How accurate is size-specific dose estimate in pediatric body CT examinations?

Abstract

Background

Size-specific dose estimate is gaining increased acceptance as the preferred index of CT dose in children. However it was developed based on non-clinical data.

Objective

To compare the accuracy of size-specific dose estimate (SSDE) based on geometric and body weight measures in pediatric chest and abdomen CT scans, versus the more accurate $\overline{\mathrm{SSDE}}$ (mean SSDE based on water-equivalent diameter).

Materials and methods

We retrospectively identified 50 consecutive children (age <18 years) who underwent chest CT examination and 50 children who underwent abdomen CT. We measured anteroposterior diameter (D_AP) and lateral diameter (D_LAT) at the central slice (of scan length) of each patient and calculated D_AP+LAT (anteroposterior diameter plus lateral diameter) and D_ED (effective diameter) for each patient. We calculated the following in each child: (1) SSDEs based on D_AP, D_LAT, D_AP+LAT, D_ED, and body weight, and (2) SSDE based on software calculation of mean water-equivalent diameter ($\overline{\mathrm{SSDE}}$ adopted standard within our study). We used intraclass correlation coefficient (ICC) and Bland–Altman analysis to compare agreement between the SSDEs and $\overline{\mathrm{SSDE}}$.

Results

Gender and age distribution were similar between chest and abdomen CT groups; mean body weight was 37 kg for both groups, with ranges of 6–130 kg (chest) and 8–107 kg (abdomen). SSDEs had very strong agreement (ICC>0.9) with $\overline{\mathrm{SSDE}}$. SSDEs based on D_LAT had 95% limits of agreement of up to 43% with $\overline{\mathrm{SSDE}}$. SSDEs based on other parameters (body weight, D_AP, D_AP+LAT, D_ED) had 95% limits of agreement of up to 25%.

Conclusion

Differences between SSDEs calculated using various indications of patient size (geometric indices and patient weight) and the more accurate $\overline{\mathrm{SSDE}}$ calculated using proprietary software were generally small, with the possible exception for lateral diameter, and provide acceptable dose estimates for body CT in children.