ESTRO 2025 - Abstract Book

S650

Clinical - CNS

ESTRO 2025

Material/Methods: This retrospective study included 36 patients with a total of 74 brain metastases. Each lesion was contoured independently by an experienced radiation oncologist and a neuroradiologist using both black-blood MRI and 3D T1 post-contrast GRE sequences. The contoured volumes from each sequence were measured and compared using the Wilcoxon signed-rank test. Additionally, the DICE similarity coefficient was calculated to quantify the concordance between the two imaging modalities, with further analysis performed to explore how lesion size impacted this concordance. To assess the effect of margin application, a 2mm PTV margin, as recommended by the radiosurgery mask manufacturer, was applied, and the DICE index was re-evaluated. Results: The mean volume for GTVs contoured on the 3D T1 post-contrast GRE sequence was 1.86cc (±3.21cc), while the mean volume for the black-blood MRI sequence was 2.28cc (±3.77cc), with a statistically significant difference (W=184, p<0.001). The median DICE similarity index between the sequences was 0.76 (range: 0.50-0.93), with larger lesions demonstrating higher concordance values. When a 2mm PTV margin was applied, the DICE index increased to 0.84 (range: 0.68-0.95), indicating improved overlap between the contours when a standard margin was considered. Conclusion: Black blood MRI sequences show differences in GTV volumes and demonstrate higher concordance in larger lesions compared to 3D T1 post-contrast GRE sequences. Applying a 2mm PTV margin further enhances concordance, suggesting that black blood MRI could allow for margin reduction without compromising local control, potentially optimising radiotherapy treatment planning. Digital Poster The Neurocognitive Effects of Intracranial Progression & Subsequent Courses of Stereotactic Radiosurgery: Lessons Learned from a Prospective Registry Eyub Y. Akdemir 1 , Selin Gurdikyan 1 , Thailin C. Reyes 1 , Yazmin Odia 1 , Robert H. Press 1 , Sreenija Yarlagadda 1 , Omer Gal 1 , D Jay Wieczorek 1 , Yongsook C. Lee 1 , Ranjini Tolakanahalli 1 , Alonso N. Gutierrez 1 , Michael W. McDermott 2 , Minesh P. Mehta 1 , Rupesh Kotecha 1 1 Radiation Oncology, Miami Cancer Institute, Miami, USA. 2 Neurosurgery, Miami Neuroscience Institute, Miami, USA Purpose/Objective: The neurocognitive outcomes of patients treated with multiple courses of stereotactic radiosurgery (SRS) or fractionated SRS (FSRS) are poorly understood. The objective of this study was to evaluate the effects of additional courses of radiotherapy on neurocognitive function using data from a prospective observational study utilizing a novel, multi-dimensional, tablet-based neurocognitive assessment (NCA) battery (NCT05504681). Material/Methods: Multi-dimensional neurocognitive outcomes were compared in patients with a history of SRS/FSRS who were categorized as “high-risk” (receiving subsequent SRS/FSRS courses for distant intracranial failures) or “low-risk” (receiving no further radiotherapy). The reliable change index (RCI) for controlling practice effects, with a cutoff of ≤ - 1.645, was used to identify neurocognitive decline (ND) between baseline and follow-up scores across seven tests spanning five domains. Additionally, participants provided feedback on their experiences with the digital battery after completing two or more assessments. Keywords: Metastasis, Contouring, Black Blood 344