with common Figure F-5 lifetime attributable risk.eps 433 computed tomography examinations and the associated lifetime attributable risk of cancer.
From page 434...
... Berrington de Gonzalez for this report to focus specifically on future breast cancers, taking into account the increase in imaging rates since these papers were published, and including cancer risks associated with the additional imaging examinations not covered in these prior reports. These calculations were based on estimates of the number of imaging tests conducted annually, the age distribution of patients undergoing those tests, radiation delivered by those tests, organ-specific doses, and models of carcinogenesis, including the biological effectiveness of the radiation, underlying cancer risks of the population, lag time between exposure and cancer induction, and mortality in the population undergoing imaging.
From page 435...
... An important assumption in the estimation of lifetime radiation-related cancer risk is the life expectancy of persons receiving CT scans. There is a lag between radiation exposure and cancer diagnosis (which can be as short as 2 years for leukemia and 10 years for brain cancer [Preston et al., 2007]
From page 436...
... Cancers Associated with Cardiac Nuclear Medicine Imaging (Berrington de Gonzalez et al., 2010) Nuclear cardiac perfusion tests are used in the assessment of coronary artery disease, and they represent the second largest source of medical radiation exposure in the United States.
From page 437...
... 2009. Projected cancer risks from computed tomographic scans performed in the United States in 2007.
From page 438...
... . Thus she estimates an additional 560 breast cancers would result from the remaining radiation exposure from angiography and interventional radiology procedures, and from the nuclear medicine procedures not counted in this estimate.
From page 439...
... 2009. Projected cancer risks from computed tomographic scans performed in the United States in 2007.
From page 440...
... 2008. Radiation dose and cancer risk estimates in 16-slice computed tomography coro nary angiography.
From page 441...
... 2010. Historical review of occupational exposures and cancer risks in medical radiation workers.
From page 442...
... 2000. Radiation-related cancer risks at low doses among atomic bomb survivors.
From page 443...
... 2010. Cancer risks after radiation exposure in middle age.


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