Radiopharmaceutical dosage selection for pediatric nuclear medicine

To identify the most rational method for adjusting adult radiopharmaceutical dosages for children, four methods of dosage computation were examined from the perspectives of diagnostic adequacy and radiation absorbed dose. For static imaging, information density is the most important factor in study quality, and adjustment of dosage by body weight (Wt) for 'thick' organs, and body surface area (BSA) for 'thin' organs is recommended. Compared with adults, small children receive less radiation exposure if radiopharmaceutical dosages are adjusted by Wt, and slightly greater exposure if dosages are adjusted by BSA. For dynamic imaging studies, dosage requirements are governed by the spatial resolution needed for region of interest assignment, and the statistical reliability of the time-activity data. For dynamic renal imaging, renograms of similar quality are obtained if dosages are adjusted by height (Ht). Dynamic cardiac studies might appear to require dosages even larger than those adjusted by Ht which would result in higher radiation absorbed doses to pediatric patients. However, smaller dosages can be used in children by prolonging the imaging time and accepting lower temporal resolution. Dosage requirements for dynamic studies depend on which physiologic characteristics are measured from the time-activity data. Since the measurements of some characteristics demand higher count rates than others, dosage requirements ultimately depend on which measurements are clinically necessary. Close attention to the factors that determine these requirements may yield significant reduction in dosages, and thus in radiation exposure, for patients of all ages.