How long would you wait after a cycle of IT MTX to treat a spinal lesion causing cord compression in a patient with stage IV DLBCL?  

Intrathecal methotrexate has biphasic half-lives of about 5 hours and 14 hours (Bleyer, Cancer Treat Rep 1977). ILROG recommends typically waiting minimum interval 2 weeks between last IT or high-dose IV methotrexate before starting CNS radiotherapy for CNS leukemia, but urgent radiotherapy may be c...