Development and Validation of the Realistic Anthropomorphic Flexible (RAF) Phantom

Abstract

Voxel phantoms developed by segmenting computed tomography images are known to be more anatomically accurate than mathematical phantoms. However, due to their lack of flexibility and the complexity of voxel datasets, the use of voxel phantoms in dosimetry is often impractical. This paper describes the development of the realistic anthropomorphic flexible (RAF) polygonal mesh phantom, a novel phantom based on Boundary Representation (B-Rep) that merges anatomical accuracy and flexibility. Rather than using segmentation of tomography images, the modeling of the phantom's organs was based on freely and commercially available anatomical atlases, ICRP 89, and recent medical literature. To validate the phantom, a high-resolution voxel version was created for the MCNPx transport code. The voxelized RAF phantom was validated by comparing it with the ICRP 110 male phantom for external irradiations with parallel beams of photons and electrons. Dose coefficients obtained from simulations with the RAF phantom were compared with those from ICRP Publication 116. Relevant differences in organ doses were found.

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“…These phantoms do exist, e.g. ( 20 ) and the use together with a positioning system needs to be further explored. In addition, when comparing simulation results from the three Monte-Carlo codes, and also against measurements, it is worth mentioning that the used model of the patient can greatly affect the simulation results due to two different aspects; the complexity of the model (BOMAB or a voxelised phantom) and how it fits the actual dimensions of the patient.…”

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“…The differences can be ascribed to the surface smoothing used to eliminate artifacts from CT, the discretization error introduced by the marching cubes algorithm and the conservative nature of the voxelization algorithm. 35 The Hausdorff distance, used to compare the meshes of the segmented pathology and the model adapted to the phantom, had mean values below 0.64 cm. These differences were expected since they are attributed to the mesh modification applied when fitting to the lungs of the phantom and the smoothing to eliminate the staircase effect from the CT.…”

“…Modeling started from the realistic anthropomorphic flexible (RAF) phantom, a full body male phantom developed by Lombardo et al 7 using polygonal mesh modeling. This type of geometrical representation is widely used in computer graphic modeling 8 and describes the phantom with a collection of polygons that share vertices and edges fulfilling certain rules.…”

“…The polygonal mesh models were then exported separately and loaded into voxelization software. 7 The latter software tool is based on the work of Laine 17 and is optimized such that the mass and thickness of the organs is preserved. The algorithm uses a conservative eightseparating voxelization method by calculating intersections between the triangles and quads from the meshes with a cube used as the test object.…”

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