Case study: Evaluating the new University of Florida hybrid pediatric phantoms and tissue weighting factors from ICRP Publication 103 for diagnostic dosimetry

Objectives: In 1987 Christy-Eckerman developed phantoms, which were comprised of stylized organs built of simple geometries defined by mathematical surface equations describing the inner anatomy and outer body contour. These phantoms has been used extensively in dosimetric calculations since then. Recently the University of Florida (UF) developed new non-uniform rational B-spline (NURBS) and polygon mesh (PM) surface based computational hybrid phantoms for pediatric patients. The purpose of this diagnostic dosimetry case study was to compare results from the Cristy-Eckerman stylized pediatric phantoms and tissue weighting factors from ICRP Publication 60 with the new UF hybrid pediatric phantoms with tissue weighting factors from ICRP Publication 103. Methods: Whole-body diagnostic PET/CT-images was acquired for a 15 year old female after administration of 68Ga-DOTATATE. Normal tissues contours drawn on the PET/CT images were the spleen, liver, kidneys, adrenal glands, brain, heart, lungs, thyroid gland, pituitary gland, salivary glands, testes, red marrow (L1-L5), muscle (right thigh) and whole-body. Dosimetric calculations were performed using an UF hybrid pediatric phantom for a 15 year old female with tissue weighting factors from ICRP Publication 103 and compared with OLINDA/EXM version 1 to represent the Cristy-Eckerman stylized pediatric phantoms using the phantom for a 15 year old and tissue weighting factors from ICRP Publication 60. Results: The calculated effective dose coefficient was 17 μSv/MBq using the Cristy-Eckerman stylized pediatric phantom for a 15 year old and tissue weighting factors from ICRP Publication 60 compared with 14 μSv/MBq using the new UF hybrid phantom for a 15 year old female with tissue weighting factors from ICRP Publication 103. Conclusions: The new more detailed and realistic UF hybrid phantoms including more target and source organs/tissues than the previous Christy-Eckerman stylized phantoms and showed a lower calculated effective dose coefficient using the new tissue weighting factors from ICRP publication 103 and in general lower normal organ/tissue absorbed doses.