Analysis of material composition and attenuation characteristics of anthropomorphic torso phantoms for dosimetry using dual energy CT technology

Abstract

Anthropomorphic phantoms are often used to estimate organ absorbed doses. However, the material composition of these phantoms is not identical to that of the human body, which may cause errors in the measurement results. The purpose of this study was to analyze the material composition of several anthropomorphic torso phantoms using dual energy computed tomography (DECT), and to clarify the differences in attenuation characteristics among the phantoms. Anthropomorphic torso phantoms (ATOM, RANDO, and PBU-60) from different manufacturers were scanned with DECT. The target organs were lung, soft tissue, liver, bone, and bone surface, and a spectral Hounsfield unit curve (HU curve) was created from the relationship between energy and CT values. Ideal CT values were estimated from the mass attenuation coefficient and density proposed by the International Commission on Radiation Units and Measurements report 44 (ideal value) and compared with the values of each phantom. There were large differences in attenuation characteristics among the phantoms for soft tissue, liver, and bone. The respective ideal, ATOM, RANDO, and PBU-60 CT values of soft tissue were 59.82, 14.17, 34.22, and - 70.11 at 45 keV; and 53.13, 24.41, 3.97, and - 5.75 at 70 keV. The phantom closest to the ideal value may differ depending on the energy. Differences in HU curve and CT values indicate that some organs in the phantom have different material composition and attenuation characteristics to human tissues. When the phantoms available for dosimetry are limited, it is important to understand the attenuation characteristics of each phantom used.

Keywords: Anthropomorphic phantom; Dosimetry; Dual energy computed tomography; Human body equivalent phantom; Radiological protection; Spectral hounsfield unit curve.