Objective:

To evaluate the potential role of diagnostic

131

I scan (Dx) in the ma

nagment of totally thyroidectomizedpapillary carcinoma of the thyroid (PTC) in patients with unexplained hyperthyroglobulinemia.

Methods:

Totally thyroidectomized PTC patients with suppressed thyroglobulin levels higher than 1 ng/mL and no radiographic evidence of thyroid remnant or percistent/recurrent/metastatic disease were consecutively enrolled from March 2019 to February 2022. A Dx of spot imaging of 10 min covering from cranial base to transverse septum was performed 24 h after an oral administration of

131

I (74 MBq). Single photon emission computed tomography (SPECT)/computed tomography (CT) was immediately added if planar imaging showed inconclusive findings (the localization of lesions accumulating

131

I was unclear or a malignant lesion could not be ruled out). A therapeutic activity of

131

I was prescribed immediately after the goal of treatment was clarified by Dx. Three days later

a planar post-therapeutic whole-body scan (Rx) was conducted with SPECT/CT fusion imaging when needed.

Results:

In total of 67 PTC patients with unexplained hyperthyroglobulinemia

8 (11.9%) of patients were identified with positive Dx

with a coincidence rate of 97.0% between Dx and Rx and a negative predictive value of 94.9%. In patients with Dx-postive

two and six were identified with mediastinal and cervical lymph node metastasis

repectively. Biochemical remssion

stablization and progression were 87.5% (7/8)

12.5% (1/8)

and 0.0% (0/8)

respectively. After the exclusion of one patient who switched to targeted therapy

biochemical remission

stabilization

and progression were achieved in 79.3% (46/58)

12.1% (7/58) and 8.6% (5/58) of 58 patients with negative Dx

respectively. No significant difference in biochemical response was found in the two groups (

P

=0.542).

Conclusion:

The findings of Dx is highly consistent with those of Rx in totally thyroidectomized PTC patients with unexplained hyperthyroglobulinemia. Radiodine

-avid focis were detected or excluded

which is helpful to clarify the purpose of treatment

warranting therapeutic response.