Feasibility of real‐time motion tracking using cine MRI during MR‐guided radiation therapy for abdominal targets

Abstract

Purpose: Real-time high soft-tissue contrast magnetic resonance imaging (MRI) from the MR-Linac offers the best opportunity for accurate motion tracking during radiation therapy delivery via highfrequency two-dimensional (2D) cine imaging. This work investigates the efficacy of real-time organ motion tracking based on the registration of MRI acquired on MR-Linac. Methods: Algorithms based on image intensity were developed to determine the three-dimensional (3D) translation of abdominal targets. 2D and 3D abdominal MRIs were acquired for 10 healthy volunteers using a high-field MR-Linac. For each volunteer, 3D respiration-gated T2 and 2D T2/T1weighted cine in sagittal, coronal, and axial planes with a planar temporal resolution of 0.6 for 60 s was captured. Datasets were also collected on MR-compatible physical and virtual four-dimensional (4D) motion phantoms. Target contours for the liver and pancreas from the 3D T2 were populated to the cine and assumed as the ground-truth motion. We performed image registration using a research software to track the target 3D motion. Standard deviations of the error (SDE) between the groundtruth and tracking were analyzed. Results: Algorithms using a research software were demonstrated to be capable of tracking arbitrary targets in the abdomen at 5 Hz with an overall accuracy of 0.6 mm in phantom studies and 2.1 mm in volunteers. However, this value is subject to patient-specific considerations, namely motion amplitude. Calculation times of < 50 ms provide a pathway of real-time motion tracking integration. A major challenge in using 2D cine MRI to track the target is handling the full 3D motion of the target. Conclusions: Feasibility to track organ motion using intensity-based registration of MRIs was demonstrated for abdominal targets. Tracking accuracy of about 2 mm was achieved for the motion of the liver and pancreatic head for typical patient motion. Further development is ongoing to improve the tracking algorithm for large and complex motions.

Fundamental study on quality assurance (QA) procedures for a real‐time tumor tracking radiotherapy (RTRT) system from the viewpoint of imaging devices

“…Recently, new technologies for tracking of respiratory motion using positron emission tomography (PET) and magnetic resonance imaging (MRI) has also been reported. 24,25 However, in terms of versatility and popularity, tracking technologies using kV planner imaging will likely be the mainstream for the time being in radiotherapy. Especially in planner kV imaging systems using tracking with pattern matching, those QA indicators are well worth considering for assuring accuracy of 3D tracking.…”

“…This finding seems to involve interindividual variances in input/output characteristics and differences in spatial frequency characteristics. In other words, since the RTRT system using a colored II has six detectors with different spatial frequency characteristics, verification is needed for each of these detectors.In this study, if we adopt the lower limit determined in results 3.A, the ∫NEQ for RGB components needed to exceed the lower limit (3σ 3D < 0.5 mm) was 136 25,. 337.56, and 116.60 with Device A and 52.48, 232.83, and 128.97 with Device B.…”

“…Each possible combination of tube voltage (80 kV), tube current(10,25, 50, 80, 100, and 200 mA) and pulse width (1, 2, 3, and 4 ms) was adopted as the fluoroscopic setting for acquisition of images used for the evaluation of NPS. For simulating a standard patient, a PMMA thickness of 10 and 20 cm with the tube voltage of 80 kV was applied.…”

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.…”

MR-Guided Radiotherapy for Liver Malignancies

“…On the 0.35 T system, cine MR imaging is at a rate of eight frames per second and beam-gating is automatic, through a deformable registration-based tracking algorithm ( 83 ). On the 1.5 T system, beam-gating is presently manual but still based on real time MRI target (or adjacent surrogate) monitoring ( 101 ). On both systems, breath-hold delivery may improve efficiency of treatment, and combinations of patient visual feedback and/or audio respiratory coaching have been utilized successfully.…”