3001 - Efficacy and Safety of the Contrast Agent Gadoterate in the Context of MR-Guided Stereotactic Body Radiotherapy for Upper Abdominal Tumors: A Preliminary Investigation

W. Jiang¹, X. Shi², X. Zhang¹, Z. Li², and J. Yue¹; ¹Department of Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China, ²Department of Radiation Oncology Physics and Technology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China

Purpose/Objective(s): The purpose of this study was to evaluate the efficacy and safety of using the contrast agent gadoterate in MR-guided stereotactic body radiotherapy (SBRT) for various types of upper abdominal tumors. Materials/

Methods: A total of 20 patients with pancreatic ductal adenocarcinoma (PDAC), hepatocellular carcinoma, or pancreatic, splenic, or hepatic metastases were enrolled. Half-doses of gadoterate were used in daily MR guidance for patients receiving 5-fraction SBRT who had poor tumor visualization on MR images without contrast. Contrast-to-Noise Ratios (CNRs) were evaluated to reflect contrast resolution with and without enhancement. Five radiation oncologists defined gross tumor volumes (GTVs) offline on daily MR images with and without enhancement, and the interobserver variability of GTVs was assessed by comparing the Hausdorff distances of individual GTVs to their intersections. Safety was assessed by collecting adverse events (AEs) during RT and 3-month follow-up.
Results: Among patients with different types of upper abdominal tumors, PDAC patients benefited most from the use of gadoterate (mean CNR 7.60 vs 1.76, p = 0.0017). The use of gadoterate significantly improved the interobserver reliability of the adaptive GTV definition (p < 0.01, vs plain T1-weighted MR; p < 0.001, vs T2-weighted MR) in patients with poor tumor visualization. The safety of gadoterate was considered excellent, with no gadoterate-related AEs during RT or 3-month follow-up.
Conclusion: The use of gadoterate can be an effective, convenient, and safe solution to the poor tumor visualization during MR-guided SBRT for upper abdominal tumors.