A study in The Journal of Nuclear Medicine reported that circulating tumor DNA profiling can better select patients for radium-223 (^223Ra) radiopharmaceutical therapy in metastatic castration-resistant prostate cancer (mCRPC). The approach aims to identify which patients are most likely to benefit from treatment. By linking ctDNA findings to response selection for ^223Ra, the work moves patient stratification toward a simple blood-based biomarker strategy. For theranostics, that matters because it can reduce exposure in unlikely responders while improving clinical decision-making. If validated in larger cohorts, the biomarker could become part of routine pretreatment workflows for mCRPC management.