A new technique to more accurately calculate radiation dose to a fetus may help comfort pregnant women who undergo a computed tomography (CT) scan, suggests research being presented at the 57th Annual Meeting of the American Association of Physicists in Medicine (AAPM).
Doctors sometimes order CT scans for pregnant women to check for internal bleeding after trauma (such as a car accident), or if there are signs of pulmonary embolism (blood clot in the lung). But women and their doctors often worry about the risks of radiation to the developing fetus.
"As medical physicists, we regularly are asked about the radiation risk to the fetus - either the physician is asking whether it is OK to scan a pregnant patient or, more often, a woman had a scan without realizing she was pregnant, and now is worried about the risk," said Michael McNitt-Gray, Ph.D., a medical physicist and professor of the department of radiology at David Geffen School of Medicine at UCLA. "This work improves upon previous methods of estimating radiation dose by taking into account patient size and composition through a measure called the Water Equivalent Diameter; this allows a better characterization of patient size and therefore a better estimate of the dose to the fetus. The information we provide usually is not only comforting to the patient, it's comforting to the physician who is trying to comfort the patient."
Based on 18 pregnant patients who previously had CT scans, the new dose-estimation technique factors in the patient's size, as well as the size and age of the fetus. Medical physicists could use this technique to determine if the fetus received or would receive a dose that is greater than recommended by guidelines, which is rarely the case after one scan, Dr. McNitt-Gray said.
"We often get asked 'Can we do a CT scan?' or 'Can you lower the dose?' when the question really should be, 'Does the patient need a CT?'" said Dr. McNitt-Gray. "In other words, the radiation dose for our protocols should already be the minimum we can use to get a diagnostic image - any less wouldn't provide adequate information so the CT would be meaningless."
In addition to Dr. McNitt-Gray, collaborators on the study being presented at AAPM are: K. McMillan, M. Bostani and E. Angel.