An anthropomorphic abdominal phantom for deformable image registration accuracy validation in adaptive radiation therapy.
OBJECTIVE
To design and construct a three-dimensional (3D) anthropomorphic abdominal phantom for geometric accuracy and dose summation accuracy evaluations of deformable image registration (DIR) algorithms for adaptive radiation therapy (ART).


METHODS
Organ molds, including liver, kidney, spleen, stomach, vertebra, and two metastasis tumors, were 3D printed using contours from an ovarian cancer patient. The organ molds were molded with deformable gels made of different mixtures of polyvinyl chloride (PVC) and the softener dioctyl terephthalate. Gels with different densities were obtained by a polynomial fitting curve that described the relation between the Hounsfield unit (HU) and PVC-softener blending ratio. The rigid vertebras were constructed by molding of white cement and cellulose pulp. The final abdominal phantom was assembled by arranging all the fabricated organs inside a hollow dummy according to their anatomies, and sealed by deformable gel with averaged HU of muscle and fat. Fiducial landmarks were embedded inside the phantom for spatial accuracy and dose accumulation accuracy studies. Two channels were excavated to facilitate ionization chamber insertion for dosimetric measurements. Phantom properties such as deformable gel elasticity and HU stability were studied. The dosimetric measurement accuracy in the phantom was performed, and the DIR accuracies of three DIR algorithms available in the open source DIR toolkit-DIRART were also validated.


RESULTS
The constructed deformable gel showed elastic behavior and was stable in HU values over times, proving to be a practical material for the deformable phantom. The constructed abdominal phantom consisted of realistic anatomies in terms of both anatomical shapes and densities when compared with its reference patient. The dosimetric measurements showed a good agreement with the calculated doses from the treatment planning system. Fiducial-based accuracy analysis conducted on the constructed phantom demonstrated the feasibility of applying the phantom for organ-wise DIR accuracy assessment.


CONCLUSIONS
We have designed and constructed an anthropomorphic abdominal deformable phantom with satisfactory elastic property, realistic organ density, and anatomy. This physical phantom can be used for routine validations of DIR geometric accuracy and dose accumulation accuracy in ART.
Department of Biomedical Engineering, Southern Medical University, Guangzhou, Guangdong, 510515, China.
Yuliang
Y
Liao
Radiotherapy Center, Affiliated Cancer Hospital & Institute of Guangzhou Medical University, Guangzhou, Guangdong, 510095, China.
Linjing
L
Wang
Department of Radiology, Guangzhou First People's Hospital, Guangzhou Medical University, Guangzhou, Guangdong, 510180, China.
Xiangdong
X
Xu
Department of Biomedical Engineering, Southern Medical University, Guangzhou, Guangdong, 510515, China.
Haibin
H
Chen
Department of Biomedical Engineering, Southern Medical University, Guangzhou, Guangdong, 510515, China.
Jiawei
J
Chen
Radiotherapy Center, Affiliated Cancer Hospital & Institute of Guangzhou Medical University, Guangzhou, Guangdong, 510095, China.
Guoqian
G
Zhang
Radiotherapy Center, Affiliated Cancer Hospital & Institute of Guangzhou Medical University, Guangzhou, Guangdong, 510095, China.
Huaiyu
H
Lei
Radiotherapy Center, Affiliated Cancer Hospital & Institute of Guangzhou Medical University, Guangzhou, Guangdong, 510095, China.
Ruihao
R
Wang
Radiotherapy Center, Affiliated Cancer Hospital & Institute of Guangzhou Medical University, Guangzhou, Guangdong, 510095, China.
Shuxu
S
Zhang
Department of Radiation Oncology, The University of Texas, Southwestern Medical Center, Dallas, Texas, 75390, USA.
Xuejun
X
Gu
Department of Biomedical Engineering, Southern Medical University, Guangzhou, Guangdong, 510515, China.
Xin
X
Zhen
Department of Biomedical Engineering, Southern Medical University, Guangzhou, Guangdong, 510515, China.
Linghong
L
Zhou
D000005:Abdomen / Q000000981:diagnostic imaging; D000465:Algorithms; D006801:Humans; D019047:Phantoms, Imaging; D011874:Radiometry; D013154:Spleen
deformable gel; deformable image registration validation; phantom construction; three-dimensional deformable phantom