2556 - Population-Based Local Control and Survival Outcomes of Brain Post-Metastasectomy Adjuvant Radiotherapy vs. Observation

Z. H. Li¹, L. Almeida², N. H. Yao², J. Wang², A. Lee³, S. Makarenko³, M. Fatehi³, H. Choi⁴, E. A. Gete⁴, F. Hsu⁵, W. Sharieff⁶, S. RAthod⁶, H. Carolan¹, J. Chan¹, R. Ma¹, A. Nichol¹, and J. Oh³; ¹Division of Radiation Oncology, Department of Surgery, University of British Columbia, Vancouver, BC, Canada, ²Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada, ³Division of Neurosurgery, Department of Surgery, University of British Columbia, Vancouver, BC, Canada, ⁴Department of Medical Physics, BC Cancer Agency, Vancouver, BC, Canada, ⁵BC Cancer - Abbotsford, Abbotsford, BC, Canada, ⁶Division of Radiation Oncology, Department of Surgery, University of British Columbia, Abbotsford, BC, Canada

Purpose/Objective(s): To assess and identify the factors associated with the outcomes of patients with surgically resected brain metastasis followed by surveillance or adjuvant surgical cavity radiotherapy (aRT). Materials/

Methods: A multi-centre retrospective chart review was conducted on patients who received brain metastases resection between 2018 – 2020, prior to institutional adoption of aRT as standard of care. Patients were excluded if they had received whole brain radiotherapy, an aRT dose of <15 Gy, or >5 fractions. Study endpoints were local recurrence, distant intracranial failure, radionecrosis (RN), and overall survival (OS). Survival analyses were performed using the Kaplan-Meier method. Univariable (UVA) and multivariable (MVA) analyses were performed using the Cox proportional hazards model to identify factors predictive for local control and OS.
Results: 113 patients were identified. The median time from brain metastasis diagnosis to surgery was 11 days (IQR: 4-35 days). The median number of brain metastases per patient was 1 (range: 1-13). 31 patients received aRT to the surgical cavity while 82 did not. There were no significant baseline differences between the two cohorts. The median time from surgery to post-op RT start was 46 days (range: 22-95 days). The median BED delivered to the aRT cohort was 47.25 Gy₂₀ (IQR: 39.0-47.25 Gy₂₀). At a median follow up of 6.6 months (range: 0.2-69.6 months), 12-month local control was 69.7% (95% CI: 50.9-88.5%) for the aRT cohort and 31.6% (95% CI: 18.1-45.1%) for the non-aRT cohort (P < 0.001). 12-month distant intracranial control was 44.4% (95% CI: 26.0-62.8%) for the aRT cohort and 46.2% (95% CI: 30.1-62.3%) for the non-aRT cohort (P = 0.9). The 12-month OS was 61.3% (95% CI: 44.2-78.4%) for the aRT cohort and 32.4% (95% CI: 22.2-42.6%) for the non-aRT cohort (P < 0.03). Cause of death analysis will be included in the final presentation. En bloc resection (P < 0.05, HR 0.48, 95% CI: 0.24-0.99) and aRT (P < 0.001, HR 0.26, 95% CI: 0.13-0.53) were predictive of local control on MVA. There was no difference in local control (P = 0.4) or OS (P = 0.4) between aRT patients and the subset of non-aRT patients who had en bloc resection. Age, ECOG, KPS, Charlson Comorbidity Index, and aRT were predictive of OS on UVA, but only aRT remained significant on MVA (P < 0.02, HR 0.57, 95% CI: 0.36-0.90). 4 patients in the aRT cohort developed RN (13%). No grade 3 or higher toxicities were reported.
Conclusion: In this population-based analysis of the patients who underwent surgical resection of brain metastasis, the subset who underwent post-operative radiation had higher local control and overall survival. A low rate of symptomatic radiation necrosis was associated with aRT. Future research could explore options to safely de-escalate aRT for patients who had en bloc resection.