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DOI: 10.1148/radiol.2483071964
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(Radiology 2008;248:995-1003.)
© RSNA, 2008

Special Reports

Converting Dose-Length Product to Effective Dose at CT1

Walter Huda, PhD, Kent M. Ogden, PhD, and Mohammad R. Khorasani, MD

1 From the Department of Radiology, Medical University of South Carolina, PO Box 250322, 169 Ashley Ave, Charleston SC 29425 (W.H.); and Department of Radiology, SUNY Upstate Medical University, Syracuse, NY (K.M.O., M.R.K.). Received November 9, 2007; revision requested January 9, 2008; revision received January 24; accepted March 25; final version accepted April 10. Address correspondence to W.H. (e-mail: huda{at}musc.edu).

Purpose: To determine effective dose (ED) per unit dose-length product (DLP) conversion factors for computed tomographic (CT) dosimetry.

Materials and Methods: A CT dosimetry spreadsheet was used to compute patient ED values and corresponding DLP values. The ratio of ED to DLP was determined with 16-section CT scanners from four vendors, as well as with five models from one manufacturer that spanned more than 25 years. ED-to-DLP ratios were determined for 2-cm scan lengths along the patient axis, as well as for typical scan lengths encountered at head and body CT examinations. The dependence of the ratio of ED to DLP on x-ray tube voltage (in kilovolts) was investigated, and the values obtained with the spreadsheet were compared with those obtained by using two other commercially available CT dosimetry software packages.

Results: For 2-cm scan lengths, changes in the scan region resulted in differences to ED of a factor of 30, but much lower variation was obtained for typical scan lengths at clinical head and body imaging. Inter- and intramanufacturer differences for ED/DLP were generally small. Representative values of ED/DLP at 120 kV were 2.2 µSv/mGy · cm (head scans), 5.4 µSv/mGy · cm (cervical spine scans), and 18 µSv/mGy · cm (body scans). For head scans, ED/DLP was approximately independent of x-ray tube voltage, but for body scans, the increase from 80 to 140 kV increased the ratio of ED to DLP by approximately 25%. Agreement in ED/DLP data for all three software packages was generally very good, except for cervical spine examinations where one software package determined an ED/DLP ratio that was approximately double that of the other two.

Conclusion: This article describes a method of providing CT users with a practical and reliable estimate of adult patient EDs by using the DLP displayed on the CT console at the end of any given examination.

© RSNA, 2008




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R. C. Opreanu, R. Samaraweera, J. P. Kepros, W. Huda, and K. M. Ogden
Effective Dose to Dose-Length Product Coefficients for Calculation of CT Effective Dose
Radiology, July 1, 2009; 252(1): 315 - 316.
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