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Stationary table CT dosimetry and anomalous scanner‐reported values of CTDI vol
Author(s) -
Dixon Robert L.,
Boone John M.
Publication year - 2014
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4845075
Subject(s) - imaging phantom , scanner , dosimetry , table (database) , nuclear medicine , computer science , medicine , artificial intelligence , data mining
Purpose: Anomalous, scanner‐reported values of CTDI vol for stationary phantom/table protocols (having elevated values of CTDI vol over 300% higher than the actual dose to the phantom ) have been observed; which are well‐beyond the typical accuracy expected of CTDI 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 vol clearly identifies the source of these anomalies.Results: For the stationary table, use of the CTDI 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 vol using the approach‐to‐equilibrium formula H ( a ) and an overbeaming correction factor serves to scale the reported CTDI vol values to more accurate levels for stationary‐table CT, as well as serving as an indicator in the detection of “bad data.”