Impact of combined FDG-PET/CT and MRI on the detection of local recurrence and nodal metastases in thyroid cancer

Match Point: Nuclear Medicine Imaging for Recurrent Thyroid Cancer in TENIS Syndrome-Systematic Review and Meta-Analysis

Background/Objectives: Disease recurrence and resistance to radioiodine (RAI) therapy are major challenges in the management of differentiated thyroid cancer (DTC). In particular, the TENIS (Thyroglobulin Elevated Negative Iodine Scintigraphy) syndrome, characterised by elevated thyroglobulin (Tg) serum levels in addition to a negative radioiodine whole body scan (WBS), complicates disease monitoring and treatment decisions. Conventional imaging techniques often fail to detect disease in WBS-negative patients with rising Tg levels, leading to limitations in therapeutic intervention. This systematic review and meta-analysis aims to evaluate the diagnostic accuracy of nuclear imaging modalities in detecting disease recurrence in patients with the TENIS syndrome and to provide insights to guide therapeutic approaches in this complex clinical scenario. Methods: A comprehensive search of PubMed/MEDLINE and EMBASE databases up to March 2024 was performed according to PRISMA guidelines. Eligible studies were selected, and quality assessment was performed with the QUADAS-2 tool. For each study, relevant data were extracted and synthesised. A meta-analysis of the diagnostic accuracy of [18F]FDG PET/CT was performed, and patient-based pooled sensitivity and specificity were calculated using a random-effects model. Statistical heterogeneity between studies was assessed using the I2 statistic. Results: Of the 538 studies initially identified, 22 were included in the systematic review, of which 18 were eligible for meta-analysis. The eligible studies, mainly focused on [18F]FDG PET/CT, showed variable sensitivity and specificity for the detection of RAI-refractory thyroid cancer lesions. For [18F]FDG PET/CT, pooled estimates displayed a sensitivity of 0.87 (95% CI: 0.82-0.90) and a specificity of 0.76 (95% CI: 0.61-0.86), with moderate heterogeneity between studies. Conclusions: [18F]FDG PET/CT remains central in the detection of disease recurrence in patients with the TENIS syndrome. The emergence of novel radiopharmaceuticals with specific molecular targets is a promising way to overcome the limitations of [18F]FDG in these patients and to open new theranostics perspectives. This review highlights the great potential of nuclear medicine in guiding therapeutic strategies for RAI-refractory thyroid cancer.

Single Institution Experience in the Management of Locally Advanced (pT4) Differentiated Thyroid Carcinomas

BACKGROUND

Locally infiltrating (T4) differentiated thyroid carcinomas (DTC) represent a challenge. Surgical strategy and adjuvant therapy should be planned balancing morbidity and oncologic outcome. A series of patients with T4 DTC who underwent multidisciplinary evaluation and treatment is reported. The main study endpoints were the oncologic outcome, complication rates, and risk factors for tumor recurrence.

PATIENTS AND METHODS

All DTC cases operated between 2009 and 2021 were reviewed and T4 DTC cases were identified. En bloc resection of inferior laryngeal nerve (ILN), tracheal, and/or internal jugular vein (IJV) was performed in cases of massive infiltration. In cases of pharyngoesophageal junction (PEJ) invasion, the shaving technique was always applied.

RESULTS

Among 4775 DTC cases, 60 were T4. ILN infiltration was documented in 45 cases (en bloc resection in 9), tracheal infiltration in 14 (tracheal resection in 2), PEJ invasion in 11 (R0 resection in 7 cases and < 1 cm residual tissue in 4 cases), IJV resection in 6, and laryngeal in 2. In total, 11 postoperative ILN palsy, 23 transient hypoparathyroidisms, and 2 hematomas requiring reoperation were registered. Final histology showed 7 pN0, 22 pN1a, and 31 pN1b tumors. Aggressive variants were observed in 47 patients. All but 1 patient underwent radioiodine treatment, 12 underwent adjuvant external beam radiation therapy (EBRT), and 2 underwent chemotherapy. At a median follow-up of 58 months, no tumor-related death was registered, and seven patients required reoperation for recurrence. Tracheal invasion was the only significant factor negatively impacting recurrence (p = 0.045).

CONCLUSIONS

A multidisciplinary approach is essential for the management of T4 DTC. Individualized and balanced surgical strategy and adjuvant treatments, in particular EBRT, ensure control of locally advanced disease with acceptable morbidity.

Diagnostic significance of MRI versus CT using identical PET data in patients with recurrent differentiated thyroid cancer: A PET/MRI study

In this retrospective study we compared magnet resonance imaging (MRI) and computed tomography (CT) each combined with identical 2-deoxy-2-[18F] fluoro-D-glucose or 2-[18F] F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) data in patients with recurrent differentiated thyroid cancer (DTC). In total 42 patients with DTC were examined. All patients underwent FDG PET/MRI and CT, the latter originating from one of the following examinations: I-131 single photon emission computed tomography/CT (32/42), low dose FDG PET/CT (5/42) or diagnostic FDG PET/CT (5/42). Two readers assessed FDG PET/MRI as well as FDG PET/CT, with the latter CT coming from one of the above examinations performed at a maximum temporal interval of 5 days from PET/MRI. Local recurrence, cervical lymph node - and pulmonary metastases were assessed in a consensus read. Lesions rated with a high malignancy score (score 4 or 5) were further analyzed. Every malignant lesion was verified if it was identified by one of both or by both modalities. In 20 of 42 patients altogether 100 malignant lesions were present. In 11/20 patients in total 15 local recurrences (15 in MRI/ 9 in CT: 9 CT/MRI, 6 MRI only, 0 CT only; P = .04) were found with a statistically significant better performance of MRI. Regarding lymph node metastases, in total 13 lesions (12 in MRI/ 8 in CT: 7 CT/MRI, 5 MRI only, 1 CT only; P = .22) in 8/20 patients were found with no significant difference between both modalities. Furthermore, in 9/20 patients in total 72 lung lesions (40 in MRI/ 63 in CT: 31 CT/MRI, 9 MRI only, 32 CT only; P = .001) were found with a statistically significant better performance of CT. In 33/42 patients follow up was available and supported the observations. In patients with recurrent DTC, PET/MRI showed superiority compared to PET/CT in evaluation of the neck region. PET/MRI was inferior to PET/CT in evaluation of the lung. PET/MRI in combination with a low dose CT of the lung may thus represent the ideal staging tool in patients with recurrent DTC.

Prognostic Value of Hybrid PET/MR Imaging in Patients with Differentiated Thyroid Cancer

Background: Hybrid positron emission tomography (PET)/magnetic resonance (MR) is an emerging imaging modality with great potential to provide complementary data acquired at the same time, under the same physiological conditions. The aim of this study was to evaluate the prognostic value of hybrid 18F-fluorodeoxyglucose (FDG) PET/MR in patients with differentiated thyroid cancer (DTC) who underwent total thyroidectomy and radioactive iodine therapy for suspicion of disease relapse. Methods: Between November 2015 and February 2017, 55 patients underwent hybrid 18F-FDG PET/MR. Assessment of positive MR was made considering all sequences in terms of malignancy based on the morphological T2-weighted features and the presence of restricted diffusivity on diffusion-weighted imaging images and both needed to be positive on the same lesion. Both foci with abnormal 18F-FDG uptake, which corresponded to tissue abnormalities on the MR, and tracer accumulation, which did not correspond to normal morphological structures, were considered positive. Results: During follow-up (mean 42 ± 27 months), 29 patients (53%) had disease recurrence. In the Cox univariate regression analysis age, serum Tg level ≥ 2 ng/mL, positive short tau inversion recovery (STIR), and positive PET were significant predictors of DTC recurrence. Kaplan−Meier survival analyses showed that patients with Tg ≥ 2 ng/mL had poorer outcomes compared to those with serum Tg level < 2 ng/mL (p < 0.05). Similarly, patients with positive STIR and positive PET had a worst outcome compared to those with negative STIR (p < 0.05) and negative PET (p < 0.005). Survival analysis performed in the subgroup of 36 subjects with Tg level ≥ 2 ng/mL revealed that patients with positive PET had a worst outcome compared to those with negative PET (p < 0.05). Conclusions: Age, serum Tg level ≥ 2 ng/mL, positive STIR, and positive 18F-FDG PET were significant predictors of DTC recurrence. However, the serum Tg level was the only independent predictor of DTC. Hybrid PET/MR imaging may have the potential to improve the information content of one modality with the other and would offer new opportunities in patients with DTC. Thus, further studies in a larger patient population are needed to understand the additional value of 18F-FDG PET/MR in patients with DTC.

PET/MRI in paediatric disease

Nuclear medicine and molecular imaging have a small but growing role in the management of paediatric and neonatal diseases. During the past decade, combined PET/MRI has emerged as a clinically important hybrid imaging modality in paediatric medicine due to diagnostic advantages and reduced radiation exposure compared to alternative techniques. The applications for nuclear medicine, radiopharmaceuticals and combined PET/MRI in paediatric diagnosis is broadly similar to adults, however there are some key differences. There are a variety of clinical applications for PET/MRI imaging in children including, but not limited to, oncology, neurology, cardiovascular, infection and chronic inflammatory diseases, and in renal-urological disorders. In this article, we review the applications of PET/MRI in paediatric and neonatal imaging, its current role, advantages and disadvantages over other hybrid imaging techniques such as PET/CT, and its future applications. Overall, PET/MRI is a powerful imaging technology in diagnostic medicine and paediatric diseases. Higher soft tissue contrasts and lower radiation dose of the MRI makes it the superior technology compared to other conventional techniques such as PET/CT or scintigraphy. However, this relatively new hybrid imaging has also some limitations. MRI based attenuation correction remains a challenge and although methodologies have improved significantly in the last decades, most remain under development.

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.

Radioiodine Retention Within Dilated Common Biliary Duct Mimicking Metastatic Thyroid Cancer Diagnosed by the Combination of SPECT/CT and MRI

A 55-year-old woman with papillary thyroid carcinoma under total thyroidectomy and cervical lymph node dissection was referred for I radioiodine therapy. Posttherapeutic whole-body scintigraphy revealed increased focal uptake in the right upper abdomen, which localized to the region of the head of the pancreas on SPECT/CT fusion images. Further evaluation with MRI affirmed the radioiodine retention corresponded to bile duct dilation.

Diagnostic performance of MRI to detect metastatic cervical lymph nodes in patients with thyroid cancer: a systematic review and meta-analysis

AIM

To evaluate the diagnostic performance of magnetic resonance imaging (MRI) in the diagnosis of metastatic cervical lymph nodes.

MATERIALS AND METHODS

Ovid-MEDLINE and EMBASE databases were searched up until 12 June 2018. Eleven articles were included in the qualitative systematic review and nine of the 11 in the quantitative analysis. Two radiologists independently performed data extraction and methodological quality assessment using the Quality Assessment of Diagnostic Accuracy Studies-2 tool. A qualitative systematic review and quantitative analysis were performed, followed by a meta-regression analysis to determine factors causing heterogeneity.

RESULTS

The pooled sensitivity and specificity in the diagnosis of metastatic cervical lymph nodes were 80% (95% confidence interval [CI]: 68-88%) and 85% (95% CI: 63-95%), respectively. The sensitivity and false-positive rate (correlation coefficient, 0.655) showed a positive correlation due to a threshold effect, which was responsible for heterogeneity across the studies, as indicated by a Q-test (p<0.01) and Higgins I² statistic (sensitivity, I²=90.11%; specificity, I²=92.49%). In the meta-regression analysis, fat-suppressed imaging, and the analysis method were significant factors influencing the heterogeneity in diagnostic performance.

CONCLUSIONS

MRI shows moderate diagnostic performance in the diagnosis of metastatic lymph nodes in patients with thyroid cancer in the neck. MRI may be an optional or complementary imaging method to ultrasound or computed tomography (CT) in thyroid cancer patients.

Diagnostic Capabilities of MRI Versus 18F FDG PET-CT in Postoperative Patients with Thyroglobulin Positive, 131I-negative Local Recurrent or Metastatic Thyroid Cancer

BACKGROUND

The detection of recurrence or metastasis might be challenging in patients, who underwent total thyroidectomy and radioactive iodine therapy for Differentiated Thyroid Carcinoma (DTC), with increased serum Thyroglobulin (Tg) levels and negative 131I whole body scan (131I-WBS) results.

AIMS

The purpose of this study was to compare the ability of Magnetic Resonance Imaging (MRI) and 18F-fluorodeoxyglucose Positron Emission Tomography/Computed Tomography (18F FDG PET-CT) to detect recurrence or cervical and upper mediastinal metastases in postoperative DTC patients who had negative 131I-WBS despite elevated serum Tg levels.

STUDY DESIGN

This study has a retrospective study design.

METHODS

We evaluated cervical and upper mediastinal MRI and 18F FDG PET-CT of 32 postoperative patients with DTC (26 patients with papillary thyroid carcinoma and 6 patients with follicular thyroid carcinoma).

RESULTS

We evaluated 44 lesions in 32 patients. For all lesions, the Positive Predictive Value, (PPV) Negative Predictive Value (NPV), sensitivity, specificity, and accuracy of MRI were 81.4%, 76.4%, 84.6%, 72.2%, and 79.5% respectively. The PPV, NPV, sensitivity, specificity, and accuracy of 18F FDG PET-CT were 100.0%, 85.7%, 88.4%, 100.0%, and 93.1%, respectively.

CONCLUSION

Although we could not replace 18F FDG PET-CT, MRI might be used as an adjunct to 18F FDG PET-CT for the evaluation of recurrent or cervical and upper mediastinal metastatic thyroid cancers; however, MRI is inadequate for the detection of metastases in small lymph nodes.

Imaging and Imaging-Based Management of Pediatric Thyroid Nodules

Thyroid nodules are less frequent in children than adults. Childhood thyroid nodules carry specific features, including a higher risk of malignancy than nodules in adults, rendering them unique in terms of management. Subsequently, they should be considered a distinct clinical entity with specific imaging recommendations. Initial evaluation requires a thorough workup, including clinical examination, and a detailed personal and familial history to determine the presence of possible risk factors. Laboratory and radiologic evaluation play an integral part in the diagnostic algorithm, with ultrasonography (US) being the first diagnostic test in all patients. US elastography has been recently introduced as an incremental method, reducing the subjectivity of the clinical diagnosis of nodule firmness associated with increased malignancy risk. However, fine-needle aspiration biopsy (FNAB) remains the mainstay in the diagnostic work-up of thyroid nodules and is documented to be best method for differentiating benign from malignant thyroid nodules. In addition, thyroid scintigraphy provides functional imaging information, which has a role both in the diagnostic management of thyroid nodules and during follow up in malignancies. Finally, despite providing additional information in certain clinical scenarios, ¹⁸F-fludeoxyglucose Positron Emission Tomography (¹⁸F-FDG-PET), computed tomography (CT), and magnetic resonance imaging (MRI) imaging are not routinely recommended for the evaluation of patients with newly detected thyroid nodules or in all cases of thyroid cancer. The objective of this review is to summarize the concepts in imaging and imaging-based management of nodular thyroid disease in the pediatric population, acknowledging the unique features that this patient group carries and the specific approach it requires.

Predictive value of LN metastasis detected by 18F-FDG PET/CT in patients with papillary thyroid cancer receiving iodine-131 radiotherapy

The aim of the present study was to predict the prognostic value of ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in the metastatic lymph nodes (mLNs) of patients with papillary thyroid carcinoma (PTC) with a negative iodine-131 (¹³¹I) whole-body scan (WBS). The present retrospective study included 32 patients with PTC undergoing standard surgery and radioiodine treatment. All patients received ¹⁸F-FDG PET/CT imaging prior to and following therapy. All mLNs were divided into an effective treatment group (group A) and ineffective treatment group (group B) based on the PET Response Criteria in Solid Tumors 1.0 guidelines. All the patients were followed up for ≥9 months. A significant difference was identified in the peak standardized uptake value (SULpeak) between group B (7.85±3.20) and group A (5.36±2.19). A cut-off value of 5.85 was used to distinguish ineffective treatment of lesions from mLNs receiving radioactive ablation based on receiver operating characteristic (ROC) curve analysis with an area under the ROC curve of 0.755. Patients with a high SULpeak (P=0.003) and extrathyroidal extension (P=0.030), confirmed by pathology, more frequently exhibited a poor prognosis. In conclusion, tracer uptake of ¹⁸F-FDG for cervical metastatic nodes was revealed as a predictor for the clinical outcome of patients with PTC treated with radioiodine therapy. The present results also indicated that high SULpeak and extrathyroidal extension are poor predictors for patients with mLNs receiving ¹³¹I therapy.

Differentiated thyroid cancer theranostics: radioiodine and beyond

The term theranostics is the combination of a diagnostic tool that helps to define the right therapeutic tool for specific disease. It signifies the "we know which sites require treatment (diagnostic scan) and confirm that those sites have been treated (post-therapy scan)" demonstrating the achievable tumor dose concept. This term was first used by John Funkhouser at the beginning of the 90s, at the same time the concept of personalized medicine appeared. In nuclear medicine, theranostics is easy to apply and understand because of an easy switch from diagnosis to therapy with the same vector. It helps in maximizing tumor dose and sparing normal tissue with high specific and rapid uptake in metastasis. The oldest application of this concept is radioactive iodine I-131 (RAI). The first treatment based on the theranostic concept was performed on thyroid cancer patients with RAI in 1946. From then on management of differentiated thyroid cancer (DTC) has evolved on the multimodality concept. We now use the term "our" patient instead of "my" patient to signify this. However, the initial surgical management followed by RAI as per the theranostics has remained the mainstay in achieving a cure in most of DTC patients. The normal thyroid cells metabolise iodine, the principle of which is utilized in imaging of the thyroid gland with isotopes of iodine. RAI treatment of DTC is based on the principle of sodium iodide symporter (NIS) expressing thyroid cells with DTC cells having the ability of trapping circulating RAI successfully helping in treatment of residual and metastatic disease. NIS is usually negative in poorly differentiated cells and is inversely proportional to Glucose transporter receptor Type 1 expression. Both positive and negative NIS are the key components of the theranostic approach in treatment of DTC. Presence or absence of NIS is documented by either whole body iodine scintigraphy (WBS) or 2-deoxy-2(18F) fludeoxyglucose (FDG) positron emission tomography computed tomography (PET-CT). Currently, single photon emission CT and CT (SPECT-CT) has significantly improved the precision and sensitivity of whole body iodine scintigraphy with its capability of accurate localization of disease foci whether iodine avid or non-avid. This has helped in a more personalized approach in treatment. This review will give an overview of the role of NIS in the theranostic approach to management with RAI, its current status and also the molecular approach to treatment in RAI refractory disease.

Recent Development of Nuclear Molecular Imaging in Thyroid Cancer

Therapies targeting specific tumor pathways are easy to enter the clinic. To monitor molecular changes, cellular processes, and tumor microenvironment, molecular imaging is becoming the key technology for personalized medicine because of its high efficacy and low side effects. Thyroid cancer is the most common endocrine malignancy, and its theranostic radioiodine has been widely used to diagnose or treat differentiated thyroid cancer. This article summarizes recent development of molecular imaging in thyroid cancer, which may accelerate the development of personalized thyroid cancer therapy.

Whole-Body 68Ga-DOTANOC PET/MRI Versus 68Ga-DOTANOC PET/CT in Patients With Neuroendocrine Tumors: A Prospective Study in 28 Patients

PURPOSE

The aim of this study was to assess the diagnostic performance of simultaneous whole-body Ga-DOTANOC PET/MRI compared with Ga-DOTANOC PET/CT for detection of distant metastatic disease in patients with well-differentiated neuroendocrine tumors (NETs).

METHODS

Patients with histologically proven, well-differentiated NET (G1 or G2) were included in this prospective, institutional review board-approved study. Patients underwent Ga-DOTANOC PET/CT and subsequent Ga-DOTANOC PET/MRI after a single tracer injection on the same day for staging or restaging purposes. Images were evaluated for the presence of NET lesions by 2 rater teams, each consisting of a nuclear medicine physician and a radiologist, in an observer-blinded fashion. Overall agreement, accuracy, sensitivity, and specificity, relative to a composite reference standard (consensus review including follow-up data), were calculated.

RESULTS

Between July 2014 and June 2016, 28 patients were enrolled. Overall agreement and accuracy between the 2 rater teams were 91.7% (95% confidence interval [CI], 87.5%-95.9%) and 97% (95% CI, 94.4%-99.6%) for PET/MRI and 92.3% (95% CI, 88.3%-96.3%) and 94.6% (95% CI, 91.2%-98.1%) for PET/CT, respectively (P = 1.00).Overall, PET/MRI reached 89.8% sensitivity (95% CI, 77.8%-96.6%) and 100% specificity (95% CI, 97%-100%); PET/CT showed 81.6% sensitivity (95% CI, 68%-91.2%) and 100% specificity (95% CI, 97%-100%) for the detection of metastatic disease in NETs.

CONCLUSIONS

Whole-body Ga-DOTANOC PET/MRI appears to be comparable to Ga-DOTANOC PET/CT for lesion detection in patients with well-differentiated NETs.

Advantage of PET/CT in Target Delineation of MRI-negative Cervical Lymph Nodes In Intensity-Modulated Radiation Therapy Planning for Nasopharyngeal Carcinoma

Introduction: In intensity-modulated radiation therapy (IMRT) planning for nasopharyngeal carcinoma (NPC), cervical lymph nodes (CLNs) that appear negative on magnetic resonance imaging (MRI) scans can be difficult to target. The purpose of this study was to assess the advantage of ¹⁸F-fluorodeoxyglucose positron emission tomography with computed tomography (¹⁸F-FDG PET/CT) for distinguishing MRI-negative CLNs and the effect of ¹⁸F-FDG PET/CT on diagnosis, target delineation, and dose prescription in IMRT planning for NPC.

Methods: Thirty-five NPC patients with 37 MRI-negative CLNs underwent ¹⁸F-FDG PET/CT imaging before treatment. Ultrasonography-guided fine-needle aspiration cytology (USgFNAC) was performed to examine the pathology of CLNs. The ¹⁸F-FDG PET/CT and cytopathological results were compared, and the diagnostic accuracy of ¹⁸F-FDG PET/CT was calculated. The cytopathologically confirmed CLNs were delineated and treated as the gross tumor volume of lymph nodes (denoted as GTVnd).

Results: Nineteen of the 37 MRI-negative CLNs were positive on ¹⁸F-FDG PET/CT, and metastasis was confirmed by USgFNAC in 16 CLNs. Of the remaining 18 ¹⁸F-FDG PET/CT-negative lymph nodes, metastasis was confirmed in one. The diagnostic accuracy, sensitivity, and specificity of ¹⁸F-FDG PET/CT were 89.2%, 94.1%, and 85.0%, respectively. The positive and negative predictive values were 84.2% and 94.4%, respectively. With a median follow-up of 48.3 months, no relapse was observed among the ¹⁸F-FDG PET/CT-positive CLNs with metastasis confirmed by USgFNAC and treated as GTVnd.

Conclusion:¹⁸F-FDG PET/CT had high accuracy, sensitivity, and specificity for distinguishing MRI-negative CLNs. ¹⁸F-FDG PET/CT-positive CLNs could reasonably be categorized as high-risk clinical tumor volume in IMRT planning for NPC.