Radiation Effective Dose From CT Scans

Parameters for Computing Radiation Dose

This program uses parameterizations of data developed by Huda and colleagues (see "References" below) to compute radiation effective dose consequential to computed tomography examinations. "Effective dose", as defined in ICRP Report Number 90, is an index (with units of millirem) that reflects radiation detriment (risk). Complete the form below and click the "Compute Dose" button to calculate the effective dose (millisieverts and millirem). Make sure you enter values for the parameters you wish to vary, consistent with the appropriate units. If you leave a field blank, a default value [shown in brackets] will be used.

Notes and References

This program is based on work by Walter Huda and colleagues, Departments of Radiology, SUNY Upstate Medical Center and University of Florida. The original references are:

1. Ware DE, Huda W, Mergo PJ, Litwiller AL. Radiation effective doses to patients undergoing abdominal CT examinations. Radiology 210:645-650 (1999).

2. Huda W, Scalzetti EM, Roskopf M. Effective doses to patients undergoing thoracic computed tomography examinations. Medical Physics 27(5): 838-844 (May 2000).

Notes:

1. Patient Mass: effective dose has been computed and parameterized for values of mass between 10 and 110 kilograms. Effective doses obtained using values of mass outside this range should be interpreted with caution. The following average body weights for various age groups (see Reference 2) are provided as a guide.

Less than or Equal to 10 Years	11 - 18 Years	Over 18 years
15.5 +/- 5.5	55.0 +/- 15.9	74.8 +/- 19.4

2. Type of CT Examination: select a value appropriate for the study of interest. The computations assume a single instance of the examination, performed under the conditions stated in the references. For chest CT, a GE Hi-Speed CT/i scanner operated at a tube potential of 120 kVp and a scan time of one second is assumed (240 - 260 mAs). For abdominal CT, a GE Hi-Speed scanner operated at 120 kVp, with mAs varying between 200 - 350 mAs (approximately, depending on patient size), is assumed.

If the data entered in the form exceed the specified ranges, the calculation will not be performed. This prevents the computation of dose factors based on extrapolation beyond accepted values for the parameters, and resulting instabilities in the parameterization functions.

3. The absolute values of effective dose are for a particular single detector CT system and cannot be applied to multi-detector systems or systems that automatically vary the tube current during acquisition.

Important Information Concerning This On-line Material

This material is for use by Duke University Radiology physicians and staff. It is intended to be a convenient tool for studying the effect of patient mass on radiation effective dose from CT, under the stated conditions. It should not be used as a primary source of information regarding CT dosimetry. Because these calculations of dose are based in part on data obtained from "phantoms", they are not strictly applicable to any individual patient. Duke University and OESO make no warranty as to the suitability of these dose computations for any other purpose.

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Copyright 2000, Robert E. Reiman, MD, OESO and Duke University Medical Center. All rights reserved.