Researchers who determined the optimal radiation dose in weight-based kilovolts (kV) technique charts for pediatric body CT discovered that a dose reduction of 30 to 50 percent at 100 and 120 kV can be achieved while maintaining clinically acceptable quality, said the study's lead author, Lifeng Yu, Ph.D., an assistant professor of radiologic physics at the Mayo Clinic in Rochester, Minn."If the intention is to reduce radiation dose, we have to keep in mind that we should not reach a point where we reduce radiation so low that diagnostic information is affected," he said.The team created and validated a low-dose tool designed to simulate images with 30, 50 and 70 percent of the original dose level for the 102 clinically indicated pediatric chest and abdominal CT exams used in the retrospective study. "Simulation tools are useful because a radiologist can actually perform virtual scans," said Cynthia McCollough, Ph.D., a professor of radiologic physics at Mayo and the project's senior author. "Radiologists don't want to miss an important diagnosis, but they are also trying to dial down the dose. This tool allows them to test how low they can go."A California law that will require radiologists to include a radiation dose index in every patient's report is among the reasons outlined in the PowerPoint, top, explaining why size-specific dose estimates are necessary, presented by Marilyn J. Goske, M.D., Ph.D., and colleagues at RSNA 2011. Middle: An illustration shows the marked difference in the patient's size, shape and tissue composition compared to an acrylic phantom, which leads to inaccuracies, according to researchers. Bottom: CT dose index is commonly measured for CT scanners and is reported on the CT console for set techniques.Size-specific Dose Estimates Based on Patient's SizePresenters with the American Association of Physicists in Medicine Task Group 204, co-chaired by John Boone, Ph.D., and Keith Strauss, M.Sc., developed easy-to-use tables that can be applied to the displayed volume CT dose index (CTDIvol), which allows radiologists to easily estimate patient dose for children and small adults. Researchers were able to estimate dose for different sized patients to within approximately 10 to 20 percent, either before or after the scan."CTDIvol is a measure of dose to a phantom, not to a patient," said Marilyn Goske, M.D., a pediatric radiologist at Cincinnati Children's Hospital Medical Center and head of the Image Gently team for the Alliance for Radiation Safety in Pediatric Imaging. Size-specific dose estimates allow users to estimate pediatric patient doses based on body size, she said.Dr. Goske led the effort to establish the first national pediatric dose registry—a project funded through a 2009-2011 RSNA Research & Education (R&E) Foundation Education Scholar Grant supported by the Derek Harwood-Nash grant endowment and Harvey and Jean Picker.Better dose estimates are needed, Dr. Goske said, for three main reasons: parents and patients are increasingly asking about estimated levels of radiation dose; estimates of patient dose must be tracked as radiology moves toward national registries; and radiologists in some parts of the country—particularly California—are being asked to include a patient's estimated radiation dose in his or her medical record."This measure can help with all three of those things," Dr. Goske said. "The final gold standard is going to be specific organ doses for patients, but that's at least five years away. This is an improvement over CTDIvol."Web ExtrasResearchers offer insight on their RSNA 2011 presentations:Lifeng Yu, Ph.D., discusses the process for his research on pediatric body CT scanning protocolsDr. Yu discusses the results of his researchDr. Yu discusses measures for optimizing scanning protocolsCynthis McCollough, Ph.D., discusses the advantages of simulation tools in reducing pediatric doseMarilyn Goske, M.D., discusses the importance of size-specific dose estimates (SSDE)Dr. Goske discusses factors driving the need for SSDETo read the 2011 American Association of Physicists in Medicine Report No. 4, Size Specific Dose Estimates in Pediatric and Adult Body Examinations, click here.
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