Study finds huge variations in pediatric nuclear medicine dosing

July 2, 2008

A survey of children’s imaging services has found a twofold variation in radiopharmaceutical doses administered during pediatric nuclear medicine exams. For some radiopharmaceuticals, the reported maximum activities varied by as much as a factor of 10, and minimum activities differed by as much as a factor of 20, suggesting the need for a consensus among nuclear physicians on appropriate doses for young patients.

A survey of children's imaging services has found a twofold variation in radiopharmaceutical doses administered during pediatric nuclear medicine exams. For some radiopharmaceuticals, the reported maximum activities varied by as much as a factor of 10, and minimum activities differed by as much as a factor of 20, suggesting the need for a consensus among nuclear physicians on appropriate doses for young patients. Based a survey of 16 selected procedures at 13 pediatric hospitals in North America, the study from Boston's Children's Hospital found that in general, however, variation was within a factor of 2. The report reveals a need for better tools to guide dosing practices, according to the authors. The report appeared in the June 2008 Journal of Nuclear Medicine."At this time, the majority of radiopharmaceutical package inserts do not provide guidance on pediatric doses," said lead author Dr. S. Ted Treves, chief of nuclear medicine at Children's and a professor of radiology at Harvard Medical School. The survey tracked the minimum and maximum administered activities, the schedule used to determine the appropriate administered activity as a function of patient size, and the corresponding factor applied, such as activity per kilogram or activity per body surface area. The minimum total doses of technetium-99m mercaptoacetyltriglycine (MAG3), a tracer frequently used during renal scintigraphy, ranged from 18.5 to 148 MBq. Activity per kilogram varied from 1.85 to 10.36 MBq and the maximum dose from 111.0 to 370.0 MBq. Overall, the greatest inconsistency was found for levels of minimum total administered activity in newborns and infants."In imaging children, physicians typically base dosages on the patient's body weight, the nature and type of problem being investigated, the equipment available, and their own experience. This has led to the variations in dosage that currently exist," Treves said. The authors speculate that since the survey uncovered differences among premier facilities, variations in the larger nuclear medicine community could be even greater. Treves identified the need for the survey when he was asked to participate in a different multicenter study that prescribed doses much higher than those he normally uses. "I knew there were no standards," he said.The survey confirmed his suspicion that significant variation exists. "We were able to characterize the variation, and this provides an opportunity to stop and think about that," he said. The study has prompted the formation of a workgroup to balance the need for high-quality images with the lowest possible activities and develop guidelines for pediatric radiopharmaceutical dosing. Members of the Pediatric Imaging Council and the Society for Pediatric Radiology who practice nuclear medicine will participate. "This group will examine administered dosages and come up with recommended radiopharmaceutical dosages over the next year." said council president Dr. Michael Gelfand.For more information from the Diagnostic Imaging archives:Pediatric imagers put dose campaign on the roadCombined strategies lower pediatric CT radiation doseReport from NCRP: Hybrid imaging poses radiation exposure challenges