(68) Ga- DOTA(0) -Tyr(3) octreotide (DOTATOC) positron emission tomography (PET)/CT in five cases of ectopic adrenocorticotropin-secreting tumours

Continuing Challenges in the Definitive Diagnosis of Cushing's Disease: A Structured Review Focusing on Molecular Imaging and a Proposal for Diagnostic Work-Up

The definitive diagnosis of Cushing's disease (CD) in the presence of pituitary microadenoma remains a continuous challenge. Novel available pituitary imaging techniques are emerging. This study aimed to provide a structured analysis of the diagnostic accuracy as well as the clinical use of molecular imaging in patients with ACTH-dependent Cushing's syndrome (CS). We also discuss the role of multidisciplinary counseling in decision making. Additionally, we propose a complementary diagnostic algorithm for both de novo and recurrent or persistent CD. A structured literature search was conducted and two illustrative CD cases discussed at our Pituitary Center are presented. A total of 14 CD (n = 201) and 30 ectopic CS (n = 301) articles were included. MRI was negative or inconclusive in a quarter of CD patients. ¹¹C-Met showed higher pituitary adenoma detection than ¹⁸F-FDG PET-CT (87% versus 49%). Up to 100% detection rates were found for ¹⁸F-FET, ⁶⁸Ga-DOTA-TATE, and ⁶⁸Ga-DOTA-CRH, but were based on single studies. The use of molecular imaging modalities in the detection of pituitary microadenoma in ACTH-dependent CS is of added and complementary value, serving as one of the available tools in the diagnostic work-up. In selected CD cases, it seems justified to even refrain from IPSS.

Head-to-head comparison of 68Ga-DOTATATE PET/CT and 18F-FDG PET/CT in localizing tumors with ectopic adrenocorticotropic hormone secretion: a prospective study

PURPOSE

Localizing the source of ectopic adrenocorticotropic hormone secretion (EAS) is challenging. This study compared the diagnostic value of 68Ga-DOTATATE PET/CT and 18F-FDG PET/CT in tumors with EAS.

METHODS

Thirty-six patients with a suspicion of EAS were enrolled to undergo both 68Ga-DOTATATE PET/CT and 18F-FDG PET/CT within 4 weeks for comparison. Twenty-three underwent surgical resection or biopsy. Immunohistochemical staining for SSTR2 and Ki-67 was performed to correlate with 68Ga-DOTATATE uptake and 18F-FDG uptake, respectively.

RESULTS

EAS tumors were observed in 20/23 patients. Among the 20 patients with histologically proven EAS tumors, 68Ga-DOTATATE PET/CT correctly identified the tumor in 15 (75.0%), with an SUVmax ranging from 1.4 to 20.7 (6.7 ± 5.5). 18F-FDG PET/CT correctly identified the tumor in 12 (60.0%) patients, with an SUVmax ranging from 1.8 to 10.0 (4.0 ± 2.1). Moreover, 68Ga-DOTATATE PET/CT unmasked the sources of EAS in 6 patients with negative 18F-FDG uptake, and 18F-FDG PET/CT unmasked the sources in 3 patients with negative 68Ga-DOTATATE uptake, resulting in EAS tumors being identified in 18 (90%) patients by combining 68Ga-DOTATATE PET/CT and 18F-FDG PET/CT.

CONCLUSIONS

68Ga-DOTATATE PET/CT and 18F-FDG PET/CT are complementary in localizing and discriminating the source of EAS. 68Ga-DOTATATE PET/CT combined with 18F-FDG PET/CT had higher detection rate than each alone.

TRIAL REGISTRATION

68Ga-DOTATATE PET/CT in Neuroendocrine Tumors (NCT04041882) URL OF REGISTRY: https://clinicaltrials.gov/ct2/show/NCT04041882.

Development of Ga-68 DOTA-CRH for PET/CT Imaging of ACTH-Dependent Cushing's Disease: Initial Study

Purpose: Adrenocorticotropic hormone (ACTH)-dependent Cushing's disease accounts for 75% cases of the endogenous Cushing's syndrome. The size of lesion is usually very small, which results in false-negative magnetic resonance imaging (MRI) even after biochemical confirmation of the disease. Corticotrophin-releasing hormone (CRH) the key controller of hypothalamus-pituitary--adrenal axis binds to CRH receptor R1 and R2. CRH R1 is overexpressed in pituitary adenomas. The present study aims to target these overexpressed receptors with Ga-68-DOTA-CRH for noninvasive imaging of ACTH-dependent pituitary adenomas. Materials and Methods: Custom-synthesized 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-CRH peptide was purified by high performance liquid chromatography (HPLC) and characterized by mass spectra. Postradiolabeling optimization with Ga-68, quality control tests were carried out to ensure the suitability of Ga-68 DOTA-CRH for intravenous administration. A pilot study consisting of 15 patients including 6 known cases of macroadenoma underwent Ga-68-DOTA-CRH regional brain positron emission tomography/computed tomography (PET/CT). The optimal imaging time and biodistribution studies were performed in five patients' whole-body and serial brain PET/CT imaging. Lesion activity was determined as SUVmax and correlated with CE-MRI and histopathology of excised tissue. Results: A retention time of 11.3 min and mass of 5145 Da was observed on HPLC and mass spectra. Radiolabeling yield of >98% was achieved under optimized conditions using 25-100 μg of conjugated peptide for 10-22 mCi of Ga-68. The quality control results were in agreement with acceptable criteria. Ga-68-DOTA-CRH was able to delineate ACTH secreting corticotropinoma in all 15 patients. Physiological uptake of radiotracer was observed in liver and spleen with diffused marrow activity. Excretion was noted by renal route. Imaging results were in correlation with CE-MRI and histopathology of excised tissue. Conclusion: Ga-68-DOTA-CRH PET/CT is a promising molecular imaging modality for detection of ACTH-dependent microadenoma.

The value of [68Ga]Ga-DOTA-TATE PET/CT in diagnosis and management of suspected pituitary tumors

Background

Gallium 68-tetraazacyclododecane-tetraacetic acid-octreotate ([68Ga]Ga-DOTA-TATE) is a selective somatostatin analogue ligand, which shows increased affinity for somatostatin receptor subtype (SSTR) 2 and has been used routinely for imaging neuroendocrine tumors with PET/CT. We investigated the utility of [68Ga]Ga-DOTA-TATE positron emission tomography/computed tomography (PET/CT) in patients with suspected pituitary pathology. We reviewed imaging for twenty consecutive patients (8 men, 12 women, mean age of 48.2, range 14–78) with suspected pituitary pathology who were referred for [68Ga]Ga-DOTA-TATE PET/CT.

Results

Nine patients presented with recurrent Cushing’s syndrome following surgical resection of pituitary adenomas due to recurrent Cushing’s disease (seven patients) and ectopic ACTH secreting tumor (2 patients). All seven patients with recurrent Cushing’s disease showed positive pituitary [68Ga]Ga-DOTA-TATE uptake while both cases of ectopic hormonal secretion had absented pituitary uptake. In 1 of these 2 patients, [68Ga]Ga-DOTA-TATE was able to localize the source of ectopic ACTH tumor.

Six patients presented de novo with Cushing’s due to ectopic ACTH secretion; [68Ga]Ga-DOTA-TATE PET/CT was able to localize ectopic tumors in six of eight patients (3 lungs, 2 pancreases, 1 mid-gut)

There was high uptake [68Ga]Ga-DOTA-TATE in 3 cases of recurrent central hyperthyroidism (SUVmax 6.6–14.3) and 2 cases of prolactinoma (SUVmax 5.5 and 11.3).

Conclusion

Absent [68Ga]Ga-DOTA-TATE activity in the pituitary fossa is useful in excluding pituitary disease in recurrent Cushing’s. Recurrent pituitary thyrotropinomas and prolactinomas showed moderate to high pituitary activity. In addition, in Cushing’s syndrome, [68Ga]Ga-DOTA-TATE is useful for detection of ectopic sources of ACTH production, especially where anatomic imaging is negative.

(Radio)Theranostic Patient Management in Oncology Exemplified by Neuroendocrine Neoplasms, Prostate Cancer, and Breast Cancer

The role of nuclear medicine in the management of oncological patients has expanded during last two decades. The number of radiopharmaceuticals contributing to the realization of theranostics/radiotheranostics in the context of personalized medicine is increasing. This review is focused on the examples of targeted (radio)pharmaceuticals for the imaging and therapy of neuroendocrine neoplasms (NENs), prostate cancer, and breast cancer. These examples strongly demonstrate the tendency of nuclear medicine development towards personalized medicine.

68Ga-DOTATOC PET/CT in detecting neuroendocrine tumours responsible for initial or recurrent paraneoplastic Cushing's syndrome

PURPOSE

Paraneoplastic Cushing's syndrome (PCS) is frequently caused by neuroendocrine tumours (NETs). Approximately 20% of tumours are still occult years later. Gallium-68 somatostatin receptor-PET/CT is promising for the detection of the causal primary NET, but its role in case of recurrent PCS is rarely reported. We report our experience with DOTATOC PET/CT in localising the causal NET in cases of initial but also recurrent PCS, and its clinical impact.

METHODS

A retrospective review of all DOTATOC PET/CTs performed in consecutive patients referred for PCS to our centre, between January 2011 and June 2017, was done. Nineteen patients underwent 26 PET/CTs, 13 for detection of a primary NET, seven for persistent or recurrent PCS after resection, and six for surveillance after resection of NETs previously detected on a DOTATOC PET/CT in our centre.

RESULTS

Among the 13 PET/CTs performed to search for primary NET, five were positive: four carcinoid lung tumours were confirmed after resection and one lung focus was not confirmed since surgery would have carried a high risk. Clinical impact was 23% (3/13). Among the seven PET/CTs performed for persistent or recurrent PCS, six were true-positive, with confirmation of metastatic lymph nodes after resection. Clinical impact was 57% (4/7). All PET/CTs performed for surveillance were true-negative.

CONCLUSIONS

DOTATOC PET/CT seems to be a valuable tool for detection of the NET responsible for persistent or recurrent PCS after surgery. In this context, DOTATOC PET/CT was more effective than for the detection of the causal tumour in initial PCS.

Diagnostic utility of Gallium-68-somatostatin receptor PET/CT in ectopic ACTH-secreting tumors: a systematic literature review and single-center clinical experience

PURPOSE

Tumors causing ectopic Cushing's syndrome (ECS) are often not visible with conventional imaging. Gallium-68-DOTATATE, DOTATOC, and DOTANOC positron emission tomography/computed tomography (⁶⁸Ga-SSTR PET/CT) reportedly exhibits greater sensitivity in identifying an ECS source, however, evidence is limited to mainly case reports and a few small retrospective studies. Previous systematic ECS imaging review has shown ⁶⁸Ga-SSTR PET/CT sensitivity is similar to CT (81.8%) in histologically-proven cases and is 100% in covert-cases, however, the number of patients was small and no occult cases were reported.

METHODS

We performed a systematic literature review of ⁶⁸Ga-SSTR PET/CT use in ECS patients. We also report 6 consecutive patients with confirmed active and occult ECS who underwent ⁶⁸Ga-DOTATATE PET/CT and were followed at our institution between 2014 and 2019.

RESULTS

We identified 33 articles (23 case-reports, 4 case-series, 5 retrospective studies and 1 prospective study) detailing ⁶⁸Ga-SSTR PET/CT in 69 ECS patients. Overall ⁶⁸Ga-SSTR PET/CT sensitivity was 64.0%, while in histologically confirmed cases (67 lesions), sensitivity was 76.1%. There were two false-positives cases, both in the adrenal glands. In covert cases, ⁶⁸Ga-SSTR PET/CT identified 50% of lesions. There were ten occult cases where all imaging failed to identify an adrenocorticotropic hormone source; source remains unknown. In our case series, ⁶⁸Ga-DOTATATE PET/CT showed decreased uptake in pancreatic neuroendocrine tumor in one patient and did not help identify an ECS source in 5 patients.

CONCLUSION

Both this systematic literature review, the largest to date, and our single- center experience demonstrate a lower than previously reported ⁶⁸Ga-SSTR PET/CT sensitivity for ECS, especially in occult lesions. We suggest that the data on ⁶⁸Ga-SSTR PET/CT in ECS is subject to publication bias, and false-negatives are likely underreported; it's diagnostic value for ECS needs further study.

Comparison of 68Ga-DOTANOC PET/CT and contrast-enhanced CT in localisation of tumours in ectopic ACTH syndrome

BACKGROUND

Localising ectopic adrenocorticotrophic hormone (ACTH) syndrome (EAS) tumour source is challenging. Somatostatin receptor-based PET imaging has shown promising results, but the data is limited to case reports and small case series. We reviewed here the performance of (68)Ga-DOTANOC positron emission tomography (PET)/computed tomography (CT) and contrast-enhanced CT (CECT) in our cohort of 12 consecutive EAS patients.

MATERIALS AND METHODS

Retrospective data analysis of 12 consecutive patients of EAS presenting to a single tertiary care centre in a period between January 2013 and December 2014 was done. CECT and (68)Ga-DOTANOC PET/CT were reported (blinded) by an experienced radiologist and a nuclear medicine physician, respectively. The performance of CECT and (68)Ga-DOTANOC PET/CT was compared.

RESULTS

Tumours could be localised in 11 out of 12 patients at initial presentation (overt cases), whereas in one patient, tumour remained occult. Thirteen lesions were identified in 11 patients as EAS source (true positives). CECT localised 12 out of these 13 lesions (sensitivity 92.3%) and identified five false-positive lesions (positive predictive value (PPV) 70.5%). Compared with false-positive lesions, true-positive lesions had greater mean contrast enhancement at 60s (33.2 vs 5.6 Hounsfield units (HU)). (68)Ga-DOTANOC PET/CT was able to identify 9 out of 13 lesions (sensitivity 69.2%) and reported no false-positive lesions (PPV 100%).

CONCLUSION

CECT remains the first-line investigation in localisation of EAS. The contrast enhancement pattern on CECT can further aid in characterisation of the lesions. (68)Ga-DOTANOC PET/CT can be added to CECT, to enhance positive prediction of the suggestive lesions.

PET imaging in ectopic Cushing syndrome: a systematic review

Cushing syndrome due to endogenous hypercortisolism may cause significant morbidity and mortality. The source of excess cortisol may be adrenal, pituitary, or ectopic. Ectopic Cushing syndrome is sometimes difficult to localize on conventional imaging like CT and MRI. After performing a multilevel thoracoabdominal imaging with CT, the evidence regarding the use of radiotracers for PET imaging is unclear due to significant molecular and etiological heterogeneity of potential causes of ectopic Cushing's syndrome. In our systematic review of literature, it appears that GalLium-based (Ga68) somatostatin receptor analogs have better sensitivity in diagnosis of bronchial carcinoids causing Cushing syndrome and FDG PET appears superior for small-cell lung cancers and other aggressive tumors. Further large-scale studies are needed to identify the best PET tracer for this condition.