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 considered within 48-72 hours for symptoms (Pinnix, Int J Radiat Oncol Biol Phys 2018). The ILROG extranodal lymphoma guideline doesn't specifically comment on this interval. Three to five of the longer half-lives is about 48-72 hours, so if the patient is stable or responding, then radiotherapy should be delayed at least that long when possible. However, if the patient has true progressive symptomatic cord compression with neurological compromise...