Clinical assessment of geometric distortion for a 0.35T MR-guided radiotherapy system

John Neylon, Kiri A. Cook, Yingli Yang, Dongsu Du, Ke Sheng, Robert K. Chin, Amar U. Kishan, James M. Lamb, Daniel A. Low, Minsong Cao

Research output: Contribution to journalArticlepeer-review

Abstract

Purpose: To estimate the overall spatial distortion on clinical patient images for a 0.35 T MR-guided radiotherapy system. Methods: Ten patients with head-and-neck cancer underwent CT and MR simulations with identical immobilization. The MR images underwent the standard systematic distortion correction post-processing. The images were rigidly registered and landmark-based analysis was performed by an anatomical expert. Distortion was quantified using Euclidean distance between each landmark pair and tagged by tissue interface: bone-tissue, soft tissue, or air-tissue. For baseline comparisons, an anthropomorphic phantom was imaged and analyzed. Results: The average spatial discrepancy between CT and MR landmarks was 1.15 ± 1.14 mm for the phantom and 1.46 ± 1.78 mm for patients. The error histogram peaked at 0–1 mm. 66% of the discrepancies were <2 mm and 51% <1 mm. In the patient data, statistically significant differences (p-values < 0.0001) were found between the different tissue interfaces with averages of 0.88 ± 1.24 mm, 2.01 ± 2.20 mm, and 1.41 ± 1.56 mm for the air/tissue, bone/tissue, and soft tissue, respectively. The distortion generally correlated with the in-plane radial distance from the image center along the longitudinal axis of the MR. Conclusion: Spatial distortion remains in the MR images after systematic distortion corrections. Although the average errors were relatively small, large distortions observed at bone/tissue interfaces emphasize the need for quantitative methods for assessing and correcting patient-specific spatial distortions.

Original languageEnglish (US)
Pages (from-to)303-309
Number of pages7
JournalJournal of Applied Clinical Medical Physics
Volume22
Issue number8
DOIs
StatePublished - Aug 2021

Keywords

  • MR-guided radiotherapy
  • MRgRT
  • geometric distortion
  • patient-specific distortion

ASJC Scopus subject areas

  • Radiation
  • Instrumentation
  • Radiology Nuclear Medicine and imaging

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