Fig. 1.

Representative T2W MRI (left) and corresponding patient-specific B₀ distortion maps (right) (a-d) and system-specific gradient non-linearity (GNL) distortion map for the 1.5 integrated magnetic resonance linac (MR-linac) (e). Red delineations outline gross-tumor-volume (GTV), and magenta delineations outline a 30 mm isotropic margin around GTV. Black dotted lines show concentric circles centered at iso-center and with radii of 50, 100, and 150 mm, respectively. Sign of the B₀ related distortion indicates the direction of the distortion: negative values indicate distortion in the anterior direction and positive distortion indicate distortion in the posterior direction. a: Adrenal gland tumor-site (patient 3), b: liver tumor-site (patient 3), c: pancreatic tumor-site (patient 3), d: prostate tumor-site (patient 2).