RadteraThyroid Cancer I-131 Therapy and Post-Therapy Scan
NM+ ContrastHead & Neck
Indications
- Remnant ablation after thyroidectomy for differentiated thyroid cancer
- Treatment of residual/metastatic papillary or follicular thyroid carcinoma
- Post-therapy whole-body scan to detect residual/metastatic disease
Patient prep
- Low-iodine diet ~1-2 weeks before therapy
- TSH stimulation: thyroid hormone withdrawal (~4-6 weeks) OR recombinant human TSH (Thyrogen) injections to raise TSH >30 mIU/L
- Avoid recent iodinated contrast (4-6 weeks)
- Negative pregnancy test required; stop breastfeeding
- Review radiation safety/isolation instructions per NRC
Contrast
AgentI-131 sodium iodide
RouteOral (capsule/liquid)
DoseRemnant ablation ~30-100 mCi (1.1-3.7 GBq); metastatic disease 100-200 mCi or dosimetry-based; diagnostic scan 1-5 mCi I-123 or 1-5 mCi I-131
TimingPost-therapy whole-body scan typically 5-8 days after therapy dose
Technique
- High-energy collimator for I-131 (364 keV)
- Whole-body anterior/posterior sweep +/- SPECT/CT for localization
- Diagnostic pre-therapy scan may use I-123 to avoid stunning
Series / Sequences
| # | Series / Sequence | Plane | Notes |
|---|---|---|---|
| 1 | Diagnostic whole-body scan (optional) | Anterior/posterior | I-123 preferred to avoid stunning; assesses remnant/uptake |
| 2 | Post-therapy whole-body scan | Anterior/posterior +/- SPECT/CT | 5-8 days post-dose; highest sensitivity for metastases |
Key points
- TSH must be elevated (>30) for optimal iodine uptake by thyroid tissue
- Low-iodine diet maximizes tumor avidity
- Strict radiation safety / NRC patient release criteria and isolation precautions apply
- Stunning concern with diagnostic I-131; prefer I-123 for pre-therapy scans
- Sialadenitis, dry mouth, transient marrow suppression are known side effects; encourage hydration and sialagogues
References
• SNMMI Procedure Standard for Therapy of Thyroid Disease with I-131
• ATA Management Guidelines for Differentiated Thyroid Cancer
• NRC 10 CFR 35.75 patient release criteria
• Radiopaedia: Radioactive iodine therapy link
• ATA Management Guidelines for Differentiated Thyroid Cancer
• NRC 10 CFR 35.75 patient release criteria
• Radiopaedia: Radioactive iodine therapy link
Source: Researched — verify against your institution
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Reference template — verify and adapt to your scanner, vendor and institution before clinical use. Not a substitute for clinical judgment.