Pharmacokinetic modeling of pediatric imaging agents

Objectives In diagnostic nuclear medicine, tissue absorbed dose is reduced with lower administered activities, but this can result in reduced diagnostic accuracy. The goal of this study was to develop biokinetic models and data that can be used as input to studies to determine this tradeoff as a function of subject age, gender, and body habitus for pediatric patients.

Methods Both image quality and radiation risk are directly affected by the biokinetics of the imaging agent. However, in pediatric patients the biokinetics are a function of age. Presently, there are no age-specific biokinetic models for the most frequently used radiopharmaceuticals in pediatric medical imaging: 99mTc-DMSA for renal, 99mTc-MDP for bone and 18F-FDG for tumor/brain imaging. As a first step of this study, we have developed pharmacokinetic (PK) models for 99mTc-DMSA and 99mTc-MDP imaging agents for pediatric patients, using the SAAM II compartmental modeling and analysis software.

Results The PK models demonstrate good agreement with the available pediatric time-activity data.

Conclusions Currently available pediatric biodistribution data are severely limited. Nevertheless, a preliminary comparison of the 99mTc-DMSA PK model with the 99mTc-DMSA pediatric data (1, 2), categorized in 5 different age groups: from newborn to adolescent years (3), demonstrated substantial age and gender differences in the kinetics. Comparisons with pediatric data from Boston Children’s Hospital are in process and the analysis will provide data for further adjusting the models.

Research Support NIH NCI R01 CA116477