Magnetic resonance imaging sequence evaluation of an MR Linac system; early clinical experience

Abstract

Objective(s): To systematically identify the preferred magnetic resonance imaging (MRI) sequences following volunteer imaging on a 1.5 Tesla (T) MR-Linear Accelerator (MR Linac) for future protocol development. Methods: Non-patient volunteers were recruited to a Research and Ethics committee approved prospective MR-only imaging study on a 1.5T MR Linac system. Volunteers attended 1-3 imaging sessions that included a combination of mDixon, T1w, T2w sequences using 2-dimensional (2D) and 3-dimensional (3D) acquisitions. Each sequence was acquired over 2-7 minutes and reviewed by a panel of 3 observers to evaluate image quality using a visual grading analysis based on a 4-point Likert scale. Sequences were acquired and modified iteratively until deemed fit for purpose (online image matching or re-planning) and all observers agreed they were suitable in 3 volunteers. Results: 26 volunteers underwent 31 imaging sessions of six general anatomical regions. Images were acquired in one or two of six general anatomical regions: male pelvis (n = 9), female pelvis (n = 4), chestwall/breast (n = 5), lung/oesophagus (n = 5), abdomen (n = 3) and head and neck (n = 5). Images were acquired using a pre-defined exam-card that on average, included six sequences (range 2-10), with a maximum scan time of approximately one hour. The majority of observers preferred T2-weighted sequences. The thorax teams were the only groups to prefer T1-weighted imaging. Conclusions: An iterative process identified sequence agreement in all anatomical regions. These sequences will now be evaluated in patient volunteers. Advances in knowledge: This manuscript is the first publication sharing the results of the first systematic selection of MRI sequences for use in on-board MRI-guided radiotherapy by end-users (therapeutic radiographers and clinical oncologists) in healthy volunteers.

Experimental evaluation of four-dimensional Magnetic Resonance Imaging for radiotherapy planning of lung cancer

“…The results of this study showed that the difference between the motion range detection capability of 4D-CT and 4D-MRI was not statistically significant when using 13 patient respiratory traces to generate pseudo-realistic phantom motion. While the use of MRI for detection, staging and surveillance of early stage lung cancer is well established [16], with recent developments in MR-guided radiotherapy [17][18][19][20], MRI simulators and the move toward MRI only workflows, results such as those reported in this study, which show equivalence between MRI and CT techniques, may be particularly relevant.…”

Use of a healthy volunteer imaging program to optimize clinical implementation of stereotactic MR-guided adaptive radiotherapy

“…SBE has been successfully applied to brachytherapy training [35] , [36] , [37] and training in on-call treatments [38] , but to the authors’ knowledge this is a novel use of SBE, and is well-suited to the nature of SMART. With the rise of MR-guided radiotherapy, healthy volunteer scans play a critical role in sequence and workflow optimization [39] , [40] , as well as providing a non-clinical training environment. Similar SBE workflows could be utilized to train residents prior to involvement in patient cases.…”

To see or not to see: Evaluation of magnetic resonance imaging sequences for use in MR Linac-based radiotherapy treatment

“…As the second institution to enter this UK study, the recruitment process and methodology followed that as described previously by Eccles and Smith et al [32] . Recruitment of suitable non-patient volunteers was achieved across the institution via email.…”

“…However, sequences used for RT guidance require additional considerations, further diverging their distinct properties from diagnostic equivalents. They need to be acquired in treatment position, be comparatively short in duration to facilitate patient compliance and minimise intrafractional motion, and furthermore sustain a high geometric fidelity over a relatively large field of view [32] . Additionally, the physical requirement for the receive coil to be suspended above the patient to be as close to, but not deform the body contour increases standoff [22] .…”