Objective: To determine the potential use of postoperative diagnostic ¹³¹I whole body scan (¹³¹I DxWBS) with single photon emission computed tomography-computed tomography (SPECT-CT) on initial staging, risk stratification and ¹³¹I therapy planning in differentiated thyroid cancer (DTC) patients classified as being at low risk of recurrence based on clinical and histopathology.

Materials and Methods: Eighty DTC patients classified as low risk using the ATA 2009 risk stratification system based on clinical and histopathology between 2014 and 2016 were retrospectively evaluated. Initial staging using the AJCC/TNM staging system seventh edition was obtained. Initial ¹³¹I treatment planning was prescribed based on the protocol agreed by the authors institution. Two nuclear medicine physicians interpreted the ¹³¹I DxWBS with SPECT-CT independently and came to a consensus. Staging, risk stratification and ¹³¹I treatment planning were re-evaluated based on additional ¹³¹I DxWBS with SPECT-CT findings.

Results: Of the 36 patients aged under 45 years, ¹³¹I DxWBS with SPECT-CT detected nodal metastases in 12 patients (33.3%, N1a=6, N1b=6), and bone with lung metastases in 1 patient (2.8%, M1=1), which changed the TNM staging in 1 patient (2.8%). Out of the 44 patients aged more than or equal to 45 years, nodal metastases were detected in 13 patients (29.5%, N1a=8, N1b=5) and nodal with lung metastases in 1 patient (2.3%, M1=1), leading to a change in the TNM staging in 14 patients (31.8%). Risk stratification was changed from low risk to intermediate risk in 25 of 80 patients (31.3%) and to high risk in 2 of 80 patients (2.5%). ¹³¹I therapy planning was altered in 27 out of 80 patients (33.8%).

Conclusion: The postoperative use of ¹³¹I DxWBS with SPECT-CT altered the initial staging, risk stratification and ¹³¹I treatment planning based on the clinical and histopathology history alone in low risk DTC patients. Nodal and distant metastases were detected leading to changes in the overall TNM staging in 18.8%, risk stratification in 33.8% and ¹³¹I treatment planning in 33.8% of the study.

Keywords: Diagnostic scan, Iodine-131, SPECT-CT, Staging, Risk stratification, Radioiodine therapy, Thyroid carcinoma