Quantitative analysis of normal and pathologic adrenal glands with 18F-FDOPA PET/CT: focus on pheochromocytomas

[18F]FDOPA PET/CT is superior to [68Ga]DOTATOC PET/CT in diagnostic imaging of pheochromocytoma

BACKGROUND

Both [18F]FDOPA (FDOPA) and [68Ga]DOTATOC PET/CT (DOTATOC) are widely used for detection of pheochromocytomas/paraganglioma (PPGL). However, direct comparisons of the performance of the two tracers are only available in small series. We conducted a retrospective comparative analysis of FDOPA and DOTATOC to assess their sensitivity and accuracy in detecting PPGL when administered based on suspicion of PPGL. We consecutively included patients referred on suspicion of PPGL or PPGL recurrence who were scanned with both FDOPA and DOTATOC. Both scans were reviewed retrospectively by two experienced observers, who were blinded to the final diagnosis. The assessment was made both visually and quantitatively. The final diagnosis was primarily based on pathology.

RESULTS

In total, 113 patients were included (97 suspected of primary PPGL and 16 suspected of recurrence). Of the 97 patients, 51 had pheochromocytomas (PCC) (in total 55 lesions) and 6 had paragangliomas (PGL) (in total 7 lesions). FDOPA detected and correctly localized all 55 PCC, while DOTATOC only detected 25 (sensitivity 100% vs. 49%, p < 0.0001; specificity 95% vs. 98%, p = 1.00). The negative predictive value (100% vs. 63%, p < 0.001) and diagnostic accuracy (98% vs. 70%, p < 0.01) were higher for FDOPA compared to DOTATOC. FDOPA identified 6 of 6 patients with hormone producing PGL, of which one was negative on DOTATOC. Diagnostic performances of FDOPA and DOTATOC were similar in the 16 patients with previous PPGL suspected of recurrence.

CONCLUSIONS

FDOPA is superior to DOTATOC for localization of PCC. In contrast to DOTATOC, FDOPA also identified all PGL but with a limited number of patient cases.

[18F] MFBG PET imaging: biodistribution, pharmacokinetics, and comparison with [123I] MIBG in neural crest tumour patients

PURPOSE

Despite its limitations, [¹²³I]MIBG scintigraphy has been the standard for human norepinephrine transporter (hNET) imaging for several decades. Recently, [¹⁸F]MFBG has emerged as a promising PET alternative. This prospective trial aimed to evaluate safety, biodistribution, tumour lesion pharmacokinetics, and lesion targeting of [¹⁸F]MFBG and perform a head-to-head comparison with [¹²³I]MIBG in neural crest tumour patients.

METHODS

Six neural crest tumour patients (4 phaeochromocytoma, 1 paraganglioma, 1 neuroblastoma) with a recent routine clinical [¹²³I]MIBG scintigraphy (interval: - 37-75 days) were included. Adult patients (n = 5) underwent a 30-min dynamic PET, followed by 3 whole-body PET/CT scans at 60, 120, and 180 min after injection of 4 MBq/kg [¹⁸F]MFBG. One minor participant underwent a single whole-body PET/CT at 60 min after administration of 2 MBq/kg [¹⁸F]MFBG. Normal organ uptake (SUV_mean) and lesion uptake (SUV_max; tumour-to-background ratio (TBR)) were measured. Regional distribution volumes (V_T) were estimated using a Logan graphical analysis in up to 6 lesions per patient. A lesion-by-lesion analysis was performed to compare detection ratios (DR), i.e. fraction of detected lesions, between [¹⁸F]MFBG and [¹²³I]MIBG.

RESULTS

[¹⁸F]MFBG was safe and well tolerated. Its biodistribution was overall similar to that of [¹²³I]MIBG, with prominent uptake in the salivary glands, liver, left ventricle wall and adrenals, and mainly urinary excretion. In the phaeochromocytoma subgroup, the median V_T was 37.4 mL/cm³ (range: 18.0-144.8) with an excellent correlation between V_T and SUV_mean at all 3 time points (R²: 0.92-0.94). Mean lesion SUV_max and TBR at 1 h after injection were 19.3 ± 10.7 and 23.6 ± 8.4, respectively. All lesions detected with [¹²³I]MIBG were also observed with [¹⁸F]MFBG. The mean DR with [¹²³I]MIBG was significantly lower than with [¹⁸F]MFBG (61.0% ± 26.7% vs. 99.8% ± 0.5% at 1 h; p = 0.043).

CONCLUSION

[¹⁸F]MFBG is a promising hNET imaging agent with favourable imaging characteristics and improved lesion targeting compared with [¹²³I]MIBG scintigraphy.

TRIAL REGISTRATION

Clinicaltrials.gov : NCT04258592 (Registered: 06 February 2020), EudraCT: 2019-003872-37A.

Usefulness of FDG-PET/CT-Based Radiomics for the Characterization and Genetic Orientation of Pheochromocytomas Before Surgery

Simple Summary

Around 40% of patients with pheochromocytomas (PHEO) carry a germline mutation. Early germline mutation identification is important for accurate treatment and follow-up in affected patients. The aim of our retrospective study was to assess the potential added value of FDG-PET/CT radiomics for the characterization of PHEO and their genetic orientation prior to surgery and genetic testing. We confirmed in an homogeneous population of 52 PHEO (49 patients) the usual avidity of these tumors for FDG (92%) and the impact of germline mutation on their phenotypic presentations with higher SUVmax observed in Cluster-1-related genes. Radiomics biomarkers provided valuable additional and independent information for discriminating genetically determined PHEO (Cluster-1 or Cluster-2-related genes) as well as sporadic forms. FDG-PET/CT is then useful for preoperative detection of PHEO, and when combined with texture features, provides evidences for a genetic predisposition.

Abstract

Purpose: To assess the potential added value of FDG-PET/CT radiomics for the characterization of pheochromocytomas (PHEO) and their genetic orientation prior to surgery and genetic testing. Methods: This retrospective monocentric study, included 49 patients (52 tumors) that underwent both FDG-PET/CT and MIBG scan before surgery. A germline mutation was secondarily identified in 13 patients in one of the genes related to Cluster 1 (n = 4) or Cluster 2 (n = 9). No mutation was identified in 32 patients and 4 did not have genetic testing. Correlation between several PET-based biomarkers, including SUVmax, metabolic tumor volume (MTV), total lesion glycolysis (TLG) and textural features, and biochemical and genetic features were analyzed. Results: Sensitivity of FDG-PET/CT alone was 92%, and 98% when combined to MIBG. The SUVmax was significantly higher for mutated tumors classified in Cluster 1 than in Cluster 2 (p = 0.002) or for tumors with no identified mutations (p = 0.04). MTV and TLG of the tumors with the most intense uptake discriminated mutated Cluster 2 from sporadic tumors, but not from Cluster 1 tumors. Textural features combined with MTV led to better differentiation between sporadic and mutated tumors (p < 0.05). Conclusion: FDG-PET/CT is useful for preoperative characterization of PHEO, and when combined with radiomics biomarkers, provides evidences for a genetic predisposition.

Surgical Approach to Endocrine Hypertension in Patients with Adrenal Disorders

Increased hormonal secretion of aldosterone, cortisol, or catecholamines from an adrenal gland can produce a variety of undesirable symptoms, including hypertension, which may be the initial presenting symptom. Consequences of secondary hypertension can result in potential cardiovascular and cerebrovascular complications at higher rates than in those with essential hypertension. Once a biochemical diagnosis is confirmed, targeted pharmacotherapy can be initiated to improve hypertension and may be corrected with surgical intervention. Adrenalectomy can be curative and can reverse the risk of cardiovascular sequelae once blood pressure control is achieved. This article discusses perioperative and operative considerations of adrenal causes of hypertension.

A side-by-side evaluation of [18F]FDOPA enantiomers for non-invasive detection of neuroendocrine tumors by positron emission tomography

Neuroendocrine tumors (NETs) are an extremely heterogenous group of malignancies with variable clinical behavior. Molecular imaging of patients with NETs allows for effective patient stratification and treatment guidance and is crucial in selection of targeted therapies. Positron emission tomography (PET) with the radiotracer L-[¹⁸F]FDOPA is progressively being utilized for non-invasive in vivo visualization of NETs and pancreatic β-cell hyperplasia. While L-[¹⁸F]FDOPA-PET is a valuable tool for disease detection and management, it also exhibits significant diagnostic limitations owing to its inherent physiological uptake in off-target tissues. We hypothesized that the D-amino acid structural isomer of that clinical tracer, D-[¹⁸F]FDOPA, may exhibit superior clearance capabilities owing to a reduced in vivo enzymatic recognition and enzyme-mediated metabolism. Here, we report a side-by-side evaluation of D-[¹⁸F]FDOPA with its counterpart clinical tracer, L-[¹⁸F]FDOPA, for the non-invasive in vivo detection of NETs. In vitro evaluation in five NET cell lines, including invasive small intestinal neuroendocrine carcinomas (STC-1), insulinomas (TGP52 and TGP61), colorectal adenocarcinomas (COLO-320) and pheochromocytomas (PC12), generally indicated higher overall uptake levels of L-[¹⁸F]FDOPA, compared to D-[¹⁸F]FDOPA. While in vivo PET imaging and ex vivo biodistribution studies in PC12, STC-1 and COLO-320 mouse xenografts further supported our in vitro data, they also illustrated lower off-target retention and enhanced clearance of D-[¹⁸F]FDOPA from healthy tissues. Cumulatively our results indicate the potential diagnostic applications of D-[¹⁸F]FDOPA for malignancies where the utility of L-[¹⁸F]FDOPA-PET is limited by the physiological uptake of L-[¹⁸F]FDOPA, and suggest D-[¹⁸F]FDOPA as a viable PET imaging tracer for NETs.

Adrenal tracer uptake by 18F-FDOPA PET/CT in patients with pheochromocytoma and controls

Context

¹⁸F-FDOPA PET/CT accurately localizes pheochromocytoma in patients with an established biochemical diagnosis. However, cut-off ¹⁸F-FDOPA levels of standardized uptake values (SUV_max) for both normal adrenal glands and pheochromocytoma are lacking.

Objective

Objectives of this study were to determine (1) reference maximum standardized uptake values (SUVmax) for normal adrenal ¹⁸F-DOPA tracer uptake and (2) the optimal diagnostic approach for pheochromocytoma localization by using ¹⁸F-DOPA SUVmax across a series of cut-off points: the affected adrenal gland (inter-individual analysis), the difference in SUVmax between the affected adrenal gland and the contralateral normal adrenal gland (intra-individual analysis), or a combination of these two.

Patients and methods

All patients with histologically confirmed pheochromocytoma diagnosed at our center between November 2009 and December 2017 were retrospectively analysed. Only those patients who underwent an ¹⁸F-FDOPA PET/CT-scan for localization purposes before adrenalectomy were included for further analysis. The control group consisted of patients who underwent ¹⁸F-FDOPA PET/CT for other indications and who had no genetic susceptibility for developing a pheochromocytoma. SUV_max of the volume of interest surrounding the adrenal glands was determined on EARL reconstructed images. Receiver operating characteristic (ROC) analysis was performed for adrenal gland SUV_max and intra-individual difference in SUV_max between affected and normal adrenal gland. In addition, binary logistic regression was performed for ROC analysis of the combined parameters.

Results

In total, 47 histologically confirmed pheochromocytomas were diagnosed in 45 patients, and 245 disease control patients were identified. In the control group, no statistical differences between the SUV_max of left and right adrenal glands were observed, and uptake values in both adrenal glands correlated significantly with each other (r = 0.865, p < 0.001). Median (range) adrenal gland SUV_max in pheochromocytomas and in the control group was 12 (2.6–50) and 2.9 (1.1–6.6), respectively (p < 0.001). ROC analysis revealed 93% sensitivity and 85% specificity at an SUV_max cut-off value of 4.1 (area under the curve (AUC) = 0.951), and 93% sensitivity and 96% specificity at an intra-individual SUV_max difference between the affected and normal adrenal gland of 1.0 (AUC = 0.992). The combination of both variables increased the AUC to 0.995.

Conclusions

¹⁸F-FDOPA PET/CT distinguishes pheochromocytoma from normal adrenal glands with the highest diagnostic accuracy when combining the SUVmax of the affected adrenal gland with the difference in SUV_max between affected and normal adrenal gland.

18F-FDOPA PET/CT Imaging of MAX-Related Pheochromocytoma

CONTEXT

MYC-associated factor X (MAX) has been recently described as a new susceptibility pheochromocytoma (PHEO) gene with a total of ~40 reported cases. At present, no study has specifically described the functional imaging phenotype of MAX-related PHEO.

OBJECTIVE, PATIENTS, AND DESIGN

The objective of the present study was to present our experience with contrast-enhanced computed tomography (CT) and 18F-fluorodihydroxyphenylalanine (18F-FDOPA) positron emission tomography (PET)/CT in six consecutive patients (four at the initial diagnosis and two at the follow-up evaluation) with rare, but clinically important, MAX-related PHEOs. In five patients, 18F-FDOPA was also compared with other radiopharmaceutical agents.

RESULTS

The patients had five different mutations in the MAX gene that caused disruption of Max/Myc interaction and/or abolished interaction with DNA based on in silico analyses. All but one patient developed bilateral PHEOs during their lifetime. In all cases, 18F-FDOPA PET/CT accurately visualized PHEOs that were often multiple within the same gland or bilaterally and detected more adrenal and extra-adrenal lesions than did CT (per-lesion sensitivity, 90.9% vs 52.4% for CT/magnetic resonance imaging). The two PHEOs missed on 18F-FDOPA PET/CT were <1 cm, corresponding to nodular adrenomedullary hyperplasia. 68Ga-DOTA,Tyr3-octreotate PET/CT detected fewer lesions than did 18F-FDOPA PET/CT in one of three patients, and 18F-fluorodeoxyglucose PET/CT was only faintly positive in two of four patients with underestimation of extra-adrenal lesions in one patient.

CONCLUSIONS

MAX-related PHEOs exhibit a marked 18F-FDOPA uptake, a finding that illustrates the common well-differentiated chromaffin pattern of PHEOs associated with activation of kinase signaling pathways. 18F-FDOPA PET/CT should be considered as the first-line functional imaging modality for diagnostic or follow-up evaluations for these patients.