MIBG Therapy Protocol for Patients
The recommended treatment protocol for patients undergoing MIBG therapy includes thyroid blockade with potassium iodide/iodate before treatment, administration of 7.4-11.2 GBq of 131I-MIBG at 3-6 month intervals, and treatment in a dedicated shielded isolation facility with appropriate radiation safety precautions. 1
Patient Selection and Preparation
Selection Criteria
- Confirmation of abnormally increased uptake of the corresponding imaging agent (123I-MIBG) at all known tumor sites 1
- Reasonable bone marrow reserve and adequate renal function 1
- Patient should be continent and self-caring to minimize radiation exposure to staff 1
Contraindications
- Pregnancy and breastfeeding 1
- Myelosuppression 1
- Renal failure (glomerular filtration rate <40 ml/min) 1
Pre-Treatment Medication Management
Thyroid Blockade: Administer potassium iodide/iodate before treatment to prevent thyroidal uptake of free radioiodine 1
- For 123I-MIBG: Start thyroid blockade before treatment and continue for 2 days 1
- For 131I-MIBG: Start thyroid blockade before treatment and continue for 5 days 1
- For iodine-allergic patients: Potassium perchlorate may be substituted (400-600 mg/day starting 4 hours before injection and continued for 2 days) 1
Discontinue Interfering Medications: 1
- Most interfering medications should be withheld for 1-3 days prior to treatment
- Labetalol must be stopped 10 days prior to MIBG administration
- Depot forms of antipsychotics require 1-month withdrawal period
- Common interfering medications include:
- Opioids
- Tricyclic antidepressants
- Sympathomimetics
- Antipsychotics
- Antihypertensive agents
Treatment Administration
Dosage and Administration
- Therapeutic Dose: 7.4-11.2 GBq (200-300 mCi) of 131I-MIBG administered at 3-6 month intervals 1
- Administration Method: Intravenous injection over at least 5 minutes to minimize adverse events 1
- Treatment Setting: Dedicated, shielded isolation facility for radiation protection 1
Treatment Schedule
- Typical treatment involves multiple doses (average 3.3 doses) 2
- Intervals between treatments typically 3-6 months 1
- Cumulative activity may range from 12-18 GBq 1
Monitoring and Management During Treatment
Side Effects Management
- Monitor for rare adverse events including tachycardia, pallor, vomiting, and abdominal pain 1
- Administer prophylactic anti-emetics for nausea and vomiting 1
- Manage pain due to radiation edema with corticosteroids and analgesics 1
Radiation Safety Considerations
- Patient should remain in a dedicated, shielded isolation facility 1, 3
- Maintain radiation exposure to public access areas below 2 microsieverts per hour 3
- Staff should follow ALARA (As Low As Reasonably Achievable) principles for radiation exposure 3
- Proper waste storage and disposal procedures must be followed 3
Post-Treatment Monitoring
Expected Toxicity
- Temporary myelosuppression occurring 4-6 weeks after therapy is the most common toxicity 1
- Myelosuppression is more severe in patients with:
- Bone marrow infiltration by tumor
- Previous chemotherapy
- Previous radionuclide therapy 1
- Myelosuppression is cumulative and may be dose-limiting after repeated treatments 1
Follow-up Evaluations
- Monitor blood counts for myelosuppression
- Evaluate tumor response 3-6 months after treatment using RECIST criteria 4
- Monitor hormone levels and blood pressure in functioning tumors 4, 5
Treatment Efficacy and Outcomes
Expected Response Rates
- Symptom control in up to 80% of patients 1
- Objective tumor response in 30% of patients 2
- Hormonal response in 45% of patients 2
- Five-year survival rate of approximately 60% 1
- Partial objective responses of 10-15% 1
- Survival benefit appears related to symptom response and initial administered activity 1
Special Considerations
- Patients with metastases to soft tissue have more favorable responses than those with bone metastases 2
- For patients with high tumor burden or rapidly progressive disease, consider alternative or additional therapies such as chemotherapy with cyclophosphamide, vincristine, and dacarbazine (CVD) 1
- For patients with somatostatin receptor-positive tumors, consider peptide receptor radionuclide therapy (PRRT) as an alternative 1
Pitfalls and Caveats
- Ensure complete thyroid blockade to prevent thyroid damage
- Carefully screen for and discontinue all medications that may interfere with MIBG uptake
- Monitor for cumulative myelosuppression which may limit the number of treatments
- Complete radiological response is rare, with most patients achieving stable disease 1
- Hormone response is not associated with survival gain 1