§ Radionuclide:131I t1/2: 8.1 days
§ Energies: 364 keV (g), 606 keV (b−)
§ 131I as sodium iodide capsule or liquid
§ Dose of radioiodine therapy:
§ * 30 – 80mCi 131I as ablative dose for residual thyroid
§ *120 – 150mCi 131I if cervical lymph nodes positive.
§ *150 – 200mCi 131I if metastatic lesions
Method of Administration: Oral (PO) capsule, through straw from
lead container for liquid.
§ (1) Differentiated papillary & follicular cancer (90%).
§ (2) Medullary thyroid cancer (6%).
§ (3) Anaplastic cancer (4%).
§ (4) Other tumors (1%).
* Isotopic thyroid scan--------cold nodule.
* Ultrasound solid-----------versus cystic nodule.
* Fine needle aspiration cytology.
§ * Any patient received a dose > 30mCi should be hospitalized
in separate room.
§ * Patient should be fasting 2 – 4 hours before 131I therapy and
2 hours after therapy.
§ * Excess intake of fluid and suck of lemon wedges to decrease
§ * No visitor except for few minutes (no pregnant or children).
§ * Food & drink in disposable containers.
§ * Chick room & laundry for contaminations.
• Ablation of residual functioning thyroid carcinoma.
• Ablation of residual functioning normal thyroid tissue after total
or partial thyroidectomy.
• Pregnancy or nursing.
• Allergy to iodine.
• Iodinated studies under way or performed recently.
• Patient taking thyroid medications or vitamins, or not on low-
• Patient extremely likely to regurgitate dose.
§ Radionuclide:131I t1/2: 8.1 days
§ Energies: 364 keV
§ Radiopharmaceutical: 131I-mIBG (-meta-iodobenzylguanidine).
§ Adult Dose Range: 131I: 500 μCi (18.5 MBq)
§ Method of Administration: Intravenous injected slowly over 5
minutes if possible.
§ Camera: Large field of view.
§ Collimator: Medium energy, general purpose
§ Or medium energy, high resolution.
vRadioactive iodine therapy
§ Dose calculation:
(A) Fixed dose: 10 – 15mCi of 131I.
(B) Multi nodular toxic goiter (Fig. 7.6 B):
§ Scan finding:
§ * Multiple hot and cold nodules.
§ * Suppression of the rest of the gland.
§ * High 131I uptake, high T3,T4.
§ * Main line of treatment is surgery.
§ * Radioiodine in larger doses 15 – 20mCi because of greater radio
resistance in nodular form with small range for β (1 – 2mm).
§ * Hypothyroidism in rare following 131I therapy in multi nodular
(c) autonomous nodule (Fig. 7.6 C)
§ Scan findings:
§ * High radioactivity in the nodule suppressing the rest of gland.
§ * Higher doses of 131I therapy 20 – 30 mCi.
§ * Recovery of the remaining thyroid is seen following 131I
§ Before Day of Injection
§ • Physician instructs the patient to take SSKI (saturated solution
potassium iodide) or Lugol’s solution to block free iodine uptake in
thyroid.This is administered 1 drop, t.i.d., beginning the day
before radiotracer administration and continuing for 6 days after
injection. If there is an allergy to iodine, perchlorate may be used.
§ • Physician instructs the patient to take bisacodyl (e.g., Dulcolax®)
10 mg PO, b.i.d. × 3 days before imaging, to reduce bowel activity.
Patient may be required to take laxatives and/or enemas on
afternoons before imaging days; check with radiologist.
§ • Physician instructs patients with atopic history (genetic
disposition to hypersensitivity or allergy to medications such as
iodine or steroids) to be treated with oral antihistamine (e.g.,
Benadryl® 50 mg)1 hour before injection of radiotracer.
§ Days of Injection
§ • Identify the patient.Verify doctor’s order. Explain the
§ • Obtain signed consent from patient and a prescription for the
§ • Ensure that the patient is not taking the following drugs:
steroids, antihypertensives, reserpine, tricyclic antidepressants,
sympathomimetics (adrenergic, stimulates release of
epinephrine), diuretics as per physician’s order. Ideally, no
medications for 2–3 weeks before the examination (see Drugs
§ [standing] hypotension).These occur within the adrenal
medulla and are frequently associated
§ with hereditary multiple endocrine neoplasia (MEN)
types 2A and 2B, neurofibromatosis, von
§ Hippel-Lindau disease, Carney’s triad, and familial
§ • Localization of site(s) of hormonal overproduction.
§ • Detection and localization of neuroectodermal (nerve
§ • Paragangliomas (tumors of the adrenal medulla,
chromaffin cells, and the paraganglia)
§ • Detection and localization of neuroblastomas
(malignant hemorrhagic tumors of cells resembling
neuroblasts of the sympathetic system, especially the
adrenal medulla, and usually occurring in childhood).
§ • Detection and localization of other neuroendocrine
tumors that share the property of amine precursor
uptake in decarboxylation (APUD), such as:
§ • Carcinoid (argentaffin cells of the intestinal tract, bile
ducts, pancreas, bronchus, or ovary that secrete
§ Detection and localization of benign and malignant
intra-adrenal and extra-adrenal pheochromocytomas
(usually benign chromaffin cell tumors of the
sympathoadrenal system that produce andsecrete
catecholamines, e.g., norepinephrine and
epinephrine, producing hypertension and orthostatic
• Allergy to iodine may be a consideration, although doses are
• Patient taking interfering medications.