Abstract
OBJECTIVE: In this study, the response to treatment in patients with extra-thyroid extension (ETE) of papillary thyroid cancer (PTC) was compared between different radioiodine treatment doses. METHODS AND MATERIALS: In this retrospective cross-sectional study, patients with pathology-proven ETE who were hospitalized for radioiodine therapy from December 2015 to May 2018 at a referral university hospital were identified. Demographic data, radioiodine doses, and off-levothyroxine thyroglobulin and antithyroglobulin levels, before and after treatment, were collected. Alterations in thyroglobulin levels before and after treatment were compared between patients receiving different doses of radioiodine. RESULTS: Sixty patients were analyzed (mean age: 44.1 ± 14.4 years; 61.7% females). On average, the thyroglobulin levels were 59.1 ± 92.0 and 45.7 ± 81.5 ng/mL at baseline and after treatment, respectively. The thyroglobulin levels decreased from 6.2 ± 6.3 to 1.7 ± 0.2 ng/mL ( p = 0.510), 55.8 ± 101.3 to 11.5 ± 17.2 ng/mL ( p = 0.07), and 62.8 ± 91 to 60.9 ± 93.1 ng/mL ( p = 0.83) in the 100- to 149-, 150- to 199-, and 200- to 250-mCi iodine therapy groups, respectively. Treatment with doses of less than 200 mCi were significantly more effective in reducing posttreatment thyroglobulin levels compared with higher doses ( p = 0.05). In the subgroup analysis, nonmetastatic cases treated with less than 200 mCi iodine had significantly greater thyroglobulin reduction compared with metastatic patients treated with ≥200 mCi iodine ( p = 0.05). Macroscopic (vs. microscopic) invasion into adjacent tissues had no impact on thyroglobulin decrease. CONCLUSION: The administration of higher radioiodine doses for the treatment of PTC patients with ETE does not yield additional therapeutic benefits in terms of posttreatment thyroglobulin reduction.