Phase 1 FLT (thymidine analog PET tracer) vs CSE-MRI (water–fat chemical shift) for active marrow mapping

University of Wisconsin–Madison is running this small, paired-imaging study in men with metastatic PSMA-positive castration-resistant prostate cancer who are already scheduled for 177Lu-PSMA radiopharmaceutical therapy (Pluvicto, Novartis). The purpose is to test whether chemical shift-encoded MRI (CSE-MRI)—which quantifies marrow fat fraction via water–fat chemical shift—can distinguish active (red) versus inactive (fatty/yellow) marrow as accurately as FLT PET, where 18F-fluorothymidine (a thymidine analog) serves as a proliferation tracer. Participants undergo same-session PET/MR on a GE SIGNA PET/MR scanner within ~7 days before their first 177Lu-PSMA dose, enabling a head-to-head comparison in the same patient rather than across separate visits. After treatment, standard-of-care serial SPECT/CT timepoints are collected to support marrow dosimetry context and therapy monitoring. Clinically, today’s care for mCRPC includes androgen-axis agents (abiraterone/enzalutamide), taxane chemotherapy, PARP inhibitors for select DNA-repair–altered tumors, and PSMA-targeted radioligand therapy; this study’s commercial/scientific angle is lowering barriers to patient-specific marrow dosimetry by replacing a PET tracer workflow with an MRI-derived surrogate.