Abstract:

Background and purpose: As one of the first-line treatment methods for differentiated thyroid cancer (DTC), ¹³¹I treatment is an important therapeutic approach for most patients with medium-high recurrence risk DTC after total or near-total thyroidectomy. Risk stratification and real-time dynamic assessment before ¹³¹I treatment after surgery are important steps in deciding on ¹³¹I treatment, enabling individualized treatment. This retrospective study aimed to explore the role of diagnostic whole body scan (DxWBS) in the decision-making of treatment for DTC after surgery and before ¹³¹I therapy. Methods: DTC patients who underwent pre-ablation evaluation were included. Patients were divided into low, medium and high sTg groups based on their pre-¹³¹I treatment stimulated thyroglobulin (sTg) levels (<1 ng/mL, 1 ng/mL≤sTg<10 ng/mL, sTg≥10 ng/mL). The concordance rates of DxWBS and post treatment whole body scan (RxWBS) in each patient of the whole cohort were compared. The lesion detection rate between DxWBS and RxWBS in different sTg level groups was also explored. The “thyroid stunning effect” by DxWBS was evaluated by RxWBS. Through these analyses, the role of DxWBS in ¹³¹I treatment decision-making and its predicting treatment objectives were assessed. This study was approved by the Ethics Committee of Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences (ethics number: JS-2151). Results: A total of 91 patients were included. The low, medium and high sTg groups accounted for 15.4% (14/91), 34.1% (31/91) and 50.5% (46/91) of the patients, respectively. Comparison of DxWBS and RxWBS results in the same patients in each sTg group showed no evidence of a stunning effect on ¹³¹I treatment. The overall concordance rate between DxWBS and RxWBS was 89.0% (81/91); In different sTg level groups was 100.0% (14/14), 90.3% (28/31), 84.8% (39/46) respectively. Taking sTg levels into consideration, DxWBS accurately predicted the need for total thyroidectomy, with a 100% (20/20) agreement with RxWBS. Among the 71 patients who received adjuvant therapy and/or remnant ablation due to suspected elevated Tg or high recurrence risk stratification or the iodine-avid metastatic lesions identified by DxWBS, 87.5% (63/71) showed only residual thyroid tissue by DxWBS; Through the purpose verification by RxWBS and single photon emission computed tomography (SPECT)/CT, only 12.7% (9/71) of cases were verified as adjuvant or tumoricidal treatment due to iodine-avid cervical lymph node and/or lung metastasis identified by RxWBS, 87.3% (62/71) were residual thyroid ablation. In the medium and high sTg group, the overall detection rate of functional cervical lymph node metastasis by DxWBS and RxWBS was 5.5% (5/91). For the detection of functional lung metastases, the overall detection rate of DxWBS was slightly lower than that of RxWBS (3.3% vs 5.5%). This indicates that DxWBS can be used to accurately pre-judge the purposes of ¹³¹I treatment, particularly for thyroid ablation and adjuvant therapy. Conclusion: DxWBS did not induce “thyroid stunning” effect. Integrating DxWBS as a theranostic tool into the real-time decision-making and evaluation system of ¹³¹I treatment, as well as with sTg and other biochemical indicators, may help to bridge the limitations of static evaluations based on pathology and clinical data, and provides a clear understanding and more precise objectives of ¹³¹I treatment.

Key words: Differentiated thyroid cancer, Diagnostic whole body scan, Thyroglobulin