Edward Lee Nickoloff DSc, Presenter: Nothing to Disclose

Zhengfeng Lu PhD, Abstract Co-Author: Nothing to Disclose

Ajoy K. Dutta MS, Abstract Co-Author: Nothing to Disclose

James So MS, Abstract Co-Author: Nothing to Disclose

Carrie Ruzel-Shapiro, Abstract Co-Author: Nothing to Disclose

Because of potential risks, the determination of CT radiation doses is important for young children. Direct patient measurements are usually not practical. Many CT scanners provide a calculation of the CTDIvolume. A unique, tiny solid state dosimeter system which has recently been developed permits the instantaneous measurement of cumulative patient entrance radiation doses during clinical CT procedures. This study compared the calculated CTDIvolume to direct measurements with this new detector in pediatric patients.

The new dosimeter system utilizes three tiny silicon detector chips 1cm x 0.5cm in size coupled to a 8cm x 10 cm x 2 cm readout with thin cables. The system digitally displays the total accumulated dose. The energy response is +/-10% between 60 and 120 kVp. These measurements were compared to values calculated by a GE CT/i scanner. Routine clinical head and body CT scans of pediatric patients ranging in age from 1 year to 18 years old were used.

Head and body data were separately plotted in mGy per 100 mAs. The CT scanner calculated data showed no variation with patient size or anatomical location. The measured data, however, indicated radiation doses that were 2-3 times greater in small children and matched the calculated data for larger sizes. At the lower mAs values utilized for pediatric body scans, the measured radiation doses ranged from 2 to 5 mGy per procedure. At the higher mAs values for pediatric head CT scans, the radiation doses were 4-9 times greater than the body doses. The values calculated by the CT scanners were inaccurate because they were based upon only two phantom sizes - 16 cm diameter for heads and 32 cm for bodies. Moreover, the calculated values were based upon uniform acrylic plastic instead of non-uniform tissue (like air in the lungs and bones).

This new solid state integrating detector system provides a new tool for the accurate and instantaneous measurement of CT radiation dose that was previously unavailable. Moreover, the data showed that the scanner calculated CT radiation doses can be in error due to patient size and tissue non-homogeneity.

Nickoloff, E, Lu, Z, Dutta, A, So, J, Ruzel-Shapiro, C, Hot Topic: New Solid State Dosimeters for Direct Dose Measurements in Pediatric CT Scans.  Radiological Society of North America 2004 Scientific Assembly and Annual Meeting, November 28 - December 3, 2004 ,Chicago IL. http://archive.rsna.org/2004/4418660.html