Predicting 131I-avidity of metastases from differentiated thyroid cancer using 18F-FDG PET/CT in postoperative patients with elevated thyroglobulin

Abstract

The quantitative relationship between iodine and glucose metabolism in metastases from differentiated thyroid cancer (DTC) remains unknown. Aim of the prospective study was to establish the value of ¹⁸F-FDG PET/CT in predicting ¹³¹I-avidity of metastases from DTC before the first radioiodine therapy. A total of 121 postoperative DTC patients with elevated stimulated serum thyroglobulin (ssTg) who underwent ¹³¹I adjuvant therapy or therapy after ¹⁸F-FDG PET/CT scan were enrolled. The Receiver operating characteristic curve was established to create an optimal cut-off point and evaluate the value of SUVmax for predicting ¹³¹I-avidity. In our study, the median SUVmax in ¹³¹I-nonavid metastatic target lesions was also significantly higher than that in ¹³¹I-avid metastatic target lesions (5.37 vs. 3.30; P = 0.000). At a cut-off value of 4.0 in SUVmax, the area under curve was 0.62 with the sensitivity, specificity, positive predictive value and negative predictive value of 75.3%, 56.7%, 76.1%, and 54.8%, respectively. These results suggest that ¹⁸F-FDG PET/CT may be of great value in identifying metastases in postoperative DTC patients with elevated ssTg before ¹³¹I administration, leading to an improved management of disease. ¹⁸F-FDG positive metastatic DTC with SUVmax of greater than 4.0 possesses higher probability of non-avidity to radioiodine.

Figure 1

Patient flow diagram of the evaluation of the role of ¹⁸F-FDG PET/CT in identifying metastatic differentiated thyroid cancers in postoperative patients with elevated stimulated serum thyroglobulin before ¹³¹I administration.

Figure 2

Comparison of SUVmax for ¹³¹I-avid and ¹³¹I-nonavid metastatic DTC lesions on ¹⁸F-FDG PET/CT. P = 0.000.

Figure 3

Receiver operating characteristic curve of SUVmax for the prediction of ¹³¹I-uptake capacity in DTC metastases.

Figure 4

¹⁸F-FDG-avid papillary thyroid carcinoma (PTC) metastatic lymph nodes non-avid for ¹³¹I. A 32-y-old female with PTC presented with suspicious metastatic disease 2 months after total thyroidectomy with elevated stimulated serum throglobulin (ssTg) of 78 ng/mL and thyroid-stimulating hormone (TSH) of 102.4 mU/L. Transaxial (A) and coronal (B) fusion images of ¹⁸F-FDG PET/CT before the administration of 5.55 MBq (150 mCi) of ¹³¹I showed obviously radiotracer-avid lymph nodes (LN) (SUVmax = 4.6) in the neck. The ¹³¹I whole body scan (C) and transaxial (D) and coronal (E) fusion images of ¹³¹I SPECT/CT of the neck revealed no ¹³¹I accumulation in the lymph node (not shown) but ¹³¹I uptake in the thyroid remnant.

Figure 5

¹⁸F-FDG-avid papillary thyroid carcinoma (PTC) metastatic sternum lesions avid for ¹³¹I. A 55-y-old male patient with PTC presented with suspected metastatic disease one month after total thyroidectomy with ssTg of 604.7 ng/mL and TSH of 60.2 mU/L. Transaxial (A) and coronal (B) image of ¹⁸F-FDG PET/CT before ¹³¹I therapy showed sternum lesions with increased ¹⁸F-FDG uptake (SUVmax = 3.6). ¹³¹I planar image (C) and SPECT/CT (D,F) after the initial administration of 7.4 MBq (200 mCi) ¹³¹I correspondingly showed the sternum metastases with increased ¹³¹I accumulation. Six months later, ssTg decreased to 125.9 ng/mL under TSH stimulation by levothyroxin withdrawl just before the second course of ¹³¹I administration.