An image-based skeletal tissue model for the ICRP reference newborn

Abstract

Hybrid phantoms represent a third generation of computational models of human anatomy needed for dose assessment in both external and internal radiation exposures. Recently, we presented the first whole-body hybrid phantom of the ICRP reference newborn with a skeleton constructed from both non-uniform rational B-spline and polygon-mesh surfaces (Lee et al 2007 Phys. Med. Biol. 52 3309-33). The skeleton in that model included regions of cartilage and fibrous connective tissue, with the remainder given as a homogenous mixture of cortical and trabecular bone, active marrow and miscellaneous skeletal tissues. In the present study, we present a comprehensive skeletal tissue model of the ICRP reference newborn to permit a heterogeneous representation of the skeleton in that hybrid phantom set-both male and female-that explicitly includes a delineation of cortical bone so that marrow shielding effects are correctly modeled for low-energy photons incident upon the newborn skeleton. Data sources for the tissue model were threefold. First, skeletal site-dependent volumes of homogeneous bone were obtained from whole-cadaver CT image analyses. Second, selected newborn bone specimens were acquired at autopsy and subjected to micro-CT image analysis to derive model parameters of the marrow cavity and bone trabecular 3D microarchitecture. Third, data given in ICRP Publications 70 and 89 were selected to match reference values on total skeletal tissue mass. Active marrow distributions were found to be in reasonable agreement with those given previously by the ICRP. However, significant differences were seen in total skeletal and site-specific masses of trabecular and cortical bone between the current and ICRP newborn skeletal tissue models. The latter utilizes an age-independent ratio of 80%/20% cortical and trabecular bone for the reference newborn. In the current study, a ratio closer to 40%/60% is used based upon newborn CT and micro-CT skeletal image analyses. These changes in mineral bone composition may have significant dosimetric implications when considering localized marrow dosimetry for radionuclides that target mineral bone in the newborn child.

Internal photon and electron dosimetry of the newborn patient—a hybrid computational phantom study

“…Non-unity sampling probabilities were assigned to newborn spongisoa and medullary marrow to accommodate the unique newborn skeletal source tissues of active marrow (AM), trabecular bone surfaces (TBS), cortical bone surfaces (CBS), trabecular bone volume (TBV), and cortical bone volume (CBV). These probabilities were made consistent with their fractional volumes (inclusive of miscellaneous skeletal tissues) as reported in Pafundi et al (2009). Volume-averaged and energy-dependent photon fluence was tracked over all individual spongiosa and medullary cavity sites, after which the skeletal DRFs were applied to calculate SAF values for these skeletal tissues.…”

Patient-Specific Dosimetry Using Pretherapy [124I]m-iodobenzylguanidine ([124I]mIBG) Dynamic PET/CT Imaging Before [131I]mIBG Targeted Radionuclide Therapy for Neuroblastoma

“…2)" rend="display" xml:id="FD2">$$S_{\mathit{\text{photon}}}false(r_T\leftarrow r_{S}false)=k\sum _j{w}_{j}false(r_{T}false)\sum _{i}true[\frac{Dfalse(r_{T}false)}{Ffalse(E_{i}false)}true]Ffalse(j\leftarrow r_S;E_{i}false)$$ where w j ( r T ) is the mass fraction of the target tissue r T in bone site j , D ( r T )/ F ( E i ) is the skeletal photon DRF for the target tissue r T at photon energy E i , F ( j ← r S ; E i ) is the photon flux emitted from the source organ r S incident on the spongiosa or medullary cavity of the bone site j for photon energy E i . The mass fraction of the skeletal tissues reported for the UF/NCI newborn phantom [25] was used for S-value to skeletal target tissue. Since photons or gamma rays emitted from any organ are the predominant particles depositing dose in the skeletal tissues, S ( r T ← r S ) ≈ S photon ( r T ← r S ) was assumed for all nonskeletal source organs to skeletal target tissues.…”

An exponential growth of computational phantom research in radiation protection, imaging, and radiotherapy: a review of the fifty-year history

“…The UF hybrid adult male phantom was used in a study by Johnson et al (2009) to calculate the effects of patient size on dose conversion coefficients. A model of electron dosimetry on infants based on the UF hybrid newborn phantom and an earlier developed skeleton tissue model (Pafundi et al 2009) was released by Pafundi et al (2010) from the UF. Hough et al (2011) released a model for skeletal based electron dosimetry in the ICRP reference male.…”