Size specific dose estimation in pediatric CT: preliminary study and conversion factors.

The objective of this paper is to compare the differences between volumetric CT dose index (CTDI_VOL) and size-specific dose estimate (SSDE_WED) based on water equivalent diameter (WED) in radiation dose measurement, and explore a new method for fast calculation of SSDE_WED. The imaging data of 1238 cases of head, 1152 cases of chest and 976 cases of abdominopelvic were analyzed retrospectively, and they were divided into five age groups: ≤ 0.5, 0.5 ~ ≤ 1, 1 ~ ≤ 5, 5 ~ ≤ 10 and 10 ~ ≤ 15 years according to age. The area of interest (A_R), CT value (CT_R), lateral diameter (LAT) and anteroposterior diameter (AP) of the median cross-sectional image of the standard scanning range and the SSDE_WED were manually calculated, and a t -test was used to compare the differences between CTDI_VOL and SSDE_WED in different age groups. Pearson analyzed the correlations between DE and age, DE and WED, f and age, and counted the means of conversion factors in each age group, and analyze the error ratios between SSDE calculated based on the mean age group conversion factors and actual measured SSDE. The CTDI_VOL in head was (9.41 ± 1.42) mGy and the SSDE_WED was (8.25 ± 0.70) mGy: the difference was statistically significant (t  = 55.04, P  < 0.001); the CTDI_VOL of chest was (2.68 ± 0.91) mGy and the SSDE_WED was (5.16 ± 1.16) mGy, with a statistically significant difference (t  = −218.78, P  < 0.001); the CTDI_VOL of abdominopelvic was (3.09 ± 1.58) mGy and the SSDE_WED was (5.89 ± 2.19) mGy: the difference was also statistically significant (t  = −112.28, P  < 0.001). The CTDI_VOL was larger than the SSDE_WED in the head except for the ≤ 0.5 year subgroup, and CTDI_VOL was smaller than SSDE_WED within each subgroup in chest and abdominopelvic. There were strong negative correlations between f and age (head: r  = −0.81; chest: r  = −0.89; abdominopelvic: r  = −0.86; P  < 0.001). The mean values of f at each examination region were 0.81 ~ 1.01 for head, 1.65 ~ 2.34 for chest and 1.71 ~ 2.35 for abdominopelvic region. The SSDE_WED could be accurately estimated using the mean f of each age subgroup. SSDE_WED can more accurately measure the radiation dose of children. For children of different ages and examination regions, the SSDE_WED conversion factors based on age subgroup can be quickly adjusted and improve the accuracy of radiation dose estimation. [ABSTRACT FROM AUTHOR]