Evaluation of a fast-volumetric four-dimensional magnetic resonance imaging technique for abdominal radiotherapy tumor motion management

Background: Motion management plays an important role in abdominal cancer radiotherapy. In this study, we investigated the motion measurement accuracy and tumor contrast in liver tumor using a fast volumetric four-dimensional magnetic resonance imaging (4D-MRI) technique using commercial sequence. Methods: Four volunteers and 34 patients with liver tumors were included in this study with institutional review board (IRB) approval, and all patients underwent routine MRI scans with additional 4D-MRI scan on a 3.0 Tesla MRI scanner. A fast-volumetric sequence [time-resolved imaging with stochastic trajectories-volumetric interpolated breath-hold examination (TWIST-VIBE)] was used to acquire 4D-MRI images. The temporal resolution of 4D-MRI was ~0.69 s per measurement. The 4D-MRI sequence was performed before and immediately after the injection of gadolinium contrast agent, termed as non-contrast 4D-MRI (in patient study) and contrast-enhanced 4D-MRI (4D-MRICE) respectively. The tumor average motion amplitude (AMA) and maximum motion amplitude (MMA) in the superior-inferior (SI), anterior-posterior (AP), and medium-lateral (ML) directions were measured in two sets of 4D-MRI and three sets of two-dimensional (2D) Cine magnetic resonance (MR) images. The tumor signal-to-noise ratio (SNR) and tumor-to-liver contrast-to-noise ratio (CNR) were also evaluated. Results: High temporal resolution (~0.69 s per measurement) and isotropic spatial resolution (~2.7 mm³ voxel size) were achieved with the fast volumetric 4D-MRI technique. Phantom experiments validated the motion measurement accuracy, showing that the average and MMAs in the SI, AP, and ML directions matched the programmed motions with errors below 3 mm. In patient studies, tumor motion amplitudes and trajectories measured by 4D-MRICE and non-contrast 4D-MRI (4D-MRINC) were comparable to conventional 2D Cine MRI in all three directions, with no statistically significant differences. Specifically, for AMA, the P values were 0.096, 0.019, and 0.009 for 4D-MRICE in the SI, AP, and ML directions, respectively, and 0.049, 0.008, and 0.016 for 4D-MRINC, respectively. For MMA, the corresponding P values were 0.054, 0.022, and 0.086 for 4D-MRICE, and 0.041, 0.007, and 0.016 for 4D-MRINC. Tumor SNR and tumor-to-liver CNR obtained with 4D-MRICE and 4D-MRINC were also comparable to those from standard diagnostic sequences (T1W, T2W) and Cine MRI, with P values <0.05, ensuring sufficient image quality for radiotherapy planning. Although minor motion artifacts were occasionally observed, the overall image quality and motion fidelity support the clinical feasibility of the method. Taken together, these results demonstrate that the TWIST-VIBE 4D-MRI technique provides accurate, high-quality volumetric motion assessment efficiently, without requiring specialized hardware or prolonged scanning times. Conclusions: Our preliminary results demonstrated that the commercially available TWIST-VIBE 4D-MRI sequence provides precise volumetric tumor motion tracking suitable for clinical abdominal radiotherapy. Its rapid acquisition and reliable image quality facilitate seamless workflow integration, potentially enhancing treatment precision and improving patient outcomes. The technique offers a practical alternative to existing imaging modalities by combining speed, spatial coverage, and soft tissue contrast without additional hardware requirements. Further efforts will target artifact minimization, optimization of spatial and temporal resolutions, improved clinical decision-making impact, and broader multi-center validation to ensure robust clinical implementation and generalizability across diverse patient populations.

Duke Scholars

Author Jing Cai Radiation Oncology