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Dosimetry of Pediatric Radiopharmaceuticals: Uniformity of Effective Dose and a Simple Aid for Its Estimation

Departments of Radiology and Medical Physics, Great Ormond Street Hospital for Children NHS Trust and the Institute of Child Health, London, United Kingdom

Correspondence: For correspondence or reprints contact: Isky Gordon, MD, Consultant Radiologist, Department of Radiology, Great Ormond Street Hospital for Children NHS Trust, Great Ormond Street, London, WC1N 3JH, United Kingdom.

ABSTRACT

Formulae were investigated for predicting the effective dose to children, per unit administered activity of various pediatric radiopharmaceuticals, based only on the weight of the patient. Their influence on the uniformity of effective dose from total administered activity was also examined. Methods: The formulae were obtained from calculations of effective dose per unit administered activity (mSv · MBq^–) for five anthropomorphic mathematical phantoms applicable for newborn, 1-yr-, 5-yr-, 10-yr- and 15-yr-old children, having body weights of 3.4, 9.8, 19, 32 and 57 kg, respectively, using published biokinetic models. Results: In general, there was good linear correlation between effective dose per unit administered activity and inverse weight but, for some radiopharmaceuticals, logarithmic regression on weight provided a better fit to the data. An administered activity schedule based on body surface area,used with these formulae, resulted in reasonable uniformity of effective dose for children of all ages, with varying degrees of uniformity for different radiopharmaceuticals (coefficient of variation (COV) up to 20%). Individual activity schedules for separate radiopharmaceuticals gave best uniformity (COV < 7%) while a single general schedule, based on the mean results of the present study, yielded acceptable uniformity (COV < 10%) over the pediatric range. Conclusion: Effective dose per unit administered activity (mSv · MBq^–) of pediatric radiopharmaceuticals can be predicted from body weight alone by using simple formulae, and appropriately choosing the administered activity schedule leads to similar values of effective dose for children of all ages from a given radiopharmaceutical procedure.

Key Words: pediatrics • radiopharmaceuticals • dosimetry • effective dose • activity schedule