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: 2.02). 06/1999; 72(858):556-61. DOI: 10.1259/bjr.72.858.10560337
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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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    • "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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    ABSTRACT: The aim of this work was to create a model of a wide-bore Siemens Somatom Sensation Open CT scanner for use with GMCTdospp, which is an EGSnrc-based software tool dedicated for Monte Carlo calculations of dose in CT examinations. The method was based on matching spectrum and filtration to half value layer and dose profile, and thus was similar to the method of Turner et al. (Med. Phys. 36, pp. 2154-2164). Input data on unfiltered beam spectra were taken from two sources: the TASMIP model and IPEM Report 78. Two sources of HVL data were also used, namely measurements and documentation. Dose profile along the fan-beam was measured with Gafchromic RTQA-1010 (QA+) film. Two-component model of filtration was assumed: bow-tie filter made of aluminum with 0.5 mm thickness on central axis, and flat filter made of one of four materials: aluminum, graphite, lead, or titanium. Good agreement between calculations and measurements was obtained for models based on the measured values of HVL. Doses calculated with GMCTdospp differed from the doses measured with pencil ion chamber placed in PMMA phantom by less than 5%, and root mean square difference for four tube potentials and three positions in the phantom did not exceed 2.5%. The differences for models based on HVL values from documentation exceeded 10%. Models based on TASMIP spectra and IPEM78 spectra performed equally well.
    Physica Medica 07/2014; 30(7):725-864. DOI:10.1016/j.ejmp.2014.06.045 · 1.85 Impact Factor
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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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    ABSTRACT: Purpose: This article is intended as a review of the methods of establishing dose reference levels (DRLs) in relation to computerized tomography (CT) and their role in the standardization and auditing of radiation dose in CT. Discussion: CT is considered a high radiation dose examination. The potential for dose reduction resulting from the establishment of DRLs is discussed. The rationale for the use of DRLs in relation to the use of appropriate radiation measurements and CT dose descriptors are discussed. The estimation of the radiation risk to the irradiated individual is given by the effective dose, which takes into consideration the type of radiation and the radiosensitivity of the irradiated tissues. The collective dose is used to describe the radiation exposure of a population from low doses of different sources of radiation. Conclusion: Dose comparison between individual imaging sites is a vital part of DRL establishment and facilitates standardization of radiation dose levels for patients attending for a CT examination. Measurements of both effective and collective dose are difficult to achieve in practice. CT dose descriptors such as CT dose index and dose length product provide the means of comparing and monitoring the effect of optimized CT scanning protocols on the radiation dose. © 2009 Elsevier Inc. All rights reserved.
    Journal of Medical Imaging and Radiation Sciences 09/2009; 40(3-3):109-115. DOI:10.1016/j.jmir.2009.06.001
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