Assessment of photon and electron internal organ dose for the University of Florida hybrid computational phantoms of the ICRP 89 reference male and female 1, 5, and 10-year-old

Objectives To address limitations of stylized and voxel phantoms, the researchers at the University of Florida have introduced the concept of hybrid phantoms by using non-uniform rational B-spline (NURBS) surfaces. Currently, a total of four hybrid pediatric phantoms representing newborn and 15-year-old male and female phantoms have been reported. In this study, we present male and female hybrid phantoms of the 1, 5, and 10-year child as defined by the ICRP.

Methods Six different computed tomography (CT) datasets of head and torso of 1, 5, and 10-year-old patients were employed to develop these hybrid phantoms. Organ contours were segmented from CT images to generate polygon mesh surfaces, which were then used for NURBS modeling to match reference organ masses to within 1%. The phantoms was plugged into the MCNPX2.5 Monte Carlo code to calculate SAFs for photons and electrons internal sources over the energy range 10 keV to 4 MeV.

Results SAFs for 60 source and target organs were calculated and compared to those from ORNL stylized and UF voxel phantoms. Comparing with ORNL phantom, major differences were caused by unrealistic inter-organ distances in ORNL phantoms. Comparing with voxel phantoms, differences were caused by the individual-specific organ masses in voxel phantom.

Conclusions This study showed that hybrid phantoms can provide more realistic and standardized internal dosimetry calculation than stylized and voxel phantoms. The new hybrid approach can be widely applied to dose evaluation in nuclear medicine where realistic and flexible computational phantoms are required.

Research Support Work supported by Grant RO1 CA116743 from the National Cancer Institute