Experts say everything in moderation
When a study published in the June 7 issue of The Lancet demonstrated that there’s an increased cancer risk associated with CT radiation in children, the findings created a stir in popular media. Yet radiology and diagnostic-imaging researchers say the findings, while significant, shouldn’t be cause for alarm.
The new study, led by Mark Pearce of Newcastle University in the United Kingdom, identified 178,000 UK patients who between 1985 and 2002 had one or more CT scans before age 22. Pearce and his colleagues extracted the number and types of CT scans, estimated the dose absorbed by patients’ brains and bone marrow, and then linked the data to cancer incidence and mortality reports in the UK National Health Service Registry. Based on their calculations, a single CT scan produced about one more case of leukemia and one more brain tumor for every 10,000 patients in the first decade after the scan.
Marilyn Goske, MD, professor at Cincinnati Children’s Hospital Medical Center and chair of the Alliance for Radiation Safety in Pediatric Imaging, noted that the retrospective study by “very credible investigators” adds to science’s body of knowledge regarding imaging dangers, yet should be considered in context with many other studies.
In fact, Pearce himself had this to say in a recent release: “The immediate benefits of CT outweigh the potential long-term risks in many settings and because of CT’s diagnostic accuracy and speed of scanning, notably removing the need for anesthesia and sedation in young patients, it will, and should, remain in widespread practice for the foreseeable future.”
Yet, questions still remain: What is the perfect balance between radiation’s risks and its benefits, particularly concerning computed tomography, which requires a much higher radiation dosage than an X-ray to be effective. And how much more vulnerable are children?
A little history
The alarm was first sounded in 2001, when a published paper found that CT scans pose a small risk of cancer in children. It was a watershed event, yet a vocal minority in the field actually scoffed at the study’s results. The study, led by David Brenner, who’s now the director of Columbia University’s Center for Radiological Research, used data collected from Japanese atomic-bomb survivors to calculate the cancer risk to a child undergoing a CT scan.
“When the Japanese data started coming in, that’s when most everyone did an about-face,” recalled Marta Hernanz-Schulman, MD, professor of Radiology and Pediatrics at Monroe Carell Jr. Children’s Hospital at Vanderbilt University in Nashville.
Chair of the American College of Radiology’s Pediatric Imaging Commission, Schulman explained that the Brenner study coincided with a study by Donald Frush, MD, now chief of Pediatric Radiology at DukeMedicine, that demonstrated that radiologists weren’t adjusting CT dosage parameters for adults versus children. Per volume of tissue, smaller patients must absorb more radiation, Schulman said, and children are more vulnerable because their tissues are dividing, and thus chromosomes are more exposed. What’s more, children will live longer. “Many of these random events caused by radiation need a long time to develop. They have a long latency period,” Schulman said, adding, “We need to do the right test at the right time for the right reasons in the right way, regardless of your age, but with children we have to be even more careful.”
Time to image gently
By 2006, Goske said, a “concerted campaign” was in the works by advocates for radiation protection for children. In 2007, the Alliance for Radiation Safety in Pediatric Imaging was founded, incorporating several academic, research and clinical organizations to help ensure safer imaging for kids. One result of the collaboration has been www.imagegently.org, an educational initiative teaching both practitioners and parents about the safe use of diagnostic imaging while being advocates for their patients and children.
“Those of us who are in the field are putting our heart and soul into it, and I think the manufacturing community is as well,” Goske said. In fact, she said newer equipment just in the past two years or so is promising radiation reductions of 40 to 50 percent and more. “I think that at some point we will find – and in the not too distant future – that the radiation dose associated with CT is going to be in the range of routine radiography,” she said. “Of course, we’re not there yet.”
Recent equipment improvements put into perspective many research findings that were based on what-is-now-obsolete equipment. “We only started turning around and saying, ‘Hey, what are we doing?’ in 2001, and the machines are much, much better now,” Schulman said.
Why CT matters
Yet one shouldn’t judge the risk of CT without also examining what came before. “The fact that CTs have increased is multi-factorial, and I am old enough to
remember what CT is replacing,” Goske said. Remember pneumoencephalography, when most of the cerebrospinal fluid was drained from around the brain and replaced with air, oxygen or helium to allow the structure of the brain to show up more clearly on an X-ray? The procedure was extremely painful, and patients took two to three months to recover.
Goske said CT is “an amazing technology, and part of the reason that the use has increased is because it does provide valuable information.” A recently published study from Boston Children’s Hospital, for example, solidifies the importance of CT when it comes to triage of severely injured pediatric patients.
“There is still a role for CT, and we should keep it in perspective,” she said. Yet, she added, a “laudable goal” is reducing the amount of tests that use ionizing radiation.
Both researchers noted that the role of parents can’t be understated, and www.imagegently.org offers parents a wealth of information to help them be better advocates for their child. Schulman said that, while CT is an effective alternative, parents should always ask if CT is necessary. Might another test be just as effective without the radiation risk? “CT is a great modality,” she said. “It is so good that it could eliminate other ways of looking at the same thing, and it shouldn’t. The CT needs to be indicated.”