skip to main content

Title: Stationary table CT dosimetry and anomalous scanner-reported values of CTDI{sub vol}

Purpose: Anomalous, scanner-reported values of CTDI{sub vol} for stationary phantom/table protocols (having elevated values of CTDI{sub vol} over 300% higher than the actual dose to the phantom) have been observed; which are well-beyond the typical accuracy expected of CTDI{sub vol} as a phantom dose. Recognition of these outliers as “bad data” is important to users of CT dose index tracking systems (e.g., ACR DIR), and a method for recognition and correction is provided. Methods: Rigorous methods and equations are presented which describe the dose distributions for stationary-table CT. A comparison with formulae for scanner-reported values of CTDI{sub vol} clearly identifies the source of these anomalies. Results: For the stationary table, use of the CTDI{sub 100} formula (applicable to a moving phantom only) overestimates the dose due to extra scatter and also includes an overbeaming correction, both of which are nonexistent when the phantom (or patient) is held stationary. The reported DLP remains robust for the stationary phantom. Conclusions: The CTDI-paradigm does not apply in the case of a stationary phantom and simpler nonintegral equations suffice. A method of correction of the currently reported CTDI{sub vol} using the approach-to-equilibrium formula H(a) and an overbeaming correction factor serves to scale the reportedmore » CTDI{sub vol} values to more accurate levels for stationary-table CT, as well as serving as an indicator in the detection of “bad data.”.« less
Authors:
 [1] ;  [2]
  1. Department of Radiology, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157 (United States)
  2. Departments of Radiology and Biomedical Engineering, University of California Davis, Sacramento, California 95817 (United States)
Publication Date:
OSTI Identifier:
22251728
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 41; Journal Issue: 1; Other Information: (c) 2014 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; ACCURACY; DOSIMETRY; PATIENTS; PHANTOMS; RADIATION DOSE DISTRIBUTIONS; RADIATION DOSES