P09.07.B CONTRAST-ENHANCED BLACK-BLOOD MRI FOR IMPROVING TARGET DELINEATION AND PLANNING ACCURACY IN STEREOTACTIC RADIOSURGERY

Abstract BACKGROUND This study aimed to evaluate the technical feasibility and clinical utility of contrast-enhanced (CE) three-dimensional (3D) T1-weighted black-blood (BB) MRI in improving gross tumor volume (GTV) delineation and treatment planning accuracy for patients with brain metastases or tumors adjacent to critical vascular structures, compared with conventional CE T1 gradient-echo (GRE) imaging. MATERIAL AND METHODS Twenty patients with suspected brain metastases or tumors adjacent to vascular structures underwent high-resolution BB-MRI and CE-GRE imaging between June 2024 and March 2025, using a 3.0 T scanner (Ingenia Elition X 3.0 T; Philips Healthcare) with a 15-channel head coil. The imaging protocol included T2 turbo spin-echo (TSE), 3D T2 TSE, 3D T1 GRE, CE 3D T1 GRE, and CE 3D T1 BB TSE sequences. After intravenous administration of gadoteridol (ProHance; 0.2 mmol/kg), CE 3D T1 GRE and CE 3D T1 BB images were sequentially acquired. For each patient, GTV delineation was independently performed on fused planning CT images with both CE 3D T1 GRE and CE BB-MRI. Lesion conspicuity, delineation confidence, target volume differences, and the impact on stereotactic radiosurgery (SRS) treatment planning were retrospectively analyzed. Radiation planning indices, including the Conformity Index (CI), Gradient Index (GI), and Homogeneity Index (HI), were also evaluated. RESULTS Compared with CE 3D T1 GRE, CE BB-MRI demonstrated superior suppression of vascular signals, leading to enhanced conspicuity of metastatic lesions and perivascular tumor infiltration. BB-MRI enabled the detection of additional small metastatic lesions that were not visible on CE-GRE imaging, resulting in more complete and accurate GTV delineation. GTVs defined on BB-MRI were generally smaller and more precise, with reduced interobserver variability. Preliminary evaluation of planning metrics, including CI and GI, suggested improved plan quality with BB-MRI-guided targeting. In particular, lesions adjacent to major cerebral vessels exhibited clearer and more distinct margins on BB imaging, allowing for more confident and accurate SRS planning. These improvements facilitated the use of tighter planning target volume margins without compromising the sparing of critical structures. CONCLUSION CE 3D T1 BB-MRI improves tumor visualization and target delineation accuracy for brain metastases and tumors adjacent to major vascular structures in SRS planning. Moreover, it enhances the technical precision of SRS planning and is expected to play a critical role in optimizing treatment planning, ultimately improving the safety and therapeutic efficacy of SRS when integrated into standard imaging protocols.