What is the recommended protocol for a MIBG (Metaiodobenzylguanidine) scan in patients with suspected or confirmed neuroblastoma?

MIBG Scan Protocol for Neuroblastoma

The recommended protocol for MIBG scanning in neuroblastoma patients includes using 123I-MIBG as the primary imaging agent, with administration of 80-400 MBq (dose adjusted by weight for pediatric patients), thyroid blockade, medication discontinuation, and imaging at 20-24 hours post-injection with both planar and SPECT/CT techniques. 1

Preparation Protocol

Thyroid Blockade

• Stable iodine administration is required to block thyroid uptake
• Begin 1 day before tracer injection and continue for 3 days for 123I-MIBG 1
• Potassium perchlorate may be substituted for iodine in iodine-allergic patients (400–600 mg/day, starting 4 hours before injection and continuing for 2 days) 1

Medication Discontinuation

• Many medications interfere with MIBG uptake and must be discontinued 1
• Most interfering medications should be withheld for 1-3 days prior to scanning 1
• Labetalol requires a longer withdrawal period of 10 days 1
• Depot forms of antipsychotics require withdrawal 1 month before scanning 1
• Common interfering medications include:
  • Opioids
  • Tricyclic antidepressants
  • Sympathomimetics
  • Antipsychotics
  • Antihypertensive agents

Administration Protocol

Dosing

• For pediatric patients: 80-400 MBq of 123I-MIBG, scaled to body weight according to EANM Paediatric Task Group schedule 1
• Slow intravenous injection over at least 5 minutes to minimize rare adverse events 1

Imaging Timing and Technique

• Imaging performed 20-24 hours after tracer injection 1
• Complete imaging protocol includes:
  • Anterior and posterior planar static images of head/neck, thorax, abdomen, and pelvis (10-15 minutes per image) 1
  • SPECT or SPECT/CT over regions showing pathological uptake 1
  • Medium-energy collimators preferred to reduce septal penetration 1

Interpretation and Scoring

• Semi-quantitative scoring of tracer uptake is essential for standardized interpretation 1
• Two validated scoring systems:
  • Modified Curie score (used in North America) 1
  • SIOPEN score (used in Europe) 1
• SPECT/CT improves sensitivity and anatomic localization of disease sites 1

Special Considerations

Non-MIBG Avid Disease

• Approximately 10% of neuroblastomas do not accumulate MIBG (false negative) 2
• 18F-FDG-PET imaging should be obtained in patients with MIBG-nonavid disease or suspected mixed-avidity disease 1
• PET/CT or PET/MRI can be useful when MIBG imaging and anatomic imaging do not correlate 1

Newer PET Tracers

• 124I-MIBG PET/CT has shown superior lesion detection compared to conventional 123I-MIBG scanning 3
• PET-based catecholaminergic tracers offer advantages including faster image acquisition, less need for sedation, and single-day examination 1

Radiation Safety

• Effective dose: 0.013 mSv/MBq for 123I-MIBG in adults, 0.037 mSv/MBq in children 1
• Breast feeding should be discontinued for at least 2 days after 123I-MIBG scintigraphy 1
• Special considerations for renal insufficiency patients as MIBG is not cleared by dialysis 1

Clinical Integration

• MIBG scanning is essential for initial staging, response assessment, and disease surveillance 1, 4
• For high-risk disease, full disease evaluation (including MIBG scan) is recommended at end of induction, start of post-consolidation, and end of therapy 1
• MIBG scan findings can change disease staging and subsequent therapy decisions 5
• Sensitivity of 123I-MIBG scintigraphy ranges from 88-100% with specificity of 83-89% 2, 6

By following this standardized protocol, MIBG scanning provides critical information for accurate staging, treatment planning, and response assessment in neuroblastoma patients, directly impacting morbidity, mortality, and quality of life outcomes.