A Comparison of the Distortion in the Same Field MRI and MR-Linac System With a 3D Printed Phantom

Xuechun Liu; Zhenjiang Li; Yi Rong; Minsong Cao; Hongyu Li; Chuntao Jia; Liting Shi; Weizhao Lu; Guanzhong Gong; Yong Yin; Jianfeng Qiu

doi:10.3389/fonc.2021.579451

A Comparison of the Distortion in the Same Field MRI and MR-Linac System With a 3D Printed Phantom

Front Oncol. 2021 Jun 3:11:579451. doi: 10.3389/fonc.2021.579451. eCollection 2021.

Authors

Xuechun Liu^{1

2}, Zhenjiang Li², Yi Rong³, Minsong Cao⁴, Hongyu Li⁵, Chuntao Jia⁵, Liting Shi¹, Weizhao Lu¹, Guanzhong Gong², Yong Yin², Jianfeng Qiu¹

Affiliations

¹ Medical Engineering and Technology Research Center, Department of Radiology, Shandong First Medical University & Shandong Academy of Medical Sciences, Tai'an, China.
² Department of Radiation Physics, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China.
³ Department of Radiation Oncology, University of California Davis Comprehensive Cancer Center, Sacramento, CA, United States.
⁴ Department of Radiation Oncology, David Geffen School of Medicine, University of California, Los Angeles, CA, United States.
⁵ Academy of Marine Science and Engineering, Shandong University of Science and Technology, Qingdao, China.

Abstract

Purpose: A 3D printed geometric phantom was developed that can be scanned with computed tomography (CT) and magnetic resonance imaging (MRI) to measure the geometric distortion and determine the relevant dose changes.

Materials and methods: A self-designed 3D printed photosensitive resin phantom was used, which adopts grid-like structures and has 822 1 cm² squares. The scanning plan was delivered by three MRI scanners: the Elekta Unity MR-Linac 1.5T, GE Signa HDe 1.5T, and GE Discovery-sim 750 3.0T. The geometric distortion comparison was concentrated on two 1.5T MRI systems, whereas the 3.0T MRI was used as a supplemental experiment. The most central transverse images in each dataset were selected to demonstrate the plane distortion. Some mark points were selected to analyze the distortion in the 3D direction based on the plane geometric distortion. A treatment plan was created with the off-line Monaco system.

Results: The distortion increases gradually from the center to the outside. The distortion range is 0.79 ± 0.40 mm for the Unity, 1.31 ± 0.56 mm for the GE Signa HDe, and 2.82 ± 1.48 mm for the GE Discovery-sim 750. Additionally, the geometric distortion slightly affects the actual planning dose of the radiotherapy.

Conclusion: Geometric distortion increases gradually from the center to the outside. The distortion values of the Unity were smaller than those of the GE Signa HDe, and the Unity has the smallest geometric distortion. Finally, the Unity's dose variation best matched with the standard treatment plan.

Keywords: 3D printed phantom; geometric distortion; magnetic resonance imaging; magnetic resonance imaging-linac; radiotherapy.