Prospective analysis of in vivo landmark point-based MRI geometric distortion in head and neck cancer patients scanned in immobilized radiation treatment position: Results of a prospective quality assurance protocol

Abstract

PurposeUncertainties related to geometric distortion are a major obstacle for effectively utilizing MRI in radiation oncology. We aim to quantify the geometric distortion in patient images by comparing their in-treatment position MRIs with the corresponding planning CTs, using CT as the non-distorted gold standard.MethodsTwenty-one head and neck cancer patients were imaged with MRI as part of a prospective Institutional Review Board approved study. MR images were acquired with a T2 SE sequence (0.5 × 0.5 × 2.5 mm voxel size) in the same immobilization position as in the CTs. MRI to CT rigid registration was then done and geometric distortion comparison was assessed by measuring the corresponding anatomical landmarks on both the MRI and the CT images. Several landmark measurements were obtained including; skin to skin (STS), bone to bone, and soft tissue to soft tissue at specific levels in horizontal and vertical planes of both scans. Inter-observer variability was assessed and interclass correlation (ICC) was calculated.ResultsA total of 430 landmark measurements were obtained. The median distortion for all landmarks in all scans was 1.06 mm (IQR 0.6–1.98). For each patient 48% of the measurements were done in the right-left direction and 52% were done in the anteroposterior direction. The measured geometric distortion was not statistically different in the right-left direction compared to the anteroposterior direction (1.5 ± 1.6 vs. 1.6 ± 1.7 mm, respectively, p = 0.4). The magnitude of distortion was higher in the STS peripheral landmarks compared to the more central landmarks (2.0 ± 1.9 vs. 1.2 ± 1.3 mm, p < 0.0001). The mean distortion measured by observer one was not significantly different compared to observer 2, 3, and 4 (1.05, 1.23, 1.06 and 1.05 mm, respectively, p = 0.4) with ICC = 0.84.ConclusionMRI geometric distortions were quantified in radiotherapy planning applications with a clinically insignificant error of less than 2 mm compared to the gold standard CT.

Prospective quantitative quality assurance and deformation estimation of MRI-CT image registration in simulation of head and neck radiotherapy patients

“…non-immobilized) MR acquisition for radiotherapy planning. This method demonstrated superior image quality, decreased geometric distortion, and better MR-CT co-registration [10], [11]. Prior work to ours has also confirmed the feasibility of MR acquisition in the treatment position [12].…”

Dosimetric Impact of MRI Distortions: A Study on Head and Neck Cancers

“…In addition, tissue magnetic susceptibility differences in this region are minimal compared with the head and neck area. Mohammed et al 28 characterized MRI distortions in the head and neck region and reported distortions of less than 2 mm but did not evaluate their dosimetric impact on RTP.…”

MR‐guided simulation is superior than FDG/PET‐guided simulation for local control in nasopharyngeal cancer patients treated with intensity‐modulated radiotherapy

“…Even though MRI has a certain degree of distortion, MRI may still provide higher confidence in target delineation compared with CT. Published trials showed that geometric distortion of MRI was quantified with a clinically significant error of less than 2 mm compared with gold standard CT, in radiotherapy planning applications 11 . In addition, the error caused by geometric distortion is relatively smaller compared to the high delineation error between interobservers in radiotherapy planning using CT 12‐14 .…”