Added value of posttherapy I-131 scans in the detection of remnant and locoregional thyroid disease: A pictorial essay

Learning Objectives 1. To emphasize the value of post therapy I-131 WB scan (PTWBS) in management of patients with differentiated thyroid cancer. 2. To compare between PTWBS and I-131 diagnostic whole body scan (DxWBS) in detection of locoregional and distant metastasis in differentiated thyroid cancer.

Differentiated thyroid cancer has an excellent prognosis in most of the cases. I-131 usually used after thyroidectomy to ablate residual remnant thyroid tissue as well as to treat any locoregional micrometastases. Many centers obtain DxWB to evaluate for macroscopic metastatic disease, the detection of which potentially changing the planned treatment dosage to be administered. The term “stunning” was used to describe the temporarily decreased a cell’s ability to concentrate iodine, but did not kill the cell after the relatively low activities of I-131 used for DxWBS (2-10 mCi I-131). Authors who support the stunning phenomenon recommend omitting the pretherapy scan and replaced by PTWBS. It is also general practice to obtain I-131 PTWBS, the idea being that the relatively larger therapeutic dosage of radioiodine will improve detection of locoregional or distant metastatic disease. Most centers currently acquire posttherapy images 4 to 10 days posttherapy. Illustrations displayed include examples of added value of I-131 PTWBS in comparison with DxWBS