Résumé
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.
Résumé
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.
Résumé
The purpose of this study provides measurements of radiation dose from MDCT of head, chest, abdomen and pelvic examinations. A series of dose quantities that are measured of patient weight to compare the dose received during MDCT examinations. Data collected included: weight together with CT dose descriptors, volume CT dose index (CTDIvol) and dose length product (DLP). The effective dose was also estimated and served as collective dose estimation data. Data from 1,774 adult patients attending for a CT examination of the head (n=520) or chest (n=531) or abdomen (n=724) was obtained from spiral CT units using a same CT protocol. Mean values of CTDIvol was a range of 48.6 mGy for head and 6.9, 10.5 mGy for chest, abdomen examinations, respectively. And mean values of DLP was range of 1,604 mGy.cm for head, 250 mGy.cm for chest, 575 mGy.cm for abdomen examinations, respectively. Mean effective dose values for head, chest, abdominal CT were 3.6, 4.2, and 8.6 mSv, respectively. The degree of CTDIvol and DLP was a positive correlation with weight. And there was a positive correlation for weight versus CTDIvol (r2=0.62), DLP (r2=0.694) in chest. And head was also positive correlation with weight versus CTDIvol (r2=0.691), DLP (r2=0.741). We conclude that CTDIvol and DLP is an important determinant of weight within the CT examinations. The results for this study suggest that CT protocol should be tailored according to patient weight.