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 language | English (US) |
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Pages (from-to) | 303-309 |
Number of pages | 7 |
Journal | Journal of Applied Clinical Medical Physics |
Volume | 22 |
Issue number | 8 |
DOIs | |
State | Published - Aug 2021 |
Keywords
- MR-guided radiotherapy
- MRgRT
- geometric distortion
- patient-specific distortion
ASJC Scopus subject areas
- Radiation
- Instrumentation
- Radiology Nuclear Medicine and imaging