Magnetic resonance imaging (MRI) has been increasingly used for radiation treatment planning (RTP) because of its superior soft tissue contrast compared with computed tomography [1, 2]. However, MR images are typically affected by system-related and object-induced distortions (Fig. 1). These distortions are further enhanced in modern scanners that use a shorter bore magnet and faster and stronger gradient systems. On the other hand, a geometrically accurate representation of the tumor and the organs at risk is essential for RTP [3]. Therefore, unavoidable distortions inherent to...

All scans were performed on a 3-T MR scanner (MAGNETOM Skyra, Siemens, Erlangen, Germany) using a body coil. We used a 200 mm diameter pin phantom (90–401 type; Nikko Fines, Japan) to cover the maximum 500 mm FOV of the scanner. Consequently, we performed phantom scans at nine separate positions (three positions for in-plane direction by three positions for through-plane direction with 80 mm overlap [see Fig. 3]) using a MR-certified laser bridge (DORADOnova MR3T; LAP, Germany) for alignment purposes. Images were obtained following four...

The representative combined images from nine positions and geometric distortion vector maps with no-DC, 2D-DC, and 3D-DC are shown in Fig. 5 (direct coronal plane) and Fig. 6 (reconstruction coronal plane from axial images). Figure 7 shows the changes in mean distortion magnitude with distance from the magnetic field center in 2D T1-SE with in-plane (a) and through-plane (b), 2D T2-FSE with in-plane (c) and through-plane (d). Figure 8 shows the changes in mean distortion magnitude with distance from the magnetic field center in 3D...

The present study provides a quantitative evaluation with respect to the directions of geometric distortion and the effectiveness of 3D-DC. More specifically, it is found that 3D-DC reduces both the in-plane and through-plane distortions. The application of DC algorithms helped substantially to reduce distortions related to various MR sequences used in radiotherapy. However, the distortions were not completely removed. It should also be mentioned that although MR images suffer from system-related distortion and patient-induced distortion, this study does not evaluate potential subject-specific distortions. Conclusively, it...

Y. Kato; Nagoya/JP - nothing to disclose M. Kumagai; Nagoya/JP - nothing to disclose K. Okudaira; Nagoya/JP - nothing to disclose T. Taoka; Nagoya/JP - nothing to disclose Y. Itoh; Nagoya/JP - nothing to disclose T. Kamomae; Nagoya/JP - nothing to disclose S. Naganawa; Nagoya/JP - nothing to disclose

Schmidt MA, Payne GS. Radiotherapy planning using MRI. Phys Med Biol. 2015; 60: 323–361. V.S. Khoo, D.P.Dearnaley, D.J. Finniganb, et al. Magnetic resonance imaging (MRI): Considerations and applications in radiotherapy treatment planning. Radiother Oncol. 1997; 42: 1–15. Seibert TM, White NS, Kim G-Y, et al. 2016 Distortion inherent to magnetic resonance imaging can lead to geometric miss in radiosurgery planning Pract. Radiat. Oncol. 2016; 6; e319–e328.