What is the procedure for Radioactive Iodine Uptake (RAIU) treatment?

Radioactive Iodine Treatment Procedure

Radioactive iodine (RAI) treatment is administered 2-12 weeks post-thyroidectomy using 30-200 mCi of I-131, with the dose determined by clinical indication (ablation vs. treatment of residual/metastatic disease), preceded by TSH stimulation via either recombinant human TSH (rhTSH) injection or thyroid hormone withdrawal. 1

Pre-Treatment Preparation

TSH Stimulation (Required for Effective Treatment)

The preferred method is recombinant human TSH (rhTSH) administration while the patient continues levothyroxine therapy 1:

• Administer 0.9 mg rhTSH intramuscularly for two consecutive days 2
• This method demonstrates equal efficacy to thyroid hormone withdrawal but with better patient acceptance and quality of life 1
• Blood sampling for thyroglobulin measurement occurs 72 hours after the second injection 2

Alternative method: Thyroid hormone withdrawal (THW) 1:

• Discontinue levothyroxine for 3-4 weeks to achieve TSH >25-30 mIU/L 2
• Use this approach when there is high likelihood of requiring therapy 1
• Results in hypothyroid symptoms but may be preferred in certain high-risk scenarios 1

Pre-Treatment Assessment

All patients must be examined, and any palpable neck disease should be surgically resected before radioiodine treatment 1:

• Ensure no gross residual disease in the neck 1
• Consider vocal cord assessment if central neck recurrence is suspected 1
• Measure baseline thyroglobulin and antithyroglobulin antibodies 1

Dosing Protocols

For Remnant Ablation (Post-Thyroidectomy)

Low-dose ablation: 30-100 mCi 1:

• Recent evidence supports successful ablation with activities as low as 30 mCi (1110-1850 MBq) 1
• Appropriate for low to intermediate risk patients without known residual disease 1
• Can be administered with rhTSH or withdrawal preparation 1

For Residual or Metastatic Disease

Higher-dose treatment: 100-200 mCi 1:

• Used for suspected or proven radioiodine-responsive residual tumor 1
• For recurrent disease with stimulated thyroglobulin >10 ng/mL, consider 100-150 mCi 1
• Consider dosimetry for distant metastases to maximize dosing 1

For metastatic disease with special considerations 1:

• Brain metastases: Use rhTSH with steroid prophylaxis 1
• Bone metastases: Consider dosimetry to maximize dosing 1
• Repeat RAI administrations every 6-12 months as long as uptake is present 1

Pediatric Adjustments

The administered activity must be adjusted for pediatric patients 1:

• Specific dosing should be calculated based on body weight or body surface area 1

Post-Treatment Protocol

Immediate Post-Treatment

Post-treatment whole body scan (WBS) imaging is performed 1:

• This highly sensitive scan can detect residual thyroid tissue or metastatic disease 1
• Helps guide further management decisions 1

Radiation Safety Measures

Patients must follow radiation safety precautions 3, 4:

• Most radioactivity is excreted via urine 3
• Specific isolation periods depend on dose administered 3
• Special protocols needed for patients who cannot swallow pills, have malabsorption, or are on dialysis 3

Risk-Stratified Indications

RAI is Recommended For 1:

• All patients with known distant metastases 1
• Documented lymph node metastases 1
• Gross extrathyroidal extension regardless of tumor size 1
• Primary tumor >2 cm even without other high-risk features 1
• High-risk patients based on pathology and staging 1

RAI is NOT Recommended For 1:

• Unifocal cancer <1 cm without other higher risk features 1
• Multifocal cancer when all foci are <1 cm without other higher risk features 1
• Very low-risk patients (pT1a, N0/NX) 1

Common Pitfalls to Avoid

Acute complications include 4:

• Nausea and vomiting 4
• Loss of taste (ageusia) 4
• Salivary gland swelling and pain 4
• These can be managed with hydration, sialagogues, and symptomatic treatment 4

Long-term complications to monitor 4:

• Recurrent sialadenitis with xerostomia 4
• Dental caries 4
• Pulmonary fibrosis (with high cumulative doses) 4
• Second primary malignancies 4
• Repeating RAI after cumulative activity of 600 mCi should be individualized 1

Absolute contraindication: Pregnancy 5:

• Must be excluded before treatment 5
• Breastfeeding must be discontinued 6

Special Circumstances

For patients with iodine contamination 7:

• rhTSH can increase thyroid radioactive iodine uptake by 88% in iodine-loaded patients 7
• May salvage treatment in patients with prior iodinated contrast exposure 7

For patients unable to follow standard protocols 3:

• Provider collaboration and treatment customization are critical 3
• Alternative administration routes may be needed for patients who cannot swallow 3
• Modified protocols required for dialysis patients 3