PET/MRI for neuroendocrine tumors: a match made in heaven or just another hype?

PET/MRI: pictorial review of hepatobiliary and pancreatic applications

PET and MRI both play valuable roles in the management of hepatobiliary and pancreatic (HBP) malignancies. Simultaneous PET/MRI combines the excellent soft-tissue resolution and anatomic details from MRI with functional information from PET in a single comprehensive examination. MRI is the main imaging modality in evaluating HCC, playing important roles in screening, characterization, local extent, and evaluating tumor response, whereas 18F-fluorodeoxyglucose (FDG) PET can help evaluate for lymph node involvement and metastatic disease. In cholangiocarcinoma and pancreatic malignancies, both PET and MRI have excellent utility in initial staging as well as assessing treatment response. In all HBP malignancies, FDG-PET/MRI is a unique problem-solving tool in complex cases and diagnostic challenges, especially after locoregional therapy and when differentiating residual or recurrent viable disease from inflammatory and other benign processes. In this manuscript, we review the role of PET/MRI in the diagnosis, staging, assessing treatment response, and characterizing post-treatment processes. With the introduction of multiple new tracers, the value of PET/MRI has not yet been fully realized, and more studies are needed to demonstrate the utility and efficacy of PET/MRI in improving patient care in hepatobiliary and pancreatic oncology.

Neuroendocrine Tumors: Diagnostics

Neuroendocrine neoplasms (NEN) are rare tumors arising from neuroendocrine cells. NEN are ideally suited for a theragnostic approach due to their specific expression of somatostatin receptors (SSTR). SSTR imaging of NEN dates back to the 1980s, but has evolved recently due to the introduction of more sensitive SSTR PET radiotracers. SSTR PET is a primary imaging modality for identifying NEN and characterizing SSTR expression. SSTR PET is complementary to anatomic imaging for assessing tumor response to treatment. SSTR PET is mandated to determine eligibility for peptide receptor radionuclide therapy. Here, the role of imaging to aid management of NEN is reviewed.

PET/MRI imaging in neuroendocrine neoplasm

Molecular imaging plays a vital role in the management of neuroendocrine neoplasms (NENs). Somatostatin receptor (SSTR) PET is critical for evaluating NENs, ascertaining peptide receptor radionuclide therapy (PRRT) eligibility, and treatment response. SSTR-PET/MRI can provide a one-stop-shop multiparametric evaluation of NENs. The acquisition of complementary imaging information in PET/MRI has distinct advantages over PET/CT and MR imaging acquisitions. The purpose of this manuscript is to provide a comprehensive overview of PET/MRI and a current review of recent PET/MRI advances in the diagnosis, staging, treatment, and surveillance of NENs.

Same-day comparative protocol PET/CT-PET/MRI [68 Ga]Ga-DOTA-TOC in paragangliomas and pheochromocytomas: an approach to personalized medicine

BACKGROUND

PET/MRI is an emerging imaging modality which enables the evaluation and quantification of biochemical processes in tissues, complemented with accurate anatomical information and low radiation exposure. In the framework of theragnosis, PET/MRI is of special interest due to its ability to delineate small lesions, adequately quantify them, and therefore to plan targeted therapies. The aim of this study was to validate the diagnostic performance of [⁶⁸ Ga]Ga-DOTA-TOC PET/MRI compared to PET/CT in advanced disease paragangliomas and pheochromocytomas (PGGLs) to assess in which clinical settings, PET/MRI may have a greater diagnostic yield.

METHODS

We performed a same-day protocol with consecutive acquisition of a PET/CT and a PET/MRI after a single [⁶⁸ Ga]Ga-DOTA-TOC injection in 25 patients. Intermodality agreement, Krenning Score (KS), SUVmax (Standard Uptake Value), target-to-liver-ratio (TLR), clinical setting, location, and size were assessed.

RESULTS

The diagnostic accuracy with PET/MRI increased by 14.6% compared to PET/CT especially in bone and liver locations (mean size of new lesions was 3.73 mm). PET/MRI revealed a higher overall lesion uptake than PET/CT (TLR 4.12 vs 2.44) and implied an upward elevation of the KS in up to 60% of patients. The KS changed in 30.4% of the evaluated lesions (mean size 11.89 mm), in 18.4% of the lesions it increased from KS 2 on PET/CT to a KS ≥ 3 on PET/MRI and 24.96% of the lesions per patient with multifocal disease displayed a KS ≥ 3 on PET/MR, that were not detected or showed lower KS on PET/CT. In 12% of patients, PET/MRI modified clinical management.

CONCLUSIONS

PET/MRI showed minor advantages over conventional PET/CT in the detection of new lesions but increased the intensity of SSRs expression in a significant number of them, opening the door to select which patients and clinical settings can benefit from performing PET/MRI.

Early Whole-Body Diffusion-weighted MRI Helps Predict Long-term Outcome Following Peptide Receptor Radionuclide Therapy for Metastatic Neuroendocrine Tumors

Purpose To evaluate the predictive value of 7-week apparent diffusion coefficient change from baseline (ADCratio_7w) at whole-body diffusion-weighted MRI (WB-DWI MRI) after one peptide receptor radionuclide therapy (PRRT) cycle to predict outcome in patients with metastatic neuroendocrine tumor (mNET). Materials and Methods From April 2009 to May 2012, participants in a prospective clinical trial investigating yttrium 90-DOTA Phe1-Tyr³-octreotide (DOTATOC) treatment for mNET (EudraCT no. 2008-007965-22) underwent WB-DWI MRI and gallium 68 (⁶⁸Ga)-DOTATOC PET/CT before and 7 weeks after one PRRT cycle. ADCratio_7w response was compared with the 7-week Response Evaluation Criteria in Solid Tumors version 1.1 and ⁶⁸Ga-DOTATOC PET/CT quantitative responses to predict overall survival (OS) and progression-free survival (PFS) with Cox regression analysis. Results Forty participants were analyzed (mean age, 60 years ± 11 [SD]; 21 men). Median PFS and OS were 10.5 months (range, 2-36 months) and 18 months (range, 3-81 months), respectively. Survival analysis showed significantly positive effects on PFS by age (hazard ratio [HR] = 0.96, P = .007), tumor grade (HR = 2.84, P = .006), Ki-67 index (HR = 1.05, P = .01), ADCratio_7w of the least-responding lesion (ADCratio_7w-least) (HR = 0.94, P < .001), and baseline mean standardized uptake values (SUV_mean) (HR = 0.89, P = .02), with ADCratio_7w-least and SUV_mean remaining significant in multivariable analysis (P < .001, P = .02, respectively). There were significantly positive effects on OS by pretreatment lesion volume (HR = 1.004, P = .004), tumor grade (HR = 2.14, P = .04), Ki-67 index (HR = 1.05, P = .01), and ADCratio_7w-least (HR = 0.97, P < .001), with pretreatment volume and ADCratio_7w-least remaining significant at multivariable analysis (P = .005, P = .002, respectively). Conclusion The ADCratio_7w after start of PRRT for mNET was an independent predictor of patient outcome. Keywords: MR-Diffusion-Weighted Imaging, Radionuclide Therapy, Whole-Body Imaging, Metastases, Tumor Response, Treatment Effects EudraCT no. 2008-007965-22 © RSNA, 2022.

Artificial Intelligence in Medical Imaging and its Impact on the Rare Disease Community: Threats, Challenges and Opportunities

Almost 1 in 10 individuals can suffer from one of many rare diseases (RDs). The average time to diagnosis for an RD patient is as high as 7 years. Artificial intelligence (AI)-based positron emission tomography (PET), if implemented appropriately, has tremendous potential to advance the diagnosis of RDs. Patient advocacy groups must be active stakeholders in the AI ecosystem if we are to avoid potential issues related to the implementation of AI into health care. AI medical devices must not only be RD-aware at each stage of their conceptualization and life cycle but also should be trained on diverse and augmented datasets representative of the end-user population including RDs. Inability to do so leads to potential harm and unsustainable deployment of AI-based medical devices (AIMDs) into clinical practice.

Applications of PET/MRI in Abdominopelvic Oncology

With PET/MRI, the strengths of PET and MRI are combined to allow simultaneous image acquisition and near-perfect image coregistration. MRI is increasingly being used for staging and restaging of abdominopelvic oncologic lesions, including prostate, hepatobiliary, pancreatic, neuroendocrine, cervical, and rectal cancers. Fluorine 18-fluorodeoxyglucose PET/CT has long been considered a cornerstone of oncologic imaging, and the development of multiple targeted radiotracers has led to increased research on and use of these agents in clinical practice. Thus, simultaneously performed PET/MRI enables the acquisition of complementary imaging information, with distinct advantages over PET/CT and MR image acquisitions. The authors provide an overview of PET/MRI, including descriptions of the major differences between PET/MRI and PET/CT, as well as case examples and treatment protocols for patients with commonly encountered malignancies in the abdomen and pelvis. Online supplemental material is available for this article. ^©RSNA, 2021.

Imaging of neuroendocrine tumors: A pictorial review of the clinical value of different imaging modalities

Neuroendocrine tumors (NETs) are multifaceted tumors occurring in a variety of organs and often present as metastatic at the time of diagnosis. Accurate staging is the most significant factor in therapy planning, but it remains a challenge. Imaging is established as the cornerstone for disease detection/diagnosis, staging, and follow up. To accurately assess and monitor tumor burden in patients with NETs, various imaging techniques have been developed and optimized. Current recommendations for the imaging of patients with NETs include a combination of both morphologic (or anatomic) and molecular imaging, but a final choice can be puzzling for clinicians. Recognizing that there is no uniform sequence consensus on the "best" imaging test, and the heterogeneity of technologic availability at different centers, we hope to provide a pictorial review of the different imaging techniques and their role and utility in management of patients with NETs, aimed to provide a practical guide for all clinicians.

Clinical Applications of PET/MR Imaging

PET/MR imaging is in routine clinical use and is at least as effective as PET/CT for oncologic and neurologic studies with advantages with certain PET radiopharmaceuticals and applications. In addition, whole body PET/MR imaging substantially reduces radiation dosages compared with PET/CT which is particularly relevant to pediatric and young adult population. For cancer imaging, assessment of hepatic, pelvic, and soft-tissue malignancies may benefit from PET/MR imaging. For neurologic imaging, volumetric brain MR imaging can detect regional volume loss relevant to cognitive impairment and epilepsy. In addition, the single-bed position acquisition enables dynamic brain PET imaging without extending the total study length which has the potential to enhance the diagnostic information from PET.

Molecular Genomic Assessment Using a Blood-based mRNA Signature (NETest) is Cost-effective and Predicts Neuroendocrine Tumor Recurrence With 94% Accuracy

INTRODUCTION

Identification of residual disease after neuroendocrine tumor (NET) resection is critical for management. Post-surgery imaging is insensitive, expensive, and current biomarkers ineffective. We evaluated whether the NETest, a multigene liquid biopsy blood biomarker, correlated with surgical resection and could predict recurrence.

METHODS

Multicenter evaluation of NET resections over 24 months (n = 103): 47 pancreas, 26 small bowel, 26 lung, 2 appendix, 1 duodenum, 1 stomach. Surgery: R0 (83), R1/R2 (20). One millilitre of blood was collected at D0 and posroperative day (POD) 30. Transcript quantification by polymerase chain reaction (normal: ≤20), CgA by NEOLISA (normal ≤108 ng/mL). Standard-of-care (SoC) follow-up costs were calculated and compared to POD30 NETest-stratification approach. Analyses: Wilcoxon-paired test, Chi-square test.

RESULTS

D BIOMARKERS

NETest: 103 of 103 (100%)-positive, whereas 23 of 103 (22%) were CgA-positive (Chi-square = 78, P < 0.0001).In the R0 group, the NETest decreased 59 ± 28 to 26 ± 23 (P < 0.0001); 36% (30/83) remained elevated. No significant decrease was evident for CgA. In the R1/R2 group the NETest decreased but 100% remained elevated. CgA levels did not decrease.An elevated POD30 NETest was present in R0 and 25 (83%) developed radiological recurrences. Normal score R0 s (n = 53) did not develop recurrence (Chi-square = 56, P < 0.0001). Recurrence prediction was 94% accurate with the NETest.

COST EVALUATION

Using the NETest to stratify postoperative imaging resulted in a cost-savings of 42%.

CONCLUSION

NETest diagnosis is more accurate than CgA (100% vs 22%). Surgery significantly decreased NETest. An elevated POD30 NETest predicted recurrence with 94% accuracy and post-surgical POD30 NETest follow-up stratification decreased costs by 42%. CgA had no surgical utility. Further studies would define the accuracy and cost-effectiveness of the NETest in the detection of postoperative recurrent disease.

Knowns and unknowns of bone metastases in patients with neuroendocrine neoplasms: A systematic review and meta-analysis

OBJECTIVE

This systematic review and meta-analysis aimed to develop an evidence-based summary of current knowledge of bone metastases (BMs) in neuroendocrine neoplasms (NENs), inform diagnosis and treatment and standardise management between institutions.

METHODS

PubMed, Medline, EMBASE and meeting proceedings were searched for eligible studies reporting data on patients with BMs and NENs of any grade of differentiation and site; poorly-differentiated large/small cell lung cancer were excluded. Data were extracted and analysed using STATA v.12. Meta-analysis of proportions for calculation of estimated pooled prevalence of BM and calculation of weighted pooled frequency and weighted pooled mean for other variables of interest was performed .

RESULTS

A total of 149 studies met the eligibility criteria. Pooled prevalence of BMs was 18.4% (95% CI 15.4-21.5). BMs were mainly metachronous with initial diagnosis of NEN (61.2%) and predominantly osteoblastic; around 61% were multifocal, with a predisposition in axial skeleton. PET/CT seemed to provide (together with MRI) the highest sensitivity and specificity for BM detection. Almost half of patients (46.4%) reported BM-related symptoms: pain (66%) and skeletal-related events (SREs, fracture/spinal cord compression) (26.2%; weightedweighted mean time-to-SRE 9.9 months). Management of BMs was multimodal [bisphosphonates and bone-modifying agents (45.2%), external beam radiotherapy (34.9%), surgery (14.8%)] and supported by little evidence. Overall survival (OS) from the time of diagnosis of BMs was long [weighted mean 50.9 months (95% CI 40.0-61.9)]. Patients with BMs had shorter OS [48.8 months (95% CI 37.9-59.6)] compared to patients without BMs [87.4 months (95% CI 74.9-100.0); p = 0.001]. Poor performance status and BM-related symptoms were also associated with worse OS.

CONCLUSIONS

BMs in patients with NENs remain underdiagnosed and undertreated. Recommendations for management of BMs derived from current knowledge are provided. Prospective studies to inform management are required.

Ga-68 DOTA-peptides and F-18 FDG PET/CT in patients with neuroendocrine tumor: A review

OBJECTIVES

The aim of the present review was to assess the role of combined ¹⁸F-Fluorodeoxyglucose (F-18 FDG) and Ga-68 DOTA-peptides positron emission tomography (PET)-computed tomography (CT) in neuroendocrine tumors (NETs).

METHODS

We have searched MEDLINE databases, including PubMed and Scopus, for studies about the combined FDG and Ga-68 DOTA-peptides PET-CT or PET/Magnetic Resonance Imaging (MRI) in NETs in the last 15 years (from 2004 to November 2019). No limits were applied to the search strategy. Abstracts, reviews, letters to editors, and editorials were excluded.

RESULTS

Seven studies met the inclusion criteria. In total 236 patients received both ⁶⁸Ga-DOTA-peptides and F-18 FDG PET-CT for the characterization of NETs. In particular, 84 patients had a neuroendocrine lung tumor while the others mainly a gastroenteropancreatic NET. The combined use of F-18 FDG and Ga-68 DOTA-peptides (mainly TOC) PET studies provides complementary information regarding different biological characteristics of the lesions, thus enabling a more accurate selection of patients for targeted radionuclide therapy and a better stratification of the prognosis.

CONCLUSIONS

Ga-68 DOTA-peptides and F-18 FDG PET should be considered complementary in patients with NETs. They should be both performed in the initial staging and during follow-up, with a specific selection of patients and in a multidisciplinary vision.