The UF family of hybrid phantoms of the developing human fetus for computational radiation dosimetry

Abstract

Historically, the development of computational phantoms for radiation dosimetry have primarily been directed at capturing and representing adult and pediatric anatomy, with less emphasis devoted to models of the human fetus. As concern grows over possible radiation-induced cancers from medical and non-medical exposures of the pregnant female, the need to better quantify fetal radiation doses, particularly at the organ-level, also increases. Studies such as the European Union’s SOLO (Epidemiological Studies of Exposed Southern Urals Populations) hope to improve our understanding of cancer risks following chronic in-utero radiation exposure. For projects like SOLO, currently available fetal anatomic models do not provide sufficient anatomical detail for organ-level dose assessment. To address this need, two fetal hybrid computational phantoms were constructed using high-quality magnetic resonance imaging (MRI) and computed tomography (CT) image sets obtained for two well-preserved fetal specimens aged 11.5 and 21 weeks post-conception. Individual soft tissue organs, bone sites, and outer body contours were segmented from these images using 3D-DOCTORTM and then imported to the 3D modeling software package RhinocerosTM for further modeling and conversion of soft tissue organs, certain bone sites, and outer body contours to deformable non-uniform rational B-spline (NURBS) surfaces. The two specimen-specific phantoms, along with a modified version of the 38-week UF hybrid newborn phantom, comprised a set of base phantoms from which a series of hybrid computational phantoms was derived for fetal ages 8, 10, 15, 20, 25, 30, 35 and 38 weeks post-conception. The methodology used to construct the series of phantoms accounted for the following age-dependent parameters: (1) variations in skeletal size and proportion, (2) bone-dependent variations in relative levels of bone growth, (3) variations in individual organ masses and total fetal masses and (4) statistical percentile variations in skeletal size, individual organ masses, and total fetal masses. The resulting series of fetal hybrid computational phantoms is applicable to organ-level and bone-level internal and external radiation dosimetry for human fetuses of various ages and weight percentiles.

Fetal organ dosimetry for the Techa River and Ozyorsk Offspring Cohorts, part 2: radionuclide S values for fetal self-dose and maternal cross-dose

“…Elemental compositions of fetal soft tissues were adopted from a combination of relevant literature sources (ICRP 2002;ICRU 1992). Mass densities of fetal soft tissues were adopted from Maynard et al (2011). Elemental compositions of fetal bone were derived through linear interpolating of the 38-week cranium and lumbar vertebrae elemental compositions reported by Pafundi et al (2009) and the ICRU reference adult cartilage elemental composition (ICRU 1992).…”

“…Elemental compositions of fetal bone were derived through linear interpolating of the 38-week cranium and lumbar vertebrae elemental compositions reported by Pafundi et al (2009) and the ICRU reference adult cartilage elemental composition (ICRU 1992). Mass densities of fetal bone (spongiosa) were linearly interpolated as needed from values given by Maynard et al (2011). Elemental compositions of maternal tissues were assumed to be equivalent to the blood-inclusive elemental compositions of the UF adult non-pregnant female phantom derived by Wayson (2012).…”

Computational Phantoms for Organ Dose Calculations in Radiation Protection and Imaging

“…The paper by Lee et al [51] was also rated one of the 10 best papers in 2007 by Physics in Medicine and Biology. In 2011, Maynard et al [117] from the UF produced a family of NURBS-based fetal phantoms. The phantoms were based on CT and MR images from fetal specimens of various ages between 10 and 30 weeks and were modified to conform to reference values.…”

Estimating fetal dose from tube current‐modulated (TCM) and fixed tube current (FTC) abdominal/pelvis CT examinations

“…More recent methods for estimating radiation conceptus dose from CT exams of pregnant patients are typically based on MC simulations of pregnant patient anatomy representing a range of gestational ages and patient sizes. [14][15][16][17][18][19][20] However, many of these studies were limited in that they were either not based on actual pregnant patient anatomy, applied only to a single scanner model, or did not include a range of gestational ages. In addition, most of these methods have thus far been limited to fixed tube current (FTC) CT exams of pregnant patients.…”