Article

Relations between physical dose quantities and patient dose in CT. BJR

Department of Radiology, Humboldt University, Berlin, Germany.
British Journal of Radiology (Impact Factor: 2.03). 06/1999; 72(858):556-61. DOI: 10.1259/bjr.72.858.10560337
Source: PubMed

ABSTRACT

Patient dose in CT is usually expressed in terms of organ dose and effective dose. The latter is used as a measure of the stochastic risk. Determination of these doses by measurements or calculations can be time-consuming. We investigated the efficacy of physical dose quantities to describe the organ dose and effective dose. For various CT examinations of the head, neck and trunk, organ doses and effective doses were determined using conversion factors. Dose free-in-air on the axis of rotation (Dair) and weighted computed tomography dose index (CTDIw) were compared with the absorbed doses of organs which are located totally within the body region examined. Dose-length product (DLP) was compared with the effective dose. The ratio of the organ dose to CTDIw was 1.37 (0.87-1.79) mSv mGy-1. DLP showed a significant correlation with the effective dose (p < 0.005). The average ratio of effective dose to DLP was 0.28 x 10(-2) mSv (mGy cm)-1 for CT of the head, 0.62 x 10(-2) mSv (mGy cm)-1 for CT of the neck and 1.90 x 10(-2) mSv (mGy cm)-1 for CT of the trunk. CTDIw and DLP can be used for estimating the organ dose and effective dose associated with CT examinations of the head, neck and trunk.

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Available from: Nico Hidajat, Jun 10, 2015
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    • "This leads to higher doses in examinations done for planning of radiation therapy than in diagnostic examinations done on the same CT scanner [9]. Effective doses and organ doses in CT examination correlate with easily measurable dosimetric quantities, such as CTDI and DLP [10], and thus can be estimated from them. The organs, for which dose estimates may be available, are not necessarily the same structures as organs at risk, for which dose constrains are formulated . "
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    • "DLP ðmGy cmÞ ¼ CTDIvol ðmGyÞ X total scan length ðcmÞ DLP correlates better with E than CTDIvol, and can easily be used as a measure of E. There is a linear relationship between DLP and E and a linear relationship between E and the stochastic risk; hence, as DLP increases with the number of scans, E also increases. DLP can thus be used to compare the stochastic risk between different CT examinations [20]. DLP is a more realistic measure of E and in calculating the DLP the measure of CTDIvol is still necessary. "
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