REF022 - Thyroid Metastases Imaging (I123 Whole Body Scan)

See REF000 - Referring to Nuclear Medicine (NLAG) for details on how to refer.

The main function of the thyroid gland is to concentrate and organify inorganic iodine, to store the iodinated compounds and then release them as active hormones into the circulation. Iodine-123 is an iodine radiopharmaceutical appropriate for thyroid imaging. Iodine-123 is therefore also able to determine the presence and extent of residual functioning thyroid tissue shortly post-thyroidectomy and, after I-131 ablation, to detect the presence and location of functioning thyroid cancer, recurrences and/or metastases.

• The referrer may be any UK registered medical practitioner currently employed in Secondary Care.
• Referrals from Primary Care will be accepted if the investigation has been suggested by a a Secondary Care Specialist or a Consultant Radiologist in a report from a previous investigation; or following discussion with a Consultant Radiologist. Details of such suggestions or discussions should be included on the request form.

• Sodium chloride for parenteral use (0.9% w/v).

• Patients should be asked to follow a low iodine diet for 2 weeks prior to imaging, ideally to achieve a 24 hour urine output of less than 50mcg of iodine, although this need not be measured on a routine basis. ^[1][2]
• Leave at least 8 weeks between administration of iodinated contrast media (as used in CT and X-ray procedures) and administration of the I-123^[2]
• Avoid iodine medications containing iodine (e.g. antiseptics, eye drops, iodinated multivitamins or mineral supplements) for a minimum of 4 weeks^[4],
• TSH should be elevated to greater than 30mIU/l. This can be achieved by withdrawing T4 for four weeks prior to imaging, with T3 replacement for two weeks and no hormone replacement for a further two weeks; or by administration of thyrogen on the two days before the administration of the I-123. ^{[1] [2]}.
  • The referrer must advise whether to use hormone withdrawal or thyrogen stimulation.
• Amiodarone can affect the uptake of radioiodines. If the patient is taking Amiodarone, this must be discussed with the ARSAC licence holder prior to administration. Note that amiodarone may have to be withdrawn for 12 months to ensure optimal conditions for I-131 ablation therapy.