How to prepare a patient with Papillary Thyroid Cancer (PTC) for Radioactive Iodine (RAI) therapy?

Preparing a Patient with Papillary Thyroid Cancer for RAI Therapy

Pre-RAI Risk Stratification

Before initiating RAI preparation, you must first determine if the patient actually needs RAI therapy based on their risk category. 1

• High-risk patients (T3-T4 tumors, extrathyroidal extension, lymph node metastases, incomplete resection, or distant metastases) should receive RAI at 100-200 mCi (3.7-7.4 GBq) 2, 1
• Intermediate-risk patients (T1 >1 cm or T2 tumors, aggressive histology, multifocal disease, or vascular invasion) generally require RAI at ≥100 mCi with either rhTSH or withdrawal 2, 1
• Low-risk patients (T1-T2, favorable histology, complete resection) may receive optional RAI at 30-100 mCi, with preference for 30 mCi if given 1, 3
• Very low-risk patients (unifocal T1 ≤1 cm, intrathyroidal, no aggressive features) should NOT receive RAI 1, 3

TSH Stimulation Method Selection

The preferred method for RAI preparation is recombinant human TSH (rhTSH/Thyrogen) rather than levothyroxine withdrawal, as it achieves equivalent efficacy while avoiding hypothyroid symptoms. 1, 3

rhTSH (Thyrogen) Protocol - Preferred Method

• Administer Thyrogen 0.9 mg intramuscularly on Day 1 and Day 2 3
• Give RAI on Day 3 (24 hours after the second Thyrogen injection) 3
• Patient continues levothyroxine throughout preparation, maintaining euthyroid state 1, 3
• This method achieves TSH levels >30 mIU/L, which is the target for adequate RAI uptake 3
• rhTSH is equally effective as withdrawal even in patients with lymph node metastases (N1 disease) 4 and distant metastases 5, 6

Levothyroxine Withdrawal - Alternative Method

• Discontinue levothyroxine for 3-4 weeks to achieve endogenous TSH elevation >30 mIU/L 2
• This method is reserved for patients with hypopituitarism (who cannot produce endogenous TSH) or when rhTSH is contraindicated or unavailable 2
• Withdrawal causes significant hypothyroid symptoms and reduced quality of life compared to rhTSH 1

Pre-RAI Dietary Preparation

Institute a low-iodine diet 1-2 weeks before RAI administration to deplete thyroid tissue iodine stores and maximize RAI uptake 2

• Avoid iodized salt, seafood, dairy products, egg yolks, and iodine-containing supplements
• This applies regardless of whether using rhTSH or withdrawal preparation 2

Timing Considerations

RAI therapy should be administered 2-12 weeks post-thyroidectomy to allow adequate healing while maintaining optimal conditions for remnant ablation 3

Risk-Specific RAI Dosing

Once TSH stimulation is achieved, the RAI dose depends on risk category:

• High-risk or metastatic disease: 100-200 mCi (3.7-7.4 GBq) 2, 3
• Intermediate-risk: ≥100 mCi (3.7 GBq) 1, 3
• Low-risk: 30-100 mCi, with strong preference for 30 mCi when using rhTSH 1, 3

Critical Contraindications

RAI is absolutely contraindicated during pregnancy and breastfeeding 3

• Verify negative pregnancy test in women of childbearing potential before RAI administration
• Advise contraception for 6-12 months post-RAI 3

Post-RAI Management Planning

After RAI administration, patients require:

• TSH suppression therapy with levothyroxine initiated immediately, with target TSH based on risk and response 1, 7
• High-risk patients with persistent disease: TSH <0.1 mIU/L 1, 7
• Intermediate-risk with biochemical incomplete response: TSH 0.1-0.5 mIU/L 1, 7
• Low-risk with excellent response: TSH 0.5-2.0 mIU/L 1, 7

Common Pitfalls to Avoid

Do not use rhTSH preparation in patients who have not undergone total thyroidectomy, as the large thyroid remnant will take up excessive RAI and reduce delivery to metastatic sites 3

Do not delay RAI beyond 12 weeks post-thyroidectomy in high-risk patients, as this may allow disease progression 3

Do not use withdrawal preparation when rhTSH is available, especially in elderly patients or those with cardiovascular disease, as withdrawal significantly increases morbidity without improving outcomes 1, 5, 4, 6