December 2012

Meaningless Use — Journal Targets the Term ‘Low Dose’ for Extinction
By Beth W. Orenstein
Radiology Today
Vol. 13 No. 12 P. 18

If you submit a paper to the journal Radiology that uses the term “low dose,” it’s not likely to be accepted. Journal editors Alexander Bankier, MD, PhD, and Herbert Kressel, MD, both of Beth Israel Deaconess Medical Center in Boston, have concluded that the term has no meaning and radiologists should stop using it.

In an editorial in the September issue of Radiology, Bankier and Kressel asked contributors to be more specific when evaluating and comparing CT dose in studies. Going forward, they would like to see four metrics—CT dose index (CTDIvol), dose length product (DLP), effective diameter, and size-specific dose estimate (SSDE)—used instead. These metrics make it easier to quantify the dose absorbed by patients and that’s more pertinent information, Bankier says.

William Hendee, PhD, editor of Medical Physics, an international medical physics and biophysics journal, hasn’t made that request yet but says he would like to follow Bankier and Kressel’s lead and ask contributors to his publication to stop using the term as well. “Once journals start to do this, it will really drive attention to the issue,” he says. “And I think over time we’ll see an elimination of this subjective expression, which doesn’t really mean very much.”

The term low dose started to appear in the early 1990s when everyone was performing CT exams the same way with the same dose, Bankier says. Europeans have long been concerned about the term and its implications, he notes. Over the past 10 years, the American radiology community also has grown increasingly concerned about the use of low dose and the lack of a clear definition for it.

Changing Parameters
The radiation doses used today are certainly lower than those used 10 or 20 years ago, Bankier says. “We are continuously improving. What was low dose 10 years ago is not today, and hopefully what we consider low dose in four or five years to be standard will be even lower,” he says.

“What we do now is considered lower dose than what we did 10 or 20 years ago,” says Donald Frush, MD, chief of the division of pediatric radiology at Duke Children’s Hospital & Health Center, “but low dose doesn’t have a fixed definition.”

While the term doesn’t have a clear definition, one concern is the implication that low dose means safer and is therefore better for patients. That’s why the term has become increasingly fashionable and appears more often even though it’s basically meaningless, the radiologists agree.

Richard Morin, PhD, chair of the ACR Dose Index Registry Committee, says imaging facilities aren’t intentionally misleading the public when they promote their scanners as low dose. “But that’s the consequence of using that terminology,” he says. “When the public sees that this place offers low-dose CT, they think it’s safer than this other place that does regular CT or high-dose CT. But the fact of the matter is that the doses for all CTs we do—the standard CTs—are not significant in terms of a safety issue and so it is misleading to the general public to use the term low dose.”

“CT already operates at what medical physicists define as the low end of the low-dose spectrum for carcinogenesis estimates,” says Michael Brant-Zawadzki, MD, executive medical director of the Neurosciences Institute at Hoag Memorial Hospital in Newport Beach, California. “So in that sense, every CT is a low-dose CT. However, people want it to be as far over to zero as possible, and so they say low dose.”

In some circles, even low dose has been undercut as the term “ultra low” is being used for doses in the submillisievert range, Frush says.

But striving for the lowest possible dose for all exams doesn’t necessarily make sense, Frush contends. “We have to be mindful of the fact that certain exams and certain populations need to be scanned at a higher dose and some at a lower dose. We probably need to better fashion our protocols and technology to address those specific needs rather than having a one-size-fits-all attitude,” he says. “We shouldn’t approach all chest CTs or abdomen CTs or gated cardiac CTs the same way but rather begin to fashion what is a more individualized or personalized CT delivery and what is the appropriate dose for that patient and that exam at that particular time.”

Dosing for all CTs should be according to the ALARA principle—as low as is reasonably achievable without compromising diagnostic quality, Bankier agrees. The goal on every exam should be to reduce dose as much as possible but still produce an exam that is meaningful, he says.

Image Quality
The problem with decreasing the radiation dose of every exam as much as as possible is that image quality may be compromised, Frush says. “You can’t always go as low as you want and reliably get diagnostic information. Optimizing dose requires weighing the potential risks against the quality of the images,” he explains.

Brant-Zawadzki says it’s good to minimize dose and “to be superconservative because you never know what the consequences can be.” However, he argues that the science doesn’t show that doses from CT studies and other exams are causing increased rates of cancer.

“The total collective effective dose to the US population from all radiation sources has essentially doubled since 1980, predominantly as a result of a large increase in medical exposures. The frequency of diagnostic radiologic examinations has increased almost tenfold between 1950 and 2006,” he says, quoting a paper by Mettler et al from the November 2009 issue of Radiology.

This is a considerable increase in exposure, Brant-Zawadzki says. “Then should we not see a rise in cancer rates in our population by now? Guess what the per capita cancer rate has done in that same time? It’s fallen annually in the first decade of this century, according to statistics from the National Cancer Institute,” he notes. “This doesn’t support the mentality of some of our colleagues that we’re causing a cancer epidemic because we’ve been using nuclide studies, barium enemas, upper GI [gastrointestinal] studies, and CT scans all these years.”

Some studies suggest that low levels of radiation may protect against cancer by stimulating body defenses. Low levels of radiation could trigger mutations, Brant-Zawadzki says. “But radiobiologists and others have taught us that our cells routinely repair mutations that occur on a daily basis from basic biochemical reactions in our system. Even if unrepaired, mutations do not necessarily lead to cancer as some mutations lead to cell death; also, our body mounts a defense to certain mutations, destroying the rogue cells, including those that could potentially be carcinogenic,” he says. “If such defense mechanisms are active, many of the very early cancer cells do not necessarily go on to cause the disease of cancer.”

Dose-Reporting Law
Lawmakers began focusing on radiation exposure because of concerns that excessive exposure causes cancer and several well publicized overexposure incidents. California recently enacted a law requiring diagnostic radiologists to include CTDIvol and DLP levels in all CT reports. The law, which took effect July 1, also requires medical physicists to conduct annual assessments of the dosage units in every protocol. (See our interview with consultant Shawn McKenzie on the dose reporting law on page 22.)

Morin isn’t convinced that reporting exact dose is better than using the term low dose. Unless the clinicians are physicists, he says, “We would not expect them to understand the significance of the dose indices.” Besides, he says, the indices are not indicative of the amount of radiation that a patient absorbs. “They are indices and while the intention is good, we’re working toward better ways to address this issue. Right now, just to put down a number is not very useful to patients or to the ordering physicians,” he says.

Radiologists are concerned that the numbers could be misinterpreted and don’t provide more useful information to patients or their clinicians than the term low dose. “The danger is patients will add the numbers up and won’t know what to do with that information,” Morin says.

Wendy Kreider, CT product manager at Siemens Healthcare, says manufacturers can confuse the issue of low dose even more when they tout equipment that produces dose savings. “If you’re starting at a really high dose, saving a percentage of that doesn’t mean much. How do you quantify that?” she asks.

That’s one reason the focus shouldn’t be on coming to a consensus on what exactly low dose is but on developing practices and protocols that provide the right dose for every scan, according to Kreider. “What we want to move toward is the right dose for that particular patient, the right dose for that particular exam you’re performing,” she says.

Achieving the right dose, Kreider says, centers on educating the technologists who are operating the scanners. “For instance, we know that lowering kilovolts substantially reduces dose to the patient. However, to maintain the image quality, the operator would need to raise the milliampere-seconds, which can be difficult and time consuming to calculate. For this reason, the majority of institutions do not adjust the kilovolt and take advantage of this dose-reduction technique,” she says.

Automating Tools
Kreider says Siemens continually integrates innovations into its CT scanners that significantly reduce radiation exposure and streamline workflow at the same time. Most recently, it introduced Care kV to help automate dose reduction. Care kV selects the correct tube voltage depending on a patient’s anatomy and the organ to be imaged. All other parameters automatically adjust to suit the selected kilovolt level. Care kV optimizes the contrast-to-noise ratio of the image and enables dose savings, she says.

Reducing dose is nothing new for Siemens, which launched its CT Low-Dose Centers of Excellence program in 2010 as the original blueprint for academic-industry partnerships. (The program’s name includes the term Bankier and Kressel are trying to eliminate.)  The program works with these institutions to help develop best-in-class clinical processes and protocols that reduce patient CT radiation dose, ensure good patient outcomes, and optimize clinical operations, Kreider says.

Ken Denison, global CT dose leader for GE Healthcare, says that new technologies, coupled with a more holistic approach to lowering dose, will enable users to continue to lower dose for some time. For example, he says, GE recently launched the GE Blueprint, an initiative to help healthcare providers build a comprehensive program for lowering dose. The initiative begins with a benchmark process to help healthcare providers obtain a baseline of their CT imaging program relative to industry guidelines and the best and better practices from around the country.

Intermountain Healthcare in Salt Lake City began implementing GE Blueprint earlier this year. According to Keith White, MD, medical director of imaging, the advantage is that the initiative doesn’t address a single aspect of radiation management but rather many of the factors that can lead to dose reduction. It includes radiologist and technologist education, training, assessment and controls for ordering exams and implementing new technologies that allow for better image quality, improved image reconstruction and noise reduction to enable further dose reductions, he says.

“The challenge of managing dose is to address each of those different areas and optimize each of those areas rather than simply buying scanners that have dose-reduction features built-in,” White says.

Although it is just starting, White is confident that the healthcare system will successfully adopt practices that lead not just to low-dose scans but also to appropriate use. Because hospitals and imaging centers typically use CT for seven to 10 years, White says it can take years for the technology that reduces dose to disseminate throughout the marketplace.

“Older scanners aren’t going to disappear overnight,” he says. Still, he believes, as do many of his colleagues, that best practices and technology can make appropriate use and decrease medical radiation throughout the imaging community in time.

— Beth W. Orenstein of Northampton, Pennsylvania, is a freelance writer and regular contributor to Radiology Today.