CHICAGO—Embracing the Hippocratic oath to “do no harm,” radiologists here at the Radiological Society of North America Annual Meeting announced a campaign to raise awareness about radiation exposures in adult imaging, most notably CT scans.
Called “Image Wisely,” the initiative aims to ensure “we use the right procedure at the right dose for the right patient,” said William R. Hendee, PhD, Distinguished Professor of Radiology, Radiation Oncology, Biophysics, and Bioethics at Medical College of Wisconsin.
Speaking here at the meeting, Dr. Hendee noted that there has been a seven-fold increase in the use of radiation-based imaging in the past 25 years.
Another study presented at the meeting suggests that the average patient is being exposed to higher doses of radiation from imaging studies than in the past. But another study suggests that the cancer risk from CT scans may have been overestimated, at least in the elderly.
“The growth of medical imaging has yielded important and life-saving benefits for millions of people, but overutilization of medical imaging can expose patients to unnecessary radiation,” said Mary Mahoney, MD, Professor of Radiology and Director of Breast Imaging at the University of Cincinnati Medical Center.
Despite the growth in imaging tests since over the past three decades, there has not been a similar rise in cancer cases or deaths in the US, said another speaker, Christoph Wald, MD, PhD, Executive Vice-Chairman of the Department of Radiology at the Lahey Clinic in Burlington, MA, and Associate Professor of Radiology at Tufts University.
Nevertheless, radiation is frequently portrayed negatively in the press, he said.
Placement of the shield did not significantly affect the dose of radiation to the breast: The dose was 21.3 mGy if placed on the chest, and 21.15, 21.8, and 22.0 mGy if elevated 1 cm, 2 cm, or 4 cm from the chest, respectively.
In 11 patients (22%), the breast shield resulted in no appreciable artifact, Dr. Healey said.
In 33 patients (66%), there was beam hardening with streak artifact that involved the adjacent skin and subcutaneous soft tissues, and in six patients (12%), beam hardening with streak artifact extended into the mediastinum.
But none of the artifacts impacted the diagnosis, Dr. Healey said. “We never missed a finding,” he said.
“We recommend elevating the shield 2 cm to 4 off the chest as that appears to reduce the number of artifacts,” he said.
Asked to comment on the findings, Judy Yee, MD, Professor and Vice Chair of Radiology at the University of California, San Francisco, agreed that there have been concerns that artifacts theoretically decrease the diagnostic ability of images, but that that has never been proven.
“There‘s no good reason not to use breast shields. The cost is relatively low and the benefit large,” she said, adding that they are now routinely used at her institution.
Breast shields are particularly beneficial for younger patients (who face more years of radiation exposure) and women, she said.
The cost of a breast shield is about $100, according to Dr. Healey. “While they‘re marketed for one-time use, we reuse them,” he added.
Estimating Cancer Risks
Dr. Hendee explained that cancer risks have largely been estimated using the Biologic Effects of Ionizing Radiation (BEIR) model, based on the National Academy of Sciences study of Japanese survivors of atomic bombs dropped on Hiroshima and Nagasaki in 1945. People at the far edge of those blasts who absorbed about 50 millisievert (mSv) of radiation appear to have an increased lifetime cancer risk of 0.05%, he said.
A series of CT exams might expose a patient to that much radiation, Dr. Hendee said.
Since the lifetime risk of cancer for the average American‘s is about 33%, the 0.05% increased risk associated with that exposure is basically negligible on an individual level, he said. But from a public health point of view for the entire population, it could be noteworthy.
According to the medical literature, 50 to 100 mSv of radiation is associated with “some increase in cancer incidence,” according to Pat A. Basu, MD, a White House Fellow on sabbatical from Stanford University.
Campaign Successful in Children
Dr. Hendee said that the “Image Wisely” campaign is built on the highly successful “Image Gently” initiative aimed at reducing radiation exposure to children.
“If we can do it for kids, why not do it for everyone?” Hendee says.
As part of the initiative, all institutions that offer imaging tests are being asked to put up signs with its icon, the owl, and a pledge to use radiation wisely, he said.
Factors Related to Overuse
Dr. Hardee pointed to the following as among the factors that contribute to overutilization of diagnostic imaging:
* The fee-for-service payment system.
* The practice of self-referral.
* The practice of defensive medicine in avoiding malpractice suits.
* Referring physician behavior.
* Often the wishes of patients who, armed with Internet advice, may request specific tests.
With technology changing so quickly, clinicians may not always know which exam is most appropriate, he added. As part of the campaign, a computerized ”decision “system” has been developed to help guide clinicians.
The “Image Wisely” initiative is supported by RSNA, the American College of Radiology, the American Association of Physicists in Medicine, and the American Society of Radiologic Technologists.
Average Annual Radiation Dose Increasing
At the meeting, University of California, San Francisco researchers reported that the average annual radiation dose that patients receive nearly tripled over 15 years, from 0.80 mSv in 1994 to 2.3 mSv in 2008.
“A small but increasing proportion of patients received high doses,” said Ingrid M. Burger, MD, PhD, a resident in the Department of Radiology.
In 1994, only 0.49% and 0.04% of those studied received doses of more than 50 and 100 mSv, respectively. In 2008, though, 2.4% and 0.47% received doses exceeding these thresholds, she said.
Dr. Burger and her colleagues reviewed patterns of medical radiation exposure from x-rays, fluoroscopy, angiography, nuclear medicine, and computed tomography among members of seven HMOs between 1994 and 2008.
The study includes 27,243,769 person-years of follow-up during which 23,900,385 exams associated with ionizing radiation were obtained.
CTs Cancer Risk Overestimated
In the other study, Dr. Basu and colleagues performed a retrospective study of Medicare claims data in patients age 65 and older from two periods—1998 to 2001 and 2002 to 2005. The earlier cohort comprised 5,267,230 individuals, and the second involved 5,555,345 individuals.
For each cohort, the researchers analyzed the number and types of CT scans that each patient received. The BEIR VII model then was used to estimate the number of cancers that would have been caused by these examinations.
According to the model, the incidence of cancer related to ionizing radiation from CT was 0.02% for the first cohort and 0.04% for the second cohort.
“We were surprised. We expected the number to be higher, because there have been suggestions that maybe 2% of cancers are CT-caused,” Dr. Basu said.
Although only elderly people were studied, the findings could apply to middle-aged people whose biological sensitivity to radiation is similar, he noted.
Max Wintermark, MD, Associate Professor of Radiology at the University of Virginia in Charlottesville, agreed, saying that elderly people account for the greatest use of imaging tests involving radiation. “In younger patients we are always trying to do something that doesn‘t involve radiation. We try to use MRI or ultrasound instead, if we can.
”Dr. Basu said a prospective study in which patients‘ radiation exposures andsubsequent cancers are tracked over time is needed.
For Lung CT, Breast Shields Reduce Radiation to Breast without Compromising Diagnostic Accuracy
CHICAGO—Breast shields should be used to reduce the dose of radiation to breast tissue in both male and female patients undergoing CT scans of the lung. So said researchers who found that while breast shields commonly resulted in beam-hardening artifacts, the artifacts did not limit diagnostic accuracy in any of their patients.
The study was presented here at the Radiological Society of North America Annual Meeting.
Research on plastic phantoms has shown that breast shields—a thin piece of bismuth placed in front of the chest—reduce the dose of radiation to the breast by about 30%, said Terrance T. Healey, MD, Clinical Assistant Professor of Diagnostic Imaging and Director of Thoracic Radiation at the Alpert Medical School of Brown University.
But many clinicians are reluctant to use the shields because they can cause artifacts so the images are not as clear as they should be, he said.
That has never been proven, however. So Dr. Healey and colleagues retrospectively reviewed the first 50 consecutive patients who had chest CTs before and after the routine use of breast shields at their institution in July 2008. The CTs were done on the same scanner.
The 100 CT studies were evaluated by two board-certified radiologists, who came to a consensus concerning the presence, extent, and clinical impact of artifacts related to the breast shield.
The most common indications for chest CT were malignancy (36% of patients), pulmonary nodule (36%), and aneurysm (6%).
The study included 24 men and 26 women with an average age of 57.6.The shield was placed on the chest; or 1 cm, 2 cm, or 4 cm away from the chest.