RADI-41. CLINICAL OUTCOMES FOLLOWING RAPID DELIVERY SINGLE ISOCENTER RADIOSURGERY FOR FIVE OR MORE BRAIN METASTASES: VOLUMETRIC MODULATED ARC THERAPY VS. DYNAMIC CONFORMAL ARC

BACKGROUND: Recent advances in the delivery of stereotactic radiosurgery (SRS) has led to wider availability and use of this technology. The ability to rapidly delivery radiosurgery to multiple targets utilizing single-isocenter techniques represents an additional step forward for these otherwise time-consuming therapies. The current retrospective study measures and compares clinical outcomes in patients with 5 or more brain metastases treated using a single-isocenter RapidArc (RA) volumetric-modulated arc therapy (VMAT) approach, with those treated using a single-isocenter dynamic conformal arc (DCA) approach. METHODS: We queried retrospectively a radiosurgery database registry of 680 patients from 11/2012- 3/2019. We included patients with 5 or more brain metastases who had documented SRS treatment plans utilizing a single-isocenter approach, either VMAT or DCA. Radiosurgery was delivered using a linac-based platform capable of delivering radiotherapy to multiple simultaneous targets. We obtained information on patient gender, age, number of lesions, primary cancer histology. Patients were separated by collimation plan (VMAT vs DCA); overall survival (OS) was estimated using Kaplan-Meier method. RESULTS: We found 49 patients that met our criteria for inclusion. Median age was 57 yrs. with a majority being females (n=28, 57.2%). Number of targets was between 5 and 20; median number of targets was 7. Most common primary site histology was non-small cell lung (51.0%), followed by breast (14.2%). For DCA collimation group, median OS was 20.5 weeks (95% CI: 12.4, 34.5), with a 6 month OS of 36.0% (95% CI: 19.2%, 54.9%). For VMAT collimation group, median OS was 20.0 weeks (95% CI: 10.8, 46.1), with a 6 month OS of 39.1% (95% CI: 11.3%, N/A). CONCLUSIONS: For patients with 5 or more brain metastases treated with rapid delivery single-isocenter radiosurgery, no significant difference in survival outcomes were demonstrated between DCA and VMAT collimation techniques.