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Objective To determine the prevalence of thyroglossal tract thyroid tissue on SPECT/ CT and to assess the contribution of this tissue to total neck radioactive iodine ( RAI) activity in patients given 131I ablation therapy after total thyroidectomy for thyroid cancer. Patients and Methods Eighty-three consecutive patients with thyroid cancer treated with total thyroidectomy underwent whole-body planar and SPECT/ CT imaging of the neck following initial RAI ablation. On SPECT/ CT, thyroglossal tract thyroid tissue was defined as RAI in the anterior neck, superior to the thyroid bed in close proximity to the midline without evidence of localization to lymph nodes. Quantification was performed using region of interest analysis on planar imaging following localization on SPECT/ CT. SPECT/ CT, and planar images were classified by two reviewers as positive, negative or equivocal with interobserver agreement quantified using a Kappa score. Disagreement was resolved using a third reviewer. Results Thyroglossal tract thyroid tissue was present in 39/83 (47%; 95% CI: 36-58%) patients on SPECT/ CT. In these 39 patients, this tissue contributed to a significant amount of total neck activity (median = 50%; IQR 19-74%). Interobserver agreement for the presence of thyroglossal tract thyroid tissue was substantial on SPECT/ CT (Kappa = 0·73) and fair on planar imaging (Kappa = 0·31). Conclusion Thyroglossal tract thyroid tissue was present in one half of our study population and contributed to a significant amount of total neck RAI activity. Given the high prevalence of this tissue, our results suggest that total neck RAI activity on planar imaging may not be suitable to assess the completeness of thyroid bed surgery. [ABSTRACT FROM AUTHOR]

Objective To evaluate the relationships between thyroid remnant 131I uptake, radiation thyroiditis and remnant ablation success rate between lower (1110 MBq) and higher (3700 MBq) initial ablative 131I dose for post-surgical ablation therapy for differentiated thyroid cancer. Design Patients having post-surgical administration of 1110 MBq (68 patients) or 3700 MBq (115 patients) 131I were retrospectively reviewed. Thyroid remnant 131I uptake on a 48 h post-administration scan was correlated with neck symptoms experienced. Patients were classified as having insignificant, mild or severe thyroiditis based on symptoms. Absent thyroid bed 131I uptake on a follow-up 74 MBq 131I study was considered successful ablation. Results 183 patients were included. Median 131I remnant uptake was 37 MBq. 21% (39/183) of patients developed thyroiditis. Incidence and severity of thyroiditis increased with increasing remnant 131I activity ( P ≤ 0·0001). Risk of thyroiditis increased by 64% for every 37 MBq increase in remnant 131I uptake. OR = 1·64 [1·36–1·99]. Severe thyoriditis was only seen with remnant 131I uptake > 73 MBq. For patients treated with 1110 MBq and 3700 MBq, incidence of thyroiditis was 12% and 27% ( P = 0·02) and remnant ablation success rate was 76% and 84% ( P = NS), respectively. Occurrence of thyroiditis did not correlate with successful ablation. Conclusions Incidence and severity of radiation thyroiditis following 131I remnant ablation therapy is directly related to thyroid remnant 131I uptake. As 1110 MBq 131I is associated with a significantly lower frequency of thyroiditis but similar remnant ablation rate to 3700 MBq, it warrants consideration for thyroid remnant ablation particularly in patients with low risk disease. [ABSTRACT FROM AUTHOR]