REF022 - I123 Whole Body Imaging

The purpose of this document is to assist clinicians in deciding on the appropriateness of the Nuclear Medicine procedure and to give guidance on the mechanism of referral.

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. It can also be used for looking for sites of ectopic thyroid tissue outside of the neck/upper thorax.

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.

Referring clinicians are reminded of the requirement to avoid unnecessary exposure to ionising radiation. The investigation may already have been requested at this hospital or elsewhere and clinicians are asked to be particularly vigilant to ensure that their request is not a double request.

Requests will only be accepted if the diagnostic question fulfills one of the referral criteria below. Appropriate clinical information must be supplied to allow the investigation to be justified. It is not acceptable to simply request the investigation without appropriate clinical information.

Requests will be returned to the referrer if:

• The diagnostic question is unclear.
• The diagnostic question cannot be answered by the investigation.
• Insufficient clinical information is supplied to justify the investigation.

Requests should be submitted on the orange stripe NUCLEAR MEDICINE (ISOTOPE SCAN) request form. Patient details, Investigation required and Reason for Test/Diagnostic Question should be fully and appropriately completed and the form signed.

Note the requirement for Patient Preparation below

Sufficient clinical information must be provided to justify the investigation proceeding.

• 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.