The Correlation of Post-Operative Radioiodine Uptake and Tc-99m Pertechnetate Thyroid Scintigraphy and the Result of Thyroid Remnant Ablation
Tanyaluck Thientunyakit MD*, Pawana Pusuwan MD*, Pongpija Tuchinda MD*, Benjapa Kiewvan MD*
Affiliation : * Division of Nuclear Medicine, Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand
Objective : Determine the relationship between postoperative thyroid remnant using 24 h radioiodine uptake and Tc-99m
pertechnetate scintigraphy, and the success of high dose radioiodine ablation.
Material and Method: Retrospectively enrolled 250 patients with DTC who underwent thyroidectomy and radioiodine
ablation. Postoperative Tc-99m pertechnetate and 24 h I-131 uptake were reviewed to evaluate thyroid remnant and the
directly compared with ablation outcome. The successful ablation was defined using negative WBS and stimulated Tg
<10 ng/ml in the absence of TgAb at six to 12 months after treatment. The relationship between success of ablation and
other variables were evaluated.
Results : One hundred twenty four patients (49.6%) were successfully ablated after single high dose radioiodine ablation.
The authors found no association with age, sex, extent of surgery, tumor histology, tumor size, mutifocal, extrathyroidal
invasion, I-131 administered dose, interval from surgery to radioiodine ablation, Tc-99m pertechnetate scan, or 24 h I-131
uptake, and successful ablation. The initial Tg level was the only variable found to be associated with success (p<0.001).
Conclusion : Neither Tc-99m pertechnetate thyroid scintigraphy nor 24 h I-131 uptake percentage in the evaluation of
postsurgical thyroid remnant can predict radioiodine ablation outcome in patients with DTC. Serum Tg level at the time of
ablation could be a reasonable predictor of the success of ablation.
Keywords : Radioiodine, I-131 uptake, Tc-99m pertechnetate, Thyroid scintigraphy, Thyroid ablation
