Relationships between physical dose quantities and patient dose in CT.

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.

Survey of computed tomography techniques and absorbed dose in Italian hospitals: a comparison between two methods to estimate the dose–length product and the effective dose and to verify fulfilment of the diagnostic reference levels

“…A similar study was carried out by Hidajat et al [19], who evaluated and compared the effective dose values for CT examination of head, neck and abdomen using the DLP and Monte Carlo simulation. They showed that E and organ doses evaluated with "conversion factors calculated by Monte Carlo methods" do not differ significantly from organ doses calculated by NRPB [16] conversion factors or measured in an anthropomorphic phantom, when the organs are located totally within the body region examined.…”

“…In general, the Monte Carlo approach has been very effective in estimating the absorbed radiation dose for CT scans [7,17,19] and has often been used with success. Although we did not analyse this aspect, such software can be used to obtain organ dose information directly from acquisition data.…”

Acetabular Anteversion with CT in Supine, Simulated Standing, and Sitting Positions in a THA Patient Population

“…Because the SS is a major parameter for assessing the position of the pelvis in the sagittal plane [31], the SS was used as a reference for the functional position of the pelvis. The radiation dose for the CT scan of the pelvis was 500 mGy Á cm, which corresponds to 9.5 mSv using the conversion ratio from Hidajat et al [13]. The standing AAA measured two times by the two observers showed a paired intraobserver difference of 2.53°.…”

Prognostic accuracy of cerebral blood flow measurement by perfusion computed tomography, at the time of emergency room admission, in acute stroke patients

“…Using a weighting factor of 0.0023mSv/(mGy ϫ cm) for the brain, the cerebral effective dose is 3.4mSv, which is quite similar to the dose level for a standard cerebral CT examination (2.5mSv). 44,46,47 Perfusion CT examination with data analysis according to the central volume principle 48 allows accurate quantitative assessment of both the rCBF and the rCBV 24 as well as definition of the cerebral infarct and penumbra, as described above. Our proposed method for the calculation of cerebral penumbra and infarct maps from the rCBF and rCBV maps provided by perfusion CT data analysis relies on (1) the reported rCBF threshold of ischemia and (2) preserved (penumbra) or altered (infarct) autoregulatory mechanisms.…”