Abstract
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Objectives: Current guidelines for administered activity to pediatric patients undergoing diagnostic nuclear medicine imaging are obtained through expert consensus. The recommended minimum injected activity is a function of whole body weight designed to yield diagnostic quality images. In previous work, it has been shown that body morphometry is an important factor when minimizing injected activity while maintaining diagnostic quality images. The present study focuses on 99mTc-DMSA for assessing renal function for 5-year-old patients. The objective of this study was to quantify the change in patient risk as a function of the minimum injected activity required to obtain a diagnostic quality image, while varying patient anatomy about the region of diagnostic interest. To achieve this goal three factors were considered: waist circumference, kidney depth, and kidney volume.
Methods: To assess dependence of waist circumference the UF/NCI anthropomorphic 5-year-old reference male and female phantom were scaled to match the 5th, 50th and 95th percentile waist circumference according to the CDC’s NHANES database. To assess the impact of kidney volume the 95th percentile waist circumference phantom’s kidneys were scaled from reference volume to the correct volume according to patient weight and subsequently varied +15% and -15%. To assess the impact of kidney depth the 95th percentile waist circumference phantom’s kidneys were shifted to proper depth based on height and weight and then varied as far as anatomically reasonable posteriorly and anteriorly. To illustrate the impact of these anatomic variations on dose optimization effective dose for each phantom using weight-based 99mTc-DMSA activity administration was calculated using PHITS version 3.02.
Results: A series of pediatric male and female phantoms were created representing current population waist circumference, renal depth, and renal volume variations. Organ level dosimetry was assessed and effective doses were computed. Conclusion: The phantoms in this study can be used to tailor dosing guidelines for pediatric nuclear medicine imaging studies about the area of interest while taking account the effects of radiation dose and image quality.