Thyroid Stunning After Diagnostic I-131

D. Thyroid stunning is reduced iodine uptake (and potentially reduced therapy efficacy) in the thyroid remnant caused by prior radiation damage from the diagnostic I-131 dose

Thyroid stunning refers to a transient reduction in iodine uptake (and potentially reduced therapy effectiveness) in thyroid tissue that results from radiation damage inflicted by the diagnostic I-131 dose. Large diagnostic doses (≥3 mCi) can stun the remnant, resulting in lower uptake during subsequent therapy and potentially decreased ablation efficacy. To minimize stunning: (1) use smaller diagnostic doses (≤1–2 mCi I-131) or prefer I-123 for pre-therapy dosimetric scanning; (2) proceed to therapy within 24–72 hours of diagnostic scan; (3) use recombinant TSH (Thyrogen) stimulation with I-123 for the diagnostic scan.