The role of FDG-PET/CT in differentiated thyroid cancer patients with negative iodine-131 whole-body scan and elevated anti-Tg level

FAPI PET/CT provides higher uptake and better target to back ground in recurrent and metastatic tumors of patients with Iodine refractory papillary thyroid cancer compared with FDG PET CT

PURPOSE

The role of fibroblast activation protein inhibitor (FAPI) PET CT scan is not well documented in papillary thyroid cancer (PTC) patients. Patients with radioiodine refractory PTC and high thyroglobulin levels need PET/CT scan which is generally done by 18F FDG. In the current study, the diagnostic performance of 68Ga FAPI and FDG PET/CT scans were compared head to head in patients with radioiodine refractory PTC.

METHOD

Fourteen patients with negative whole body Iodine scans and high thyroglobulin levels underwent whole body PET scans with, respectively, 120-310 and 145-370 MBq 68Ga FAPI-46 and 18F FDG. SUVmax of the back ground in the blood pool and liver and the hottest, largest and average neck, mediastinum, lung and bone lesions were calculated and compared.

RESULT

Ten patients had at least one active (SUVmax>blood pool) lesion similarly in two scans. The liver and blood pool SUVmax values were 1.25(0.2) and 1.7(0.2) in FAPI and 2.65(0.2) and 2.0(0.2) in FDG PET images, respectively. The difference was significant (p=0.001). Standard SUV of the hottest lesion to liver was above 3 in all FAPI scans but in half of FDG scans. Target lesion number and intensity were similar between two PET studies but in a patient out of 5 pulmonary metastatic patients, pulmonary nodules were negative (SUVmax=0.9) in FDG while positive (SUVmax= 3.8) in FAPI images (i.e. 20% patient upstaged).

CONCLUSION

FAPI accumulates in the recurrent and metastatic lesions of patients with Iodine refractory PTC at least as well as FDG with particular privileges as lower injected activity and lower back ground.

The Diagnostic Value of 18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography in Differentiated Thyroid Cancer Patients with Elevated Thyroglobulin/Thyroglobulin Antibody Levels and Negative Iodine Scintigraphy: A Systematic Review and Meta-Analysis

Background: The objective of this study is to evaluate the diagnostic accuracy of 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) in detecting recurrence in patients with differentiated thyroid cancer (DTC) who have negative whole-body scans (WBSs) but elevated serum thyroglobulin (Tg) or thyroglobulin antibody (TgAb) levels. Methods: This systematic review/meta-analysis was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis for Diagnostic Test Accuracy criteria (International Prospective Register of Systematic Reviews registration number: CRD42022340924). A comprehensive search of the MEDLINE, EMBASE, and Cochrane databases identified articles reporting the diagnostic accuracy of FDG PET/CT for the detection of recurrence in patients with DTC with negative WBS and elevated serum Tg or TgAb levels published between January 2012 and June 2023. Meta-analyses were performed to determine the diagnostic accuracy of FDG PET/CT on the total target population as well as on subgroups stratified by serum Tg or TgAb, and thyrotropin (TSH) stimulation status at the time of FDG PET/CT. The Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) framework was applied to evaluate the quality of evidence and the strength of recommendations to facilitate translation of the meta-analysis results into practical recommendations for clinical guidelines. Results: A total of 24 studies involving 1988 patients were included for analysis. The overall pooled sensitivity and specificity values were 0.87 (95% confidence interval [CI] = 0.83-0.92; I2 = 75%) and 0.84 (CI = 0.80-0.89; I2 = 44%), respectively. Subgroup analyses revealed no significant differences in the diagnostic accuracy of FDG PET/CT in patients stratified by serum Tg or TgAb levels, and TSH stimulation status at the time of PET/CT. Treatment plans were changed following FDG PET/CT imaging in 40% (CI = 34-47%; I2 = 39%) of cases. The quality level of evidence for using FDG PET/CT was moderate in both sensitivity and specificity according to the GRADE system. Conclusion: There is moderate quality evidence demonstrating the high diagnostic accuracy of FDG PET/CT in detecting recurrence in patients with DTC with negative WBS and elevated serum Tg or TgAb levels. This evidence corroborates the current guidelines' endorsement of FDG PET/CT as a diagnostic tool in such patients.

Correlation between metabolic uptake of F-18-FDG-PET/computed tomography and thyroglobulin level in differentiated thyroid cancer patients with suspected recurrence

OBJECTIVE

Our objective is to determine if there is correlation between serum thyroglobulin and SUVmax of the main lesion detected in F18-FDG-PET/CT scan, in differentiated thyroid cancer (DTC) patients with suspected recurrence.

METHODS

All DTC patients enrolled in this prospective study, received at least one dose of radioactive iodine. During follow-up, they are suspected to have a recurrence due to elevated tumor markers although negative iodine whole-body scans. For all patients, F18-FDG-PET/CT scanning was performed. A 3D volume of interest was generated over the liver and main lesion to obtain maximum standardized uptake value (SUVmax). We calculated the lesion/liver ratio. Follow-up and/or histopathological examination were the gold standard. Pearson's correlation coefficient was calculated between thyroglobulin and SUVmax of the main lesion.

RESULTS

Sixty-eight patients were recruited in this study. F18-FDG-PET/CT identified suspicious malignant lesions in 42 patients, equivocal in 18 patients, while 8 patients showed no abnormal findings. Fifty-two, 6, 8, and 2 patients were true positive, true negative, false positive, and false negative respectively. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were 72%, 57% 87%, 35%, and 69% respectively. The median SUVmax and lesion/liver ratio were significantly higher in the malignant lesions than that of benign lesions (3.9 vs. 1.3 and 1.45 vs. 0.54 respectively). We found that the main lesion SUVmax and lesion/liver ratio have a positive moderate correlation with thyroglobulin (0.338 and 0.325 respectively).

CONCLUSION

In DTC patients with suspected recurrence, SUVmax of F18-FDG-PET/CT lesion showed a moderate positive correlation with serum thyroglobulin.

An Appraisal and Update of Fluorodeoxyglucose and Non-Fluorodeoxyglucose-PET Tracers in Thyroid and Non-Thyroid Endocrine Neoplasms

Endocrine neoplasms and malignancies are a diverse group of tumors with varied clinical, histopathologic, and functional features. These tumors vary from sporadic to hereditary, isolated entities to multiple neoplastic syndromes, functioning and non functioning tumors, unifocal locally invasive, and advanced to multifocal tumors with disseminated distant metastases. The presence of various specific biomarkers and specific receptor targets serves as valuable tools for diagnosis, prognosis, and management. PET-CT with FDG and a multitude of novel and specific radiotracers towards specific therapeutic targets mandates personalization of their use, so as to ensure maximum clinical benefit in the management of these neoplasms.

Personalized management of differentiated thyroid cancer in real life - practical guidance from a multidisciplinary panel of experts

PURPOSE

The standard of care for differentiated thyroid carcinoma (DTC) includes surgery, risk-adapted postoperative radioiodine therapy (RaIT), individualized thyroid hormone therapy, and follow-up for detection of patients with persistent or recurrent disease. In 2019, the nine Martinique Principles for managing thyroid cancer were developed by the American Thyroid Association, European Association of Nuclear Medicine, Society of Nuclear Medicine and Molecular Imaging, and European Thyroid Association. In this review, we present our clinical practice recommendations with regard to implementing these principles in the diagnosis, treatment, and long-term follow-up of patients with DTC.

METHODS

A multidisciplinary panel of five thyroid cancer experts addressed the implementation of the Martinique Principles in routine clinical practice based on clinical experience and evidence from the literature.

RESULTS

We provide a suggested approach for the assessment and diagnosis of DTC in routine clinical practice, including the use of neck ultrasound, measurement of serum thyroid-stimulating hormone and calcitonin, fine-needle aspiration, cytology, and molecular imaging. Recommendations for the use of surgery (lobectomy vs. total thyroidectomy) and postoperative RaIT are also provided. Long-term follow-up with neck ultrasound and measurement of serum anti-thyroglobulin antibody and basal/stimulated thyroglobulin is standard, with ¹²³/¹³¹I radioiodine diagnostic whole-body scans and ¹⁸F-fluoro-2-deoxyglucose positron emission tomography/computed tomography suggested in selected patients. Management of metastatic DTC should involve a multidisciplinary team.

CONCLUSIONS

In routine clinical practice, the Martinique Principles should be implemented in order to optimize clinical management/outcomes of patients with DTC.

Diagnostic performance of PET in thyroid cancer with elevated anti-Tg Ab

We aimed to explore the role of the diagnostic accuracy of F-18 fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) for the detection of recurrent and/or metastatic diseases in differentiated thyroid cancer (DTC) patients with progressively and/or persistently elevated TgAb levels and negative radioactive iodine whole-body scan (RI-WBS) through a systematic review and meta-analysis. The MEDLINE, EMBASE and Cochrane Library database, from the earliest available date of indexing through June 30, 2017, were searched for studies evaluating the diagnostic performance of F-18 FDG PET/CT for the detection of recurrent and/or metastatic diseases in DTC patients with progressively and/or persistently elevated TgAb levels and negative RI-WBS. We determined the sensitivities and specificities across studies, calculated positive and negative likelihood ratios (LR+ and LR-). Across 9 studies (515 patients), the pooled sensitivity for F-18 FDG PET/CT was 0.84 (95% CI; 0.77-0.89) a pooled specificity of 0.78 (95% CI; 0.67-0.86). Likelihood ratio (LR) syntheses gave an overall positive likelihood ratio (LR+) of 3.8 (95% CI; 2.5-5.7) and negative likelihood ratio (LR-) of 0.21 (95% CI; 0.14-0.30). The pooled diagnostic odds ratio (DOR) was 18 (95% CI; 10-34). The area (AUC) under the hierarchical summary receiver-operating characteristic (HCROC) curve was 0.88 (95% CI: 0.85-0.90). F-18 FDG PET or PET/CT demonstrated moderate sensitivity and specificity for the detection of recurrent and/or metastatic diseases in DTC patients with progressively and/or persistently elevated TgAb levels and negative RI-WBS.

18F-FDG Pet-Guided External Beam Radiotherapy in Iodine-Refractory Differentiated Thyroid Cancer: A Pilot Study

Introduction

To evaluate the clinical response rate after a postoperative ¹⁸F-FDG PET/CT guided external beam radiotherapy (EBRT) in Iodine-refractory differentiated thyroid cancer.

Material and Methods

Patients with thyroid cancer locally recurrent after total thyroidectomy plus metabolic radiotherapy and treated with radical EBRT were included. Inclusion criteria were detectable thyroglobulin (Tg), negative postmetabolic radiotherapy whole body scintigraphy, and no surgical indications. The pretreatment ¹⁸F-FDG PET/CT resulted positive in all cases (loggia, lymph nodes, and lung). EBRT was delivered with IMRT-SIB technique. A ¹⁸F-FDG PET/CT revaluation and Tg dosage were performed 3 months after the treatment.

Results

Sixteen consecutive patients were included in this analysis (median follow-up: 6–44 months). Post-EBRT ¹⁸F-FDG PET/CT showed CR in 43.7%, PR in 31.2%, SD in 25.0% patients, and PD due to lung metastases in 12.5%. Overall response rate was 75.0% (CI 95%: 41.4–93.3%). Tg levels decreased in 75.0% with a median Δ of 68.0%. Two-year PFS and OS rates were 80.0% and 93.0%, respectively. Acute G3 toxicity occurred in 18.7% and late G2 toxicity in 12.5%.

Conclusions

  ¹⁸F-FDG PET/CT was useful in target definition for radiotherapy planning, identifying positive areas not detected with ¹³¹I scintigraphy. IMRT based EBRT was feasible and our results encourage future prospective studies. This clinical trial is registered with ID: NCT03191643.

Prognostic role of FDG PET/CT in patients with differentiated thyroid cancer treated with 131-iodine empiric therapy

BACKGROUND

To assess the long-term prognostic value of F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in patients with differentiated thyroid carcinoma (DTC) undergoing empiric radioiodine (RAI) therapy due to raising values of thyroglobulin (Tg).

METHODS

Forty-nine patients with histological diagnosis of DTC (31 with papillary and 18 with follicular carcinoma) follow-up for a mean period of 7.9 ± 5 years after empiric RAI therapy were retrospectively analyzed.

RESULTS

FDG-PET/CT was negative in 15 (30.6%) patients and positive in 34 (69.4%), whereas postradioiodine therapy whole body scan (t-WBS) was negative in 16 (32.7%) and positive in 33 (67.3%) patients. FDG-PET/CT and t-WBS were in agreement in 32 patients (7 both negative and 25 both positive); on the contrary, in 17 patients there was disagreement between FDG-PET/CT and t-WBS (P =ns). At short-term follow-up, Tg normalized in 19 (38.8%) patients and was unchanged or increased in 30 (61.2%). Of the 15 patients with negative FDG-PET/CT, 11 (73.3%) showed Tg normalization, whereas of the 34 patients with positive FDG-PET/CT, only 8 (23.5%) had Tg normalization (χ =8.9, P < .005). At multivariate analysis, FDG-PET/CT and Tg normalization at short-term follow-up were independent predictors of disease-free survival (χ =26.3, P < .0001), while Tg normalization was the only variable associated with overall survival χ =7.2, P < .01).

CONCLUSION

FDG-PET/CT in association with Tg normalization at short-term follow-up may be useful for long-term prognostic stratification in DTC patients.

Diagnostic Performance of 18F-FDG PET/CT in Papillary Thyroid Carcinoma with Negative 131I-WBS at first Postablation, Negative Tg and Progressively Increased TgAb Level

Differentiated thyroid cancer (DTC) patients with negative serum thyroglobulin (Tg), negative ¹³¹I whole–body scintigraphy (¹³¹I-WBS) at first post-ablation and progressively increased TgAb level are a relatively rare entity in the follow-up after total thyroidectomy and radioactive iodine therapy. The value of ¹⁸F-FDG PET/CT in detecting the recurrence of disease in these patients has only been reported in a small case series. The goal of this study was to investigate the diagnostic accuracy of ¹⁸F-FDG PET/CT in detecting recurrent disease in these specific PTC patients and to identify risk factors for patients with positive ¹⁸F-FDG PET/CT results. Eighty-two PTC patients who had ¹⁸F-FDG PET/CT scans with negative Tg, negative ¹³¹I-WBS at first post-ablation and progressively increased TgAb levels were included. We found that the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of ¹⁸F-FDG PET/CT in this patient group were determined as 84%, 72%, 92%, 57% and 82%, respectively. ¹⁸F-FDG PET/CT scan had a good diagnostic performance and should be performed routinely in PTC patients with negative Tg, negative ¹³¹I-WBS at first postablation and progressively increased TgAb level, especially when span for progressively increased TgAb level ≥ 3 years and/or progressively increased TgAb value up to 150 IU/mL.

Serum midkine as a surrogate biomarker for metastatic prediction in differentiated thyroid cancer patients with positive thyroglobulin antibody

Serum thyroglobulin (Tg) is the main post-operative tumor biomarker for patients with differentiated thyroid cancer (DTC). However, the presence of thyroglobulin antibodies (TgAb) can interfere with Tg level and invalidate the test. In this study, we aimed to investigate the predicative value of midkine (MK) as a cancer biomarker for DTC patients with positive TgAb before the first ¹³¹I therapy. MK levels were measured by enzyme-linked immunosorbent assay in 151 recruited DTC patients after exercising strict inclusion and exclusion criteria. There were 28 TgAb positive DTC patients with metastases and 123 DTC patients without metastases. The value of pre-¹³¹I-ablative MK to predict metastasis was assessed by receiver operating characteristic (ROC) curves in these two groups of patients. MK levels in the TgAb positive DTC patients were significantly higher than the DTC patients without metastases. ROC showed good predictability of MK, with an area under the curve of 0.856 (P < 0.001), and a diagnostic accuracy of 83% at the optimal cut-off value of 550 pg/ml. In conclusion, we show that MK can potentially be used as a surrogate biomarker for predicting DTC metastases when Tg is not suitable due to TgAb positivity.

Can the American Thyroid Association Risk of Recurrence Predict Radioiodine Refractory Disease in Differentiated Thyroid Cancer?

OBJECTIVE

The aim of this study was to compare the TNM staging system and the American Thyroid Association (ATA) recurrence risk classification in predicting radioiodine refractory disease (RRD) in differentiated thyroid cancer (DTC) and to analyze the correlation of stimulated thyroglobulin (Tg) levels and rate of Tg elevation with the standardized uptake value on ¹⁸F-fludeoxyglucose (FDG) PET/CT scan.

METHODS

RRD was indicated through the retrospective analysis of consecutive ¹⁸F-FDG PET/CT scans in DTC with stimulated Tg >10 ng/ml and negative ¹³¹I NaI whole-body scans (WBS). Tg elevation velocity was compared to the likelihood of a positive scan. The ATA recurrence risk and TNM staging system were compared to see which of them better predicted the subsequent development of RRD.

RESULTS

Fifty-eight of 636 subjects developed RRD: 52 papillary and 6 follicular thyroid cancer. The median time between diagnosis and a negative WBS was 24 months (range 12-240). RRD developed in 11 low-risk, 32 intermediate-risk and 15 high-risk patients. A better response to therapy was seen in the low-risk versus the intermediate- and high-risk groups. ¹⁸F-FDG PET/CT scans had a diagnostic accuracy of 94.8%, sensitivity of 97.7%, specificity of 85.7%, positive predictive value of 95.6% and negative predictive value of 92%. There was no correlation between the Tg level or rate of rise and a positive scan. Overall, PET-CT upstaged 18 (31%) cases, leading to a change in management in 20 (35%) cases.

CONCLUSION

The TNM and ATA staging systems show no significant difference in predicting the development of RRD. RRD is less likely in stage I, II and low-risk patients. There is no correlation between the level or rate of Tg rise and a positive ¹⁸F-FDG PET/CT scan.

Designing and Developing PET-Based Precision Model in Thyroid Carcinoma: The Potential Avenues for a Personalized Clinical Care

This communication enumerates the current uses and potential areas where PET could be clinically utilized for developing "precision medicine" type model in thyroid carcinoma. (1) In routine clinics, PET imaging (with fluorodeoxyglucose [FDG]) is utilized to investigate patients of differentiated thyroid carcinoma (DTC) with high thyroglobulin and negative iodine scintigraphy (TENIS) and in medullary carcinoma thyroid (MCT) when the tumor markers (eg, calcitonin and carcino embryonic antigen [CEA]) are raised postoperatively (PET with FDG, ⁶⁸Ga-DOTA-NOC/TATE, FDOPA). Both are examples of management personalization, where PET-computed tomography (CT) has been found substantially useful in detecting sites of metastatic disease and making decision with regard to feasibility and planning of surgery on an individual patient basis. (2) The next important area of management personalization is in patients of TENIS with metastatic disease not amenable to surgery through examining FDG-PET findings in tandem with radio iodine scan and ⁶⁸Ga-DOTA-TATE/NOC PET/CT. Heterogeneous behavior of the metastatic lesions is frequently observed clinically: analyzing the findings of three studies aids in sub-segmenting patients into subgroups and thereby deciding upon the best approach (observation with LT4 suppression vs PRRT vs tyrosine kinase inhibitors) that could be individualized in a given case. (3) In metastatic/inoperable MCT, ⁶⁸Ga-DOTA-TATE/NOC PET-CT helps in deciding upon feasibility of targeted PRRT in an individual patient and helps in follow-up and response evaluation. (4) Disease prognostification with FDG-PET is evolving both in DTC and MCT, where FDG avidity would indicate an aggressive biology, though the implication of this from treatment viewpoint is unclear at this point. Conversely, a negative FDG-PET in DTC and TENIS would suggest a favorable prognosis in an individual. (5) Iodine-124 PET/CT has the added potential of obtaining lesional dosimetry compared to the SPECT approach, and could help in selecting appropriate doses on an individual basis.

F18-FDG-PET for recurrent differentiated thyroid cancer: a systematic meta-analysis

Background

Positron emission tomography (PET) with fluor-18-deoxy-glucose (FDG) is widely used for diagnosing recurrent or metastatic disease in patients with differentiated thyroid cancer (DTC).

Purpose

To assess the diagnostic accuracy of FDG-PET for DTC in patients after ablative therapy.

Material and Methods

A systematic search was conducted in Medline/PubMed, EMBASE, Cochrane Library, Web of Science, and Open Grey looking for all English-language original articles on the performance of FDG-PET in series of at least 20 patients with DTC having undergone ablative therapy including total thyroidectomy. Diagnostic performance measures were pooled using Reitsma’s bivariate model.

Results

Thirty-four publications between 1996 and 2014 met the inclusion criteria. Pooled sensitivity and specificity were 79.4% (95% confidence interval [CI], 73.9–84.1) and 79.4% (95% CI, 71.2–85.4), respectively, with an area under the curve of 0.858.

Conclusion

F18-FDG-PET is a useful method for detecting recurrent DTC in patients having undergone ablative therapy.

The role of early 18F-FDG PET/CT in therapeutic management and ongoing risk stratification of high/intermediate-risk thyroid carcinoma

Little is known about the role in ongoing risk stratification of fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) performed early after radioactive iodine (RAI) ablation in differentiated thyroid carcinoma (DTC). The aim of the study is to investigate whether 18F-FDG PET/CT performed early after RAI ablation is useful to detect disease and to influence therapy and ongoing risk stratification. Patients with high/intermediate risk of recurrent DTC were included. 18F-FDG PET/CT scan was performed within 6 months after RAI ablation. We confirmed results with other imaging techniques, pathology reports, or follow-up. We classified the patient response as excellent, acceptable, or incomplete. Modified Hicks criteria were used to evaluate clinical impact. We included 81 patients with high/intermediate risk of recurrent DTC. Forty-one (50.6%) had positive uptake in 18F-FDG PET/CT, with negative (131)I whole-body scan ((131)I WBS). Sensitivity, specificity, and diagnostic accuracy of 18F-FDG PET/CT were 92.5, 90.2, and 91.4%, respectively. 18F-FDG PET/CT results had an impact on therapy in 38.3% of patients. One year after initial therapy, 45.7% showed excellent response, 8.6% acceptable response, and 45.7% incomplete response. A statistically significant relationship was found between negative 18F-FDG PET/CT and excellent response (80 vs. 12.2%, p < 0.001; OR 52.8). 18F-FDG PET/CT scan performed early in surveillance of patients with high/intermediate-risk thyroid carcinoma provides important additional information not available with conventional follow-up methods and had a high impact on therapy. A negative 18F-FDG PET/CT predicts an excellent response to therapy in the new ongoing risk stratification.

Evaluating Positron Emission Tomography Use in Differentiated Thyroid Cancer

BACKGROUND

Using the Surveillance, Epidemiology, and End Results-Medicare database, a substantial increase was found in the use of positron emission tomography (PET) scans after 2004 in differentiated thyroid cancer (DTC) patients. The reason for the increased utilization of the PET scan was not clear based on available the data. Therefore, the indications for and outcomes of PET scans performed at an academic institution were evaluated.

METHODS

A retrospective cohort study was performed of DTC patients who underwent surgery at the University of Michigan Health System from 2006 to 2011. After identifying patients who underwent a PET scan, indications, rate of positive PET scans, and impact on management were evaluated. For positive scans, the location of disease was characterized, and presence of disease on other imaging was determined.

RESULTS

Of the 585 patients in the cohort, 111 (19%) patients had 200 PET scans performed for evaluation of DTC. Indications for PET scan included: elevated thyroglobulin and negative radioiodine scan in 52 scans (26.0%), thyroglobulin antibodies in 13 scans (6.5%), rising thyroglobulin in 18 scans (9.0%), evaluation of abnormality on other imaging in 22 scans (11.0%), evaluation of extent of disease in 33 scans (16.5%), follow-up of previous scan in 57 scans (28.5%), other indications in two scans (1.0%), and unclear indications in three scans (1.5%). The PET scan was positive in 124 studies (62.0%); positivity was identified in the thyroid bed on 25 scans, cervical or mediastinal lymph nodes on 105 scans, lung on 28 scans, bone on four scans, and other areas on 14 scans. Therapy following PET scan was surgery in 66 cases (33.0%), chemotherapy or radiation in 23 cases (11.5%), observation in 110 cases (55.0%), and palliative care in one case (0.5%). Disease was identifiable on other imaging in 66% of cases. PET scan results changed management in 59 cases (29.5%).

CONCLUSIONS

In this academic medical center, the PET scan was utilized in 19% of patients. Indications for the PET scan included conventional indications, such as elevated thyroglobulin with noniodine avid disease, and more controversial uses, such as evaluation of extent of disease or abnormalities on other imaging tests. PET scan results changed management in about 30% of cases.

Fluorodeoxyglucose positron emission tomography/computerized tomography in differentiated thyroid cancer management: Importance of clinical justification and value in predicting survival

INTRODUCTION

The purpose of this study was to evaluate the added value of follow-up fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) to clinical assessment and predicting survival outcome in patients with differentiated thyroid cancers.

METHODS

This is an institutional review board approved, retrospective study of 202 biopsy-proven thyroid cancer patients at a single tertiary centre. A total of 327 follow-up or surveillance PET/CT scans done 6 or more months from initial treatment completion were included in this study. Median follow-up from completion of primary treatment was 94 months (range, 6.17-534.1 months). Overall survival benefit was measured using Kaplan-Meier plots with a Mantel-Cox log-rank test. Multivariate Cox regression model is provided with clinical covariates.

RESULTS

Of the 327 PET/CT scans from 202 patients, 161 were positive and 166 as negative for recurrence or metastasis. A total of 23 patients died during the study period. Patients with a positive PET/CT scan had shorter overall survival than those who had a negative scan (P < 0.0001, hazard ratio 6.1 (3.0-14.3) ). In the context of clinical assessment, PET/CT identified recurrence in 50% (25/50) of scans without prior clinical suspicion and ruled out recurrence in 36.8% (102/277) of scans with prior clinical suspicion. In a multivariate Cox regression model, factors associated with overall survival were stage (P < 0.0001), time to scan (P = 0.0005) and PET/CT result (P < 0.0001).

CONCLUSION

FDG PET/CT performed in follow-up more than 6 months from primary treatment completion adds value to clinical judgment and a prognostic marker of overall survival in thyroid cancer patients.