Abstract
PURPOSE: Accurate internal target volume (ITV) estimation is essential for effective and safe radiation therapy in liver cancer. This study evaluates the clinical value of an ultraquality 4-dimensional magnetic resonance imaging (UQ 4D-MRI) technique for ITV estimation. METHODS AND MATERIALS: The UQ 4D-MRI technique maps motion information from a low spatial resolution dynamic volumetric MRI onto a high-resolution 3-dimensional MRI used for radiation treatment planning. It was validated using a motion phantom and data from 13 patients with liver cancer. ITV generated from UQ 4D-MRI (ITV(4D)) was compared with those obtained through isotropic expansions (ITV(2 mm) and ITV(5 mm)) and those measured using conventional 4D-computed tomography (computed tomography-based ITV, ITV(CT)) for each patient. RESULTS: Phantom studies showed a displacement measurement difference of <5% between UQ 4D-MRI and single-slice 2-dimensional cine MRI. In patient studies, the maximum superior-inferior displacements of the tumor on UQ 4D-MRI showed no significant difference compared with single-slice 2-dimensional cine imaging (P = .985). Computed tomography-based ITV showed no significant difference (P = .72) with ITV(4D), whereas ITV(2 mm) and ITV(5 mm) significantly overestimated the volume by 29.0% (P = .002) and 120.7% (P < .001) compared with ITV(4D), respectively. CONCLUSIONS: UQ 4D-MRI enables accurate motion assessment for liver tumors, facilitating precise ITV delineation for radiation treatment planning. Despite uncertainties from artificial intelligence-based delineation and variations in patients' respiratory patterns, UQ 4D-MRI excels at capturing tumor motion trajectories, potentially improving treatment planning accuracy and reducing margins in liver cancer radiation therapy.