The Added Benefit of a Dedicated Neck F-18 FDG PET-CT Imaging Protocol in Patients With Suspected Recurrent Differentiated Thyroid Carcinoma

TSH Stimulation before PET/CT as Our Frenemy in Detecting Thyroid Cancer Metastases-Final Results of a Retrospective Analysis

Introduction: Non-iodine avid metastases of differentiated thyroid cancer (DTC) can be found using PET/CT with a fluorine-18-labeled glucose analog ([18F]FDG). There are ongoing discussions on the appropriateness of using exogenous thyrotropin (TSH) stimulation before this examination. Material and Methods: In a retrospective study, 73 PET/CT scans with [18F]FDG performed after exogenous stimulation with recombinant human TSH (rhTSH) and without such stimulation were analyzed. All analyzed patients were suspected of having non-iodine-avid foci of DTC. Results: The stimulation with rhTSH before the PET/CT did not affect the percentage of positive results: 37.5% (18/48) with rhTSH and 40% (10/25) without rhTSH (p = 0.83). The analysis of the ROC curves established the cut-off thyroglobulin point for a positive PET/CT result separately for both subgroups. There was no statistically significant difference between obtaining a positive PET/CT result and the baseline thyroglobulin concentration (both stimulated and unstimulated). The exogenous stimulation of TSH prior to the PET/CT had no effect on the [18F]FDG uptake in the PET/CT lesions. Conclusions: PET/CT with [18F]FDG remains a useful method for the diagnosis of non-iodine-avid DTC lesions; in the presented group, a positive effect of rhTSH stimulation on the number of DTC foci visible in the PET/CT was found, but without affecting its effectiveness.

Usefulness of PET-CT scan in recurrent thyroid cancer

The aim of this paper is to discuss the risk of recurrence in patients with differentiated thyroid cancer and emphasize the importance of risk-group stratification, early recurrence identification and application of new imaging modalities, what is the PET-CT. Moreover, follow-up of patients with thyroid carcinoma should be carried out by specialized teams throughout life. Therefore, interdisciplinary case discussions in tumor conferences may improve the use of multimodal therapy especially in patients with poorly differentiated thyroid carcinomas. After baseline follow-up, if there is a suspicion of thyroid carcinoma, early PET-CT should be used for early detection and appropriate planning. Fortunately, due to the good localization possibility, the PET-CT enables a focused surgical procedure with avoidance of an unnecessary tumor search and thereby a reduction of the risk of injury of neighboring structures which is a concern with reoperative neck surgery.

Optimization of a dedicated protocol using a small-voxel PSF reconstruction for head-and-neck 18FDG PET/CT imaging in differentiated thyroid cancer

Background

¹⁸FDG PET/CT is crucial before neck surgery for nodal recurrence localization in iodine-refractory differentiated or poorly differentiated thyroid cancer (DTC/PDTC). A dedicated head-and-neck (HN) acquisition performed with a thin matrix and point-spread-function (PSF) modelling in addition to the whole-body PET study has been shown to improve the detection of small cancer deposits. Different protocols have been reported with various acquisition times of HN PET/CT. We aimed to compare two reconstruction algorithms for disease detection and to determine the optimal acquisition time per bed position using the Siemens Biograph6 with extended field-of-view.

Methods

Twenty-one consecutive and unselected patients with DTC/PDTC underwent HN PET/CT acquisition using list-mode. PET data were reconstructed, mimicking five different acquisition times per bed position from 2 to 10 min. Each PET data set was reconstructed using 3D-ordered subset expectation maximisation (3D-OSEM) or iterative reconstruction with PSF modelling with no post filtering (PSF_allpass). These reconstructions resulted in 210 anonymized datasets that were randomly reviewed to assess ¹⁸FDG uptake in cervical lymph nodes or in the thyroid bed using a 5-point scale. Noise level, maximal standard uptake values (SUVmax), tumour/background ratios (TBRs) and dimensions of the corresponding lesion on the CT scan were recorded. In surgical patients, the largest tumoral size of each lymph node metastasis was measured by a pathologist.

Results

The 120 HN PET studies of the 12 patients with at least 1 ¹⁸FDG focus scored malignant formed the study group. Noise level significantly decreased between 2 and 4 min for both 3D-OSEM and PSF_allpass reconstructions (p < 0.01). TBRs were similar for all the acquisition times for both 3D-OSEM and PSF_allpass reconstructions (p = 0.25 and 0.44, respectively). The detection rate of malignant foci significantly improved from 2 to 10 min for PSF_allpass reconstruction (20/26 to 26/26; p = 0.01) but not for 3D-OSEM (15/26 to 19/26; p = 0.26). For each of the five acquisition times, PSF_allpass detected more malignant foci than 3D-OSEM (p < 0.01). In the seven surgical patients, PSF_allpass evidenced smaller malignant lymph nodes than 3D-OSEM at 8 and 10 min. At 10 min, the mean size of the lymph node metastases neither detected with PSF_allpass nor 3D-OSEM was 3 ± 0.6 mm vs 5.8 ± 1.1 mm for those detected with PSF_allpass only and 10.9 ± 3.3 for those detected with both reconstructions (p < 0.001).

Conclusions

PSF_allpass HN PET improves lesion detectability as compared with 3D-OSEM HN PET. PSF_allpass with an acquisition time between 8 and 10 min provides the best performance for tumour detection.

Incremental Value of a Dedicated Head and Neck Acquisition during 18F-FDG PET/CT in Patients with Differentiated Thyroid Cancer

Objectives

¹⁸F-FDG-PET/CT is a useful tool used to evidence persistent/recurrent disease (PRD) in patients with differentiated thyroid cancer and iodine-refractory lesions. The aim of this study was to compare the diagnostic value at the cervical level of the routine whole-body (WB) acquisition and that of a complementary head and neck (HN) acquisition, performed successively during the same PET/CT study.

Methods

PET/CT studies combining WB and HN acquisitions performed in 85 consecutive patients were retrospectively reviewed by two nuclear medicine physicians. ¹⁸F-FDG uptake in cervical lymph nodes (LN) or in the thyroid bed was assessed. Among the 85 patients, the PET/CT results of the 26 who subsequently underwent neck surgery were compared with surgical and pathological reports. The size of each largest nodal metastasis was assessed by a pathologist.

Results

In the 85 patients, inter-observer agreement was excellent for both WB and HN PET/CT interpretation. Of the 26 patients who underwent surgery, 25 had pathology proven PRD in the neck. Of these 25 patients, 15 displayed FDG uptake on either WB or HN PET. In these 15 patients, HN PET detected more malignant lesions than WB PET did (21/27 = 78% vs. 12/27 = 44%, P = 0.006). Node/background ratios were significantly higher on HN than on WB PET (P<0.0001). Three false-negative studies (20%) on WB PET were upstaged as true-positive on HN PET. The mean size of the largest LN metastasis was 3 mm for the LN detected neither on WB nor on HN PET, 7 mm for the metastasis detected on HN but not on WB PET, and 13 mm for those detected on both acquisitions (P = 0.0004). Receiver-Operating Characteristic analysis showed that area under the curve was higher for HN PET than for WB PET (0.97 [95%CI, 0.90–0.99] vs 0.88 [95%CI, 0.78–0.95], P = 0.009).

Conclusions

HN acquisition improves the ability to detect PRD in the neck compared with WB acquisition alone. We recommend systematically adding an HN acquisition when PET/CT is performed to detect PRD in the neck.

[Importance of PET for surgery of recurrent thyroid cancer]

BACKGROUND

The early detection of recurrent thyroid cancer and focussed surgery are essential for patients' prognosis. Using I-131 whole body scintigraphy is often not sufficient to detect recurrent carcinoma making other imaging methods necessary to identify the tumor. Recent studies showed that positron emission tomography-computed tomography (PET/CT) is able to identify recurrent carcinoma and metastasis at an early stage.

OBJECTIVE

The aim of this study was an evaluation of the impact of PET/CT on diagnostic and operation strategies in recurrent thyroid cancer.

METHODS

A review of the literature was carried out combined with a case report from the daily practice. Furthermore, flow charts were created to clarify the aftercare procedure.

RESULTS

In patients with recurrent thyroid cancer PET/CT significantly increased the identification of recurrent tumors and metastases. Depending on the subtype of cancer, different tracers are used. The use of a metabolically active tracer which shows the increase of tumor metabolism and the morphological correlation of the tumor using a CT scan enable preoperative planning for a focussed surgical approach.

CONCLUSIONS

The PET/CT procedure should be an integral part of the aftercare procedure in thyroid cancer for early identification of recurrent tumors and to enable focussed surgery.

Recurrent thyroid cancer diagnosis: ROC study of the effect of a high-resolution head and neck 18F-FDG PET/CT scan

RATIONALE AND OBJECTIVES

(18)F-fluorodeoxyglucose positron emission tomography/computed tomography ((18)F-FDG PET/CT) has demonstrated significant value in the evaluation of patients with indication of recurrent thyroid cancer with negative conventional workup. The hypothesis of this study was that the addition of a dedicated, high-resolution head and neck scan (HNS) to the standard whole-body scan (WBS) improves the accuracy of the detection and diagnosis of recurrent thyroid cancer.

MATERIALS AND METHODS

Forty-three consecutive patients suspected for recurrent thyroid cancer, as indicated by increased tumor markers, prospectively underwent a WBS and a HNS with (18)F-FDG PET/CT. The patients were followed up to establish ground truth. A receiver operator characteristic (ROC) study with two observers was conducted to evaluate the impact of the additional HNS on the detection and diagnosis of recurrent thyroid cancer. Indices of performance included the area under the ROC curve (AUC), the number of detected abnormal foci, and the size of the detected foci without and with the HNS images.

RESULTS

ROC results showed that the addition of the HNS to the standard WBS increased the average AUC index of performance from 0.69 to 0.96, a statistically significant difference with a confidence interval (CI) of -0.33 to -0.19. Diagnosis was also improved with the average AUC increasing from 0.79 to 0.87 but differences were not statistically significant (CI, -0.19 to 0.04). Interreader agreement was "good" in the detection task and "excellent" in the diagnostic task. The addition of the HNS increased the number of detected foci in the positive patients by an average of 37%, whereas false-positive detections in the negative patients increased by an average of 10%. Reported average maximum lesion size also increased with the HNS addition by an average of 11%.

CONCLUSIONS

The addition of a high-resolution HNS to the standard whole-body PET/CT imaging improves readers' performance in the detection and diagnosis of recurrent thyroid cancer and could greatly benefit patient care.

The value of positron emission tomography (PET) in the management of patients with thyroid cancer

For more than a decade, positron emission tomography (PET) has had an important role in the management of thyroid cancer patients. It may be involved in initial, sometimes inadvertent, diagnosis; in postoperative evaluation; in detection of occult metastases; in the evaluation of thyroid nodules; and in prognostication of metastatic disease. In this review we will update the advances in the application of PET scanning to optimal patient management. The majority of the published studies to date have used 18F-fluoro-deoxyglucose (FDG) as the PET isotope, and unless specifically noted, all references to PET scanning will imply that this tracer has been used.