RADI-21. Feasibility of Gamma Knife Surgery for patients with 20 or more brain metastases

BACKGROUND: The current standard-of-care treatment for brain metastases (BM)≥20 is Whole Brain Radiotherapy (WBRT), which can cause neurocognitive decline detrimental to patients’ quality of life, especially if their functional status is good on presentation. The benefits of Gamma Knife Surgery (GKS) have been shown for BM≤10, but there is no consensus on the upper limit where GKS is no longer beneficial. We hypothesize that selected patients with ≥20 BM may benefit by replacing WBRT with GKS to preserve neurocognition without compromising intracerebral tumor control and overall survival, with additional treatments as needed. METHODOLOGY: This is retrospective analysis of 31 patients with ≥20 BM who underwent single-session GKS between 2016–2021. Twenty-two patients had ECOG of 0 at the time of GKS. Median number of BM at GKS was 30 (20–79) with median total tumour volume 4cm(3) (2–28 cm(3)). Median marginal dose was 20Gy (10-25Gy). RESULTS: Median overall survival following GKS was 14-months (95%CI 4-24months), justifying GKS in this population. 11/12 patients that died succumbed due to extracranial disease, while 1 patient, who was treated with WBRT before GKS, succumbed to intracranial tumor progression. Local tumor control achieved was achieved for 63% of patients at 2-years and distal tumor control in 24% of patients at 1.5-years without additional radiation treatment. Salvage GKS was given in seven patients and salvage WBRT in three. One local recurrence was surgically resected. Systemic treatment given to most patients probably contributed to intracranial tumor control. No patients developed significant neurocognitive deficits attributable to GKS during the follow-up period of median 7-months (Q1-Q3: 3-12months). CONCLUSION: Most patients treated with GKS for ≥20 BM have sufficient survival time to benefit from the treatment. Local and distal recurrences can be managed with systemic treatment, salvage GKS, or WBRT, resulting in intracerebral tumor control in vast majority of cases.