2630 - Memory Circuit Dosimetry in Patients Treated with SRS for Brain Metastases
Presenter(s)
N. Lo1, S. J. Wadi-Ramahi2, H. Wang3, D. Dimitriadou2, R. J. Lalonde2, T. McCaw2, K. Sarna1, A. H. Zureick2, and S. Choi2; 1UPMC Hillman Cancer Center, Pittsburgh, PA, 2Department of Radiation Oncology, UPMC Hillman Cancer Center, Pittsburgh, PA, 3University of Pittsburgh School of Medicine, Pittsburgh, PA
Purpose/Objective(s): Reduction of radiation dose to the hippocampus decreases radiation-induced neurocognitive toxicities in patients with brain metastases. Dose reduction to additional substructures in the memory circuit (hippocampus, amygdala, fornix, and corpus callosum) may further reduce patients’ neurocognitive toxicities. This study aims to report memory circuit (MC) dosimetry from single-fraction LINAC-based stereotactic radiosurgery (SRS) plans for patients with increasing number of brain metastases. We sought to determine the feasibility of the Sparing Memory with Advanced Radiosurgical Targeting (SMART) technique where SRS treatment plans are re-optimized to reduce MC dose without sacrificing target coverage.
Materials/Methods: Retrospective contouring of the MC was performed on 77 single-fraction monoisocentric SRS plans delivered between March 2022 – December 2022 for patients with increasing number of brain metastases: 1, 2-4, 5-9 and 10+. Linear regression analysis, one-way ANOVA, and Tukey’s multiple comparison test were performed to compare dosimetric parameters: mean, Dmax (0.03 cc) and median doses to MC, cumulative PTV and MC volume. Spearman correlation coefficient (r) was calculated for parameter relationships. Seven plans were reoptimized using SMART by maximizing dose reduction to MC while maintaining >95% PTV coverage. Dosimetric parameters were compared between the original and re-optimized plans using the paired t test.
Results: Out of the 77 patients consecutively selected, 29 had 1 lesion, 28 with 2-4 lesions, 13 with 5-9 lesions, and 7 with 10+ lesions. Patients with 10+ metastases received significantly higher mean and median doses to the MC (3.5 vs 0.52 Gy; 3.3 vs 0.36 Gy, p < 0.05) compared to those with one metastasis. A significant difference was observed in Dmax (0.03 cc) to the MC between 1 vs 10+ metastases (12.0 vs 3.2 Gy, p < 0.0001). A moderate correlation was found between cumulative PTV and mean/median doses to the MC (r = 0.61; r = 0.59, p < 0.05). Compared to original plans, SMART plans yielded a significant decrease in mean, median, and Dmax doses to the MC (3.5 vs 2.1 Gy; 3.3 vs 1.9 Gy; 12.0 vs 9.2 Gy, p < 0.05).
Conclusion: Patients treated for 10+ brain metastases received increased mean/median/ Dmax doses to the MC compared to patients with less than 10 metastases. MC-sparing was achieved in all SMART plans while maintaining comparable PTV coverage. Our initial results show that sparing the MC during SRS planning is feasible. Prospective studies evaluating the neurocognitive benefits of SMART are warranted, particularly for patients with 10+ brain metastases and/or higher cumulative brain metastases volume.