Outpatient ablation treatment with two doses of 30 mCi of radioactive iodine for non-low-risk papillary thyroid cancer

: Outpatient ablation therapy with low-dose radioactive iodine (RAI) is applied to non-low-risk papil-lary thyroid cancer patients due to a chronic shortage of inpatient RAI treatment wards in Japan. We used the maximum dosage available for outpatient therapy of 30 mCi of RAI for ablation and diagnostic (Dx) whole-body scintigraphy (WBS). This study aimed to examine the significance of the second dose of 30 mCi. DxWBS was per- formed 6 months after ablation, and assessment of success or failure was performed 12 months after ablation. A second WBS was performed in the remaining RAI accumulation cases in the neck on DxWBS. The criteria for successful ablation was negative cervical accumulation on WBS, thyroid stimulating hormone-suppressed thyro-globulin (sup-Tg) below 1.0 ng / mL, and no increase in thyroglobulin antibody (TgAb) level. At the time of DxWBS, 35 / 68 cases met the successful criteria, and 45 cases achieved success at assessment. Sup-Tg values decreased sig-nificantly after ablation and decreased further after DxWBS in successful ablation cases, whereas those were not changed in ablation failure cases. Findings indicated that RAI used in DxWBS had therapeutic effects. It makes sense to use 30 mCi for DxWBS, given the current difficulty of inpatient ablation therapy with high-dose RAI. J. Med. Invest. 70 : 17-21, February, 2023