Abstract
Purpose: The purpose of this study was to preliminarily estimate patient-specific organ doses in chest CT examinations for Chinese adults, and to investigate the effect of patient size on organ doses. Methods: By considering the body-size and body-build effects on the organ doses and taking the mid-chest water equivalent diameter (WED) as a body-size indicator, the chest scan images of 18 Chinese adults were acquired on a multi-detector CT to generate the regional voxel models. For each patient, the lungs, heart, and breasts (glandular breast tissues for both breasts) were segmented, and other organs were semi-automated segmented based on their HU values. The CT scanner and patient models simulated by MCNPX 2.4.0 software (Los Alamos National LaboratoryLos Alamos, USA) were used to calculate lung, breast, and heart doses. CTDIvol values were used to normalize simulated organ doses, and the exponential estimation model between the normalized organ dose and WED was investigated. Results: Among the 18 patients in this study, the simulated doses of lung, heart, and breast were 18.15 ± 2.69 mGy, 18.68 ± 2.87 mGy, and 16.11 ± 3.08 mGy, respectively. Larger patients received higher organ doses than smaller ones due to the higher tube current used. The ratios of lung, heart, and breast doses to the CTDIvol were 1.48 ± 0.22, 1.54 ± 0.20, and 1.41 ± 0.13, respectively. The normalized organ doses of all the three organs decreased with the increase in WED, and the normalized doses decreased more obviously in the lung and the heart than that in the breasts. Conclusions: The output of CT scanner under ATCM is positively related to the attenuation of patients, larger-size patients receive higher organ doses. The organ dose normalized by CTDIvol was negatively correlated with patient size. The organ doses could be estimated by using the indicated CTDIvol combined with the estimated WED.
Highlights
X-ray computed tomography (CT) has become a widely used technique in medical imaging, but there is a trade-off between patient benefit and radiation risk [1,2,3]
With a relatively greater tube current reduction for ATCM [24], represent one of the most frequently scanned body regions in clinical application [25,26], and as lung and breast are the most radiosensitive organs fully exposed in the imaged region, we further investigated chest CT imaging for more accurate organ dose estimations in this study
Even though the CTDIvol can be used to normalize organ doses from fixed tube current CT examinations, it is useless in tube current modulation (TCM) exams due to varying tube current, which is a function of patient attenuation and wholly patient-specific
Summary
X-ray computed tomography (CT) has become a widely used technique in medical imaging, but there is a trade-off between patient benefit and radiation risk [1,2,3]. CT scanners display a Computed Tomography Dose Index (CTDIvol) and Dose Length Product (DLP) to indicate the dose output of the machine. These indicators are useful for comparing different CT units or scan protocols, but are unable to show the dose distribution in the human body [6] because they do not take into account the patient’s body size, shape, and composition. For this reason, the size-specific dose estimate (SSDE) was proposed by AAPM Task Group 204 [7] as an improved approach to characterize the CT radiation dose to the center of the scan volume with a conversion factor of patient size. SSDE could not represent radiation doses of a specific organ, and SSDE was primarily determined from fixed tube current (FTC) scans
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