Investigation of tumor and vessel motion correlation in the liver

Abstract

Intrafraction imaging-based motion management systems for external beam radiotherapy can rely on internal surrogate structures when the target is not easily visualized. This work evaluated the validity of using liver vessels as internal surrogates for the estimation of liver tumor motion. Vessel and tumor motion were assessed using ten two-dimensional sagittal MR cine datasets collected on the ViewRay MRIdian. For each case, a liver tumor and at least one vessel were tracked for 175 s. A tracking approach utilizing block matching and multiple simultaneous templates was applied. Accuracy of the tracked motion was calculated from the error between the tracked centroid position and manually defined ground truth annotations. The patient's abdomen surface and diaphragm were manually annotated in all frames. The Pearson correlation coefficient (CC) was used to compare the motion of the features and tumor in the anterior-posterior (AP) and superior-inferior (SI) directions. The distance between the centroids of the features and the tumors was calculated to assess if feature proximity affects relative correlation, and the tumor range of motion was determined. Intra-and interfraction motion amplitude variabilities were evaluated to further assess the relationship between tumor and feature motion. The mean CC between the motion of the vessel and the tumor were 0.85 ± 0.11 (AP) and 0.92 ± 0.04 (SI), 0.83 ± 0.11 (AP) and −0.89 ± 0.06 (SI) for the surface and tumor, and 0.80 ± 0.17 (AP) and 0.94 ± 0.03 (SI) for the diaphragm and tumor. For intrafraction analysis, the average amplitude variability was 2.47 ± 0.77 mm (AP) and 3.14 ± 1.49 mm (SI) for the vessels, 2.70 ± 1.08 mm (AP) and 3.43 ± 1.73 mm (SI) for the surface, and 2.76 ± 1.41 mm (AP) and 2.91 ± 1.38 mm (SI) for the diaphragm. No relationship between distance and motion correlation was observed. The motion of liver tumors and liver vessels was well correlated, making vessels a suitable surrogate for tumor motion in the liver.

Clinical Implementational and Site-Specific Workflows for a 1.5T MR-Linac

“…A sagittal and coronal cine MRI (TE: 3.8 ms, TR: 1.92 ms, flip angle: 40 deg) are acquired over 60 s to capture multiple breathing cycles. First, a cine MRI with no abdominal compression is acquired where the motion of the diaphragm in the superior/inferior and anterior/posterior directions are measured as a surrogate for the liver tumor [ 17 ]. If the magnitude of this motion is clinically unacceptable (>15 mm Euclidian), abdominal compression is applied, and a cine MRI is again acquired to reassess the motion magnitude of the diaphragm.…”

Real-Time 2D MR Cine From Beam Eye’s View With Tumor-Volume Projection to Ensure Beam-to-Tumor Conformality for MR-Guided Radiotherapy of Lung Cancer

“…In this predictive strategy, a high correlation between the diaphragm and tumor motions was assumed, which is often true for a lung or liver tumor that is located near the diaphragm ( 25 – 27 ). If a tumor is away from the diaphragm, its motion amplitude should be only a fraction of that of the diaphragm.…”

Surface guidance compared with ultrasound-based monitoring and diaphragm position in cone-beam computed tomography during abdominal stereotactic radiotherapy in breath-hold

“…A marker was affixed to the patient surface inferior of the costal arch, defining the gating point and the DIBH window (±2 mm) in relation to the isocenter for SGRT. Subsequently, a reference US dataset was acquired in DIBH and a suitable echogenic monitoring structure (Gross Tumor Volume [GTV] itself or a nearby surrogate vessel [46] ) was contoured offline.…”