MO‐F‐213CD‐02: A Series of NURBS and MicroCT‐Based Reference Skeletal Dosimetry Models of Pediatric and Adolescent Skeleton

Purpose: The hematopoietically active tissues of the skeleton are an important target tissue for dosimetric analysis, both in terms of diagnostic risk optimization and evaluating treatment efficacy. In the work presented here, a recently published dosimetry model of the adult is extended to all pediatric ages of the ICRP reference series. Methods: NURBS/PM‐based computational phantoms of the ICRP 89 reference newborn, 1‐year, 5‐year, 10‐year, and 15‐year male and female were constructed from image segmentation of age and gender‐matched CT images. Bone samples were subsequently acquired from autopsy harvest of two female newborns and one 18‐year male subject. Individual bones were collected and segmented following high‐resolution ex‐vivo CT to yield fractional volumes of cortical bone and spongiosa. Cored samples of spongiosa were later imaged under microCT to yield fractional volumes of bone trabeculae and marrow tissues and to provide a 3D geometry for radiation transport. Previously acquired pathlength distributions of trabecular spongiosa for a 1.7‐year and 9‐year child were used to supplement the dataset. Results: A comprehensive set of absorbed fractions of energy for internally emitted electrons are presented for active and shallow marrow targets in all bones, all ages, and over the energies 1 keV to 10 MeV. These electron absorbed fractions were then used to assemble photon fluence‐to‐dose response functions permitting detailed marrow dosimetry for both externally incident (e.g., CT) and internally emitted (e.g., nuclear medicine) photons by bone site and subject age. Techniques and issues for patient‐specific adjustments are discussed. Conclusions: Marrow dosimetry is a critical component to nuclear medicine risk assessment and therapy treatment planning. This work provides state‐of‐the‐art methods for pediatric marrow dosimetry that supplants those developed previously for simpler stylized models of the pediatric skeleton. R01 CA116743, R01 CA96441, DE‐FG07‐06ID14773