June 10, 2013

CT scans—with radiation and cancer risk—rose in children

But ‘Image Gently’ could prevent many cancers—HMORN Cancer Research Network

Seattle, WA—Use of computed tomography (CT) scans—and thus exposure to ionizing radiation—increased over 15 years in children at a set of nonprofit health care delivery systems in a new study. But currently available strategies could greatly reduce this cancer risk, according to the HMORN Cancer Research Network study, published in JAMA Pediatrics.

Led by Diana L. Miglioretti, PhD, and Rebecca Smith-Bindman, MD, the study also documented substantial variation in the radiation doses that were used in CT scans. This is an important area where quality can be improved by lowering and standardizing the doses to which children are exposed, the authors said. Dr. Miglioretti is a senior investigator at Group Health Research Institute and a professor of biostatistics at the UC Davis School of Medicine. Dr. Smith-Bindman is a professor of Radiology and Biomedical Imaging; Epidemiology and Biostatistics; and Obstetrics, Gynecology, and Reproductive Medicine at UC San Francisco (UCSF) and a radiologist at the UCSF Medical Center.

>Diana L. Miglioretti, PhD“We estimated that the number of cancers caused by CT scans performed on children could fall dramatically—by 62 percent—if dose-reduction strategies like that instituted by the Image Gently initiative were targeted to exams with the highest quarter of doses and if CT scans were used only when medically necessary,” lead author Dr. Miglioretti said. Image Gently, an initiative of the Alliance for Radiation Safety in Pediatric Imaging, aims to change practice by increasing awareness of chances to promote radiation protection in medical imaging of children.

“Many people have focused on eliminating unnecessary CT scans, which is a worthy goal and could reduce future cancers caused by radiation from CT scans by around a third, since experts believe around a third of exams are unneeded,” Dr. Miglioretti added. “But we were surprised to find we could reduce cancers caused by CT imaging even more than that—by 43 percent—simply by lowering the radiation from the highest-dose exams. We found the biggest gains would come from targeting the highest quarter of doses.” Combining the two strategies would reduce 62 percent of cancers.

In Europe, setting target levels for CT radiation dose metrics (diagnostic reference levels) does just that. When the dose for an exam exceeds the 75th percentile for that exam type, the high dose must be justified. “Following this strategy in the United States, which now has no diagnostic reference levels, could greatly reduce the number of cancers that CT scans cause, especially in children.” said Dr. Miglioretti’s co-author Dr. Smith-Bindman.

Use of CT doubled for children younger than age 5 years, and nearly tripled for children age 5–14 years, at six U.S. health care systems—Group Health, Marshfield Clinic, and Kaiser Permanente Colorado, Georgia, Hawaii, and Northwest—from 1996 to 2005. But CT use was stable between 2006 and 2007, and it started to decline from 2008 to 2010, particularly among younger children. In 2011, Dr. Miglioretti started working with Group Health’s radiation technologists and radiation safety committee to minimize radiation exposure from CT scans in children and adults.

The research team also calculated radiation doses absorbed by each organ and the effective (overall) dose from 744 CT scans in children conducted between 2001 and 2011 at four of these systems (Group Health, Marshfield Clinic, and Kaiser Permanente Hawaii and Northwest) and at the Henry Ford Health System. Those doses per scan varied widely, and many scans delivered an effective dose of 20 mSv or higher—the yearly limit set for people who work with radiation in Europe.

“Effective dose is a somewhat crude way to summarize how much radiation the patient’s whole body is exposed to,” Dr. Miglioretti explained. But it is useful, because it accounts for not only the settings that are used on the machine (i.e., how much radiation the CT scan produces) but also the sensitivity of the different organs to developing cancer from radiation.

“Children tend to absorb more radiation from imaging than adults do, because their bodies are smaller,” Dr. Miglioretti said.  “And the radiation children absorb will lead to greater harm, because they are more likely than adults to develop cancer from radiation exposure.” Children’s small size also means that they need less radiation exposure from CT than do adults to produce images that are sharp enough for clinicians to use for diagnosis. “That’s why radiology technologists should use lower settings for children than for adults,” she said. “But that doesn’t necessarily always happen.”

She and her team used a new, improved approach to estimating both organ and effective doses in children, which National Cancer Institute researchers recently developed. And they used models developed by the Biological Effects of Ionizing Radiation (BEIR) committee, based on sources including the Life Span Study of survivors of the atomic bombing of Hiroshima and Nagasaki, Japan, to estimate how the radiation doses they observed translated into increased risk of developing cancer during the children’s remaining lifetimes.

The researchers project that the 4 million CT scans of the head, abdomen/pelvis, chest, or spine that are performed each year in American children could cause 4,870 future cancers. But these could be reduced by 62 percent if the highest doses were reduced—by using standardized protocols and guidelines like Image Gently—and by eliminating unnecessary imaging. “These are all things we could easily do right now,” Dr. Miglioretti said.

“CT scans are extremely useful for diagnosing many conditions in children,” Dr. Smith-Bindman said. But they deliver ionizing radiation doses that are 100 to 500 times higher than those from conventional X-rays. “We need to be judicious in using CT in children because of their greater sensitivity of developing cancer from radiation exposure, and the long life spans ahead of them,” she said. “CT exams should be used only when this information will improve diagnosis and clinical care.” To detect some conditions, alternatives to CT scans include magnetic resonance imaging (MRI) and ultrasound, which involve no ionizing radiation.

“The most important result of our study is that we can substantially reduce the risk of cancer from CT simply by reducing the doses used at the highest dose range,” Dr. Smith-Bindman said. “There is rarely any advantage in using such high doses.”

Projected risks of solid cancers are higher for younger children and girls than for older children and boys—and also for patients who get CT scans of the abdomen/pelvis or spine rather than other sites, Dr. Smith-Bindman said. In girls, one radiation-induced solid cancer is projected to result from every 300–390 abdomen/pelvis scans, 330–480 chest scans, and
270–800 spine scans, depending on age. The risk of leukemia is highest from head scans in children younger than 5 years: 1.9 cases per 10,000 CT scans.

Other recent related research found CT increased the risk of cancer in Australian children and teens; but those authors surmised that radiation doses from newer scanners, since 2005, might be lower than the ones they studied, suggesting that radiation exposure may be less concerning now than in the past. “But we really do not have evidence that the doses from CT scans are coming down,” Dr. Smith-Bindman said. “New scanners often have greater capacity to perform sophisticated exam types that sometimes deliver higher doses. And in fact we found children were typically exposed to higher radiation doses than the Australia team estimated.”

The study was supported by the National Cancer Institute-funded Cancer Research Network Across Health Care Systems (U19CA79689), the National Cancer Institute-funded R21CA131698 and the National Institutes of Health-funded K24CA125036.

Eric Johnson, MS
E. Johnson,
MS
Drs. Miglioretti and Smith-Bindman’s co-authors were Biostatistician Eric Johnson, MS, of Group Health Research Institute, in Seattle; Andrew Williams, PhD, of the Center for Health Research, Kaiser Permanente Hawaii, in Honolulu; Robert T. Greenlee, PhD, MPH, at the Epidemiology Research Center, Marshfield Clinic Research Foundation, in Marshfield, WI; Sheila Weinmann, PhD, MPH, at the Center for Health Research, Kaiser Permanente Northwest, in Portland, OR; Leif I. Solberg, MD, at HealthPartners Institute for Education and Research, in Minneapolis; Heather Spencer Feigelson, PhD, MPH, at the Institute for Health Research, Kaiser Permanente, in Denver; Douglas Roblin, PhD, at the Center for Health Research, Kaiser Permanente Southeast, in Atlanta; Michael J. Flynn, PhD, at the Department of Radiology, Henry Ford Health System, in Detroit; and Nicholas Vanneman, MA, at the Institute of General Practice, Johann Wolfgang Goethe University, in Frankfurt, Germany.

HMORN Cancer Research Network
The HMORN Cancer Research Network (CRN) is a National Cancer Institute-funded initiative to support and facilitate cancer research based in nine non-profit integrated health care delivery settings that belong to the HMO Research Network. The CRN welcomes collaborations that result in research projects that improve knowledge about cancer etiology, prevention, early detection, treatment and prognosis, and that decreases the burden of cancer across the cancer care spectrum. The integrated health care settings provide unique advantages for conducting population sciences research.

HMO Research Network
The HMO Research Network includes 18 research centers, each associated with a health care delivery system. Researchers at the centers collaborate on multi-site studies in real-world health care settings across the United States and in Israel. With access to information on more than 15 million ethnically and geographically diverse patients, these researchers are finding solutions for common and rare health problems. Since 1994, the Network has been answering pressing questions about keeping people healthy and delivering effective care.

Image Gently
The Image Gently campaign, an initiative of the Alliance for Radiation Safety in Pediatric Imaging, aims to change practice by increasing awareness of chances to promote radiation protection in medical imaging of children. It has brochures for parents and health care providers, including “My Child’s Imaging Record,” to keep track of imaging as is done with immunizations.

UC Davis School of Medicine
A national reputation for life-changing biomedical discoveries, a passion for clinical care, and a commitment to engaging people from underserved communities are the hallmarks of a UC Davis School of Medicine education. Our faculty specialize in translational research covering a wide range of areas and are engaged in innovative, interdisciplinary collaborations, both within the UC Davis community and with other highly regarded institutions.

UC San Francisco
UC San Francisco (UCSF) is a leading university dedicated to promoting health worldwide through advanced biomedical research, graduate-level education in the life sciences and health professions, and excellence in patient care.

Kaiser Permanente
Kaiser Permanente is committed to helping shape the future of health care. We are recognized as one of America’s leading health care providers and not-for-profit health plans. Founded in 1945, our mission is to provide high-quality, affordable health care services and to improve the health of our members and the communities we serve. We currently serve more than 9.1 million members in nine states and the District of Columbia. Care for members and patients is focused on their total health and guided by their personal physicians, specialists and team of caregivers. Our expert and caring medical teams are empowered and supported by industry-leading technology advances and tools for health promotion, disease prevention, state-of-the-art care delivery and world-class chronic disease management. Kaiser Permanente is dedicated to care innovations, clinical research, health education and the support of community health.

Henry Ford Health System
Henry Ford Health System, one of the country's largest and most comprehensive integrated health care systems, is a national leader in clinical care, research and education. The system includes the 1,200-member Henry Ford Medical Group, seven hospitals, Health Alliance Plan (a health insurance and wellness company), Henry Ford Physician Network, a 150-site ambulatory network and many other health-related entities throughout southeast Michigan, providing a full continuum of care. Henry Ford ranks in the top 20 percent of all institutions granted funding by the NIH and U.S. Public Health Service, and ranks first in Michigan for NIH-research funding for non-university based health care systems.

Marshfield Clinic
Marshfield Clinic Research Foundation (MCRF), a division of Marshfield Clinic, was founded in 1959. It’s the largest private medical research institute in Wisconsin. MCRF consists of research centers in clinical research, agricultural health and safety, epidemiology, human genetics, and biomedical informatics. Marshfield Clinic investigators publish extensively in peer-reviewed medical and scientific journals addressing a wide range of diseases and other health issues, including cancer, heart disease, diabetes, eye disease, neurological disease, pediatrics, radiology, women's health, agricultural safety and genetics. The Marshfield Clinic system provides patient care, research and education with more than 50 locations in northern, central and western Wisconsin, making it one of the largest comprehensive medical systems in the United States.

Group Health Research Institute
Group Health Research Institute does practical research that helps people like you and your family stay healthy. The Institute is the research arm of Seattle-based Group Health Cooperative, a consumer-governed, nonprofit health care system. Founded in 1947, Group Health Cooperative coordinates health care and coverage. Group Health Research Institute changed its name from Group Health Center for Health Studies in 2009. Since 1983, the Institute has conducted nonproprietary public-interest research on preventing, diagnosing, and treating major health problems. Government and private research grants provide its main funding.

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