18F-DOPA PET/CT in the evaluation of hereditary SDH-deficiency paraganglioma-pheochromocytoma syndromes

Paragangliomas and Pheochromocytomas: Positron Emission Tomography/Computed Tomography Diagnosis and Therapy

Molecular imaging evaluation of pheochromocytomas and paragangliomas depends on multiple factors, such as localized versus metastatic disease, the genetic, and biochemical profile of tumors. Positron emission tomography/computed tomography (PET/CT) imaging of these tumors outperforms Meta-Iodo-Benzyl-Guanidine (MIBG) scintigraphy in most cases. A few PET radiotracers have been studied in evaluating these patients with somatostatin receptor PET imaging and have shown superior performance compared with other agents in most of these patients. 18F-fluorodeoxyglucose PET/CT imaging is useful in select patients, such as those with succinate dehydrogenase complex subunit B-associated disease. Treatment strategy depends on multiple factors and necessitates a multidisciplinary approach.

Hybrid imaging of neuroendocrine tumors in the heart: Union is strength

Cardiac neuroendocrine tumors (NETs) are particularly rare tumors that can lead to a very poor clinical outcome, partly because of metastases but mainly because of manifestations of the hormonal activity they exhibit. Prompt diagnosis is important in order to start the most effective treatment for their removal or management, with the fewest complications. They are often difficult to diagnose, especially in their early stages. One of the reasons for this is that the heart is an organ with a high rate of metabolism and is located in close proximity to other high-metabolism organs. In addition, the anatomic location and their small size render their diagnosis extremely challenging. In recent years, hybrid imaging methods have revolutionized the diagnostic approach to oncology patients and have established a place in the diagnosis of cardiac NETs, because they provide both anatomical and functional information at the same time. Positron emission tomography/computed tomography (PET/CT), PET/magnetic resonance imaging (PET/MRI) and single-photon emission computed tomography/CT (SPECT/CT) are widely used in clinical practice because of the very important metabolic information, the high sensitivity and specificity. However, prospective studies are needed to confirm the true clinical and prognostic value of various hybrid imaging diagnostic techniques in cardiac NETs.

Silent pheochromocytoma and paraganglioma: Systematic review and proposed definitions for standardized terminology

Pheochromocytomas and paragangliomas (PPGLs) are rare neuroendocrine tumors with heterogeneous clinical presentations and potential lethal outcomes. The diagnosis is based on clinical suspicion, biochemical testing, imaging and histopathological confirmation. Increasingly widespread use of imaging studies and surveillance of patients at risk of PPGL due to a hereditary background or a previous tumor is leading to the diagnosis of these tumors at an early stage. This has resulted in an increasing use of the term "silent" PPGL. This term and other variants are now commonly found in the literature without any clear or unified definition. Among the various terms, "clinically silent" is often used to describe the lack of signs and symptoms associated with catecholamine excess. Confusion arises when these and other terms are used to define the tumors according to their ability to synthesize and/or release catecholamines in relation to biochemical test results. In such cases the term "silent" and other variants are often inappropriately and misleadingly used. In the present analysis we provide an overview of the literature and propose standardized terminology in an attempt at harmonization to facilitate scientific communication.

Three-step two-pot automated production of NCA [18F]FDOPA with FlexLab module

Automated three-step two-pot production of no-carrier-added (NCA) [¹⁸F]FDOPA was first implemented in the iPHASE FlexLab module. Decay-corrected radiochemical yield (RCY) of [¹⁸F]FDOPA synthesized by this method was 10~14% (n = 7) with a synthesis time of ~110 min [¹⁸F]FDOPA was obtained in > 95% of radiochemical purity with a molar activity of ~431 GBq/μmol. With the method successfully implementing on the commercial FlexLab module and its built-in step-by-step activity monitoring, further processes optimization would be achieved.

Norepinephrine Transporter as a Target for Imaging and Therapy

The norepinephrine transporter (NET) is essential for norepinephrine uptake at the synaptic terminals and adrenal chromaffin cells. In neuroendocrine tumors, NET can be targeted for imaging as well as therapy. One of the most widely used theranostic agents targeting NET is metaiodobenzylguanidine (MIBG), a guanethidine analog of norepinephrine. ¹²³I/¹³¹I-MIBG theranostics have been applied in the clinical evaluation and management of neuroendocrine tumors, especially in neuroblastoma, paraganglioma, and pheochromocytoma. ¹²³I-MIBG imaging is a mainstay in the evaluation of neuroblastoma, and ¹³¹I-MIBG has been used for the treatment of relapsed high-risk neuroblastoma for several years, however, the outcome remains suboptimal. ¹³¹I-MIBG has essentially been only palliative in paraganglioma/pheochromocytoma patients. Various techniques of improving therapeutic outcomes, such as dosimetric estimations, high-dose therapies, multiple fractionated administration and combination therapy with radiation sensitizers, chemotherapy, and other radionuclide therapies, are being evaluated. PET tracers targeting NET appear promising and may be more convenient options for the imaging and assessment after treatment. Here, we present an overview of NET as a target for theranostics; review its current role in some neuroendocrine tumors, such as neuroblastoma, paraganglioma/pheochromocytoma, and carcinoids; and discuss approaches to improving targeting and theranostic outcomes.

Catecholamine-Induced Chest Pain Mimicking Infarction Due to an MIBG-Negative and DOPA-Positive Succinate Dehydrogenase Syndrome Subunit B-Related Pheochromocytoma

This 16-year-old boy presented with acute retrosternal pain possibly representing acute myocardial infarction. Cardiac enzymes were within reference ranges. There were marked increases in metanephrine to 3299 μg/24 h (reference, <400 μg/24 h), normetanephrine to 1309 μg/24 h (reference, 0-390 μg/24 h), and chromogranin A to 1605 ng/mL (reference, 0-150 μg/24 h). An incidental left adrenal mass was found during CTPA performed to exclude pulmonary embolism. I-MIBG scintigraphy was negative, and genetic screening detected SDHB (succinate dehydrogenase syndrome subunit B) gene mutation. Based on the gene mutation, F-DOPA PET/CT was performed, confirming a left-sided pheochromocytoma.

Dopamine concentration in blood platelets is elevated in patients with head and neck paragangliomas

BACKGROUND

Plasma 3-methoxytyramine (3-MT), a metabolite of dopamine, is elevated in up to 28% of patients with head and neck paragangliomas (HNPGLs). As free dopamine is incorporated in circulating platelets, we determined dopamine concentration in platelets in patients with a HNPGL.

METHODS

A single center cohort study was performed between 2012 and 2014. Thirty-six patients with a HNPGL were compared to healthy controls (68 for dopamine in platelets and 120 for plasma 3-MT).

RESULTS

Dopamine concentration in platelets was elevated in HNPGL patients compared to healthy controls (median [interquartile ranges] 0.48 [0.32-0.82] pmol/109 platelets vs. 0.31 [0.24-0.47] pmol/109 platelets; p<0.05), whereas plasma 3-MT concentration did not differ between both groups (0.06 [0.06-0.08] nmol/L vs. 0.06 [0.06-0.06] nmol/L; p=0.119). Based on 68 healthy controls, the reference interval for dopamine concentration in platelets was 0.12-0.97 pmol/109 platelets. Six (16.7%) patients with a HNPGL demonstrated an increased dopamine concentration in platelets compared to three (8.3%) patients with an increased plasma 3-MT level (p=0.053). The sensitivity and specificity were 16.7% and 98.5% for platelet dopamine and 8.3% and 97.5% for plasma 3-MT concentration (p=0.37).

CONCLUSIONS

Dopamine concentration in platelets is elevated in patients with a HNPGL compared to healthy subjects, and may be a novel biomarker for dopamine producing paraganglioma.

Molecular imaging in hereditary succinate dehydrogenase mutation-related paragangliomas

Multiple paraganglioma (PGL) syndromes related to succinate dehydrogenase (SDH) gene mutations are rare hereditary conditions. These present with heterogeneous clinical signs and symptoms and in many cases are difficult to classify. We summarize the pathophysiological, clinical, laboratory, and morphological and functional imaging characteristics of SDH gene mutation PGLs, emphasizing F-FDG and F-DOPA PET/CT. We correlate clinical and genetic features of SDH-related PGLs with specific PET radiopharmaceuticals, with the aim to obtain an "individualized" diagnostic approach.

Integrated whole-body PET/MRI with 18F-FDG, 18F-FDOPA, and 18F-FDA in paragangliomas in comparison with PET/CT: NIH first clinical experience with a single-injection, dual-modality imaging protocol

PURPOSE

Paragangliomas (PGLs) are tumors that can metastasize and recur; therefore, lifelong imaging follow-up is required. Hybrid PET/CT is an essential tool to image PGLs. Novel hybrid PET/MRI scanners are currently being studied in clinical oncology. We studied the feasibility of simultaneous whole-body PET/MRI to evaluate patients with PGLs.

METHODS

Fifty-three PGLs or PGL-related lesions from 8 patients were evaluated. All patients underwent a single-injection, dual-modality imaging protocol consisting of a PET/CT and a subsequent PET/MRI scan. Four patients were evaluated with F-FDG, 2 with F-fluorodihydroxyphenylalanine, and 2 with F-fluorodopamine. PET/MRI data were acquired using a hybrid whole-body 3-tesla integrated PET/MRI scanner. PET and MRI data (Dixon sequence for attenuation correction and T2-weighted sequences for anatomic allocation) were acquired simultaneously. Imaging workflow and imaging times were documented. PET/MRI and PET/CT data were visually assessed (blindly) in regards to image quality, lesion detection, and anatomic allocation and delineation of the PET findings.

RESULTS

With hybrid PET/MRI, we obtained high-quality images in an acceptable acquisition time (median, 31 minutes; range, 25-40 minutes) with good patient compliance. A total of 53 lesions, located in the head and neck area (6 lesions), mediastinum (2 lesions), abdomen and pelvis (13 lesions), lungs (2 lesions), liver (4 lesions), and bones (26 lesions), were evaluated. Fifty-one lesions were detected with PET/MRI and confirmed by PET/CT. Two bone lesions (L4 body, 8 mm, and sacrum, 6 mm) were not detectable on an F-FDA scan PET/MRI, likely because F-FDA was washed out between PET/CT and PET/MRI acquisitions. Coregistered MRI tended to be superior to coregistered CT for head and neck, abdomen, pelvis, and liver lesions for anatomic allocation and delineation.

CONCLUSIONS

Clinical PGL evaluation with hybrid PET/MRI is feasible with high-quality image and can be obtained in a reasonable time. It could be particularly beneficial for the pediatric population and for precise lesion definition in the head and neck, abdomen, pelvis, and liver.