Stationary table CT dosimetry and anomalous scanner-reported values of CTDIvol

Robert L. Dixon, John M Boone

Research output: Contribution to journalArticle

11 Scopus citations

Abstract

Purpose: Anomalous, scanner-reported values of CTDIvol for stationary phantomtable protocols (having elevated values of CTDIvol over 300 higher than the actual dose to the phantom) have been observed; which are well-beyond the typical accuracy expected of CTDIvol 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 CTDIvol clearly identifies the source of these anomalies. Results: For the stationary table, use of the CTDI100 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 CTDIvol using the approach-to-equilibrium formula H(a) and an overbeaming correction factor serves to scale the reported CTDIvol values to more accurate levels for stationary-table CT, as well as serving as an indicator in the detection of bad data.

Original languageEnglish (US)
Article number011907
JournalMedical Physics
Volume41
Issue number1
DOIs
StatePublished - Jan 2014

Keywords

  • Computed Tomography (CT)
  • CT Dosimetry

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging

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