Waldenstrom's Macroglobulinaemia Refractory

The goal of this clinical trial is to evaluate whether iopofosine I 131 is more effective than the combination Rituximab-Cyclophosphamide-Dexamethasone (R-CD). The main question the study aims to answer is: • Does iopofosine I 131 work better than R-CD when looking at the length of time during and after the treatment that a patient lives with WM but it does not get worse. Participants will: * Be randomly assigned to received either iopofosine I 131 or R-CD. * If assigned to iopofosine I 131, have it administered via infusion 2 times each cycle for a total of 2 cycles (each cycle is about 3 months long). * If assigned to R-CD, it will be administered for up to six cycles, and each cycle is 3-weeks long * Visit the clinic once every 3 weeks for checkups and testing. * Report any side effects or new medications.