The usefulness of iodine-123 whole-body scans in evaluating thyroid carcinoma and metastases.

OBJECTIVE It is recognized that diagnostic doses of (131)I larger than 3 mCi will cause some cell injury to the tissue in which it concentrates and reduce subsequent uptake of (131)I administered therapeutically. Iodine-123 has been suggested as an alternate radiopharmaceutical to perform whole-body scans since its primary emissions are photons with minimal particulate radiation and it does not cause thyroid stunning and cell injury. The purpose of this study was to assess the effectiveness of (123)I for whole-body scans. METHODS We examined 12 patients who had (123)I whole-body scans for known papillary/follicular thyroid cancer and 1 patient with Hurthle cell carcinoma, all with suspected metastases. All patients had undergone neck surgery and were given 0.81-0 mCi (123)I. Twenty-four hours later a whole-body image and static views of relevant areas were obtained. If abnormal uptake was noted, patients were treated with large doses of (131)I and then had whole-body (131)I scans 7-10 d post-therapy. These images were compared to (123)I whole-body scans. RESULTS All 13 patients had abnormal (123)I scans and were treated with therapeutic doses of (123)I, followed by whole-body scans 7-10 d later. In 11 patients the activity seen on the 123I scans correlated well with that seen on (131)I scans. In 1 patient, additional lesions were noted on the (131)I images. In another patient, neck activity was seen on the (123)I scan but not on the subsequent (131)I post-therapy scan. The (123)I activity was felt to represent esophageal lumen activity. CONCLUSION We found (123)1 effective in demonstrating residual thyroid tissue, thyroid carcinoma and metastases, and recommend its use for whole-body iodine scans since it does not cause thyroid stunning.