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Evaluation of Synthetic CT Generation Technique Using An Anthropomorphic Multi-Modality (CT/MRI) Pelvic Phantom for MRgRT

H Jin1*, S Lee1, H An1, J Park1, C Choi1, E Chie1, H Kim2, H Kim1, J Kim1, (1) Seoul National University Hospital, Seoul, KR, (2) GenAi Lab, Seoul, KR


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: CT generation is a promising technique that provides the electron density information in magnetic resonance-guided radiotherapy. However, there are few studies for evaluating the algorithm with a standardized phantom. We fabricated an anthropomorphic multi-modality (MM) pelvic phantom and evaluated the synthetic CT image generated from the phantom MR image.

Methods: polyurethane materials and one silicone-based material were prepared in various concentrations of silicone oil to determine the tissue surrogate. The cylinders containing these materials were scanned on ViewRay system (MRIdian, Oakwood, USA) and Brilliance CT Big Bore (Philips Healthcare, Cleveland, OH). Five tissue surrogates were determined by comparing the organ intensity with patient CT and MR images. The patient-specific organ modeling for 3D printing was performed by manual delineation of the interested structures. The MM phantom was finally fabricated by casting materials for each structure. For quantitative evaluation, the mean and standard deviations were measured within the regions of interest (ROIs) on the MR, CT, and synthetic CT images.

Results: the prostate, the mean values of MR were 108.6 ± 13.6 and 93.2 ± 4.6 for the patient and the phantom, respectively. The intensity of the synthetic image was measured as 56.8 ± 3.0 which is higher than those of the real CT phantom image. The soft tissue surrogate shows only 6.3 HU and 7.3 discrepancies for CT and MR between phantom and patient cases. The original and Synthetic CT values of the soft tissue in phantom were measured as 45.4 ± 10.9 and 64.4 ± 2.9, respectively.

Conclusion: study demonstrated that anthropomorphic pelvic phantoms were fabricated similarly to organs physiologically and geometrically using 3D printing technology and evaluate the synthetic CT technique quantitatively. This phantom will be a useful tool for quality assurance of the emerging image processing techniques of the CT and MR images.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by Radiation Technology R&D program through the National Research Foundation of Korea funded by the Ministry of Science and ICT (2019M2A2B4096540)


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