Intrathecal Injection Pemetrexed And Bevacizumab in Patients With Leptomeningeal Metastases in NSCLC

Intrathecal pemetrexed 50mg,twice per week (d1, d8) for 1 week, then once per 4 weeks

Intrathecal bevacizumab, once (d8)for 1 week, then once per 4 weeks.The initial dose of intrathecal bevacizumab is 5 mg, escalated to 10 mg, and then 25 mg, and then 37.5mg, and then 50mg.