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

Signe Winther Hasler*, Jesper Folsted Kallehauge, Rasmus Hvass Hansen, Eva Samsøe, Dennis Tideman Arp, Henrik Dahl Nissen, Jens M. Edmund, Uffe Bernchou, Faisal Mahmood

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review


Background: 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.

Original languageEnglish
JournalActa Oncologica
Issue number11
Pages (from-to)1551-1560
Publication statusPublished - 2023
Event21st Acta Oncologica Symposium—BiGART 2023 - Biology-Guided Adaptive Radiotherapy - Aarhus, Denmark
Duration: 20. Jun 202321. Jun 2023


Conference21st Acta Oncologica Symposium—BiGART 2023 - Biology-Guided Adaptive Radiotherapy


  • Geometric distortion
  • magnetic resonance imaging
  • MRI sequences
  • MRI-guided radiation therapy
  • radiotherapy


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