Sjirk Jan Westra MD, Presenter: Nothing to Disclose

Mannudeep Karanvirsingh Kalra MD, Abstract Co-Author: Nothing to Disclose

Bob Liu PhD, Abstract Co-Author: Nothing to Disclose

Valerie Buckley MS, Abstract Co-Author: Nothing to Disclose

Timothy G. Ferris MD, Abstract Co-Author: Nothing to Disclose

Longitudinal automatic exposure control (Auto mA, GE Healthcare) modulates the CT radiation dose according to attenuation factors calculated from the scanogram. Because of the increased radiosensitivity of children, risk estimates in obese children for future cancer induction are increased compared to lean children and adults. In a Quality Assurance study of an a-select sample of all pediatric body CT scans, we assessed radiation dose and image quality of scans performed with Auto mA on obese children and compared them to fixed mA technique based on patient age

In our sample of 150 pediatric body CT scans, 9 were identified as dose outliers (> 2 SD above group mean). We recorded kV, mA (with mA range when Auto mA was used), rotation time and table speed, in order to calculate CTDIvol. In scans obtained with Auto mA, we compared CTDIvol with that from a corresponding age-adjusted fixed mA acquisition at 120 kV. We measured image noise as standard deviation of attenuation values (in HU) within a homogeneous region of interest placed in the subcutaneous fat. We compared dose and image noise of scans performed with Auto mA with historic scans performed with fixed mA, when available

All dose outliers occurred in obese children. 5/6 abdominal CT and 1/3 chest CT dose outliers were scanned at 140 kV. Dose in these outliers was between 1.6 and 3.6 times dose calculated for scans performed at 120 KV and with fixed mA. Noise varied between 8-24 HU in the abdominal and between 7-10 HU in the chest CT dose outliers, and in none did noise interfere with diagnostic image quality

Obese children are getting substantially higher doses when using 140 kV and/or Auto mA without specified maximum mA, than when using age-based fixed mA settings, but these higher doses may be required in order to limit noise. Further study is needed to determine whether these "adult" settings are appropriate in obese pediatric patients, or whether use of age-specific reduced mA settings would result in unacceptable image noise

The decision whether to treat obese children as adults or children will determine the delicate balance between optimizing image quality and reducing risk from CT radiation exposure

Westra, S, Kalra, M, Liu, B, Buckley, V, Ferris, T, Radiation Exposure of Obese Children from Body CT: Are They Appropriately Treated as Adults?.  Radiological Society of North America 2007 Scientific Assembly and Annual Meeting, November 25 - November 30, 2007 ,Chicago IL. http://archive.rsna.org/2007/5008891.html