Geometric distortions in clinical MRI sequences for radiotherapy: insights gained from a multicenter investigation

AbstractBackground As magnetic resonance imaging (MRI) becomes increasingly integrated into radiotherapy (RT) for enhanced treatment planning and adaptation, the inherent geometric distortion in acquired MR images pose a potential challenge to treatment accuracy. This study aimed to evaluate the geometric distortion levels in the clinical MRI protocols used across Danish RT centers and discuss influence of specific sequence parameters. Based on the variety in geometric performance across centers, we assess if harmonization of MRI sequences is a relevant measure.Materials and methods Nine centers participated with 12 MRI scanners and MRI-Linacs (MRL). Using a travelling phantom approach, a reference MRI sequence was used to assess variation in baseline distortion level between scanners. The phantom was also scanned with local clinical MRI sequences for brain, head/neck (H/N), abdomen, and pelvis. The influence of echo time, receiver bandwidth, image weighting, and 2D/3D acquisition was investigated.Results We found a large variation in geometric accuracy across 93 clinical sequences examined, exceeding the baseline variation found between MRI scanners (σ = 0.22 mm), except for abdominal sequences where the variation was lower. Brain and abdominal sequences showed lowest distortion levels ([0.22, 2.26] mm), and a large variation in performance was found for H/N and pelvic sequences ([0.19, 4.07] mm). Post hoc analyses revealed that distortion levels decreased with increasing bandwidth and a less clear increase in distortion levels with increasing echo time. 3D MRI sequences had lower distortion levels than 2D (median of 1.10 and 2.10 mm, respectively), and in DWI sequences, the echo-planar imaging read-out resulted in highest distortion levels.Conclusion There is a large variation in the geometric distortion levels of clinical MRI sequences across Danish RT centers, and between anatomical sites. The large variation observed makes harmonization of MRI sequences across institutions and adoption of practices from well-performing anatomical sites, a relevant measure within RT.Keywords: Geometric distortionradiotherapyMRI-guided radiation therapyMRI sequencesmagnetic resonance imaging AcknowledgementsWe thank the radiographers at all participating centers for skillful assistance during data collection. We would like to thank Claus P. Behrens and Ivan R. Vogelius for contributing with discussions regarding the clinical relevance of the study.Disclosure statementOdense University Hospital has research agreements with Philips (Eindhoven, The Netherlands) and Elekta AB (Stockholm, Sweden).Data availability statementThe raw image data of this study are available from the corresponding author, SWH, upon request. The authors confirm that the data supporting the findings of this study are available within the article’s supplementary materials (Table S2 and S3).Additional informationFundingThis work was supported by the DCCC Radiotherapy (The Danish National Research Center for Radiotherapy, Danish Comprehensive Cancer Center and The Danish Cancer Society); under Grant [R191-A11526]; The Danish Cancer Society under Grant [R231-A13852]; and OUH & RH Research Fund under Grant [58-A2857]. The work was supported by MANTRA (New MAgNetic resonance Technology for Response Adapted radiotherapy), a Frontline Research Center based at Odense University Hospital, Denmark.