Single- versus 2-session Gamma Knife surgery for symptomatic midsize brain metastases: a propensity score–matched analysis

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Abstract
OBJECTIVE: Two-session Gamma Knife surgery (GKS) has recently been demonstrated to be an effective and less-invasive alternative for large brain metastases not treatable by microsurgical resection. This raises the clinical question of whether the 2-session GKS strategy further improves treatment outcomes for patients with symptomatic midsize brain metastases (2–10 cm 3 ) as compared to single-session GKS. The present study aimed to compare the local therapeutic effects and toxicities of single-session and 2-session GKS for treating these lesions. METHODS: Patients with focal neurological deficits attributable to midsize brain metastases who underwent upfront GKS during the period from 2010 to 2018 were retrospectively identified from an institutional database. Patients for whom both post-GKS imaging studies and neurological evaluations from outpatient visits were available were eligible. Using propensity score–matching (PSM) analysis, unique matched pairs which had a similar likelihood of receiving 2-session GKS were generated. The main outcome measure was a composite of imaging and/or neurological worsening of the lesion of interest. Functional improvement and overall survival (OS) were also compared between the 2 treatment arms. RESULTS: In total, 219 cancer patients with 252 symptomatic midsize brain metastases were eligible. Of these 252 tumors, 176 and 76 were treated with single- and 2-session GKS, respectively. After PSM, 68 pairs of tumors were obtained. The Gray test showed that 2-session GKS achieved a longer local progression–free interval than single-session GKS (1-year local control rate: 84% vs 53%; HR 0.31, 95% CI 0.16–0.63, p = 0.001). Two-session GKS was also associated with greater functional improvement in KPS scores (mean 18.3 ± 14.6 vs 12.8 ± 14.1, p = 0.040). The median OS did not differ significantly between single- and 2-session GKS (15.6 vs 24.7 months; HR 0.69, 95% CI 0.44–1.10, p = 0.11). CONCLUSIONS: Two-session GKS achieved more durable local tumor control and greater functional improvement than single-session GKS for patients with symptomatic midsize brain metastases, although there was no OS advantage.

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