Memory circuit dosimetry in patients with brain metastases treated with Sparing Memory with Advanced Radiosurgery Targeting (SMART) technique.

Abstract

PurposeRadiation dose reduction to major memory circuit substructures (e.g., hippocampus, amygdala, fornix, and corpus callosum) may reduce patients' neurocognitive toxicities. We evaluated memory circuit (MC) dosimetry and determined the feasibility of the "Sparing Memory with Advanced Radiosurgery Targeting" (SMART) technique in patients with brain metastases.Materials and methodsRetrospective contouring of MC substructures was performed for 101 patients that received single-fraction, linear accelerator (LINAC)-based, monoisocentric SRS plans for increasing numbers of brain metastases: 1, 2-4, 5-9 and ≥ 10. Patients with ≥10 lesions (n = 13) were reoptimized using SMART by maximizing dose reduction to MC while maintaining >95% PTV coverage (V100% > 95%). Dosimetric parameters such as Dmean, Dmax, and Dmedian to MC, cumulative PTV and MC volume were evaluated.ResultsPatients with ≥10 brain metastases received significantly higher Dmean (2.9 vs. 0.41 Gy, p median (2.9 vs. 0.34 Gy, p max (9.0 vs. 1.9 Gy, p mean, Dmedian, Dmax, and D₁₀₀ doses to the MC when compared to clinical dosimetry (2.9 vs. 1.8 Gy, p = 0.0001; 2.9 vs. 1.8 Gy, p = 0.0002; 9.0 vs. 4.7 Gy, p = 0.0007; 1.5 vs. 0.98 Gy, p = 0.0010, respectively).ConclusionIncreased number of brain metastases results in higher MC doses. Patients with ≥10 lesions received increased Dmean/Dmedian/Dmax doses to the MC compared to patients with <10 brain metastases. SMART technique is clinically feasible. Studies evaluating the neurocognitive benefits of SMART are warranted.