01
Hyperthyroidism — 5 to 15 mCi typical, calculated or fixed activity
Graves' disease and toxic multinodular goitre use small-to-mid activities. Calculated-activity approach: A (mCi) = target dose (μCi/g) × gland mass (g) / [24-hour thyroid uptake (%) × 1000]. Fixed-activity approach (widely used for logistical simplicity): 10 – 15 mCi for Graves', 15 – 25 mCi for toxic nodular disease. EANM 2022 accepts either method; ATA 2015 has weak preference for calculated approach in Graves'.
Source: EANM procedure guideline for I-131 therapy (2022); ATA 2015 Adult Thyroid Nodules + DTC Management Guidelines.
02
DTC ablation — remnant ablation typically 30 to 100 mCi
Post-thyroidectomy remnant ablation for low-risk differentiated thyroid cancer uses 30 mCi (ATA 2015 low-risk) to 100 mCi (intermediate-risk, historical practice). The 2015 ATA guidelines moved toward the lower 30 mCi dose for low-risk DTC after the ESTIMABL / HiLo randomised trials showed non-inferiority — a meaningful change from prior practice. Intermediate + high-risk DTC still receive 100 – 200 mCi depending on stratification.
Source: ATA 2015 Management Guidelines §Recommendation 51; ESTIMABL (Schlumberger 2012) + HiLo (Mallick 2012) trials.
03
DTC persistent / metastatic disease — 100 to 200 mCi, dosimetry-guided in centres capable
Persistent locoregional disease or distant metastases (lung, bone) receive 100 – 200 mCi empirically. Dosimetry-guided activity selection (blood dosimetry per Benua-Leeper, or lesion dosimetry) is recommended by EANM 2022 for centres with the imaging + calculation capability, with the goal of maximising tumour dose while keeping the whole-blood dose < 2 Gy and lung-retention 48-hour < 80 mCi to avoid pulmonary toxicity.
Source: EANM 2022 §Dosimetry-guided activity selection; Benua RS + Leeper RD historical dosimetry method.
04
Patient preparation — TSH stimulation + low-iodine diet before the dose
For DTC ablation: TSH stimulated to > 30 mIU/L either by 4 – 6 week thyroid hormone withdrawal or by recombinant human TSH (Thyrogen) protocol — rhTSH now preferred for low-risk ablation to spare patients hypothyroid symptoms. Low-iodine diet (< 50 μg iodine/day) for 1 – 2 weeks pre-therapy improves I-131 uptake; iodine-containing medications and contrast studies must be interrupted long enough (2 – 8 weeks depending on agent) that the iodine load has cleared.
Source: ATA 2015 §Recommendations 49–50; EANM 2022 §5 Patient preparation.
05
Hospital-stay logic — outpatient at low activity, admission at high
Under AERB / IAEA SRS 63, patients treated with < 30 mCi can typically be released outpatient with radiation-protection advice to household + travel. Above 30 mCi (India varies by state) or when a patient's living situation cannot support home isolation (young children, pregnancy in household, shared bathroom), the patient is admitted to a dedicated I-131 therapy ward and released once contact dose rate at 1 m falls below the AERB threshold (typically ~5 μSv/h). The ward requires shielded walls, dedicated waste tank for excreta, and RSO-signed release documentation per admission.
Source: IAEA Safety Reports Series No. 63 (2009); AERB SC/MED-4 §Therapy ward requirements; ICRP Publication 94.
