The 600% increase in medical radiation exposure to the US population since 1980 has provided immense benefit, but increased potential future cancer risks to patients. Most of the increase is from diagnostic radiologic procedures. The objectives of this review are to summarize epidemiologic data on cancer risks associated with diagnostic procedures, describe how exposures from recent diagnostic procedures relate to radiation levels linked with cancer occurrence, and propose a framework of strategies to reduce radiation from diagnostic imaging in patients. We briefly review radiation dose definitions, mechanisms of radiation carcinogenesis, key epidemiologic studies of medical and other radiation sources and cancer risks, and dose trends from diagnostic procedures. We describe cancer risks from experimental studies, future projected risks from current imaging procedures, and the potential for higher risks in genetically susceptible populations. To reduce future projected cancers from diagnostic procedures, we advocate the widespread use of evidence‐based appropriateness criteria for decisions about imaging procedures; oversight of equipment to deliver reliably the minimum radiation required to attain clinical objectives; development of electronic lifetime records of imaging procedures for patients and their physicians; and commitment by medical training programs, professional societies, and radiation protection organizations to educate all stakeholders in reducing radiation from diagnostic procedures. CA Cancer J Clin 2012. © 2012 American Cancer Society.

Epidemiological studies of medical radiation workers have found excess risks of leukemia, skin and female breast cancer in those employed before 1950 but little consistent evidence of cancer risk increases subsequently. Occupational radiation-related dose–response data and recent and lifetime cancer risk data are limited for radiologists and radiologic technologists and lacking for physicians and technologists performing fluoroscopically guided procedures. Survey data demonstrate that occupational doses to radiologists and radiologic technologists have declined over time. Eighty mostly small studies of cardiologists and fewer studies of other physicians reveal that effective doses to physicians per interventional procedure vary by more than an order of magnitude. For medical radiation workers, there is an urgent need to expand the limited information on average annual, time-trend and organ doses from occupational radiation exposures and to assess lifetime cancer risks of these workers. For physicians and technologists performing interventional procedures, more information about occupational doses should be collected and long-term follow-up studies of cancer and other serious disease risks should be initiated. Such studies will help optimize standardized protocols for radiologic procedures, determine whether current radiation protection measures for medical radiation workers are adequate, provide guidance on cancer screening needs, and yield valuable insights on cancer risks associated with chronic radiation exposure.

Background: Pediatric differentiated thyroid cancer (DTC) rates have increased over time in the United States and worldwide. Improvements in imaging for the diagnosis of DTC have been hypothesized as a potential driver of these increases. This study stratifies temporal trends in pediatric DTC by stage and tumor size to assess whether rates of large, late‐stage cancers, which are likely to be clinically meaningful, are increasing over time. Methods: Age‐standardized incidence rates (ASRs) of DTC and annual percent changes (APCs) in primary DTC rates were estimated for 0‐ to 19‐year‐olds with data from 39 US cancer registries during 1998‐2013. Results: During 1998‐2013, 7296 cases of DTC were diagnosed (6652 papillary cases and 644 follicular cases). APCs of pediatric DTCs significantly increased by 4.43%/y [95% CI, 3.74%/y‐5.13%/y], primarily because of increases in papillary histologies. Increasing trends were observed for children aged 10 to 19 years for both sexes and for non‐Hispanic whites, non‐Hispanic blacks, and Hispanics. Rates increased significantly over the time period for all tumor stages (APC _localized , +4.06%/y [95% CI, 2.84%/y‐5.29%/y]; APC _regional , +5.68%/y [95% CI, 4.64%/y‐6.73%/y]; APC _distant , +8.55%/y [95% CI, 5.03%/y‐12.19%/y]) and across tumor sizes (APC _<1 cm , +9.46%/y [95% CI, 6.13%/y‐12.90%/y]; APC _1‐2 cm , +6.92%/y [95% CI, 4.31%/y‐9.60%/y]; APC _>2 cm , +4.69%/y [95% CI, 2.75%/y‐6.67%/y]). Conclusions: Significantly increasing rates of DTC over time among 10‐ to 19‐year‐olds in the United States are unlikely to be entirely explained by increases in medical surveillance during childhood because rates of large and late‐stage DTC are increasing over time. Future studies should examine environmental and other factors that may be contributing to rising DTC rates.

To enhance understanding of etiology, we examined international population‐based cancer incidence data for lymphoid leukemia, non‐Hodgkin lymphoma, Hodgkin lymphoma and myeloid leukemia among children aged 0–19. Based on temporal trends during 1978–2007 in 24 populations, lymphoid leukemia and myeloid leukemia incidence rates generally have not changed greatly and differences in rates for non‐Hodgkin and for Hodgkin lymphoma have diminished in some regions. Lymphoid leukemia rates during 2003–2007 in 54 populations varied about 10‐fold, with rates highest in US white Hispanics (50.2 per million person‐years) and Ecuador (48.3) and lowest in US blacks (20.4), Tunisia (17.7) and Uganda (6.9). Non‐Hodgkin lymphoma rates varied 30‐fold, with very high rates in sub‐Saharan Africa (146.0 in Malawi and 54.3 in Uganda) and low rates (≤10) in some Asian populations (China, Japan, India, the Philippines and Thailand) and U.S. Asian‐Pacific Islanders, eastern and northern European populations and Puerto Rico. Hodgkin lymphoma rates varied 15‐fold, with rates highest in Italy (21.3) and lowest in China (1.7) . Myeloid leukemia rates varied only about fivefold, with rates highest in the Philippines and Korea (exceeding 14.0) and lowest in Eastern Europe (5.9 in Serbia and 5.3 in the Czech Republic) and Uganda (2.7). The boy/girl average incidence rate ratios were 2.00 or lower. Age‐specific patterns differed among the four hematopoietic malignancies, but were generally consistent within major categories world‐wide, except for non‐Hodgkin lymphoma. A systematic world‐wide approach comparing postulated etiologic factors in low‐ versus high‐risk populations may help clarify the etiology of these childhood malignancies.

Follicular lymphoma (FL) has been linked with cigarette smoking and, inconsistently, with other risk factors. We assessed associations of medical, hormonal, family history, lifestyle, and occupational factors with FL risk in 3530 cases and 22639 controls from 19 case–control studies in the InterLymph consortium. Age-, race/ethnicity-, sex- and study-adjusted odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using logistic regression. Most risk factors that were evaluated showed no association, except for a few modest or sex-specific relationships. FL risk was increased in persons: with a first-degree relative with non-Hodgkin lymphoma (OR = 1.99; 95% CI = 1.55 to 2.54); with greater body mass index as a young adult (OR = 1.15; 95% CI = 1.04 to 1.27 per 5kg/m² increase); who worked as spray painters (OR = 2.66; 95% CI = 1.36 to 5.24); and among women with Sjögren syndrome (OR = 3.37; 95% CI = 1.23 to 9.19). Lower FL risks were observed in persons: with asthma, hay fever, and food allergy (ORs = 0.79–0.85); blood transfusions (OR = 0.78; 95% CI = 0.68 to 0.89); high recreational sun exposure (OR = 0.74; 95% CI = 0.65 to 0.86, fourth vs first quartile); who worked as bakers or millers (OR = 0.51; 95% CI = 0.28 to 0.93) or university/higher education teachers (OR = 0.58; 95% CI = 0.41 to 0.83). Elevated risks specific to women included current and longer duration of cigarette use, whereas reduced risks included current alcohol use, hay fever, and food allergies. Other factors, including other autoimmune diseases, eczema, hepatitis C virus seropositivity, hormonal drugs, hair dye use, sun exposure, and farming, were not associated with FL risk. The few relationships observed provide clues suggesting a multifactorial etiology of FL but are limited in the extent to which they explain FL occurrence.