Radiation Dosimetry
Comparison of SSDE values based on effective diameter and water equivalent diameter in head CT examination of adult patients
Jian Xu, Dewang Mao, Jianguo Xu, Huawei Xiao, Qiaowei Song, Fuhua Chen
Published 2018-07-25
Cite as Chin J Radiol Med Prot, 2018, 38(7): 535-540. DOI: 10.3760/cma.j.issn.0254-5098.2018.07.010
Abstract
ObjectiveTo compare and quantify the differences in size-specific dose estimates (SSDE) obtained by effective diameter and water-equivalent diameter from the central slice of the scan range in head CT examination.
MethodsA total of 111 consecutive adult patients who underwent head CT examination were enrolled in this study. All of CTDIvol values in the dose report were documented. The dataset was assigned into group A and group B, based on the individual size-dependent conversion factors (f) of effective diameter (deff) and water-equivalent diameter (dw) at the central slice multiplied by normalized volume computed tomography dose index (CTDIvol ) respectively. Body size, f and SSDE were calculated. With SSDEgross served as the reference level, the performance of SSDEdeff and SSDEdw was evaluated.
ResultsStatistically significant differences were found in body size (t=47.587, P<0.05) and f(z=-9.242, P<0.05) between group A and group B. Statistically significant difference also existed in SSDE (t=-46.687, P<0.05), (56.20±2.66) and (53.49±2.48) mGy for group A and group B respectively. Strongly positive correlation was shown in body size (r=0.873, R2 =0.761) and SSDE (r=0.974, R2 =0.949) between group A and group B(all P<0.05). Positive correlation was also found between SSDEdeff and SSDEgross(r=0.900, R2 =0.809), SSDEdw and SSDEgross (r=0.904, R2 =0.817, all P<0.05). Mean absolute difference was 2.34 and 0.78 mGy, for SSDEdeffvs. SSDEgross and SSDEdwvs. SSDEgross respectively; mean absolute relative difference was 4.38%, 1.40%; root mean square difference was 1.17 mGy (2.17%), 1.06 mGy (1.91%). Interquartile range and full range of SSDEdeff and SSDEdw were 3.22 vs. 2.39 mGy, 13.65 vs. 12.48mGy, respectively. A less degree of variation was observed in SSDEdw than that in SSDEdeff.
ConclusionsSSDEdw values based on the water-equivalent diameter at the central slice of the scan range got better agreement with those derived from all slices, which could serve as a simpler and more valid indicator to represent the average value of size-specific dose estimates of the whole scan range in head CT examination.
Key words:
Head; CTDIvol; Effective diameter; Water equivalent diameter; Size-specific dose estimate
Contributor Information
Jian Xu
Department of Radiology, Zhejiang Provincial People′s Hospital, People′s Hospital of Hangzhou Medical College, Hangzhou 310014, China
Dewang Mao
Jianguo Xu
Huawei Xiao
Qiaowei Song
Fuhua Chen
