Videos | March 22, 2011

Child-Size Radiation Dose

There is no doubt that medical imaging procedures save lives. However, one size does not fit all. Because children are three to five times more sensitive to radiation than adults,1 and cumulative radiation exposure can have adverse effects, it is critical for doctors to lower radiation levels when imaging a child.

Thatâ??s why in 2007, the Society for Pediatric Radiology (SPR) initiated the Alliance for Radiation Safety in Pediatric Imaging. Not long after, the American College of Radiology (ACR), the American Society of Radiologic Technologists (ASRT), and the American Association of Physicists in Medicine (AAPM) joined the Alliance. The Image Gently campaign is the Allianceâ??s initiative to raise awareness for lowering radiation dose used in pediatric imaging. The Alliance is actively working with imaging manufacturers to standardize dose assessment and display for children.

Although disagreements about the accuracy of the risk models or the degree to which the risks of radiation are emphasized are ongoing within the medical community, the message of the Image Gently campaign is clear: Reduce or â??child-sizeâ? the amount of radiation used when obtaining a CT scan in children. To â??child-sizeâ? the amount of radiation used, Image Gently encourages doctors to ask their medical physicist to determine the baseline radiation dose for an adult for that siteâ??s equipment and compare that dose with the ACR Standards.2

While these guidelines are clear, it is not certain how widely doctors have implemented these radiation-reducing measures to date. To gage the impact Image Gently on medical imaging practices, Imaging Technology News (ITN) spoke with Marilyn Goske, M.D., chair of the Alliance, and Neil Johnson, M.D., president of the Society for Pediatric Imaging, both practice at Cincinnati Childrenâ??s Hospital.

ITN: How serious a risk does radiation imaging pose to children?

Dr. Goske: One of the first things we need to remember is when children have imaging it is being done for an indicated medical condition and for a benefit for that patient. That is really what the Image Gently campaign revolves around. Once a study if medically indicated it behooves all of us in pediatric imaging to promote radiation protection and try to lower the dose and still maintain the quality of the exam so that we get the diagnostic information that we need. We know from studies, particularly from the atomic bomb survivors in Japan, that if children receive radiation from a bomb blast such as that one, they are more sensitive to radiation. Now medical imaging is different as itâ??s a different form of energy and quite diffrent in how itâ??s given for the imaging test, but itâ??s the best we have. The data from that tells us that we need to be overly cautious and conservative, and that if we are going to use this technology, we want to use it in the safest way possible.

ITN: How exactly is the Alliance standardizing dose assessment and display for children?

Dr. Goske: We are working together under the direction of Keith Straus, who is the medical physicist at Boston Childrenâ??s Hospital, Mr. Tom Toth, who is the former chief physicist at GE Healthcare, and Stephen Vastaghat the Medical Imaging Technology Alliance (MITA).

The four major CT vendors have signed on to come up with more standardized dose displays so that when we complete a CT scan and we look at the images on task and that we have the information we need to interpret the information more accurately. Under the current system the CT dose that is displayed, which is the CT dye volume and the DLC are based on 32-centimeter adult-size phantoms. So if the patient is on the table and is exactly the same size as the phantom, the dose display is reasonably accurate. But in our patient population where you have an infant who weighs 5 lbs., for example, the younger they are, the smaller they are compared to the size of the phantom, and the more discrepant the dose display is. According Mr. Strauss in a paper that he published,3 the dose display can be off by a factor of three. So we are actually underestimating radiation dose for those small patients. We are working with numbers to get those displays more accurate so that radiologists, radiologic technologists and medical physicists have a better idea of what our smaller patients are really getting in terms of radiation dose during CT scans and other imaging procedures.

Dr. Johnson: Itâ??s a very simplistic but important idea that we give our patients the right dose. We use the analogy of flying. We all fly in a commercial aircrafts, so we take risks. But there is a huge benefit when we minimize the risk. What we are trying to do is minimize the dose of radiation to children. We are not trying to stop these scans when they are needed medically. We are trying to do them with the minimum dose possible.

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