RADI-24. VENTRICULOMEGALY AFTER STEREOTACTIC RADIOSURGERY (SRS) FOR BRAIN METASTASES (BM): A PILOT ANALYSIS OF TWO INSTITUTIONAL EXPERIENCES

INTRODUCTION: Ventriculomegaly, or dilatation of the cerebrospinal fluid (CSF) space, occurs after whole-brain radiation (WBRT) of brain metastasis (BM) patients due to either 1) hydrocephalus or 2) cerebral atrophy from radiation-induced white matter injury. In this study, we examined whether cumulative radiation from repeat stereotactic radiosurgery (SRS) increases the risk of ventriculomegaly. METHODS: Patients were included if they underwent SRS of BM from 2007–2017 and had imaging follow-up. We examined a cohort of 214 patients treated at the University of California San Diego (1,106 BM) and a second cohort of 148 patients (1,760 BM) treated at Karolinska Institutet. Ventriculomegaly was defined according to established morphometric criteria. Patients were grouped according to the development of new ventriculomegaly at last follow-up. Demographic, clinical, and dosimetric factors were compared between groups using univariable and multivariable logistic regressions. RESULTS: In the UCSD cohort, 63 patients (29%) presented with ventriculomegaly before SRS. Of 151 remaining patients with normal ventricular size before first SRS, 30 (20%) developed new ventriculomegaly. The odds of developing ventriculomegaly increased with history of WBRT (OR 5.247, p< 0.001) and trended toward significance with a greater number of SRS treatments (OR 1.296, p=0.075). In the Karolinska cohort, the odds of developing new ventriculomegaly trended towards significance with a greater number of SRS treatments (OR 1.605, p=0.26). To test whether this trend would achieve significance in a larger sample, we repeated the analysis in the combined cohort of 362 patients. The association between number of SRS treatments and developing ventriculomegaly reached significance (OR 1.254, p=0.049). CONCLUSIONS: These pilot findings suggest that cumulative radiation from repeat stereotactic radiosurgery (SRS) potentially increases the risk of ventriculomegaly. Based on our study, a prospective study of >350 patients will be needed to further test this hypothesis.