Theranostics in Nuclear Medicine: Historical, Regulatory, and Evidence Context for the Practicing Nuclear Medicine Physician.

Theranostic radiopharmaceutical therapy has moved from niche practice to mainstream oncology, anchored by approvals of lutetium Lu 177 dotatate for somatostatin receptor-positive neuroendocrine tumors and lutetium Lu 177 vipivotide tetraxetan for PSMA-positive prostate cancer. Yet the field's future depends on rigorous clinical trial design, realistic operational planning, and workforce readiness. This review summarizes how theranostics evolved, outlines current regulatory and trial-design yardsticks (including dose optimization and expectations for assessment of late-toxicity), and provides a practical framework for nuclear medicine physicians to assess protocols and prepare their practices for expanding indications and combinations.