Clinical relevance of 18F-FDG PET/CT in the postoperative follow-up of patients with history of medullary thyroid cancer

Abstract

Background: The aim of the study was evaluation of ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography with computed tomography (PET/CT) in the detection of active disease in the patients with suspected recurrence of the medullary thyroid carcinoma (MTC).

Patients and methods: ¹⁸F-FDG PET/CT investigation was performed in 67 patients, investigated from 2010 to 2019. _ Follow up was performed from 6 to 116 months after surgery (median 16.5 months, x± SD = 29±28.9 months). Twenty five of 67 patients underwent ^99mTc-dimercaptosuccinic acid (^99mTc-DMSA) scintigraphy, 11 underwent somatostatin receptor scintigraphy (SRS) with ^99mTc-HYNIC TOC while 11 ¹²³I-metaiodobenzylguanidine (MIBG) scintigraphy.

Results: From 67 patients, 35 (52.2%) had true positive ¹⁸F-FDG PET/CT findings (TP). Average maximal standardized uptake value (SUVmax) for all TP lesions was 5.01+3.6. In 25 (37.3%) patients findings were true negative (TN). Four (6%) patients had false positive (FP) findings while three (4.5%) were false negative (FN). Thus, sensitivity of the ¹⁸F-FDG PET/ CT was 92.11%, specificity 86.21%, positive predictive value 89.74%, negative predictive value 89.29% and accuracy 89.55%. In 27 patients (40%) ¹⁸F-FDG PET/CT finding influenced further management of the patient.

Conclusions: ¹⁸F-FDG PET/CT has high accuracy in the detection of metastases/recurrences of MTC in patients after thyroidectomy as well as in evaluation and the appropriate choice of the therapy.

Keywords: 18F-FDG PET/CT; follow up; medullary thyroid carcinoma; postoperative.

Figure 1

Patient with diagnosis of MTC after total thyroidectomy. (A, B) FDG PET/CT confirmed high uptake metastases in the mediastinal lymph nodes and uneven distribution of FDG in the liver. (C) ^99mTc-DMSA spot view scintigraphy finding is negative. (D) ^99mTc - tektrotyd SPECT finding is negative. (E) ¹²³I – MIBG WB finding showed high uptake in multiple liver metastases. (F) ¹²³I – MIBG SPECT finding showed high uptake in multiple liver metastases.

Figure 2

Patient with diagnosis of MTC after total thyroidectomy. (A, B) FDG PET/ CT confirmed high uptake metastases in the lymph nodes of the neck, mediastinum and abdomen. (C) ^99mTc-DMSA planar spot view scintigraphy showed uptake only in the few lymph nodes in the neck and mediastinum.

Figure 3

Patient with diagnosis of MTC after total thyroidectomy. (A) FDG PET/CT confirmed high uptake in metastases in the mediastinal lymph nodes. (B) ^99mTc- tektrotyd scintigraphy confirmed high uptake in metastases in the mediastinal lymph nodes. (C) ^99mTc-DMSA planar spot view scintigraphy finding was negative showed uptake only in the few lymph nodes in the neck and mediastinum.

Figure 4

Kaplan Meier progression-free survival curve in positive FDG patients with median survival of 15 months (95% CI 11.14 ± 18.85 months), while median survival in disease free patients was 30 months (95% CI 1.08+58.92 months).