RDTA-02 FRACTIONATED REPEAT GAMMA KNIFE STEREOTACTIC RADIOSURGERY FOR LOCALLY RECURRENT BRAIN METASTASES

Abstract The proportion of individuals surviving for relatively prolonged periods of time with metastatic disease of the central nervous system (CNS) is increasing. Consequently, local disease recurrence of previously treated CNS lesions has become more prevalent. Therefore, selection of an appropriate salvage therapy is necessary. Stereotactic radiosurgery (SRS) is a highly conformal radiation modality which may impart excellent local control (LC) with minimal treatment related toxicity. We conducted a retrospective chart of review of patients with radiographic evidence of metastatic brain lesions undergoing repeat fractionated SRS for locally recurrent lesions. Primary endpoints were LC and toxicity as defined by CTCAE V.5. Secondary endpoints included distant control (DC), and overall survival (OS). Utilizing the Kaplan-Meier method we analyzed the time to LC, DC, and OS for each recurrent lesion treated with SRS. Finally, a Cox-proportional hazard model analyzed the relationship between independent variables and the time to local failure. Our cohort consisted of 45 patients with a median age of 62 years (IQR: 56.3-68.0). The median lesion volume at the time of repeat SRS was 3.3 cm3 (IQR: 0.75-8.8). Patients were treated with a median prescription dose of 27.0 Gy (IQR: 25.0-30.0) over a median of 5 fractions (range: 1-5). Actuarial LC rates at 3,6,12, and 24 months were: 79.4%, 72.2%, 61.7%, and 54.9% respectively. There was no grade 3 or higher treatment related toxicity. On univariate analysis KPS >70 (HR: 0.17, 95% CI: 0.06-0.5), p=0.001) and the presence of extracranial disease at SRS (HR: 2.7, 95% CI: 1.04-6.97, p=0.04) were significantly associated with overall survival. The local control rate in our series is consistent with previous literature. Additionally, predictors of improved survival in this patient population are good performance status and systemic disease control at the time of SRS.