I-131 Hyperthyroidism Dose Calculator

Calculated (dosimetric) ¹³¹I activity from target dose per gram, gland mass, and 24-hour uptake, with the fixed-activity reference

Evidence BINF#tool#endocrine#therapy#thyroid#i-131

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Estimates the administered ¹³¹I activity for benign hyperthyroidism by the calculated (dosimetric) method: activity scales with the target absorbed dose per gram and gland mass, and inversely with the 24-hour radioiodine uptake. Enter the estimated gland mass (palpation or ultrasound), the measured 24-hour RAIU, and the target dose per gram (institution- and diagnosis-specific — toxic nodular disease is more radioresistant than Graves' and is usually given a higher target). The fixed-activity ranges are shown alongside for comparison. This is an educational estimate for benign disease; differentiated thyroid cancer ablation/treatment uses separate fixed or lesion-dosimetry regimens and is not modeled here.

Calculated ¹³¹I activity — benign hyperthyroidism

Diagnosis (sets a typical target)

Target dose per gram

µCi/g

Estimated gland mass

24-hour RAIU

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administered activity

Calculated method: activity (µCi) = target dose per gram (µCi/g) × gland mass (g) ÷ fractional 24-h RAIU. Typical targets: Graves' ~120–200 µCi/g, toxic nodular disease ~200 µCi/g (more radioresistant). Fixed-activity alternative: Graves' commonly ~10–15 mCi (370–555 MBq); toxic nodular ~15–30 mCi (555–1110 MBq). Calculated and fixed methods have comparable cure rates — method and target are institution- and physician-specific. µCi/g and gland mass are estimates; RAIU is patient-specific. Contraindicated in pregnancy and breastfeeding. Educational estimate only — verify against your written directive and local protocol.

Evidence & sources

BSNMMI procedure standard / EANM guideline — therapy of benign thyroid disease: the calculated (dosimetric) and fixed-activity ¹³¹I methods, and target absorbed dose per gram of thyroid tissue.

BCalculated vs fixed activity — comparable cure rates in benign hyperthyroidism; the target dose per gram and choice of method are institution- and physician-specific.

INFGland mass and target µCi/g are estimates — the definitive prescribed activity is the physician's written directive for the individual patient.