Fetal dose from emergency CT examination: fetal simulation and dose measurements

Chrissy Lo, Martin Law, Francis Cho, Dominic Pang, Patricia Cheng, Lawrance Yip, Wendy Lam


Objective: To experimentally simulate a late stage fetus, to measure fetal irradiation dose and to estimate associated risks resulting from an emergency thorax-abdominopelvic CT imaging for a pregnant patient with suspected aorta dissection.


Material and methods: To simulate the fetal body with a physics CTDI cylindrical phantom placed into the abdomen of a standard female humanoid phantom. Layers of beeswax were used to make the maternal dimension similar to the pregnant patient. A 10 cm pencil chamber was used to measure the dose at each quadrant location and at the center of the CTDI phantom and the fetal dose was obtained by averaging these measured doses. Stochastic effect of childhood cancer risk induction (0.4% per 10 mGy irradiation) was estimated as reference to monitor the growth the newborn child.


Results: The fetal dose was measured as 20 mGy for a single acquisition according to the patient scanning protocol. Since the patient had both pre- and post-contrast CT acquisition, the total fetal dose was therefore 40 mGy. The lifetime risk of developing childhood cancer was estimated as 1.6%.


Conclusion: By using readily available equipment in a radiology department, fetal simulation and then dose measurements can be efficiently performed with the moulding technique. Results obtained are useful as reference value to monitor the growth of the newborn.

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