This is an open-label, multicenter, Phase 1 study to determine the safety and efficacy of multiple doses at defined intervals of rhenium (186Re) obisbemeda (rhenium-186 nanoliposome, 186RNL) administered via intraventricular catheter for any primary solid tumor cancer with leptomeningeal metastases to identify an MTD/MFD for a given dose, interval duration, and number of doses.