MIBG (metaiodobenzylguanidine) scintigraphy is the preferred functional imaging for pheochromocytoma. Which radiolabelled isotope is used for MIBG therapy (as opposed to diagnosis)?

• A I-123 (123I) for both diagnosis and therapy
• B Tc-99m for therapy due to longer half-life
• C Ga-68 for MIBG therapy via PET platform
• D I-131 (131I) for therapy due to beta emission ✓

Explanation

MIBG imaging uses I-123 (123I-MIBG) for diagnosis: it emits 159 keV gamma rays ideal for gamma camera imaging with a 13-hour half-life and low radiation dose. MIBG therapy uses I-131 (131I-MIBG): iodine-131 emits beta particles (maximum energy 0.6 MeV) that cause local tissue destruction in catecholamine-secreting tumours (pheochromocytoma, paraganglioma, neuroblastoma) after selective cellular uptake via norepinephrine transporter. I-131 also emits gamma rays (364 keV) used for post-therapy dosimetry imaging. The long half-life of I-131 (8 days) allows sustained therapeutic beta irradiation.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.