I-131 Thyroid Imaging Guidelines

Standard Approach

The American College of Radiology recommends I-131 whole-body scintigraphy for post-treatment evaluation of differentiated thyroid cancer patients after thyroidectomy and radioiodine ablation 1, 2
The scan is interpreted qualitatively by visual assessment of uptake patterns rather than through SUV quantification, as recommended by the American College of Radiology 1
For patients who have undergone thyroidectomy and radioiodine ablation, any visible uptake in the thyroid bed on follow-up scans may indicate residual thyroid tissue, according to the American College of Radiology 1

In diagnostic thyroid scanning, uptake is typically measured as a percentage of the administered dose rather than as an SUV, as stated by the American College of Radiology 3

I-131 whole-body scans are performed after radioiodine therapy to evaluate for residual disease, as recommended by the American College of Radiology 1
In intermediate and high-risk DTC patients, whole-body scintigraphy has a role in evaluating initial response to radioiodine ablation, according to the American College of Radiology 1
If there has been excellent response to therapy, WBS is usually not performed for ongoing surveillance, as stated by the American College of Radiology 1

For routine surveillance of low-risk patients without suspicion for recurrence and normal thyroid ultrasound, I-131 whole-body scanning is not utilized, as recommended by the American College of Radiology 1
Ultrasound is the preferred first-line imaging for early follow-up after treatment of differentiated thyroid cancer, according to the American College of Radiology 1, 4
FDG-PET/CT scanning is not recommended for routine surveillance if there is no residual disease, as stated by the American College of Radiology 1

In differentiated thyroid cancer follow-up, scan results are interpreted alongside serum thyroglobulin measurements, which serve as a biochemical marker of residual or recurrent disease, as recommended by clinical guidelines from the American Society of Clinical Oncology 5
For thyroid remnant ablation, a fixed dose approach is often used rather than calculations based on SUV, with doses like 50 or 100 mCi being standard, according to the American Thyroid Association 5

When SUV measurements are needed, such as in research settings or with FDG-PET/CT, standardization of protocols is essential to ensure consistency, as emphasized by the National Cancer Institute 6
Standardization of SUV protocols is crucial for ensuring consistency and comparability of results across different studies and institutions, as highlighted by the European Association of Nuclear Medicine 7

The American College of Radiology (ACR) guidelines recognize that free iodide from contrast media influences iodide uptake into the thyroid, directly interfering with nuclear diagnostic procedures like thyroid scintigraphy, and recommends careful planning of imaging sequences for patients with differentiated thyroid cancer requiring both contrast-enhanced CT and radioiodine therapy 8
In high-risk patients with suspected recurrence of differentiated thyroid cancer, the ACR recommends ultrasound and I-123 whole body scans as complementary procedures, with CT neck with IV contrast as a second-line study only when appropriate timing can be ensured 8