ROLE AND TIMING OF CAVITY-BOOST RADIOTHERAPY FOLLOWING SURGICAL RESECTION OF BRAIN METASTASES: A 5-YEAR, INTERIM ANALYSIS

Abstract AIMS Postoperative cavity-boost radiotherapy offers good local control and reduced neurocognitive side-effects, when compared to WBRT. However, studies have failed to demonstrate significant overall survival (OS) benefit. Fur- thermore, optimal timing and impact on quality of life remains debated. Our study aims to investigate the role and timing of cavity-boost radiotherapy on survival, local recurrence and functional outcomes in patients undergoing surgical resection of brain metastases. METHODS 163 patients (M:64, F:99) with histologically confirmed brain metastases receiving surgical treatment from 2016- 2021 at a tertiary neurosurgical centre were included. Primary tumour, staging, total intracranial metastases, steroid treatment, KPS, operation details and local recurrence were collected. Univariate testing was performed and OS Kaplan-Meier Curves were compared using the Logrank test or Restricted Mean Survival Time (RMST) where there was evidence of non-proportional hazards, verified with Schoenfield testing. RESULTS OS was significantly improved with patients who received cavity-boost radiotherapy at any interval post- operatively (n=50, 31%) – 1-year OS: 40% versus 22% (p<0.05). Cumulative average OS benefits were significant at: 1-year = 2 months (p<0.001), 2-year = 3.85 months (p < 0.01), 3-year =4.94 months (p<0.05) and 4-year = 5.56 months (p=0.06). 1-year local recurrence was significantly reduced – 15% versus 37% (p<0.05). Postoperative KPS>70 was more likely with cavity boost (93.87% versus 79.4%, OR = 3.91, 95% CI: 1.10 - 21.65, p<0.05). Time to local recurrence was significantly improved when patients received cavity-boost radiotherapy within 45 days of surgery (p < 0.0001). Schoenfield Individual Testing demonstrated a significant increasing risk to OS the longer the interval between surgery and cavity-boost (p<0.001); but an absolute interval cut-off was not determinable. CONCLUSION Cavity boost to operated metastases confers survival benefit, functional improvement and reduces local recur- rence. This is more effective if timed prior to local recurrence and if cavity-boost is given sooner rather than later after surgery.