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SU‐C‐217A‐03: Position Sensitivity of Calculated Dose‐Length‐Product‐To‐Effective‐ Dose Conversion Factors in Computed Tomography Examination

Publication ,  Conference
Gao, Y; Ding, A; Caracappa, P; xu, X
Published in: Medical Physics
January 1, 2012

Purpose: To quantify the sensitivity of Dose Length Product to Effective Dose conversion factors (k‐factors) to scan length and position. Methods: To convert the recorded Dose Length Product (DLP) to an estimate of Effective Dose (E), a set of conversion factors, known as k‐factors, are used. These published k‐factors were developed for a limited set of standard protocols with fixed scan lengths, and most are based on stylized models of the human body. Using realistic models of male and female (RPI‐AM and RPI‐AF) and a validated model of the CT source, Monte Carlo simulations are preformed to calculate the dose to each organ on a slice‐by‐slice basis. For each slice, the organ doses are converted into ‘local’ k‐factors. Over a full scan length, the effective doses from the individual slices and the DLPs are summed, so the k‐factor for the scan is equivalent to the average of the local k‐factors in the scan range. Results: Simulations of 1‐cm thick CT slices were performed over the entire range of the torso for the RPI‐AM and RPI‐AF phantoms. The local k‐factors calculated range from a minimum of 0.0128 in the upper shoulder region (above most of the radio‐sensitive organs of the chest), to a maximum of 0.0369 in the region around the female gonads. The calculated k‐factor for a standard chest scan was 0.0289, which compares favorably to published values. However, the k‐factor decreases as the scan range is expanded. Consequently, a chest scan that is only 10 cm longer would have a k‐factor 18% lower when compared to the standard protocol. Conclusion: By improving the understanding of the sensitivity of k‐factors to scan length and position, more accurate estimates of effective dose from CT examination can be provided without sacrificing the efficiency and simplicity that k‐factors provide. This project was funded by National Institutes of Health (National Institute of Biomédical Imaging and Bioengineering R42EB010404). © 2012, American Association of Physicists in Medicine. All rights reserved.

Duke Scholars

Published In

Medical Physics

DOI

ISSN

0094-2405

Publication Date

January 1, 2012

Volume

39

Issue

6

Start / End Page

3607

Related Subject Headings

  • Nuclear Medicine & Medical Imaging
  • 5105 Medical and biological physics
  • 4003 Biomedical engineering
  • 1112 Oncology and Carcinogenesis
  • 0903 Biomedical Engineering
  • 0299 Other Physical Sciences
 

Citation

Published In

Medical Physics

DOI

ISSN

0094-2405

Publication Date

January 1, 2012

Volume

39

Issue

6

Start / End Page

3607

Related Subject Headings

  • Nuclear Medicine & Medical Imaging
  • 5105 Medical and biological physics
  • 4003 Biomedical engineering
  • 1112 Oncology and Carcinogenesis
  • 0903 Biomedical Engineering
  • 0299 Other Physical Sciences