Variants and Pitfalls of PET/CT in Neuroendocrine Tumors

Nuclear medicine imaging for bone metastases assessment: what else besides bone scintigraphy in the era of personalized medicine?

Accurate detection and reliable assessment of therapeutic responses in bone metastases are imperative for guiding treatment decisions, preserving quality of life, and ultimately enhancing overall survival. Nuclear imaging has historically played a pivotal role in this realm, offering a diverse range of radiotracers and imaging modalities. While the conventional bone scan using 99mTc marked bisphosphonates has remained widely utilized, its diagnostic performance is hindered by certain limitations. Positron emission tomography, particularly when coupled with computed tomography, provides improved spatial resolution and diagnostic performance with various pathology-specific radiotracers. This review aims to evaluate the performance of different nuclear imaging modalities in clinical practice for detecting and monitoring the therapeutic responses in bone metastases of diverse origins, addressing their limitations and implications for image interpretation.

68Ga-DOTATATE Avid Metastatic Vertebral Renal Cell Carcinoma in the Setting of von Hippel-Lindau Syndrome

Although rare, a metastatic renal cell carcinoma could present with 68Ga-DOTATATE avidity. A 66-year-old man with von Hippel-Lindau syndrome (VHL) presented with 68Ga-DOTATATE uptake in the pancreatic head, splenic hilar region, and multiple osseous sites, including the right lateral portion of the T9 vertebrae. Biopsy of the T9 lesion confirmed metastatic renal cell carcinoma. Various VHL-associated cancers may display 68Ga-DOTATATE avidity, which can change and guide clinical decisions for the patient.

Cutting-Edge Imaging of Cardiac Metastases from Neuroendocrine Tumors: Lesson from a Case Series

With the increasing availability of high-performance medical imaging for the management of patients with neuroendocrine tumors (NETs), a progressive growth of asymptomatic and incidentally detected cardiac metastases (CMs) has been observed in the recent years. In clinical practice, CMs of NENs are often incidentally detected by whole-body 68Ga-labeled somatostatin analogs or 18F-fluorodihydroxyphenylalanine positron emission tomography/computed tomography, and afterwards accurately characterized by cardiac magnetic resonance (CMR) and/or gated cardiac computed tomography when CMR is contraindicated or not available. The interpreting physician should familiarize with the main imaging features of CM, a finding that may be encountered in NETs patients more than previously thought. Herein, we present a case series of four patients with CMs from small-intestine NETs highlighting strengths and weaknesses of a multimodality imaging approach in clinical practice.

Value of Somatostatin Receptor PET/CT in Patients With MEN1 at Various Stages of Their Disease

CONTEXT

Despite the growing evidence of the clinical value of somatostatin receptor (SSTR) positron emission tomography (PET) in the evaluation of neuroendocrine tumors (NETs), its role remains to be clarified at different time points in the journey of patients with multiple endocrine neoplasia type 1 (MEN1). The rarity of the disease is however a significant impediment to prospective clinical trials.

OBJECTIVE

The goals of the study were to assess the indications and value of SSTR PET/computed tomography (CT) in patients with MEN1.

METHODS

We retrospectively included patients from 7 French expert centers for whom data on SSTR PET/CT and morphological imaging performed at the same period were available. Detection rates of PET study were analyzed.

RESULTS

One hundred and 8 patients were included. SSTR PET/CT was performed at screening (n = 33), staging (n = 34), restaging (n = 37), and for peptide receptor targeted radiotherapy selection (n = 4). PET detected positive pancreatic lesions in 91% of cases at screening, with results comparable with magnetic resonance imaging but superior to CT (P = .049). Metastases (mostly lymph node [LN]) were present at the screening phase in 28% of cases, possibly due to the suboptimal value of screening morphological imaging in the assessment of nodal metastases and/or a long delay between imaging studies. SSTR PET/CT was considered superior or complementary to the reference standard in the assessment of LN or distant metastases in the vast majority of cases and regardless of the clinical scenario.

CONCLUSION

This study shows the potential added value of SSTR PET in the assessment of MEN1-associated NETs and provides great impetus toward its implementation in the evaluation of patients with MEN1.

A Negative Correlation Between Blood Glucose Level and 68 Ga-DOTA-TOC Uptake in the Pancreas Uncinate Process

PURPOSE

⁶⁸ Ga-DOTA-TOC uptake in the pancreas uncinate process is often found due to physiologic expression of somatostatin receptors (SSTR). We investigated the association of physiologic ⁶⁸ Ga-DOTA-TOC uptake in the pancreas uncinate process with blood glucose level.

METHODS

⁶⁸ Ga-DOTA-TOC PET scans acquired from 44 patients (male:female = 20:24, age = 50.8 ± 14.8y [mean ± SD]) were retrospectively analyzed. The blood glucose level (BGL) was examined before ⁶⁸ Ga-DOTA-TOC injection. Patients diagnosed with diabetes mellitus and patients with BGL over 200 mg/dl were excluded. ⁶⁸ Ga-DOTA-TOC uptake was measured by the maximum standardized uptake values (SUVmax). Additionally, SSTR-positive volume (SV) in the pancreas uncinate process was measured with two different thresholds: by SUV cutoff of 2.5 (SV_2.5) and 40% of SUVmax (SV_40%). These measurements on ⁶⁸ Ga-DOTA-TOC PET were correlated with BGL.

RESULTS

The mean of SUVmax of the pancreas uncinate process was 6.51 ± 2.04. SV_2.5 was 17.81 ± 7.14 cm³, and SV_40% was 18.20 ± 8.83 cm³. A significant negative correlation was found between SUVmax of the pancreas uncinate process and BGL (r = -0.37, p = 0.01). The ratio between SUVmax of the pancreas uncinate process and SUVmean of the pancreas body also showed a significance negative correlation with BGL (r = -0.40, p = 0.01). SV_2.5 (r = 0.27, p = 0.07) and SV_40% (r = -0.151, p = 0.32) were not significantly correlated with BGL.

CONCLUSION

Physiologic ⁶⁸ Ga-DOTA-TOC uptake in the pancreas uncinate process was negatively correlated with BGL. Our results suggested that glycemia could affect physiologic uptake of ⁶⁸ Ga-DOTA-TOC.

Values of 68Ga-DOTATOC and Carbidopa-assisted 18F-DOPA PET/CT for insulinoma localization

To assess the value of ⁶⁸Ga-DOTATOC and carbidopa-assisted ¹⁸F-DOPA in 21 hypoglycaemic patients. Methods: All patients who underwent ⁶⁸Ga-DOTATOC and/or carbidopa-assisted ¹⁸F-DOPA PET/CT for suspicion of insulinoma from January 2019 to January 2021 were retrospectively analysed. Insulinoma final diagnosis was defined according to pathological reports or consensus. Results: During the study period, 21 patients underwent both ⁶⁸Ga-DOTATOC and ¹⁸F-DOPA PET/CT. A final diagnosis of insulin-secreting tumour was reached in 12 cases, including 11 insulinomas and 1 small mixed neuroendocrine/non-neuroendocrine neoplasm. ¹⁸F-DOPA and ⁶⁸Ga-DOTATOC PET/CT were positive in 5 (45%) and 7 (64%) of 11 cases, respectively, with 4 concordant positive findings. Moreover, 1 insulinoma was visualized exclusively by ¹⁸F-DOPA PET/CT and 3 by ⁶⁸Ga-DOTATOC PET/CT only. ¹⁸F-DOPA and ⁶⁸Ga-DOTATOC PET/CT were falsely positive in 1 non-functioning pancreatic neuroendocrine tumour. Conclusion: When ⁶⁸Ga-exendin-4 is not available, ⁶⁸Ga-SSTR PET/CT should be the first choice for insulinoma functional imaging.

Comparison of 68Ga-DOTANOC and 18F-FDG PET-CT Scans in the Evaluation of Primary Tumors and Lymph Node Metastasis in Patients With Rectal Neuroendocrine Tumors

BACKGROUND

Lymph node metastasis of rectal neuroendocrine tumors (RNETs) predicts poor prognosis. However, the assessment of lymph node metastasis remains a challenge. It has been reported that 68Ga-DOTANOC and 18F-FDG PET-CT scans could be employed in the work-up of rectal neuroendocrine tumors (RNETs). This study aimed to assess both tracers' ability to identify primary tumors and lymph node (LN) metastasis in RNETs.

METHODS

A total of 537 patients with RNETs were enrolled from January 2014 to January 2021. Both 68Ga-DOTANOC and 18F-FDG PET-CT scans were used to evaluate primary tumors and LN group metastasis. PET images were evaluated through visual and semiquantitative assessment. Receiver Operating Characteristics (ROC) curve analysis was used to investigate the performance of SUVmax of 68Ga-DOTANOC and 18F-FDG PET in predicting LN group metastasis.

RESULTS

Fifty-two patients with preoperative 68Ga-DOTANOC with 18F-FDG PET-CT scans underwent endoscopic biopsy or dissection of the primary tumor, while 11 patients underwent rectal surgery together with regional LN dissection. For primary tumors, 68Ga-DOTANOC had a sensitivity of 89.58% and a positive predictive value (PPV) of 95.56% through visual assessment, while 18F-FDG PET-CT showed 77.08% sensitivity and 97.37% PPV. For the prediction of LN group metastasis, 68Ga-DOTANOC PET-CT had 77.78% sensitivity and 91.67% specificity, while 18F-FDG PET-CT had 38.89% sensitivity and 100% specificity according to visual assessment. The area under the ROC curves (AUC) for 68Ga-DOTANOC PET/CT was 0.852 (95%CI:0.723-0.981) with an optimal SUVmax cut-off value of 2.25, while the AUC for 18F-FDG PET were 0.664 (95%CI:0.415-0.799) with an optimal SUVmax cut-off value of 1.05.

CONCLUSIONS

This study showed that 68Ga-DOTANOC PET-CT was a promising tool for detecting LN metastasis in RNETs with high sensitivity and specificity in visual assessment and semiquantitative assessment, which was better than 18F-FDG PET-CT.