Diagnostic 123I Whole Body Scan Prior to Ablation of Thyroid Remnant in Patients With Papillary Thyroid Cancer: Implications for Clinical Management

Objectives The use of I-123 whole body scintigraphy (WBS) before I-131 radioiodine ablation (RIA) of the post-surgical thyroid remnant in patients with papillary thyroid cancer (PTC) remains debated. The American Thyroid Association's guidelines state that WBS may be useful before RIA (rating Cexpert opinion). Some institutions do not use I-123 WBS before RIA in their routine clinical protocol. We were therefore prompted to evaluate the impact of I-123 WBS prior to ablation of thyroid remnant in patients with PTC. Methods We reviewed data from 152 consecutive patients with PTC who had total thyroidectomy and were referred for RIA between August 2007 and February 2009 at our institution. The group included 107 women and 45 men, 13-82 years old (mean SD: 45.5 18.3). Three endocrinologists blinded to the results of the I-123 WBS reviewed patients' data including sex, age, pathology, thyroglobulin (Tg) level, anti-Tg antibodies, thyroid stimulating hormone (TSH) level and ultrasound results. Each endocrinologist then returned a form with the recommended I-131 dose for each participant, according to the following rules: 50-75 mCi (remnant ablation), 75-125 mCi (lymph nodes metastases), 150 mCi (lung metastases), and 200 mCi (bone metastases). We compared their recommended doses with the actual I-131 doses prescribed after the pre-therapy I-123 WBS. Results All three endocrinologists recommended the same dose in 98.7% of the cases. The dose prescribed by the endocrinologists matched the dose administered after analyzing the I-123 WBS in 77 patients (51%). However, for 46 patients (30%) the endocrinologists would have given a lower dose, for 18 patients (12%) a higher dose than that administered based on the results of the I-123 WBS, while 11 patients (7%) would have been treated unnecessarily (5/11 had no I-123 uptake and 6/11 had I-123 uptake in the breasts). Conclusions Our study suggests a significant role of the pre-therapy I-123 WBS in PTC patients referred for I-131 ablation post-thyroidectomy. The actual I-131 dose that was administered based on the I-123 WBS differed from the dose recommended in the absence of the I-123 WBS in 49% of the cases.