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Dose Uniformity Analysis Among Ten 16-Slice Same-Model CT Scanners

Erdi, Yusuf Emre DSc, DABR

Journal of Computer Assisted Tomography: January/February 2012 - Volume 36 - Issue 1 - p 154–156
doi: 10.1097/RCT.0b013e31823ed149
Technical Developments

Purpose With the introduction of multislice scanners, computed tomographic (CT) dose optimization has become important. The patient-absorbed dose may differ among the scanners although they are the same type and model. To investigate the dose output variation of the CT scanners, we designed the study to analyze dose outputs of 10 same-model CT scanners using 3 clinical protocols.

Materials and Methods Ten GE Lightspeed (GE Healthcare, Waukesha, Wis) 16-slice scanners located at main campus and various satellite locations of our institution have been included in this study. All dose measurements were performed using poly (methyl methacrylate) (PMMA) head (diameter, 16 cm) and body (diameter, 32 cm) phantoms manufactured by Radcal (RadCal Corp, Monrovia, Calif) using a 9095 multipurpose analyzer with 10 × 9-3CT ion chamber both from the same manufacturer. Ion chamber is inserted into the peripheral and central axis locations and volume CT dose index (CTDIvol) is calculated as weighted average of doses at those locations. Three clinical protocol settings for adult head, high-resolution chest, and adult abdomen are used for dose measurements.

Results We have observed up to 9.4% CTDIvol variation for the adult head protocol in which the largest variation occurred among the protocols. However, head protocol uses higher milliampere second values than the other 2 protocols. Most of the measured values were less than the system-stored CTDIvol values. It is important to note that reduction in dose output from tubes as they age is expected in addition to the intrinsic radiation output fluctuations of the same scanner.

Conclusion Although the same model CT scanners were used in this study, it is possible to see CTDIvol variation in standard patient scanning protocols of head, chest, and abdomen. The compound effect of the dose variation may be larger with higher milliampere and multiphase and multilocation CT scans.

From the Diagnostic X-Ray Quality Assurance Section, Department of Medical Physics, Memorial Sloan-Kettering Cancer Center (MSKCC), New York, NY.

Received for publication September 7, 2011; accepted October 25, 2011.

Reprints: Yusuf Emre Erdi, DSc, DABR, Diagnostic X-Ray Quality Assurance Section, Department of Medical Physics, Memorial Sloan-Kettering Cancer Center (MSKCC), New York, NY 10065 (e-mail:

This work was partially presented at 2008 RSNA meeting.

The author reports no conflicts of interest.

© 2012 Lippincott Williams & Wilkins, Inc.