Thyroglobulin Value Predict Iodine-123 Imaging Result in Differentiated Thyroid Cancer Patients

This study was prompted to assess the diagnostic performance of I-123-Dx-WBS-SPECT/CT in the identification of incomplete structural response in the early follow-up of DTC patients and derived optimized basal-Tg thresholds as a yardstick for scintigraphic imaging. In this light, we reviewed the records of 124 low or intermediate-risk DTC patients who underwent thyroid surgery followed by radioiodine therapy. The response to initial treatments was evaluated 6-12 months after radioiodine therapy. According to 2015 ATA criteria, 87, 19 and 18 patients were classified to have excellent response (ER), indeterminate/incomplete biochemical response (BIndR/BIR) or structural incomplete response (SIR), respectively. Among 37 patients with less than ER, 18 had a positive I-123-Dx-WBS-SPECT/CT. Interestingly, metastatic disease noted at I-123-Dx-WBS-SPECT/CT mainly involved lymph nodes of the central compartment with a corresponding negative ultrasound of the neck. The optimized basal-Tg cut-off was settled at 0.39 ng/mL by ROC curve analysis (AUC = 0.852) aiming to discriminate patients with positive or negative I-123-Dx-WBS-SPECT/CT, respectively. Basal-Tg exceeding this cutoff level independently predicts a positive I-123-Dx-WBS-SPECT/CT. In conclusion, I-123-WBS-SPECT/CT identified lymph node metastases in 14/37 patients with less than ER and negative neck ultrasound, thus modifying the management of such patients. The diagnostic performance of I-123-Dx-WBS-SPECT/CT imaging significantly increases in patients with basal-Tg levels >= 0.39 ng/mL.Background: In differentiated thyroid cancer (DTC) patients, the response to initial treatments is evaluated 6-12 months after radioiodine therapy (RIT) according to the 2015 American Thyroid Association (2015 ATA) criteria. In selected patients, diagnostic 131-radioiodine whole-body scintigraphy (Dx-WBS) is recommended. We evaluated the diagnostic performance of I-123-Dx-WBS-SPECT/CT imaging in detecting incomplete structural responses in the early follow-up of DTC patients and, additionally, derived optimized basal-Tg value as a yardstick for scintigraphic imaging. Methods: We reviewed the records of 124 low or intermediate-risk DTC patients with negative anti-thyroglobulin antibody. All patients had undergone (near)-total-thyroidectomy followed by RIT. The response to initial treatments was evaluated 6-12 months after RIT. Results: According to the 2015 ATA criteria, 87, 19 and 18 DTC patients were classified to have excellent response (ER), indeterminate/incomplete biochemical response (BIndR/BIR) or structural incomplete response (SIR), respectively. Among patients with less than ER, 18 had a positive I-123-Dx-WBS-SPECT/CT. Metastatic disease at I-123-Dx-WBS-SPECT/CT mainly involved lymph nodes within the central compartment, and corresponding neck ultrasound examinations were negative. The ROC curve analysis was performed to define the best basal-Tg cut-off (i.e., 0.39 ng/mL; AUC = 0.852) able to discriminate patients with and without positive I-123-Dx-WBS-SPECT/CT, respectively. The overall sensitivity, specificity, accuracy, PPV and NPV were 77.8%, 89.6%, 87.9%, 56.0% and 95.9%, respectively. Basal-Tg cut-off was an independent risk factor for having a positive I-123-Dx-WBS-SPECT/CT.Conclusion: I-123-Dx-WBS-SPECT/CT identified lymph node metastases in 14/37 patients with less than ER and a negative neck ultrasound, thus modifying the management of such patients. The diagnostic performance of I-123-Dx-WBS-SPECT/CT significantly increased in patients with basal-Tg values >= 0.39 ng/mL.