F-18 FDG-PET/CT Evaluation of Patients With Differentiated Thyroid Cancer With Negative I-131 Total Body Scan and High Thyroglobulin Level

The role of 18 F-FDG-PET/CT in the management of differentiated thyroid cancer

INTRODUCTION

In previous literature, 18 F-FDG-PET/ CT imaging significantly impacted differentiated thyroid cancer (DTC) therapy. Low thyroglobulin (Tg) levels and negative Iodine-131 (131I) whole-body scan (WBS), along with negative 18 F-FDG-PET/ CT, suggested a lesser likelihood of active illness. Positive 18 F-FDG-PET/CT findings, however, were associated with a variety of signs of local recurrence and regional or distant metastases in patients with suspected WBS. We aim to evaluate the utility of 18 F-FDG-PET/CT in managing DTC patients with negative 131I post-therapy WBS and elevated Tg.

MATERIAL AND METHODS

We retrospectively reviewed 55 patients with DTC (76% papillary and 24% follicular). Patients underwent total thyroidectomy or several radioactive iodine (RAI) treatments or both. WBS was performed 5-7 days after RAI treatment. Inclusion criteria were elevated serum Tg, negative anti-Tg auto-antibodies (AbTg) during long-term follow-up, presence of 18F-FDG-PET/CT images, and negative or suspicious WBS.

RESULTS

54% of 18 F-FDG-PET/CTs detected at least one lesion, mainly, cervical lymph nodes (49.9%), mediastinal lymph nodes (40.4%), local recurrence (34%), and bone or tissue metastasis (36.2%). The three major sites of metastasis were lung, bone, and liver. 18 F-FDG-PET/CT identified recurrence or metastasis in 45% of patients with high serum Tg and negative WBS, modifying therapeutic management in half the patients for suitable treatment modality (surgery vs. tyrosine kinase inhibitor).

CONCLUSION

The findings redemonstrate that elevated Tg with negative or suspicious WBS necessitates 18 F-FDG-PET/CT for localization of recurrence. 18 F-FDG-PET/CT is useful in managing locally recurrent or metastatic DTC with high Tg levels. It influences treatment and accurately assesses disease severity.

FDG PET/CT in differentiated thyroid cancer patients with low thyroglobulin levels

OBJECTIVE

To evaluate the usefulness of [18F]fluorodeoxyglucose (FDG) positron emissive tomography (PET)/CT in patients with low detectable thyroglobulin levels suspicious for persistent or recurrent differentiated thyroid cancer (DTC).

METHODS

A retrospective case series study evaluating FDG PET/CT in patients with detectable thyroglobulin (Tg) levels (≥0.20 and <10.00 ng/mL) after initial treatment with total thyroidectomy and I-131 thyroid remnant ablation for pT1-3aN0-1bM0 DTC. Sensitivity, specificity, positive (PPV) and negative predictive value (NPV) of FDG PET/CT were calculated.

RESULTS

Twenty-seven patients underwent FDG PET/CT. Median Tg level at FDG PET/CT was 2.00 ng/mL (range 0.30-9.00). FDG PET/CT was positive in 14 patients (51.9%): lesions suspicious for lymph node metastases were depicted in 12 patients, and lung metastases in 2. DTC was confirmed in 13/14 FDG PET/CT-positive patients. In 9/13 patients with a negative FDG PET/CT, DTC was confirmed ≤3 months after FDG PET/CT. The sensitivity, PPV, specificity and NPV were 59.1, 92.9, 80.0 and 30.8%, respectively.

CONCLUSIONS

This case series shows that FDG PET/CT might be useful to detect persistent or recurrent DTC in patients with low detectable Tg. However, when FDG PET/CT is negative, this does not rule out DTC and further investigations are necessary.

Comparison between Two Different Scanners for the Evaluation of the Role of 18F-FDG PET/CT Semiquantitative Parameters and Radiomics Features in the Prediction of Final Diagnosis of Thyroid Incidentalomas

The aim of this study was to compare two different tomographs for the evaluation of the role of semiquantitative PET/CT parameters and radiomics features (RF) in the prediction of thyroid incidentalomas (TIs) at ¹⁸F-FDG imaging. A total of 221 patients with the presence of TIs were retrospectively included. After volumetric segmentation of each TI, semiquantitative parameters and RF were extracted. All of the features were tested for significant differences between the two PET scanners. The performances of all of the features in predicting the nature of TIs were analyzed by testing three classes of final logistic regression predictive models, one for each tomograph and one with both scanners together. Some RF resulted significantly different between the two scanners. PET/CT semiquantitative parameters were not able to predict the final diagnosis of TIs while GLCM-related RF (in particular GLCM entropy_log2 e GLCM entropy_log10) together with some GLRLM-related and GLZLM-related features presented the best predictive performances. In particular, GLCM entropy_log2, GLCM entropy_log10, GLZLM SZHGE, GLRLM HGRE and GLRLM HGZE resulted the RF with best performances. Our study enabled the selection of some RF able to predict the final nature of TIs discovered at ¹⁸F-FDG PET/CT imaging. Classic semiquantitative and volumetric PET/CT parameters did not reveal these abilities. Furthermore, a good overlap in the extraction of RF between the two scanners was underlined.

Characterization of focal hypermetabolic thyroid incidentaloma: An analysis with F-18 fluorodeoxyglucose positron emission tomography/computed tomography parameters

BACKGROUND

Incidentally found thyroid tumor (thyroid incidentaloma, TI) on F-18 fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET-CT) is reported in 2.5%-5% of patients being investigated for non-thyroid purposes. Up to 50% of these cases have been diagnosed to be malignant by cytological/histological results. Ultrasonography (US) and fine-needle aspiration cytology are recommended for thyroid nodules with high FDG uptake (hypermetabolism) that are 1 cm or greater in size. It is important to accurately determine whether a suspicious hypermetabolic TI is malignant or benign.

AIM

To distinguish malignant hypermetabolic TIs from benign disease by analyzing F-18 FDG PET-CT parameters and to identify a cut-off value.

METHODS

Totally, 12761 images of patients who underwent F-18 FDG PET-CT for non-thyroid purposes at our hospital between January 2016 and December 2020 were retrospectively reviewed, and 339 patients [185 men (mean age: 68 ± 11.2) and 154 women (mean age: 63 ± 15.0)] were found to have abnormal, either focal or diffuse, thyroid FDG uptake. After a thorough review of their medical records, US, and cytological/histological reports, 46 eligible patients with focal hypermetabolic TI were included in this study. The TIs were categorized as malignant and benign according to the cytological/histological reports, and four PET parameters [standardized uptake value (SUV)_max, SUV_peak, SUV_mean, and metabolic tumor volume (MTV)] were measured on FDG PET-CT. Total lesion glycolysis (TLG) was calculated by multiplying the SUV_mean by MTV. Both parametric and non-parametric methods were used to compare the five parameters between malignant and benign lesions. Receiver operating characteristic (ROC) curve analysis was performed to identify a cut-off value.

RESULTS

Each of the 46 patients [12 men (26.1%; mean age: 62 ± 13.1 years) and 34 women (73.9%; mean age: 60 ± 12.0 years)] with focal hypermetabolic TIs had one focal hypermetabolic TI. Among them, 26 (56.5%) were malignant and 20 (43.5%) were benign. SUV_max, SUV_peak, SUV_mean, and TLG were all higher in malignant lesions than benign ones, but the difference was statistically significant (P = 0.012) only for SUV_max. There was a positive linear correlation (r = 0.339) between SUV_max and the diagnosis of malignancy. ROC curve analysis for SUV_max revealed an area under the curve of 0.702 (P < 0.05, 95% confidence interval: 0.550-0.855) and SUV_max cut-off of 8.5 with a sensitivity of 0.615 and a specificity of 0.789.

CONCLUSION

More than half of focal hypermetabolic TIs on F-18 FDG PET-CT were revealed as malignant lesions, and SUV_max was the best parameter for discriminating between malignant and benign disease. Unexpected focal hypermetabolic TIs with the SUV_max above the cut-off value of 8.5 may have a greater than 70% chance of malignancy; therefore, further active assessment is required.

Prognostic Role of 2-[18F]FDG PET/CT Metabolic Volume Parameters in Patients Affected by Differentiated Thyroid Carcinoma with High Thyroglobulin Level, Negative 131I WBS and Positive 2-[18F]-FDG PET/CT

The clinical and prognostic role of 2-deoxy-2-[¹⁸F]fluoro-D-glucose positron emission tomography/computed tomography (2-[¹⁸F]FDG PET/CT) in the study of patients affected by differentiated thyroid carcinoma (DTC) with positive serum thyroglobulin (Tg) level and negative [¹³¹I] whole-body scan ([¹³¹I]WBS) has already been demonstrated. However, the potential prognostic role of semi-quantitative PET metabolic volume features, such as metabolic tumor volume (MTV) and total lesion glycolysis (TLG), has not yet been clearly investigated. The aim of this retrospective study was to investigate whether the main metabolic PET/CT parameters may predict the prognosis. We retrospectively included 122 patients with a positive 2-[¹⁸F]FDG PET/CT for DTC disease after a negative [¹³¹I]WBS with Tg > 10 ng/mL. The maximum and mean standardized uptake value (SUVmax and SUVmean), MTV and TLG of the hypermetabolic lesion, total MTV (tMTV) and total TLG (tTLG) were measured for each scan. Progression-free survival (PFS) and overall survival (OS) curves were plotted according to the Kaplan-Meier analysis. After a median follow up of 53 months, relapse/progression of disease occurred in 87 patients and death in 42. The median PFS and OS were 19 months (range 1-132 months) and 46 months (range 1-145 months). tMTV and tTLG were the only independent prognostic factors for OS. No variables were significantly correlated with PFS. The best thresholds derived in our sample were 6.6 cm³ for MTV and 119.4 for TLG. In patients with negative WBS and Tg > 10 ng/mL, 2-[¹⁸F]FDG PET/CT metabolic volume parameters (tMTV and tTLG) may help to predict OS.

The Use of 18F-FDG PET/CT in Patients with Recurrent Differentiated Thyroid Cancer

Objectives:

¹⁸Fluorine-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) is used to monitor the recurrence in thyroid cancer patients when there is suspicion of metastases. De-differentiated lesions become ¹⁸F-FDG avid with a more aggressive clinical course. The aim of this study was to investigate the use of ¹⁸F-FDG PET/CT in differentiated thyroid cancer.

Methods:

Forty-six patients, either with a negative radioiodine scan or clinical progression and suspicions for metastases with differentiated thyroid cancer that were referred to our department for ¹⁸F-FDG PET/CT scan and evaluated retrospectively. PET/CT findings were correlated with clinical and histopathological findings, serum thyroglobulin (Tg), and anti-Tg levels.

Results:

Twenty-six patients (56.2%) were positive for recurrence in ¹⁸F-FDG PET/CT images. Positive ¹⁸F-FDG PET/CT findings were significantly correlated with the disease stage and Tg levels. Maximum standardized uptake value did not correlate with other findings or patients’ profiles. The cut-off value for Tg was at 52.5 ng/mL having 73.08% sensitivity, 75% specificity, 79.17% positive predictive value, and 68.18% negative predictive value for ¹⁸F-FDG PET/CT imaging.

Conclusion:

¹⁸F-FDG PET/CT is useful for detecting recurrence in differentiated thyroid cancer. Increased Tg levels and stage of the disease were significantly correlated with ¹⁸F-FDG positivity. ¹⁸F-FDG positivity may also provide information about the de-differentiation process that may support the treatment plan.

[18F]-FDG-PET/CT and [18F]-FAZA-PET/CT Hypoxia Imaging of Metastatic Thyroid Cancer: Association with Short-Term Progression After Radioiodine Therapy

PURPOSE

To examine the relationships between 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]-FDG) and hypoxia tracer [¹⁸F]fluoro-azomycinarabinofuranoside ([¹⁸F]-FAZA) and between ¹³¹I and [¹⁸F]-FAZA uptake in patients with metastatic thyroid cancer and to evaluate imaging features associated with short-term progression after ¹³¹I therapy.

PROCEDURES

The study population was 20 patients (17 women and 3 men; mean age, 67 years) with metastatic thyroid cancer who underwent both [¹⁸F]-FDG- and [¹⁸F]-FAZA-positron emission tomography (PET)/X-ray computed tomography (CT) examinations before ¹³¹I therapy. Short-term response to radioiodine was assessed (mean follow-up, 19 months ± 9). PET parameters including [¹⁸F]-FDG-SUVmax, [¹⁸F]-FAZA-SUVmax, and [¹⁸F]-FAZA-tumor-to-muscle [T/M] were obtained. Mann-Whitney U, Wilcoxon signed-rank, or χ² tests were used to assess differences between two quantitative variables or compare categorical data. Predictive factors for short-term progression were investigated with logistic regression analysis.

RESULTS

Eleven lymph node metastatic lesions were identified in 9 patients and 46 distant metastatic lesions (lung, 19; bone, 17; and liver, 10) in 14 patients. A total of 24 ¹³¹I-positive and 33 ¹³¹I-negative lesions were detected. SUVmax was significantly lower with [¹⁸F]-FAZA-PET/CT (1.3 ± 0.6) than with [¹⁸F]-FDG-PET/CT (6.4 ± 5.9, p < 0.001). No significant correlation was observed between [¹⁸F]-FAZA-PET/CT and ¹³¹I imaging concerning visibility (p = 0.36). After ¹³¹I therapy, 31 of 57 metastatic lesions displayed short-term progression. Multivariate logistic regression revealed that [¹⁸F]-FDG-SUVmax (p = 0.022) and [¹⁸F]-FAZA-T/M (p = 0.002) showed significant associations with short-term progression.

CONCLUSIONS

Although [¹⁸F]-FAZA uptake was low in metastatic thyroid cancers, not only glucose metabolism but also hypoxic conditions may be associated with progression after ¹³¹I therapy in patients with metastatic thyroid cancer.

Head-to-Head Comparison of Neck 18F-FDG PET/MR and PET/CT in the Diagnosis of Differentiated Thyroid Carcinoma Patients after Comprehensive Treatment

Simple Summary

The most advanced positron emission tomography–magnetic resonance (PET/MR) combines the high soft tissue contrast of MRI with the high functional/metabolic sensitivity of PET and has the potential to achieve the highest level of diagnostic performance for refractory malignancies in differentiated thyroid cancer (DTC) patients. The utility of PET/MR in the postoperative follow-up of DTC patients has been relatively ambiguous. This retrospective study compared ¹⁸F-fluorodeoxyglucose neck PET/MR with PET/CT head-to-head, in order to evaluate the diagnostic efficacy of PET/MR in assessment malignancy in DTC patients after comprehensive treatment. We determined that PET/MR presented better detection rates, image conspicuity, and sensitivity than PET/CT in recurrent DTC lesions and cervical lymph node metastases. The addition of neck PET/MR scan after whole-body PET/CT may provide more favorable diagnostic information.

Abstract

We explored the clinical value of ¹⁸F-FDG PET/MR in a head-to-head comparison with PET/CT in loco-regional recurrent and metastatic cervical lymph nodes of differentiated thyroid carcinoma (DTC) patients after comprehensive treatment. ¹⁸F-FDG PET/CT and neck PET/MR scans that were performed in DTC patients with suspected recurrence or cervical lymph node metastasis after comprehensive treatment were retrospectively analyzed. Detection rates, diagnostic efficacy, image conspicuity, and measured parameters were compared between ¹⁸F-FDG PET/CT and PET/MR. The gold standard was histopathological diagnosis or clinical and imaging follow-up results for more than 6 months. Among the 37 patients enrolled, no suspicious signs of tumor were found in 10 patients, 24 patients had lymph node metastasis, and 3 patients had both recurrence and lymph node metastases. A total of 130 lesions were analyzed, including 3 malignant and 6 benign thyroid nodules, as well as 74 malignant and 47 benign cervical lymph nodes. Compared with PET/CT, PET/MR presented better detection rates (91.5% vs. 80.8%), image conspicuity (2.74 ± 0.60 vs. 1.9 ± 0.50, p < 0.001, especially in complex level II), and sensitivity (80.5% vs. 61.0%). SUVmax differed in benign and malignant lymph nodes in both imaging modalities (p < 0.05). For the same lesion, the SUVmax, SUVmean, and diameters measured by PET/MR and PET/CT were consistent and had significant correlation. In conclusion, compared with ¹⁸F-FDG PET/CT, PET/MR was more accurate in determining recurrent and metastatic lesions, both from a patient-based and from a lesion-based perspective. Adding local PET/MR after whole-body PET/CT may be recommended to provide more precise diagnostic information and scope of surgical resection without additional ionizing radiation. Further scaling-up prospective studies and economic benefit analysis are expected.

PET/CT in the management of differentiated thyroid cancer

The standard treatment of differentiated thyroid cancer (DTC) consists of surgery followed by iodine-131 (¹³¹I) administration. Although the majority of DTC has a very good prognosis, more aggressive histologic subtypes convey a worse prognosis. Follow-up consists of periodically measurements of serum thyroglobulin, thyroglobulin antibodies and neck ultrasound and ¹²³I/¹³¹I whole-body scan. However, undifferentiated thyroid tumors have a lower avidity for radioiodine and the ability of DTC to concentrate ¹³¹I may be lost in metastatic disease. Positron emission tomography (PET)/computed tomography (CT) has been introduced in the evaluation of patients with thyroid tumors and the 2-[18F]-fluoro-2-deoxyd-glucose (¹⁸F-FDG) has been largely validated as marker of cell's metabolism. According to the 2015 American Thyroid Association guidelines, ¹⁸F-FDG PET/CT is recommended in the follow-up of high-risk patients with elevated serum thyroglobulin and negative ¹³¹I imaging, in the assessment of metastatic patients, for lesion detection and risk stratification and in predicting the response to therapy. It should be considered that well-differentiated iodine avid lesions could not concentrate ¹⁸F-FDG, and a reciprocal pattern of iodine and ¹⁸F-FDG uptake has been observed. Beyond ¹⁸F-FDG, other tracers are available for PET imaging of thyroid tumors, such as Iodine-124 (¹²⁴I), ¹⁸F-tetrafluoroborate and Gallium-68 prostate-specific membrane antigen. Moreover, the recent introduction of PET/MRI, offers now several opportunities in the field of patients with DTC. This review summarizes the evidences on the role of PET/CT in management of patients with DTC, focusing on potential applications and on elucidating some still debating points.

Value of 18F-FDG Hybrid PET/MR in Differentiated Thyroid Cancer Patients with Negative 131I Whole-Body Scan and Elevated Thyroglobulin Levels

Purpose

To evaluate the diagnostic performance of ¹⁸F-FDG PET/MR in detecting recurrent or metastatic disease in patients with differentiated thyroid cancer (DTC) who have increased thyroglobulin (Tg) levels but a negative ¹³¹I whole-body scan (WBS). The relationship between ¹⁸F-FDG PET/MR and serum Tg levels was explored. We also evaluated the therapeutic impact of PET/MR on patient clinical management.

Patients and Methods

Twenty-nine DTC patients with a negative ¹³¹I-WBS of the last post-therapeutic and increased Tg levels under thyroid-stimulating hormone suppression treatment who underwent ¹⁸F-FDG PET/MR examination were retrospectively analyzed.

Results

Of those 29 patients, ¹⁸F-FDG PET/MR findings were true positive, true negative, false positive, and false negative in 18, 7, 2, and 2 patients, respectively. The overall sensitivity, specificity, and accuracy were 90.0%, 77.8%, and 86.2%, respectively. We noticed significant differences in serum Tg levels between the PET/MR-positive and PET/MR-negative patient groups (P=0.049). Receiver operating characteristic curve analysis showed that a Tg level of 2.4 ng/mL was the optimal cut-off value for predicting PET/MR results. The sensitivity, specificity, and accuracy of PET/MR were higher in patients with Tg levels greater than 2.4 ng/mL than in patients with lower levels. By detecting recurrent or metastatic disease, ¹⁸F-FDG PET/MR altered the clinical management in 7 patients (24.1%) of the overall population.

Conclusion

¹⁸F-FDG PET/MR has high diagnostic accuracy for detecting recurrent or metastatic diseases in DTC patients and is useful for clinical management.

Critical Role of 2-[18F]-fluoro-2-deoxy-glucose in Hormonally Active Malignancies

2-[18F]-fluoro-2-deoxyglucose (FDG) is the most commonly used radiotracer and provides valuable information about glucose metabolism. With the advent of newer receptor-based tracers in the management of hormonally active malignancies, the focus has been shifted from FDG. These tracers might be more specific than FDG because they target specific hormone receptors. But because FDG is widely available, this review discusses what information still can be harnessed from this workhorse of molecular imaging. The personalized implementation of FDG imaging in undifferentiated malignancies will help in characterization of tumor and may aid in patient management.

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.

Role of Thyroglobulin Doubling Time in Differentiated Thyroid Cancer and Its Relationship with Demographic-Histopathologic Risk Factors and 18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography Parameters

Background: Aim of this study was to investigate the relationship between thyroglobulin doubling time (TgDT) and basal risk factors and metabolic parameters derived from ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in differentiated thyroid cancer (DTC). Materials and Methods: An analysis of 95 DTC patients who had rising serum thyroglobulin (Tg) levels under levothyroxine (LT4) suppression after radioiodine therapy was made. TgDT was calculated for 28/95 patients. The relationship between TgDT and basal demographic and histopathologic risk factors, preablative Tg, and antithyroglobulin antibody (ATg) levels and metabolic parameters was analyzed. Results: In 28 patients (15M, 13F, mean age: 52.6 ± 17.6) that TgDT could be calculated, ¹⁸F-FDG PET/CT was positive in 12 patients. Median TgDT was lower in ¹⁸F-FDG PET/CT positive patients compared to the negative cases (p < 0.05). Patients with skeletal metastasis or local recurrence had a shorter DT compared to the patients with lung metastasis. TgDT was correlated with peak standardized uptake value (SUV_peak) (p < 0.05). Maximum standardized uptake value (SUV_max) was correlated with tumor size (p < 0.05) and mean standardized uptake value (SUV_mean) with tumor size and vascular invasion (p < 0.05). Median SUV_max and SUV_mean were higher in follicular cancer or poor histological variants of papillary DTC compared to papillary cancer classical variant patients Conclusion: TgDT may be predictive of a positive ¹⁸F-FDG PET/CT in DTC. Skeletal metastasis and local recurrence are related to shorter TgDT. Greater tumor size, vascular invasion, and follicular cancer or poor variants of papillary carcinoma are related with higher SUV_max and SUV_mean. Larger scale studies are needed to confirm results and to calculate a possible cutoff of TgDT for a positive ¹⁸F-FDG PET/CT study.

68Ga-DOTA-RGD2 Positron Emission Tomography/Computed Tomography in Radioiodine Refractory Thyroid Cancer: Prospective Comparison of Diagnostic Accuracy with 18F-FDG Positron Emission Tomography/Computed Tomography and Evaluation Toward Potential Theranostics

Background: Radioiodine therapy (¹³¹I) forms a principal cornerstone in the management of differentiated thyroid cancer. Radioiodine-refractory differentiated thyroid cancer (RAIR-DTC) presents a challenge in detection of structural disease in patients with evidence of biochemical disease and in treatment of the disease using alternate therapies. The present study was conducted to compare the diagnostic accuracy (in terms of sensitivity and specificity) of ⁶⁸Ga-DOTA-RGD₂ positron emission tomography (PET)/computed tomography (CT) as a neoangiogenesis imaging modality with ¹⁸F-FDG PET/CT, the current standard in diagnostic algorithm of RAIR-DTC, and to evaluate the radiotracer avidity on ⁶⁸Ga-DOTA-RGD₂ PET/CT for potential theranostics. Methods: Forty-four RAIR-DTC patients with negative post-therapy ¹³¹I scan were prospectively enrolled. Serum thyroglobulin (sTg) and anti-thyroglobulin (ATg) measurements were performed with levothyroxine withdrawal (thyrotropin-stimulated state), and ¹⁸F-FDG PET/CT and ⁶⁸Ga-DOTA-RGD₂ PET/CT studies were performed within 1 week of each other. Follow-up was performed with histopathology/sTg/ATg/conventional imaging. The findings of ¹⁸F-FDG PET/CT and ⁶⁸Ga-DOTA-RGD₂ PET/CT were compared with the reference standard to obtain sensitivity, specificity, and overall accuracy. Degree of radiotracer uptake on ⁶⁸Ga-DOTA-RGD₂ PET/CT was described as tumor to background (T/B) and tumor to liver (T/L) ratios of standardized uptake value. Results:⁶⁸Ga-DOTA-RGD₂ PET/CT detected a total of 123 lesions, with an overall sensitivity, specificity, and accuracy of 82.3%, 100%, and 86.4%, respectively. ¹⁸F-FDG PET/CT detected a total of 144 lesions, with an overall sensitivity, specificity, and accuracy of 82.3%, 50%, and 75%, respectively. Most commonly identified disease sites were nodal metastases (82.9%), followed by thyroid bed lesions (10.5%). 82.1% of patients positive on ⁶⁸Ga-DOTA-RGD₂ PET/CT showed lesional radiotracer uptake higher than the liver (grade IV and grade V). Conclusions:⁶⁸Ga-DOTA-RGD₂ PET/CT showed a similar sensitivity to, but higher specificity and overall accuracy than ¹⁸F-FDG PET/CT in detection of lesions in RAIR-DTC patients. This novel application of the angiogenesis imaging modality can prove useful in RAIR-DTC, especially in patients with negative/suspicious ¹⁸F-FDG PET/CT. Furthermore, since the majority of patients (82.1%) positive on ⁶⁸Ga-DOTA-RGD₂ PET/CT showed radiotracer avidity toward the higher end of the spectrum (grade IV and grade V), novel ¹⁷⁷Lu-based theranostics can be a potential treatment for these patients.

Head-to-head comparison of F-18 FDG PET/CT in radioidine refractory thyroid cancer patients with elevated versus suppressed TSH levels a pilot study

Introduction

To perform a head-to-head comparison of the uptake pattern of F-18 fluorodeoxyglucose in positron emission computed tomography (FDG PET/CT) in radioiodine refractory thyroid carcinomas (RAIR) in the same patient under elevated TSH levels (eTSH) and suppressed TSH levels (sTSH).

Methods

FDG PET/CT studies were performed under two conditions: levothyroxine intake (sTSH) and 30 days after hormonal withdrawal (eTSH). SUVmax values and the number of lesions detected (local recurrence and metastases in cervical and distant lymph nodes, lungs and bone) where blindly evaluated. Blood serum TSH and Tg levels were obtained prior to both studies. FDG PET/CT imaging, neck ultrasound, biopsy and follow-up were considered the reference standard.

Results

Fifteen patients performed both eTSH and sTSH FDG PET/CT studies. Both were positive for metastases in 80% of the patients. eTSH FDG PET/CT studies did not reveal increased uptake (p = 0.0640) and did not demonstrate a higher number of lesions (p = 0.320) when compared to sTSH FDG PET/CT studies. There was no change in the clinical management of these patients.

Conclusions

eTSH FDG PET/CT in patients with RAIR did not show more metastases in comparison to sTSH FDG PET/CT and there was no impact in clinical management of patients. Elevating TSH levels (whether by hormonal withdrawal or recombinant TSH) in patients being submitted to FDG PET/CT may not be necessary.

A Review of TENIS Syndrome in Hospital Pulau Pinang

Introduction:

The treatment for differentiated thyroid cancers (DTCs) has always been radioactive iodine 131I therapy after definitive surgical management. Clinicians are faced with therapeutic challenges when dealing with patients having thyroglobulin-elevated negative iodine scintigraphy (TENIS) syndrome (elevated serum thyroglobulin [Tg] levels but negative whole-body scans [WBSs]).

Objective:

The aim of the study was to determine the prevalence of TENIS syndrome in our local setting and to evaluate the use of 18-fluoro-2-deoxyglucose (18F-FDG) positron emission tomography-computed tomography (PET-CT) in the management.

Methodology:

The data from DTC patients treated in the Department of Nuclear Medicine, Hospital Pulau Pinang from December 1, 2010, to November 30, 2016, with negative WBS and elevated Tg were reviewed. These patients should have undergone 18F-FDG PET-CT to be included in the study.

Results:

Only forty (10.4%) out of a total of 386 patients treated in Hospital Pulau Pinang during the study fulfilled the inclusion criteria. There were 28 women (70%) with median age of 59 years old. Thirty-four patients (85%) had papillary thyroid cancer (PTC) and six patients had follicular thyroid cancer. The use of 18F-FDG PET-CT revealed 23 patients (57.5%) with 18F-FDG avid metastases suggesting dedifferentiation of thyroid cancers. Based on this study, the probability of detecting FDG-avid disease is higher (P = 0.03) if 18F-FDG PET-CT was performed when Tg ≥15 ng/mL.

Conclusion:

TENIS syndrome constitutes a significant number of cases in our setting. Our data suggest a cutoff Tg ≥15 ng/mL for performing 18F-FDG PET-CT for these patients would be more beneficial than the currently American Thyroid Association recommended cutoff of 10 ng/mL.

A Case of Thyroid Papillary Carcinoma: Remarkable Decrease in Multiple Lung Metastases within 40 Years after a Single Administration of Radioiodine without Thyroidectomy and with Later Anaplastic Transformation

Differentiated thyroid carcinoma is an uncommon malignancy of childhood and adolescence that is unique because it has an overall favorable prognosis despite its relatively high rate of nodal and distant metastases. Total thyroidectomy and positive ¹³¹I therapy are recommended for cases with pulmonary metastases. In contrast, anaplastic thyroid cancer is one of the most aggressive malignancies that have an unfavorable and miserable prognosis. We report a case with an impressively long history. The patient had multiple pulmonary metastases that had been diagnosed by ¹³¹I administration when he was 14 years old, about 45 years before he underwent thyroidectomy. He had been kept unaware of his disease by his family and received no treatment for most of his life. Pulmonary nodules were noted at several medical checkups and showed a remarkable decrease in size during the untreated 44-year period after the ¹³¹I administration. At age 58, his thyroid cancer was first detected and total thyroidectomy was performed, with subsequent radioiodine therapy for pulmonary metastases. Unfortunately, anaplastic carcinoma developed and he died of disseminated tumors later.

Usefulness of PET/CT in the diagnosis of recurrent or metastasized differentiated thyroid carcinoma

The aim of the present study was to determine the usefulness of the positron emission tomography/computed tomography (PET/CT) with ¹⁸F-fluorodeoxyglucose (FDG) in the detection of recurrence or metastasization of differentiated thyroid carcinoma (DTC) in patients with abnormal thyroglobulin levels and negative findings on the ¹³¹I-diagnostic whole-body scanning (dWBS). Fifteen patients with DTC, abnormal thyroglobulin levels, and negative ¹³¹I-dWBS findings were scanned using the ¹⁸F-FDG PET/CT. Positive diagnosis was based on postoperative histologic findings, and clinical and imaging follow-up results obtained in the subsequent 6 months. In addition, preoperative and postoperative thyroglobulin levels were compared. Using the findings of ¹⁸F-FDG PET/CT and data on confirmed positive diagnosis, sensitivity and positive predictive value (PPV) were calculated. Sensitivity and PPV of PET/CT in detecting recurrence or metastasisization of DTC were 93.30 and 91.40%, respectively. Furthermore, postoperative thyroglobulin levels were markedly lower compared to the preoperative levels (respectively, 4.67±1.71 vs. 58.53±18.34 ng/ml; p<0.05). PET/CT scan with ¹⁸F-FDG is an informative technique for the detection of recurrent or metastasized DTC in patients with abnormal thyroglobulin levels and negative ¹³¹I-dWBS findings.

Clinical Usefulness of F-18 FDG PET/CT in Papillary Thyroid Cancer with Negative Radioiodine Scan and Elevated Thyroglobulin Level or Positive Anti-thyroglobulin Antibody

PURPOSE

Elevated thyroglobulin (Tg) levels, along with a negative radioiodine scan, present a clinical problem for the diagnosis of recurrence in papillary thyroid cancer (PTC) patients. The purpose of this study was to assess (1) the usefulness of (18)F-fluorodeoxyglucose (F-18 FDG) positron emission tomography (PET)/computed tomography (CT) for PTC patients with negative diagnostic radioiodine scan and elevated serum Tg level or positive anti-thyroglobulin antibody (TgAb), and (2) the effect of endogenous thyroid stimulating hormone (TSH) stimulation (ETS) on detecting recurrence in these circumstances.

METHODS

Eighty-four patients with negative diagnostic radioiodine scan and elevated serum Tg or positive TgAb under ETS were included. Correlation with clinicopathological features and recurrence, detectability of FDG PET/CT and cut-off value of serum Tg for recurrence in PTC patients with these circumstance were assessed. In addition, detectability of F-18 FDG PET/CT under ETS and suppression were compared.

RESULTS

In Cox regression analysis, only serum Tg level was significantly associated with recurrence (P < 0.001, HR = 1.13; 95 % CI, 1.061-1.208). The cut-off level of Tg was 21.5 ng/mL (AUC, 0.919; P < 0.001) for discriminating the recurrence in the patients with positive PET/CT finding. The sensitivity, specificity, PPV, NPV, and accuracy of F-18 FDG PET/CT for detecting recurrence were 64 %, 94 %, 86 %, 81 %, and 83 %. In the analysis of F-18 FDG PET/CT under ETS, the sensitivity, specificity, PPV, NPV and accuracy was 64 %, 94 %, 88 %, 81 % and 83 %. Those under TSH suppression were 67 %, 92 %, 80 %, 85 % and 83 %.

CONCLUSIONS

F-18 FDG PET/CT, although less sensitive, showed high specificity, PPV, NPV, and accuracy and therefore can be useful for the patients with negative diagnostic radioiodine scan and elevated serum Tg or positive TgAb. In addition, FDG PET/CT under ETS does not seem to have an additive role in detecting recurrence in these patients.

Prognostic role of 18F-FDG PET/CT in the postoperative evaluation of differentiated thyroid cancer patients

PURPOSE

The aim of this study was to evaluate the role of F-FDG PET/CT performed after surgery but before radioiodine therapy in patients with differentiated thyroid cancer.

PROCEDURES

FDG PET/CT was performed off l-thyroxine in 60 newly diagnosed differentiated thyroid cancer patients. Clinical and hematological evaluation as well as high-resolution neck ultrasound were performed. All patients underwent a complete follow-up (range, 6-67 months; mean [SD], 31.7 [20.6] months). The date of recurrence or the most recent office visit was recorded. Progression-free survival (PFS) is the primary end point of this study. Analysis was performed by Cox proportional hazards model. Survival curves were generated using Kaplan-Meier estimates, and the log-rank test was used to assess significance.

RESULTS

FDG PET/CT was negative in 63% of patients, 20% had FDG thyroid bed uptake, 5% distant metastases, and 12% lymph node FDG uptake. In patients with positive FDG PET/CT scan (ie, those with distant metastases or lymph node uptake), a higher rate of recurrence was observed (50% vs 6%, P < 0.05). Thyroglobulin, neck ultrasound, stage, and FDG PET/CT correlated with PFS at univariate analysis. At multivariate analysis, only thyroglobulin and FDG PET/CT continued to be predictors of PFS. Patients with a negative FDG PET/CT scan have a better PFS either in the whole group or in those with elevated thyroglobulin level (both >2 ng/mL and >10 ng/mL).

CONCLUSIONS

FDG PET/CT was abnormal in 17% of patients. Moreover, FDG PET/CT has an independent prognostic role, with a better PFS in patients with a negative scan.

PET/CT in the management of thyroid cancers

OBJECTIVE

Thyroid cancer is the most common endocrine cancer. This review evaluates the established use of (18)F-FDG PET/CT in papillary, follicular, Hürthle cell, anaplastic, and medullary thyroid cancers. The significance of incidental diffuse and focal thyroid FDG uptake is discussed. The evolving value of non-FDG radiotracers, including (124)I, (18)F-dihydroxyphenylalanine, and (68)Ga somatostatin analogs, is summarized.

CONCLUSION

PET/CT is a valuable imaging test, in the appropriate clinical context, for the management of thyroid cancers.

Diagnostic value of 18F-FDG PET/CT in patients with TENIS syndrome: correlation with thyroglobulin levels

OBJECTIVE

The aim of the study was to disclose the place of (18)F-FDG PET/CT to predict recurrent disease in patients with differentiated thyroid cancer (DTC), negative radioiodine whole-body scan (WBS) and high serum thyroglobulin (Tg).

METHODS

Seventy-one patients who underwent total thyroidectomy followed by radioactive iodine ablation and had negative radioiodine WBS but elevated Tg levels underwent PET/CT. They were followed up for 6-50 months (median 23) for the occurence of recurrent disease as detected by either clinical findings, other imaging modalities or histopathological examination. The place of PET/CT findings at baseline to predict the presence of recurrent disease was evaluated. Correlation between PET/CT findings and Tg levels was examined and a threshold for Tg level above which the predictive value of PET/CT was highest was determined.

RESULTS

PET/CT was positive for recurrent disease in 38 (53.5%) patients. The sensitivity, specificity, PPV, NPV and diagnostic accuracy of PET/CT to predict the occurence of recurrent disease at follow-up were 68.8, 78.3, 86.8, 54.5 and 71.9%, respectively. The sensitivity, accuracy and PPV of PET/CT increased with increasing Tg levels. The highest diagnostic accuracy of PET/CT, with a sensitivity of 76.2% and a specificity of 100% to detect recurrent disease appeared to be at a Tg level greater than 29 ng/mL.

CONCLUSION

Our findings suggest that (18)F-FDG-PET/CT is a valuable tool to predict the occurence of recurrent disease in patients with DTC, negative WBS and elevated Tg levels. PET/CT positivity has been shown to be strongly and positively correlated with Tg levels in this patient subset.

Therapeutic impact of (18)F-FDG PET/CT in recurrent differentiated thyroid carcinoma

PURPOSE

(18)F-fluorodeoxyglucose-positron emission tomography/computed tomography (PET/CT) has proved effective in detecting recurrent or metastatic differentiated thyroid carcinoma (DTC) in the follow-up of operated DTC patients with high thyroglobulin (Tg) levels and negative findings on radioiodine whole-body scan. The aim of this retrospective study was to assess the impact of PET/CT on the planning of appropriate treatment for known recurrent disease in operated DTC patients.

MATERIALS AND METHODS

The study concerned 44 consecutive DTC patients (36 papillary, 8 follicular), who underwent total thyroidectomy and thyroid remnant ablation with (131)I and PET/CT. All patients had proven or strongly suspected recurrent disease judging from neck ultrasound (US) and fine-needle aspiration cytology, and detectable basal Tg levels.

RESULTS

PET/CT findings were positive in 25/44 patients (56.81 %) and negative in 19. A positive PET/CT result predicted resectable tumour recurrences in 19/25 patients, but also detected additional tumour sites that prompted changes to the treatment plan in 6/25 patients (24 %). A negative PET/CT result led to clinical monitoring for 11/19 patients (57.89 %).

CONCLUSIONS

PET/CT can help select patients, who might benefit from a tailored therapy by improving the detection of local recurrences not apparent on neck US or metastases.

Correlation of 18F-FDG PET/CT findings with histopathological results in differentiated thyroid cancer patients who have increased thyroglobulin or antithyroglobulin antibody levels and negative 131I whole-body scan results

AIM

This study aimed to investigate the correlation of 18F-FDG PET/CT findings with histopathological results in defining the recurrence of the disease in patients with differentiated thyroid cancer (DTC) who have increased thyroglobuline (Tg) or anti-Tg antibody (TgAb) levels and negative 131I whole-body scan (WBS) result.

PATIENTS AND METHODS

A total of 59 patients with DTC (44 women, 15 men; mean [SD] age, 48.2 [22.6] years) were included in the study. All of the patients had previous papillary thyroid cancer, and all of them had undergone radioiodine ablation after a total or near-total thyroidectomy. After radioiodine ablation, patients were followed up for approximately 2.5 years. In the follow-up, the patients with negative 131I-WBS results and increased Tg or TgAb levels under thyroid-stimulating hormone-stimulated conditions underwent an 18F-FDG PET/CT scan to determine any recurrence of disease. There were negative or uncertain findings in the neck ultrasonography and/or thorax CT in most of the patients. The 18F-FDG PET/CT findings were compared with the histopathological results in all patients.

RESULTS

Although 49 patients had increased Tg levels, the remaining 10 patients had increased TgAb levels. In patients with high Tg levels, 18F-FDG PET/CT scan results were negative in 10 and positive in 39 patients. In this patient group, 18F-FDG PET/CT findings were true positive, true negative, false positive, and false negative in 32, 3, 7, and 7 patients, respectively. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of 18F-FDG PET/CT in this group were calculated as 82%, 30%, 80%, 30%, and 71%, separately. In the receiver operating characteristic analysis, a 4.5 cutoff SUV(max) was calculated with 75% sensitivity and 70% specificity for predicting disease recurrence. Cutoff Tg level was calculated as 20.7 ng/mL with 75% sensitivity and 55% specificity. In 10 patients with high TgAb levels, 18F-FDG PET/CT was true positive, true negative and false positive in 6, 2, and 2 patients, respectively. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of 18F-FDG PET/CT in this patient group were calculated as 100%, 50%, 75%, 100%, and 80%, respectively.

CONCLUSIONS

18F-FDG PET/CT may be a useful imaging modality in defining recurrence of the disease in patients with DTC who have increased Tg or TgAb levels, negative 131I-WBS results, and negative or suspicious neck ultrasonography and/or thorax CT results. Although 18F-FDG PET/CT seems to be a more sensitive method in patients with increased TgAb levels, the number of patients is not enough to make a substantiated comment.

18-fluorodeoxyglucose positron emission tomography in the early diagnostic workup of differentiated thyroid cancer patients with a negative post-therapeutic iodine scan and detectable thyroglobulin

BACKGROUND

Surgery and high-dose radioactive iodine ((131)I) treatment are the cornerstones in the treatment of differentiated thyroid cancer. Patients without (131)I uptake on the post-therapeutic whole body scan (WBS), but with detectable thyroglobulin (Tg) during thyroxine withdrawal (Tg-off), are evaluated with an 18-fluorodeoxyglucose positron emission tomography ((18)F-FDG-PET) for tumor localization within three months. The yield of (18)F-FDG-PET imaging and clinical usefulness of a Tg-off cutoff value to predict a positive scan were assessed.

METHODS

From 2002 to 2011, 52 patients with a negative WBS and concurrent detectable Tg-off were evaluated. Thirty-five PET scans were performed during initial treatment, 17 after recurrent disease. Thirty-two patients were on substitution therapy, 17 were evaluated with endogenous thyrotropin elevation, and 3 after recombinant human thyrotropin stimulation. To determine the Tg-off cutoff value, a receiver operating characteristic curve was used.

RESULTS

Nine (17%) (18)F-FDG-PET scans were true positive, 3 (6%) false positive, 36 (69%) true negative, and 4 (8%) false negative (sensitivity 69%, specificity 92%). In 13%, a true-positive scan resulted in a change in the clinical management. The area under the receiver operating characteristic curve is 0.82 [CI 0.64-0.99] (p<0.01), and the Tg-off cutoff value is 38.00 ng/mL (sensitivity 67%, specificity 95%). Ninety percent of (18)F-FDG-PET true-positive patients had a Tg-off >2.00 ng/mL.

CONCLUSIONS

An (18)F-FDG-PET within three months after a negative WBS with detectable Tg-off showed additional tumor localization in 17% of the patients, leading to a change in clinical management in 13%. A clinically useful Tg-off cutoff value was not found, but 90% of positive (18)F-FDG-PET scans occurred in patients with a Tg-off >2.00 ng/mL.

Elevated 99mTc 3PRGD2 activity in benign metastasizing leiomyoma

PET/CT scan was performed in a 43-year-old woman to evaluate pulmonary nodules/masses. The images showed that there was only minimal FDG activity in the masses. However, these soft tissue masses in the lungs had significantly elevated (99m)Tc 3PRGD(2) activity. Pathological examination demonstrated that this patient suffered benign metastasizing leiomyoma.

Increasing the yield of recombinant thyroid-stimulating hormone-stimulated 2-(18-fluoride)-flu-2-deoxy-D-glucose positron emission tomography-CT in patients with differentiated thyroid carcinoma

OBJECTIVE

The aim of this study was to assess the accuracy of recombinant thyroid-stimulating hormone (rTSH)-stimulated 2-(18-fluoride)-flu-2-deoxy-D-glucose ((18)F-FDG) positron emission tomography (PET)-CT in detecting recurrence in patients with differentiated thyroid cancer.

METHODS

Consecutive (18)F-FDG PET-CT scans performed with rTSH stimulation between 2007 and 2010 in patients with a history of papillary or follicular thyroid carcinoma were reviewed. PET-CT findings were correlated with thyroglobulin levels, and histological, clinical and radiological follow-up.

RESULTS

58 rTSH PET-CT scans were performed in 47 patients with a previous thyroidectomy and radioiodine ablation. The only indication for PET-CT was a raised thyroglobulin level in 46 of 58 scans, with the remainder for characterisation of equivocal radiology or staging. 25 (43%) of PET-CT scans were positive for recurrent disease. Histological correlation was available for 21 (36%) scans. The overall sensitivity, specificity, positive predictive value and negative predictive value were 69%, 76%, 72% and 73%, respectively. Median unstimulated thyroglobulin in true-positive scans was 33 µg l(-1) and 2.2 µg l(-1) in the remainder (p=0.12). 4 of 35 (11%) patients with unstimulated thyroglobulin levels <10 µg l(-1) had true-positive scans. Median stimulated thyroglobulin in true-positive scans was 320 µg l(-1), and 10 µg l(-1) in the remainder (p=0.046), with no positive scans with a stimulated thyroglobulin <8 µg l(-1). PET-CT directly influenced patient management in 17/58 (29%) scans.

CONCLUSION

rTSH PET-CT is a useful imaging technique for detecting disease recurrence in patients with iodine-resistant differentiated thyroid cancer. Low stimulated thyroglobulin levels are potentially useful in identifying patients unlikely to benefit from a PET-CT scan.

Value of the negative PET-FDG in the middle term follow-up of differentiated thyroid cancer in patients with negative 131 I-Na scan and elevated thyroglobulin serum levels

OBJECTIVE

This study has aimed to analyze the evolution of patients diagnosed with differentiated thyroid carcinoma (DTC) with a negative (131)I-Na whole body scan (WBS), high levels of serum thyroglobulin (Tg) and negative (18F)fluorodeoxyglucose positron emission tomography (PET-FDG) study.

MATERIAL AND METHODS

Twenty-three patients diagnosed and treated for DTC were studied retrospectively. Patients were aged between 23 and 83 and had shown, between January 2001 and December 2002, negative WBS, Tg values in a range of suspected recurrence or metastasis (Tg>2 ng / mL with thyroid hormone withdrawal) and a negative PET-FDG study. The patients were monitored clinically, radiologically and analytically for a minimum period of 4 years. After this, a new evaluation was made of their state of disease with a control WBS, also observing the evolution of Tg. All WBS were performed with a 185 MBq diagnostic dose of (131)I-Na.

RESULTS

In 18/23 patients, Tg decreased and in 5 it increased. Four patients (17%) were free of active disease (negative WBS Tg<2 ng / mL). A total of 16 patients (70%) were free of disease according to the WBS but had elevated Tg. Three patients (13%) had disease and high levels of Tg, two of them with positive WBS and the third with (99m)Tc-MIBI scan and CT positive.

CONCLUSIONS

Most patients with a negative WBS, high Tg serum levels and negative FDG PET had good evolution, with descending Tg levels, normal levels even being reached in a significant percentage of them.

Effectiveness of [(124)I]-PET/CT and [(18)F]-FDG-PET/CT for localizing recurrence in patients with differentiated thyroid carcinoma

Although the prognosis of patients with differentiated thyroid carcinoma (DTC) is generally encouraging, a diagnostic dilemma is posed when an increasing level of serum thyroglobulin (Tg) is noted, without detection of a recurrent tumor using conventional imaging tools such as the iodine-131 whole-body scanning (the [(131)I] scan) or neck ultrasonography (US). The objective of the present study was to evaluate the diagnostic value of [(124)I]-PET/CT and [(18)F]-FDG-PET/CT in terms of accurate detection of both iodine- and non-iodine-avid recurrence, compared with that of conventional imaging such as the [(131)I] scan or neck ultrasonography (US). Between July 2009 and June 2010, we prospectively studied 19 DTC patients with elevated thyroglobulin levels but who do not show pathological lesions when conventional imaging modalities are used. All involved patients had undergone total thyroidectomy and radioiodine (RI) treatment, and who had been followed-up for a mean of 13 months (range, 6-21 months) after the last RI session. Combined [(18)F]-FDG-PET/CT and [(124)I]-PET/CT data were evaluated for detecting recurrent DTC lesions in study patients and compared with those of other radiological and/or cytological investigations. Nine of 19 patients (47.4%) showed pathological [(18)F]-FDG (5/19, 26.3%) or [(124)I]-PET (4/19, 21.1%) uptake, and were classed as true-positives. Among such patients, disease management was modified in six (66.7%) and disease was restaged in seven (77.8%). In particular, the use of the described imaging combination optimized planning of surgical resection to deal with locoregional recurrence in 21.1% (4/19) of patients, who were shown to be disease-free during follow-up after surgery. Our results indicate that combination of [(18)F]-FDG-PET/CT and [(124)I]-PET/CT affords a valuable diagnostic method that can be used to make therapeutic decisions in patients with DTC who are tumor-free on conventional imaging studies but who have high Tg levels.

I-131 SPECT/CT elucidates cryptic findings on planar whole-body scans and can reduce needless therapy with I-131 in post-thyroidectomy thyroid cancer patients

BACKGROUND

Interpreting I-131 whole-body scans (WBSs) after thyroidectomy for thyroid cancer is not simple. There are scans in which interpretation is speculative because of cryptic findings (CF). Complexity is added in scans that are done a week after an ablative or therapeutic dose of I-131 because not only is I-131-labeled thyroxine (T4) distributed throughout the body, but inorganic I-131 that is derived from the de-iodination of T4 may be also detected. We present our observations regarding the analysis of CF on WBS using I-131 single-photon emission computed tomography (SPECT) in fusion with noncontrast computed tomography (CT), referred to here and elsewhere as I-131 SPECT/CT.

METHODS

Forty of 184 WBSs in 38 thyroidectomized thyroid cancer patients were followed up with I-131 SPECT/CTs. The SPECT/CT images were acquired after a tracer dose of I-131 (n=82) or a week after an ablative or therapeutic dose of I-131 (n=102).

RESULTS

Among 184 WBSs, 40 (22%) had CF. In 35 patients the WBS was negative for metastatic disease except for the CF and 5 patients had evidence of thyroid cancer in addition to the CF. There were 49 CF in the planar scans that were localized by SPECT/CT. These were characterized as physiological uptake in gingiva, thymus, gall bladder, menstrual blood, uterine fibroid, recto-sigmoid, colon, and bladder. Also observed was uptake in sites that represented nonthyroidal pathology including dental abscess, hiatal hernia, renal cyst, and struma ovarii. SPECT/CT suggested that 10 of the CF were actually of thyroid origin. In 40 SPECT/CT scans, the images contributed to interpreting the scan. In 15 of 40 patients the SPECT/CT analysis of WBS was performed with tracer doses of I-131 and was important for determining whether to administer ablative I-131 treatment. In another 25 patients, in whom SPECT/CT was performed after ablative or therapeutic doses of 131-I, information regarding the characterization of CF by SPECT/CT was useful in determining if thyroid cancer metastases or thyroid remnants were present.

CONCLUSIONS

I-131 SPECT/CT is a useful tool to characterize atypical or CF on WBS by differentiating thyroid remnant or cancer from physiologic activity or nonthyroid pathology. In the past, uptake on a WBS that was not explicable as physiologic activity was identified as putative or possible thyroid cancer and generally was treated with I-131. Now, by identifying activity in some possible cancer sites as not thyroid cancer, SPECT/CT can reduce inappropriate treatment with I-131. SPECT/CT of WBS performed after ablative doses of 131-I is useful in determining the nature of CF and therefore likely providing prognostic information.

PET-CT scans in recurrent or persistent differentiated thyroid cancer: is there added utility beyond conventional imaging?

BACKGROUND

Integrated positron emission tomography (PET)-computed tomography (CT) may have advantages over conventional imaging in localizing recurrent or persistent differentiated thyroid cancer.

METHODS

A retrospective review of patients who underwent PET-CT scans was performed. Results were compared with contrast CT, magnetic resonance imaging, ultrasonography, and radioactive iodine (RAI) scans.

RESULTS

Thirty patients (mean age, 49.9 ± 17 years) underwent 36 PET-CT scans, mostly for elevated thyroglobulin levels and negative RAI scans (30 scans). Fifty percent (18/36) of PET-CT scans showed increased uptake in the neck, 11 of 36 (31%) in the chest, 3 of 36 (8.3%) in bone, and 6 of 36 (16.6%) in other areas. PET-CT had overall sensitivity, specificity, and positive predictive values of 73.9%, 61.5%, and 77.3% respectively. To assess the added value of PET-CT, we focused on the 21 scans performed after conventional imaging in 20 patients. PET-CT provided additional information in 2 (10%) patients, both of whom were spared interventions. However, PET-CT underestimated extent of disease in 3 (15%) patients and led to unnecessary interventions in 3 (15%) additional patients.

CONCLUSION

PET-CT has reasonable sensitivity in the detection of recurrent thyroid cancer. However, the added value of PET-CT may be seen only in a limited number of patients after good quality, conventional imaging. Further studies are needed to determine the most cost-effective approach to managing these patients.