Reducing Radiation Dose in Kids: How Low Can You Go
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Hospitals quickly got their acts together, with the SNM organization mobilizing multi-association workgroups and coordinating with independent campaigns like Image Gently and the European Association of Nuclear Medicine (EANM). Outliers quickly modified their behavior, as the mantra "the right test, at the right time, on the right patient, for the right clinical condition" took hold. According to S. Ted Treves, MD, chief of the division of nuclear medicine and molecular imaging at Children's Hospital Boston and professor of radiology at Harvard Medical School, whose 2008 survey sparked the pediatric dose movement, hospitals have pursued three interconnected methods for reducing radiation exposure: the modification of existing protocols (or establishing them to begin with), the use of advanced image processing and technological improvements to radiation-inducing modalities.
Setting the bar, and lowering it
After reporting the dosing disorder, Treves spearheaded efforts to establish dosimetry baselines and formulate guidelines, which were released in February in The Journal of Nuclear Medicine and will be permanently available for free online. Moreover, the prevalence of dosage cards and calculators like those on EANM's website allow physicians to quickly administer the currently recommended dose (available at www.eanm.org/scientific_info/dosagecard/dosagecard.php)."For every patient who has previous cross-sectional images for reference, we are able to lower voltage from 100 to 80 kVp and current from 100 to 40 mAs for PET/CT studies," bringing exponential dose reductions, explains Helen R. Nadel, MD, a pediatric radiologist at British Columbia Children's Hospital in Vancouver, Canada. Nadel's department also has switched to using 18F-FDG for lymphoma and even inflammation imaging, significantly reducing doses by totally eliminating the far more radioactive I-111 or Ga-67.
Cutting out a scan
Compared with the more ubiquitous filtered back projection (FBP), Treves and colleagues were able to cut radiation dose in half for bone and renal SPECT using ordered subset expectation maximization (OSEM) iterative reconstruction, while producing higher quality images. "It's not a new technique, but previously computers needed a full day to make the computations, now it takes on the order of one or two minutes," Treves notes. His findings are especially important for pediatrics because the method allows physicians to shorten scan time by half, a plus for fidgety children.In addition to fusing PET and SPECT with prior CTs to spare an exam, Nadel secures the same savings by foregoing a low-dose attenuation correction CT scan prior to a post-contrast diagnostic CT and performing a single post-contrast CT, at lower kVp and mAs.
But kids take the back seat
Some technological advances for dose reduction have spilled over to benefit kids, with more sensitive gamma cameras offering twice the detectors—more counts with less radiation—as one of the more notable advances. Unfortunately, little people generate a smaller nuclear imaging market, meaning that few system advances have been directed at pediatric imaging because adult cardiology and oncology are simply more profitable. Treves thinks much of the technology is there, it's just a matter of optimizing them for pediatric patients. "If you could take some of these machines, which offer quicker acquisition times—as much as four times quicker—and adapt them to children, you could really lower doses."While standardization has no doubt had the widest effect, Nadel highlights the new paradigm of dose reduction, citing R. Paul Guillerman, a radiologist at Texas Children's Hospital in Houston: "It's no longer just how low can you go, but how can you go low."