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Objective:To explore the influence of different size related parameters of common CT scanned body parts on body-specific dose estimate (SSDE) , in order to establish rapid conversion factors for SSDE.Methods:A total of 189 clinical cases were collected from 6 common CT scanned body parts, including head, nasal bone, sinus, neck, chest, abdomen and pelvis, at Beijing Tongren Hospital, Capital Medical University from March 8 to May 10, 2021. Batch-processing of image was carried out by using Matlabcode. The axial images′area, anteroposterior (AP) dimension, lateral (LAT) dimension and average CT values were calculated. The conversion factors for estimating body-specific dose values were obtained from the real effective diameter ( De) and water equivalent diameter ( Dw) of the clinical cases, and the differences in values were compared between SSDE ED and SSDE WED. Based on the information on AP, LAT, AP + LAT, estimated De, the real De and Dw obtained in clinical practices, the SSDE rapid correction factors for adult body parts were established. The convenient conversion relation between Dw and De was obtained. Based on the correction factors for Dw, the relative errors of the correction factors for various sizes related parameters were compared. Results:The SSDE fast conversion factors for the real De of the 6 body parts were 1.01, 1.01, 1.01, 0.97, 1.28, 1.32, and those for Dw were 0.87, 0.97, 0.98, 0.99, 1.42, 1.36, respectively. The relative errors of different conversion factors ranged from 0.68% to 18.05%. The conversion factors for abdomen and pelvis had the smallest difference, and those for AP and LAT of the chest had the smallest error. The differences between CTDI vol, SSDE ED and SSDE WED in sinus, chest and abdomen were statistically significant ( tsinus=2.44, 4.23, tchest=17.67, 17.00, tabdomen and pelvis =17.93, 18.75, P<0.05) . The differences between CTDI vol and SSDE WED in head, nasal bone, were statistically significant ( t=-22.27, 2.80, P<0.05) , but not with SSDE ED ( P>0.05) . The difference between CTDI vol and SSDE ED in neck was statistically significant ( t=-3.06, P<0.05) but without statistical insignificance in camparison with SSDE WED ( P>0.05) . Conclusions:SSDE WED can be used to accurately evaluate the body-specific dose estimatates, and different size related parameters can be selected for correction in different scanned body parts. The rapid conversion factor can be easily used in clinical practice to improve the accuracy of estimated radiation dose.
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Objective:To explore the value of size-specific dose estimate (SSDE) based on effective diameter and water equivalent diameter ( Dw) in pediatric head CT. Methods:A retrospective analysis of 187 children underwent unenhanced head CT scanning were reviewed and divided into 3 groups according to the age: Group 1 (<1 m), Group 2(≥1 m~6 y), Group 3 (≥6~14 y). All CTDI vol values were recorded. The central axial image in the scanning range was selected. The region of interest (ROI) containing all anatomical structures (including skin) was outlined and the area of ROI ( AROI), head circumference, average CT value (CT ROI) were measured. The Dw, conversion factor fH16 and SSDE were calculated. The CTDI vol, SSDE and the rate of change( Δvalue)were compared among groups. The regression model between CTDI vol and SSDE was established. Results:The Dw values of groups 1-3 were (11.24±0.51), (14.48±1.47), (16.69±0.90)mm, respectively. The CTDI vol values were(15.36±2.78), (18.83±4.60), (23.24±4.13)mGy, respectively. SSDE values were(27.92±4.91), (29.16±6.64), (32.38±5.35)mGy, respectively. The differences among Dw, CTDI vol and SSDE groups were all statistically significant ( F=207.69、38.48、8.15, P<0.001). The values of Dw, CTDI vol and SSDE were gradually increasing while the age was increasing. However, the Δ value gradually was decreasing with increasing age. The linear regression equation of CTDI vol and SSDE was established as SSDE=7.252 + 1.137×CTDI vol. Conclusions:The radiation dose of children′s head CT can be accurately assessed based on Dw combined with head conversion factor fH16 to estimate the body-specific dose SSDE. The radiation dose of children′s head CT was underestimated with the greater degree for smaller age.
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Objective To compare the differences in radiation doses from CT scanning between children of different age groups and adult patients by using both traditional radiation dose assessment parameters and size-specific dose estimates (SSDE).Methods A total of 406 patients undergoing lung CT examination were studied.They were sampled retrospectively and continuously from the Union Hospital and divided into six groups by age distritution (0-2,3-6,7-10,11-14,15-18,＞18 years old).The CTDIvol and DLP values were randomly sampled using MATLAB platform-based dicom data software.The SSDE and water equivalent diameter were also calculated according to the AAPM 220 Report.The differences in radiation doses from lung CT scaning between children and adult patients were analysed.Results The CTDIvol values for all age groups were significantly lower than the SSDE values.The differences were statistically significant (t =-36.36,-32.83,-30.36,-28.74,-23.89,P＜0.05).The SSDE values were 137％,94％,79％,57％ and 42％ higher than the CTDIvol values,respectively.The CTDIvol values for the adult group were also lower than the SSDE values,and the difference was statistically significant (t=-21.92,P＜0.05),and the SSDE value was about 41％ higher than the CTDIvol value.With the increased age,CTDIvol value,DLP value,Dw value and SSDE value for children of all age groups gradually increased and were significantly smaller than those for the adult group.The difference was statistically significant (F=63.39,203.28,89.27,103.44,P＜0.05).The conversion coefficient f for all age groups decreased significantly with age,which was significantly higher than that for the adult group,and the difference was statistically significant (F =109.83,P ＜ 0.05).Conclusions In lung CT scanning,the CTDIvol value significantly underestimated the radiation doses to children as compared to adults.CTDIvol values are more easily underestimated for younger patients.The SSDE method allows for more accurate reflection of the radiation doses to different patients,taking into account differences in the examined patient size.
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Objective To investigate the effect of scan table on size-specific dose estimate ( size-specific dose estimate, SSDE) in children's CT scan. Methods CT imaging data and CTDIvol of 44 children ( 15 heads, 13 chests, 16 abdomen-pelvis) who underwent Siemens SOMATOM Definition AS+ 64 row 128-slice CT scan were retrospectively collected. CTDIvol of each patient was recored, WED ( water equivalent diameter) was calculated by two different methods ( with or without table) , donated as WED-T and WED-NT, then the corresponding SSDEWED ( SSDEWED-T and SSDEWED-NT ) was calculated. And the SSDEWED-NT was used as reference to evaluate the difference between WED and SSDEWED obtained by two different methods. Results Including part of table will lead to the overestimate for WED, with mean differences of 0. 10％, 2. 82％ and 2. 54％ for head, chest and abdomen-pelvis, respectively, while SSDEWED will be underestimated by 0. 06％ ( head ) , 2. 70％ ( chest ) and 1. 59％ ( abdomen-pelvis ) . Conclusions Including par of the patient table has a certain effect on SSDEWED for children, more attention should be paid for the application of SSDEWED.
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Objective@#To 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.@*Methods@#A 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.@*Results@#Statistically 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 SSDEdeff vs. SSDEgross and SSDEdw vs. 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.@*Conclusions@#SSDEdw 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.
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Objective To explore the validity of the size-specific dose estimate (SSDE) derived from the water-equivalent diameter (Dw)value of the slice located in the middle of the scan range in the head CT examination. Methods A total of 197 patients underwent head CT nonenhanced scan were enrolled in this retrospective study. The Dw, size-dependent conversion factor (f), normalized volume CT dose index (CTDIvol) and SSDE values of all slices were calculated. Two sets of SSDE, SSDEgroand SSDEcenbased on the Dwvalues slice by slice (Dw-gro) and the Dwvalues of the slices in the middle of the scan range (Dw-cen), were obtained across all patients. Pearson correlation analysis and linear regression analysis were performed for Dw-grovs Dw-cen, Spearman correlation analysis and linear regression analysis for SSDEgrovs SSDEcen, SSDE vs Dw, CTDIvolvs Dw. With the reference of SSDEgrovalue, mean absolute relative difference (MARD) of SSDEcen values were calculated to assess its accuracy and the correlated factors of MARD was analyzed with multivariate linear stepwise regression analysis. Results The minimal Dwvalue close to the roof of the skull corresponded to the maximal value of f and SSDE, which was the minimal value of CTDIvol. The significant positive correlation was showed between Dw-grovs Dw-cen, SSDEgrovs SSDEcen, SSDE vs Dw, CTDIvolvs Dw(r=0.947, 0.931, 0.416, 0.626;P＜0.05). The values of Dw,groand Dw-cenwere (16.94±0.69) and (18.50±0.62) cm respectively. The values of SSDEgroand SSDEcenwere [54.10 (52.29, 56.39)] mGy and [53.77 (51.85, 55.25)] mGy respectively. An approximation of SSDEcenvalues with an average of 1.62% of the gross MARD was found to match the reference value. Multivariate linear stepwise regression analysis indicated that MARD had negative correlation with Dw(β=–1.319,P＜0.05), positive correlation with CTDIvol(β=0.202,P＜0.05), and f was not included in the multivariate regression equation. Conclusion SSDEcenbased on the Dwvalue of the slice located at the center of the scan range yields small MARD value and can represent a reliable SSDE estimation in the head CT examination.