Comparison between the different doses of radioactive iodine ablation prescribed in patients with intermediate-to-high-r
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ORIGINAL ARTICLE
Comparison between the different doses of radioactive iodine ablation prescribed in patients with intermediate‑to‑high‑risk differentiated thyroid cancer Yusuke Iizuka1 · Tomohiro Katagiri1 · Kengo Ogura1 · Takashi Mizowaki1 Received: 18 February 2019 / Accepted: 2 April 2019 © The Japanese Society of Nuclear Medicine 2019
Abstract Objective This study aimed to compare the clinical outcomes of patients who received radioactive iodine (RAI) ablation after undergoing thyroidectomy for intermediate-to-high-risk differentiated thyroid carcinoma (DTC) according to the American Thyroid Association (ATA) criteria. Methods We retrospectively examined patients who underwent RAI ablation for DTC after surgical resection without macroscopic residual lesions or metastatic lesions between December 2011 and August 2016. Among 147 patients who underwent RAI ablation, those whose initial pathological stages or RAI ablation results were unknown and whose distant metastases were confirmed during RAI ablation were excluded. Low-dose therapy was defined as administration of 1110 MBq of 131iodine (131I), while high-dose therapy referred to administration of 2960–3700 MBq of 131I. We defined initial success of RAI ablation as a serum thyroglobulin concentration of 2 Status Primary Recurrent Histology Papillary Follicular Other T stage T4 T3 T2 T1 T0 N stage N1b N1a N1x N0 ATA risk Low Intermediate High Pre-Tg (mean, interquartile range) (ng/ml)
39 (32.7%) 80 (67.2%) 54 (9–78) 90 (75.6%) 29 (24.4%) 0 (0%) 103 (86.6%) 16 (13.4%) 115 (96.6%) 2 (1.7%) 2 (1.7%) 25 (21.0%) 76 (63.4%) 2 (1.7%) 15 (12.6%) 1 (0.8%) 74 (62.1%) 25 (21%) 3 (2.5%) 17 (14.3%) 0 (0%) 79 (66.4%) 40 (33.6%) 4.1 (0.17–2.5)
ATA risk categories: low risk (pT1–pT2 and pN0), high risk (pT4 or positive surgical margin and any N stage), and intermediate risk (others). Pre-Tg indicates the serum thyroglobulin level without TSH stimulation before the administration of 131Iodine ECOG-PS Eastern Cooperative Oncology Group performance status, ATAAmerican Thyroid Association
A total of 14 patients tested positive for anti-Tg antibody. On univariate analysis, pretreatment Tg level (> 4 ng/mL), a significant factor in patients with anti-Tg antibodies, showed negative correlation with RAI ablation failure. On multivariate analysis, pretreatment Tg level was a significant risk factor for RAI ablation failure.
Discussion We evaluated the success rate of RAI ablation in patients with intermediate-to-high-risk DTC who received the prescribed dose of 131 I. IPTW analysis revealed that
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there was no significant difference between the low-dose (1110 MBq) group and high-dose (2970–3700 MBq) group. Both risk groups had success rates of about 70%, and the pretreatment Tg level (> 4 ng/ml) was considered to be a significant factor for RAI ablation failure. However, in high-risk patients, although no significant difference was observed, the success rate differed by more than 10%, suggesting that patients with high-risk DTC may benefit from high-d
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