Value of follow-up diagnostic radioiodine scans in differentiated thyroid cancer

Background: The most important part of the follow-up of differentiated thyroid carcinoma (DTC) is the measurement of serum thyroglobulin (Tg). An increase of Tg levels indicates likely tumor recurrence. According to the guidelines of the European Society of Medical Oncology (ESMO), the follow-up should consist of serum Tg assays and a neck ultrasound, while the American Thyroid Association (ATA) recommends serum Tg assays, neck ultrasounds, and a diagnostic radioiodine whole-body scan (WBS) if non-stimulated Tg is greater than 10 ng/mL or if Tg is rising. This study questions the necessity of a diagnostic WBS in patients with low stimulated Tg levels during the initial follow-up. Design: This study is a retrospective data analysis. Methods: The data of 185 patients, who were in regular treatment and aftercare between 2015 and 2018 at the Department of Nuclear Medicine in Vienna, as well as the data of 185 patients who were treated in Tbilisi between 2015 and 2019, were analyzed. Results: There was a highly significant relationship between low stimulated Tg levels (<0.5 ng/mL) and the outcome of the diagnostic WBS at the first follow-up (chi (2 )= 14.7, P < 0.001). In total, 31 out of 370 patients (8.4%) had positive findings in the diagnostic WBS. Seventy-five of 370 patients (19.74%) had stimulated Tg levels >0.5 ng/mL. Conclusion: Our data suggest that the first follow-up, 4-12 months after the initial therapy of DTC, including the measurement of basal and stimulated Tg levels and Tg antibody levels, does not mandate a diagnostic WBS on all patients. Significance statement: In this study, we examined the still commonly used routine diagnostic radioiodine whole-body scan in the first follow-up of patients with differentiated thyroid carcinoma. We questioned the necessity of the scan in patients with low stimulated thyroglobulin levels. Therefore, we combined retrospective data from the University Hospital in Vienna and in Tbilisi to analyze 370 patients. We were able to demostrate a highly significant relationship between low stimulated thyroglobulin levels (<0.5 ng/mL) and the outcome of the diagnostic scan at the first follow-up (chi = 14.7, P < 0.001).