Leptomeningeal seeding in patients with brain metastases treated by gamma knife radiosurgery.

To characterize the development of leptomeningeal seeding (LMS) in patients with brain metastases after gamma knife radiosurgery (GKRS). Eight hundred and twenty-seven patients that underwent GKRS as a part of an initial treatment plan for brain metastases between January 2002 and December 2010 were included in the study. Six hundred and fifty patients were treated with GKRS alone and 177 patients received GKRS combined with upfront whole brain radiation therapy (WBRT). Actuarial curves for overall survival (OS) and the development of LMS were plotted using the Kaplan-Meier method. Median overall survival for all patients was 55 weeks (95 % CI, 47.8-62.2), and the overall incidence of LMS was 5.3 %. The actuarial rates for LMS at 6 and 12 months were 3.1 and 5.8, respectively. Uni- and multivariate analysis suggested that breast cancer and a large number of metastases (n ≥ 4) are significant risk factors of LMS (P < 0.05). Regarding treatment modalities, the addition of WBRT was found to have a significant impact on lowering the risk of LMS by multivariate analysis (P = 0.045). LMS is an important pattern of CNS failure. The risk of LMS following GKRS may be associated with multiple lesions, breast cancer, and the omission of WBRT. Additional data from large-scale, randomized controlled trials are required to identify risk factors associated with the LMS more accurately.