A risk index for pediatric patients undergoing diagnostic imaging with (99m)Tc-dimercaptosuccinic acid that accounts for body habitus

Abstract

Published guidelines for administered activity to pediatric patients undergoing diagnostic nuclear medicine imaging are currently obtained through expert consensus of the minimum values as a function of body weight as required to yield diagnostic quality images. We have previously shown that consideration of body habitus is also important in obtaining diagnostic quality images at the lowest administered activity. The objective of this study was to create a series of computational phantoms that realistically portray the anatomy of the pediatric patient population which can be used to develop and validate techniques to minimize radiation dose while maintaining adequate image quality. To achieve this objective, we have defined an imaging risk index that may be used in future studies to develop pediatric patient dosing guidelines. A population of 48 hybrid phantoms consisting of non-uniform B-spline surfaces and polygon meshes was generated. The representative ages included the newborn, 1 year, 5 year, 10 year and 15 year male and female. For each age, the phantoms were modeled at their 10th, 50th, and 90th height percentile each at a constant 50th weight percentile. To test the impact of kidney size, the newborn phantoms were modeled with the following three kidney volumes: -15%, average, and +15%. To illustrate the impact of different morphologies on dose optimization, we calculated the effective dose for each phantom using weight-based (99m)Tc-DMSA activity administration. For a given patient weight, body habitus had a considerable effect on effective dose. Substantial variations were observed in the risk index between the 10th and 90th percentile height phantoms from the 50th percentile phantoms for a given age, with the greatest difference being 18%. There was a dependence found between kidney size and risk of radiation induced kidney cancer, with the highest risk indices observed in newborns with the smallest kidneys. Overall, the phantoms and techniques in this study can be used to provide data to refine dosing guidelines for pediatric nuclear imaging studies while taking into account the effects on both radiation dose and image quality.

Figures

Figure 1

Rendering of 10th, 50th, and 90th percentile height at constant 50th percentile weight newborn, 1 year-old, 5 years-old, 10 years-old, and 15 years-old hybrid phantoms.

Figure 2

Comparison of effective dose per AA (mSv/MBq) calculated in this study versus those provided in ICRP Publication 128 for pediatric patients undergoing a DMSA imaging study.

Figure 3

Effective dose (mSv) for 10th, 50th, and 90th percentile height pediatric patients at 50th percentile weight from a DMSA imaging study compared to annual natural background radiation an individual is exposed to.

Figure 4

RI for reference pediatric patients undergoing DMSA imaging studies due to dose to kidneys and other target organs.

Figure 5

RI for 10th, 50th, and 90th percentile height newborn males and females using 18.5 MBq and 6.8 MBq administered activities compared with RI of 1 year-olds.

Figure 6

Kidney size effect on RI for newborn males and females.