Diagnostic yield of thyroid CT in differentiated thyroid carcinoma according to treatment response.

[OBJECTIVES] To evaluate the diagnostic yield of thyroid CT in patients with post-treatment differentiated thyroid carcinoma (DTC) stratified by treatment response.

[MATERIALS AND METHODS] This retrospective study included DTC patients who underwent total thyroidectomy and radioactive iodine ablation, followed by thyroid CT. Patients were categorized into response assessment groups according to the American Thyroid Association guidelines: excellent response (ER), biochemical incomplete response (BIR), indeterminate response (IR), and structural incomplete response (SIR). Diagnostic yield was defined as the proportion of patients with recurrent tumors among all patients. The yields of ER, BIR, and IR were compared. For IR, subgroup analyses were performed based on the presence of indeterminate lesions on ultrasound (US). Chi-squared tests with Bonferroni correction were used to compare the diagnostic yields between groups.

[RESULTS] A total of 450 patients (mean age, 44.9 ± 13.4 years; 164 men) were included. The overall diagnostic yield of thyroid CT was 15.3% (69/450; 95% confidence interval [CI]: 12.3-19%). Yields for the ER, BIR, and IR groups were 2% (4/201; 95% CI: 0.6-5.2%), 23.1% (12/52; 95% CI: 13.6-36.3%), and 26.9% (53/197; 95% CI: 21.2-33.5%), respectively. Among IR patients, the yield was significantly lower in US-negative patients (7.5%, 7/93; 95% CI: 3.5-15%) compared to those with indeterminate US lesions (44.2%, 46/104; 95% CI: 35.1-53.8%) (p < 0.001).

[CONCLUSION] The diagnostic yield of thyroid CT varies according to the treatment response; it was low in ER and US-negative IR but higher in BIR and IR with indeterminate US lesions.

[KEY POINTS] Question Guidelines recommend considering CT for follow-up in DTC based on treatment response, but the diagnostic yield of CT remains underexplored. Findings The diagnostic yield of CT was low in an ER and US-negative IR but higher in BIR and US-positive IR. Clinical relevance The diagnostic yield of thyroid CT varies according to treatment response. Utilizing CT based on treatment response may enhance the detection of recurrent tumors or clarify unclear findings on US.