Currently, two classes of the computational phantoms have been developed for dosimetry calculation: (1) stylized (or mathematical) and (2) voxel (or tomographic) phantoms describing human anatomy through mathematical surface equations and three-dimensional labeled voxel matrices, respectively. Mathematical surface equations in stylized phantoms provide flexibility in phantom design and alteration, but the resulting anatomical description is, in many cases, not very realistic. Voxel phantoms display far better anatomical realism, but they are limited in terms of their ability to alter organ shape, position, and depth, as well as body posture. A new class of computational phantoms—called hybrid phantoms—takes advantage of the best features of stylized and voxel phantoms—flexibility and anatomical realism, respectively. In the current study, hybrid computational phantoms representing reference 15-year male and female body anatomy and anthropometry are presented. For the male phantom, organ contours were extracted from the University of Florida (UF) 14-year series B male voxel phantom, while for the female phantom, original computed tomography(CT) data from two 14-year female patients were used. Polygon mesh models for the major organs and tissues were reconstructed for nonuniform rational B-spline (NURBS) surface modeling. The resulting NURBS/polygon mesh models representing body contour and internal anatomy were matched to anthropometric data and reference organ mass data provided by the Centers for Disease Control and Prevention (CDC) and the International Commission on Radiation Protection (ICRP), respectively. Finally, two hybrid 15-year male and female phantoms were completed where a total of eight anthropometric data categories were matched to standard values within and organ masses matched to ICRP data within with the exception of total skin. To highlight the flexibility of the hybrid phantoms, 10th and 90th weight percentile 15-year male and female phantoms were further developed from the 50th percentile phantoms through adjustments in the body contour to match the total body masses given in CDC pediatric growth curves. The resulting six NURBS phantoms, male and female phantoms representing their 10th, 50th, and 90th weight percentiles, were used to investigate the influence of body fat distributions on internal organdoses following CTimaging. The phantoms were exposed to multislice chest and abdomen helical CT scans, and in-field organ absorbed doses were calculated. The results demonstrated that the use of traditional stylized phantoms yielded organdose estimates that deviate from those given by the UF reference hybrid phantoms by up to a factor of 2. The study also showed that use of reference, or 50th percentile, phantoms to assess organdoses in underweight 15-year-old children would not lead to significant organdose errors (typically less than ). However, more significant errors were noted (up to ) when reference phantoms are used to represent overweight children in CTimagingdosimetry. These errors are expected to only further increase as one considers CTorgandoses in overweight and obese individuals of the adult patient population, thus emphasizing the advantages of patient-sculptable phantom technology.
This work was performed with the National Cancer Institute Grant No. RO1 CA116743 (subcontract from Rensselaer Polytechnic Institute) with the University of Florida.
II. MATERIALS AND METHODS
II.A. Phantom development
II.A.1. Source anatomy
II.A.2. NURBS surface modeling
II.A.3. Standardization of hybrid phantoms
II.A.4. Phantoms of non-50th weight percentiles
II.A.5. Voxelization of the NURBS and polygon mesh model
II.B. Applications to computed tomographydosimetry
III. RESULTS AND DISCUSSION
III.A. UF hybrid 15-year-old male and female phantoms
III.B. CTdosimetry calculation
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