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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 investigate the feasibility of size-specific dose estimate of head based on pediatric patients′ age.Methods:A retrospective study was conducted on plain head CT scans of 210 patients in Tianjin Children′s Hospital from January to March in 2022. The volume CT dose index (CTDI vol) values, age and sex of the patients were recorded. The anteroposterior diameter (AP) and lateral diameter(LAT), aera and CT value in the middle slice of the scan region were measured on the workspace. According to the AAPM reports 220 and 293, the water equivalent diameter ( DW) of head, size-specific conversion factors ( fmeasuredH16), and size-specific dose estimate (SSDE measured) were calculated. The effective diameter ( Deff; WHO) was calculated for male and female individuals using the ralationship between the standard head circumference and age of children provided by World Health Organization (WHO). The effective diameter ( Deff; WHO) was converted into a water equivalent diameter ( DW; WHO), using a correlation established from the Deff and DWwhich were measured in 210 image sets of male and female patients. Then the corresponding fWHOH16 and SSDE WHO of head can be calculated. The correlation between DW and DW; WHO, fmeasuredH16 and fWHOH16, the correlation and consistency between SSDE measured and SSDE WHO, and the conversion relationship between age and fWHOH16 were analyzed for male and female patients. Results:A significant correlation were found between the measured DW and DW; WHO(female: r=0.917, P<0.01; male: r=0.873, P<0.01), fmeasuredH16 and fWHOH16(female: r=0.916, P<0.01; male: r=0.883, P<0.01), SSDE measured and SSDE WHO( r=0.991, P<0.01; male: r=0.992, P<0.01). The Bland-Altman test indicated that there was good coherence between SSDE measured and SSDE WHO. Maximal mean root-mean-square errors of SSDE measured and SSDE WHO were 5.61% in female and 5.25% in male. The conversion relationship between fWHOH16 and patient age in different genders was obtained by curve fitting. Conclusion:The SSDE of head in pediatric patients can be estimated simply and accurately by directly using the patient′s age.
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Objective:To study the feasibility that using size-specific dose estimation (SSDE) to estimate organ dose and effective dose in coronary CT angiography (CTA).Methods:Totally 421 consecutive patients with coronary artery CTA were included and retrospectively analized. All patients were scanned using the 3rd generation dual-source Force CT with prospectively ECG gated axis scan mode. The size specific dose estimation(SSDE) for each patient was conducted by calculate water equivalent diameters with Radimetrics. The organ doses of heart, lung, liver and breast, were estimated with Monte Carlo method. Patient-specific effective dose was calculated as a weighted sum of simulated organ doses with the coefficients from ICRP 103. Linear correlation analysis was used to validate the relationship between SSDE and organ doses as well as effective dose, and to derive coefficients for patient specific dose estimation. The mean error rate was used to evaluate estimation accuracy.Results:The CTDI vol, SSDE and effective dose were (16.8±8.7)mGy, (20.8±8.8)mGy and (4.4±2.9)mSv, respectively. The linear fitting formula for estimating organ dose based on SSDE were: Y=1.2 X-6.4 ( R2=0.91, P<0.05, mean error 0.1%) for heart, Y=1.4 X-7.4 ( R2=0.91, P<0.05, mean error 7.9%) for breast, Y=0.89 X-4.6 ( R2=0.86, P<0.05, mean error 8.3%) for lung, and Y=0.36 X-1.8 ( R2=0.64, P<0.05, mean error -17.9%) for liver. The linear fitting formula for estimating the individual effective dose based on SSDE were: Y=0.21 X-1.2 ( R2=0.92, P<0.05, mean error 0.2%) for men, Y=0.39 X-2.2 ( R2=0.93, P<0.05, mean error 1.7%) for women. Conclusions:In coronary artery CTA, the absorbed dose of the organs and patient specific effective dose could be estimated with SSDE and the corresponding conversion coefficients, which will help to achieve personalized assessment and precise management of patient radiation dose and risk in clinical practice.
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Objective:To investigate the value of the size-specific dose estimate (SSDE) on dose estimations of children's head CT scans.Methods:A retrospective study was conducted on plain head CT scans of 252 patients with the 64-row detector CT device of Discovery 750HD in the Union Hospital, Tongji Medical College, Huazhong University of Science and Technology from January to September in 2019. The volume CT dose index (CTDI vol)values were recorded. The head circumference (HC), area, and CT value were measured using a self-developed computer program, and the water equivalent diameter (WED), size-specific conversion factors ( f293 and f220), and absorbed dose (SSDE 293 and SSDE 220) were calculated according to the AAPM reports 293 and 220.The patients were divided into three groups by the quartering meth odaccording to their HC(<47.8 cm, 47.8-52.7 cm, >52.7 cm)and four groups based on their ages(0-2, 3-6, 7-10 and 11-14 years old). The difference between parameters ( f220 and f293, SSDE 220 and SSDE 293、SSDE 293 and CTDI vol) were compared for different groups, and the correlation of HC with f293 and SSDE 293 was analyzed. Results:There was an overestimation of f220 by 11.11% ( t=252.61, P<0.05) compared with f293. SSDE 220 was overestimated by 10.31% ( t=228.21, P<0.05) compared with SSDE 293, and SSDE 293 was underestimated by 9.60% ( t=-31.34, P<0.05)compared with CTDI vol. For the three HC groups, SSDE 220 was overestimated by 8.54%, 10.37%, and 11.57% ( t=73.73, 438.58, 275.52, P<0.05)compared with SSDE 293, and SSDE 293 was underestimated by 1.30%, 9.79%, and 14.61% ( t=-1.91, -60.95, -47.64, P<0.05)compared with CTDI vol. For the four age groups SSDE 220 was overestimated by 8.45%, 10.00%, 10.57%, and 11.36% ( t=63.58, 232.29, 247.84, 302.95, P< 0.05)compared with SSDE 293, and SSDE 293 was underestimated by 1.49%, 8.27%, 10.63%, and 13.78% ( t=-1.83, -28.27, -37.30, -49.80, P< 0.05)compared with CTDI vol. Furthermore, HC was highly correlated with f293 and SSDE 293 ( r2=0.88 and 0.76, respectively, P< 0.05). Conclusions:The radiation dose in children′s head CT scanning can be more accurately estimated according to the AAPM Report 293, while it can be overestimated by CTDI vol. Meanwhile, the CT radiation dose can be patently overestimated with the AAPM Report 220 compared with Report 293.HC is closely correlated with f293 and SSDE 293 and it can be used to estimatee more accurately for SSDE and the radiation dose received by children during head CT scanning.
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To explore a method for calculating water equivalent diameter () based on localizer CT images for calculation of the size specific dose estimates (SSDE).GE Revolution CT and LightSpeed VCT were used to scan CT dose index phantoms 16 cm and 32 cm in diameter at the tube voltages of 80, 100 and 120 kV to obtain the axial image and anteroposterior localizer radiograph. According to the definition of CT Hounsfield unit, the axial images were used to calculate the conversion factors that convert the phantom thickness to water equivalent thickness. The gray value of the localizer radiograph and the water equivalent thickness were calibrated with a linear equation, and the parameters of the calibration were used to calculate the water equivalent thickness. The method was verified using 2 CT dose index phantoms and in 22 patients undergoing chest and abdominal CT examination.Comparison of the water equivalent diameter () based on the localizer radiograph and axial image of the 2 phantoms showed that the percentage difference between from the axial images and from the localizer radiograph was below 3%. The trend of variations with location in the two methods was sonsistent. The difference in in intermediate region of interest between the axial image and the localizer radiograph from the 22 patients was below 6.6%. With the mean in the ROI, the maximum percentage difference was 7.5%.Calibration of the gray value of the localizer radiograph and the water equivalent thickness using the axial image and localizer radiograph of CT dose index phantoms allows quick calculation of the SSDE based on the parameters of calibration.
Sujets)
Humains , Calibrage , Fantômes en imagerie , Dose de rayonnement , Tomodensitométrie , EauRésumé
Objective To investigate the application value of CTDIvol and size-specific dose estimate( SSDE) in evaluating the radiation dose of adult chest CT. Methods A retrospective analysis was made on the CTDIvol and SSDE of 128 patients who underwent chest CT scanning in the First Affiliated Hospital of Zhejiang Chinese Medical University from March to April 2017 and all images are adequate for diagnosis. The subjects were divided into three groups according to body mass index ( BMI):Group A,38 cases with 16≤BMI<21. 1 kg/m2; Group B,53 cases with 21. 1≤BMI<23. 9 kg/m2; Group C,37 cases with 23. 9≤BMI<34. 1 kg/m2. The diameters of anterior-posterior (AP) and left-right (LAT) of each patient were measured in the slice of nipple level, and CTDIvol , effective diameter ( ED) , conversion factor ( fsize ) and SSDE of each patient were recorded and calculated. Meanwhile, the differences between CTDIvol and SSDE in different BMI groups were compared. Results SSDE of each group was higher than CTDIvol , and increased by 50. 13％, 42. 83％ and 33. 68％ in group A, B and C, respectively. There were significant differences in radiation dose between CTDIvol and SSDE in the three groups ( t=-48. 873,-57. 001, -32. 651, P<0. 05) . There were significant differences in ED, fsize , CTDIvol and SSDE among the three groups ( F=51. 456, 47. 749, 113. 916, 106. 449, P<0. 05) . Conclusions SSDE can evaluate the radiation dose absorbed by patients with different body types in chest CT, while CTDIvol underestimated the radiation dose. The lower BMI, the greater the underestimated dose value, the more radiation dose absorbed.
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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 investigate the difference of size-specific dose estimates ( SSDEs ) based on effective diameter ( def ) and water equivalent diameter ( dw ) in coronary computed tomography angiography ( CCTA) and explore the causes. Methods A total of 99 patients undergoing CCTA were enrolled in this retrospective study. SSDEs ( SSDEd ef and SSDEdw ) were calculated in two approaches using def and dw , respectively. Mean absolute relative difference ( MARD) was computed as an index to quantify the consistency of SSDEd ef and SSDEdw . Multivariate stepwise regression analysis was performed to study the factors influencing MARD. Results The values def and dw were positively correlated with body mass index (BMI) (r=0. 869, 0. 823, P<0. 05). The median (interquartile range) of SSDEdef and SSDEdw were 12. 34 ( 11. 75, 12. 98) mGy, 13. 78 ( 13. 02, 15. 04) mGy, respectively. SSDEdef was lower by 10. 45％ than SSDEdw( Z=-8. 186, P<0. 05) . Both SSDEdef and SSDEdw were negatively correlated with BMI and dw(r=-0. 765, -0. 680, -0. 701, -0. 840, P<0. 05). MARD of SSDEdef and SSDEdw was generally at 11. 39％. No statistical significance was found in the correlation of MARD with BMI ( r=0. 031, P>0. 05) , however, positive correlation was shown between MARD and def ( r=0. 251, P<0. 05) , but negative correlation for MARD and dw(r=-0. 379, P<0. 05). With respect to the factors influencing MARD, four variables were included into the regression equation. MARD was positively correlated with the area of both air-filled lungs ( Arealow ) and soft tissues ( Areasoft ) (β=0. 634, 0. 102, P<0. 05) , and negatively correlated with the area of bone, enhanced cardiac chambers and aorta ( Areahigh ) and the CT value of air-filled lungs ( SIlow ) (β=-0. 234,-0. 343, P<0. 05) . Conclusions SSDEdef was approximately 10. 45％ lower than SSDEdw , which was predominantly influenced by the area of air-filled lungs due to the characteristics of low X-ray attenuation in CCTA.
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Objective@#To investigate the application value of CTDIvol and size-specific dose estimate(SSDE) in evaluating the radiation dose of adult chest CT.@*Methods@#A retrospective analysis was made on the CTDIvoland SSDE of 128 patients who underwent chest CT scanning in the First Affiliated Hospital of Zhejiang Chinese Medical University from March to April 2017 and all images are adequate for diagnosis. The subjects were divided into three groups according to body mass index (BMI): Group A, 38 cases with 16≤BMI<21.1 kg/m2; Group B, 53 cases with 21.1≤BMI<23.9 kg/m2; Group C, 37 cases with 23.9≤BMI<34.1 kg/m2. The diameters of anterior-posterior (AP) and left-right (LAT) of each patient were measured in the slice of nipple level, and CTDIvol, effective diameter (ED), conversion factor (fsize) and SSDE of each patient were recorded and calculated. Meanwhile, the differences between CTDIvol and SSDE in different BMI groups were compared.@*Results@#SSDE of each group was higher than CTDIvol, and increased by 50.13%, 42.83% and 33.68% in group A, B and C, respectively. There were significant differences in radiation dose between CTDIvol and SSDE in the three groups (t=-48.873, -57.001, -32.651, P<0.05). There were significant differences in ED, fsize, CTDIvol and SSDE among the three groups (F=51.456, 47.749, 113.916, 106.449, P<0.05).@*Conclusions@#SSDE can evaluate the radiation dose absorbed by patients with different body types in chest CT, while CTDIvol underestimated the radiation dose.The lower BMI, the greater the underestimated dose value, the more radiation dose absorbed.
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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 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 estimate the lifetime attributable risk (LAR) of lung cancer,stomach cancer,liver cancer,thyroid cancer,breast cancer and leukemia for 1-,5-and 10-year old children undergoing chest CT scan.Methods Chest CT images of children was retrieved from the picture archiving and communication system (PACS) and the average CT number and area of the region of interest (ROI) were read on the CT work station.Water equivalent diameter were calculated according to the method recommended by the American Association of Physicists in Medicine (AAPM).Furthermore,the size-specific dose estimation (SSDE) was made based on the water equivalent diameter and the volume computed tomography dose index(CTDIvol).Based on the method recommended by Caro Franck,the SSDE then was converted into average organ doses to lung,stomach,liver,thyroid,breast and blood for children at different ages and of different sex undergoing chest CT scan.On the basis of average organ dose,the cancer risk prediction model from the National Academy of Science's Biological Effects of Ionizing Radiation-Ⅶ (BEIR-Ⅶ) was used to predict the LAR for different cancers mentioned above.For lung cancer,gastric cancer,liver cancer and leukemia,the calculating sequence was from average organ dose to excess relative risk (ERR) to LAR,whereas for the thyroid cancer and breast cancer,the sequence was from ERR to average organ dose to LAR.Results The average organ dose to lung,stomach,liver,thyroid,breast and blood for children at different age and of different sex undergoing chest CT scan was obtained.The age had a statistically significant impact on the SSDE (t =24.28,P ＜ 0.05),but sex has not (P ＞ 0.05).LAR for lung cancer,gastric cancer,liver cancer,thyroid cancer,breast cancer and leukemia for 1-,5-and 10-year old children undergoing chest CT scan was obtained,among whom the LAR for thyroid cancer and breast cancer was relatively high.The LAR for women breast cancer was 10.9 per 100 000 persons for 1 year old children,30.8 per 100 000 persons for 5 years old and 34.5 per 100 000 persons for 10 years old.Conclusions With introduction of new technologies,the radiation dose due to chest CT scan is on the decline.But the induced radiation dose is still significant compared with general diagnostic radiography.The risk of cancer still deserves more attention and should be taken into consideration in the justification of diagnostic radiology.
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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.
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Abstract. In order to have a more accurate estimation of the dose delivered for computed tomography (CT) studies, and given that the current dose estimates do not include the size of the patient, a retrospective study was conducted on a sample of 388 patients from the radiology department of a general hospital, to make a better assessment of the dose delivered for CT scans of the chest, abdomen and pelvis in adult and paediatric patients. A comparison was made between the volume computed tomography dose index (CTDIvol) delivered by the scanner and CTDIvol value corrected by the incorporation of the effective patient diameter according to the report 204 of the American Association of Physicists in Medicine (AAPM). It was found that the values of CTDIvol vary in all cases when the patient size parameter is included, with this variation being greater as sizes go to extremes.
Resumen. Con el objetivo de tener una estimación de dosis más exacta entregada por los estudios de tomografía computarizada (TC) y dado que los estimadores de dosis actuales no incluyen el tamaño del paciente en la estimación, se realizó un estudio retrospectivo en una muestra de 388 pacientes de un servicio de radiología de un hospital general, para calcular las dosis entregadas en exámenes de TC de tórax, abdomen y pelvis en pacientes adultos y pediátricos. Se elaboró y realizó una comparación entre el índice de dosis de TC (CTDI VOL) entregado por el equipo y el CTDI VOL corregido mediante la incorporación del parámetro del diámetro efectivo del paciente según el reporte 204 de la Asociación Americana de Físicos Médicos (AAPM). Se pudo comprobar que los valores de CTDI VOL varían en la totalidad de los casos al ingresar el parámetro de tamaño del paciente y que esta variación es mayor a medida que los tamaños se van a los extremos.
Sujets)
Humains , Enfant , Adulte , Dose de rayonnement , Tomodensitométrie/méthodes , Tomodensitométrie/normes , Études rétrospectives , Fantômes en imagerieRésumé
Objective To compare the difference between volume computed tomography dose index (CTDIvol) and size-specific dose estimates (SSDE) in evaluating the radiation dose of abdominal CT scan.Methods Abdominal CT scan were performed on 180 patients with a Philips 256-slices spiral CT.The anterior-posterior dimension (AP) and lateral dimension (LAT) of each patients were measured at the level of left renal vein, and the effective diameter (ED) and SSDE were calculated with recorded CTDIvol Patients were categorized into 3 groups depending on body mass index (BMI): group A, BMI ＜ 20.0 kg/m2;group B, 20.0-24.9 kg/m2;group C, BMI ＞ 24.9 kg/m2.The differences between CTDIvoland SSDE of 180 patients and three different BMI groups were compared respectively.Results There was a significant difference between CTDIvol and SSDE of the 180 patients (t =-13.354, P ＜ 0.01), CTDIvol and SSDE were (9.91 ± 2.91) and (14.01 ± 2.82) mGy, respectively.For group A, CTDIvol and SSDE were (7.96 ± 1.83) and (12.83 ± 2.52) mGy, respectively (t =-8.417, P ＜ 0.01).Group B, CTDIvol and SSDE were (9.28 ± 1.76) and (13.62 ±2.18) mGy, respectively (t =-15.051, P ＜ 0.01).Group C, CTDIvol and SSDE were (12.19 ± 3.65) and (15.39 ± 3.47) mGy, respectively (t =-4.535, P ＜ 0.01).In addition, the mean percentage values of difference between CTDIvol and SSDE for the three groups were 62.83％, 47.80％, 28.40％, respectively, which meant CTDIvol underestimated the radiation dose compared to SSDE.With the BMI increasing, the values of difference between CTDIvol and SSDE decreased.Conclusions SSDE can be used to estimate the radiation dose of abdominal CT scan for a given size person.