Differentiated Thyroid Cancer Outcomes After Surgery and Activity-Adjusted 131I Theragnostics

Purpose The aim of this study was to determine clinical outcomes in patients with differentiated thyroid cancer after surgery and activity-adjusted 131I therapy informed by diagnostic 131I scans with SPECT/CT (Dx scan). Methods Single-institution retrospective cohort study analysis of clinical outcomes after 1 to 5 years (mean, 39.6 ± 23.4 months) of follow-up in 350 patients with differentiated thyroid cancer associated with histopathologic risk factors, nodal metastases, and/or distant metastases. Postoperatively, all patients underwent Dx scans for completion of staging and risk stratification, and 131I therapy was based on integration of information from histopathology, stimulated thyroglobulin and scintigraphy. Results Twenty-three patients (6.6%) underwent reoperative neck dissection for removal of unsuspected residual nodal metastases identified on Dx scans. Clinical outcomes were as follows: 84.3% complete response, 1.4% biochemical incomplete response, 2.3% indeterminate response, and 12% structural incomplete response. Of the entire cohort, only 8 patients (2.3%) had persistent iodine-avid metastatic disease, which required repeated 131I therapy. Of 31 patients with iodine-avid distant metastases identified on Dx scans, 13 patients (42%) achieved complete response with a single 131I treatment. Conclusions Detection of regional and distant metastases on postoperative Dx scans permits adjustment of prescribed 131I activity for targeted treatment, as compared with fixed-activity ablation. This approach resulted in complete response after a single 131I treatment in 88% patients with histopathologic risk factors and regional metastases and 42% patients with distant metastases. Most patients with structural incomplete response (81%) had elevated thyroglobulin levels with negative follow-up 131I scans and positive PET/CT and/or CT scans consistent with altered tumor biology (non–iodine-avid disease).

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