Related content: CT, Safety, Pediatrics

Karmazyn B, Ai H, Klahr P, Ouyang F, Jennings SG. How accurate is size-specific dose estimate in pediatric body CT examinations? Pediatr Radiol. 2016;46(9):1234-40.

Dose estimation – let’s keep it simple

Accurate estimation of radiation doses is of great importance, especially because children are more sensitive to radiation-induced adverse effects. The size-specific dose estimate (SSDE) has gained importance for dose estimation within the last years. It is defined as the product of CTDIvol and a size-specific conversion factor.

The “SSDE“ was introduced in 2015 and is based on patient geometry and also include the different attenuations of the patient’s body parts, such as bone tissue and air. The water-equivalent diameter (Dw) accounts for these difference in attenuation.
Boat Karmazyn, Riley Hospital for Children, Indianapolis, USA, and colleagues retrospectively compared the accuracy of SSDE and SSDE values in different body areas of children, who had routine chest and abdomen CT scans.

Method

Karmazyn et al. included 50 children who had undergone an abdominal CT and 50 children who had been scheduled for a chest CT. They determined the anteroposterior diameter (DAP) and lateral diameter (DLAT) at the central slice (of scan length) for each child and calculated the effective diameter (DED = DAP x DLAT).

They calculated SSDE based on scanner’s estimated CTDIvol, and one of the geometric parameters (DLAT, DAP, DAP+DLAT, DED) or body weight (bw). Karmazyn et al. also determined water-equivalent diameter (Dw) and calculated the SSDE with the help of a software and the size-specific conversion factor dependent on slice-specific Dw for each child.

Karmazyn used intraclass correlation coefficient (ICC) and Bland–Altman analysis to compare SSDE and the different SSDEs of each child.

Results

A Bland–Altman analysis showed that SSDE based on body weight were in very good accordance with SSDE - with a window of 95% limits of agreement <16%.

All SSDEs showed a very strong agreement with the median SSDE in chest and abdominal CT according to intraclass correlation coefficient analysis (ICC>0.9 and p< 0.05 for all).

Conclusion

Calculation of SSDE requires specific software; however Kamarzyn observed a good agreement between radiation dose estimations using various indications of patient size (geometric indices and patient weight) and SSDE.