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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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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.
Subject(s)
Humans , Calibration , Phantoms, Imaging , Radiation Dosage , Tomography, X-Ray Computed , WaterABSTRACT
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 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.