Reducing Radiation Exposure from PET Patients

Objective: This study measured the typical emitted radiation rate from the urinary bladder of PET patients after their scan and investigated simple methods for reducing the emitted radiation before discharge. Methods: The study included 83 patients, 63 [¹⁸F]FDG and 20 [¹⁸F]NaF. Emitted radiation from the patients' urinary bladder was measured with an ionization survey meter at a 1-meter distance, presuming the urinary bladder to be the primary source of radiation. The measurements were taken at different time points after PET image acquisition: immediate (pre-void 1), voided (post-void 1), after waiting 30 min in the uptake room while drinking 500 mL of water (pre-void 2) and voided again (post-void 2). Results: For [¹⁸F]FDG patients, the reduction of emitted radiation due to drinking water and voiding alone from pre-void 1 to decay corrected post void 2 was an average of 22.49 ± 7.48% (13.65 ± 3.42 µSv/h to 10.48 ± 2.37 µSv/h, P = 0). As for [¹⁸F]NaF patients, the reduction was an average of 25.80 ± 10.03% (9.83 ± 2.01 µSv/h to 7.23 ± 1.49 µSv/h, P = 0). Conclusion: In addition to the physical decay of the radiotracers, utilizing the biological clearance properties have resulted in a significant decrease of the emitted radiation in this study. Implementing additional water consumption to facilitate voiding with 30 minutes of wait time before discharging certain [¹⁸F]FDG and [¹⁸F]NaF patients that need to be in close contact with others such as elderly, caregivers and inpatients, might facilitate lowering their emitted radiation by an average of 22-25% due to voiding, not counting in the physical decay which should add an additional 17% reduction.

68Ga-DOTATATE PET/CT: The Optimum Standardized Uptake Value (SUV) Internal Reference

RATIONALE AND OBJECTIVES

Standardized Uptake Value (SUV) is an important semiquantitative measurement used in the clinical and research domains to assess radiopharmaceutical concentration in tumors versus normal organs, but is susceptible to many factors beyond the tumor biological environment. So, the aim of this study is to identify the optimum internal reference among organs with physiological uptake in ⁶⁸Ga-DOTATATE PET/CT (DOTA PET/CT) scans.

MATERIALS AND METHODS

This HIPAA-compliant, IRB-approved study with waiver of consent included retrospective imaging review of 180 consecutive patients with neuroendocrine tumors presenting for DOTA PET/CT image acquisition: Ga-⁶⁸ DOTATATE dose was reported as (0.054 mCi/Kg) scans between September 2018 and May 2019. Mean value of body weight normalized SUV (SUV_bw) and lean body mass normalized SUV (SUL) of liver and spleen were measured. Information about the patients and scan characteristics were collected. The paired Grambsch test was used to compare variance among the measured SUVs. Spearman's rank correlation coefficient was used to assess correlation between SUVs and potential patient- and scan-specific confounding factors.

RESULTS

Variance of SUL was significantly lower than variance of SUV_bw in both liver and spleen (p-value < 0.0001). Variances of liver SUV_bw and SUL were significantly lower than the corresponding spleen SUVs. Liver SUL showed the lowest variance (3.69% ± 1.25%) among all measured SUVs.

CONCLUSION

SUL is a more reproducible, less variable, and therefore more reliable quantitative measure in DOTA PET/CT scans, compared SUV_bw. Among the available organs with physiological uptake, liver SUL is the optimum internal reference given the liver's larger size and uniform SUL values resulting in lower variability and better reproducibility.

Nuclear Imaging of Neuroendocrine Tumors

Consensus guidelines acknowledge the role of gallium Ga-68 (⁶⁸Ga) 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic (DOTA) somatostatin receptor (SSTR) positron emission tomography/computed tomography (PET/CT) in management of neuroendocrine tumor (NET) patients. ⁶⁸Ga-DOTA-SSTR PET/CT demonstrates superior performance to conventional imaging in initial detection, staging, detection of recurrent tumor, and detection of unknown primary in known metastatic disease. ⁶⁸Ga-DOTA-SSTR PET/CT is low yield for NET detection in the setting of symptoms or elevated biomarkers when conventional imaging is negative, but may still guide management. The role of ⁶⁸Ga-DOTA-SSTR PET/CT is not established in monitoring response to systemic therapy but may identify progression through detection of new metastases.

First-in-Humans Study of 68Ga-DOTA-Siglec-9, a PET Ligand Targeting Vascular Adhesion Protein 1

Sialic acid–binding immunoglubulinlike lectin 9 (Siglec-9) is a ligand of vascular adhesion protein 1. A ⁶⁸Ga-labeled peptide of Siglec-9, ⁶⁸Ga-DOTA-Siglec-9, holds promise as a novel PET tracer for imaging of inflammation. This first-in-humans study investigated the safety, tolerability, biodistribution, and radiation dosimetry of this radiopharmaceutical. Methods: Six healthy men underwent dynamic whole-body PET/CT. Serial venous blood samples were drawn from 1 to 240 min after intravenous injection of 162 ± 4 MBq of ⁶⁸Ga-DOTA-Siglec-9. In addition to γ-counting, the plasma samples were analyzed by high-performance liquid chromatography to detect intact tracer and radioactive metabolites. Radiation doses were calculated using the OLINDA/EXM software, version 2.2. In addition, a patient with early rheumatoid arthritis was studied with both ⁶⁸Ga-DOTA-Siglec-9 and ¹⁸F-FDG PET/CT to determine the ability of the new tracer to detect arthritis. Results:⁶⁸Ga-DOTA-Siglec-9 was well tolerated by all subjects. ⁶⁸Ga-DOTA-Siglec-9 was rapidly cleared from the blood circulation, and several radioactive metabolites were detected. The organs with the highest absorbed doses were the urinary bladder wall (0.38 mSv/MBq) and kidneys (0.054 mSv/MBq). The mean effective dose was 0.022 mSv/MBq (range, 0.020–0.024 mSv/MBq). Most importantly, however, ⁶⁸Ga-DOTA-Siglec-9 was comparable to ¹⁸F-FDG in detecting arthritis. Conclusion: Intravenous injection of ⁶⁸Ga-DOTA-Siglec-9 was safe and biodistribution was favorable for testing of the tracer in larger group of patients with rheumatoid arthritis, as is planned for the next phase of clinical trials. The effective radiation dose of ⁶⁸Ga-DOTA-Siglec-9 was within the same range as the effective radiation doses of other ⁶⁸Ga-labeled tracers. Injection of 150 MBq of ⁶⁸Ga-DOTA-Siglec-9 would expose a subject to 3.3 mSv. These findings support the possible repeated clinical use of ⁶⁸Ga-DOTA-Siglec-9, such as in trials to elucidate the treatment efficacy of novel drug candidates.

Pediatric applications of Dotatate: early diagnostic and therapeutic experience

In recent years, new somatostatin receptor agents (SSTRs) have become available for diagnostic imaging and therapy in neuroendocrine tumors. The novel SSTR ligand DOTA-DPhel-Tyr3-octreotate (Dotatate) in particular can be linked with ⁶⁸Gallium for diagnostic imaging purposes, and with the β-emitter ¹⁷⁷Lutetium for radiotherapy in the setting of neuroendocrine tumors. Dotatate imaging offers distinct advantages in the evaluation of neuroendocrine tumors compared to standard techniques, including greater target-to-background ratio and lesion conspicuity, high sensitivity/specificity, improved spatial resolution with positron emission tomography (PET)/CT or PET/MR, and decreased radiation exposure. Although currently off-label in pediatrics, Dotatate theranostics in children are being explored, most notably in the setting of neuroblastoma and hereditary neuroendocrine syndromes. This article provides a multicenter case series of Dotatate imaging and therapy in pediatric patients in order to highlight the spectrum of potential clinical applications.

[18F]FET-βAG-TOCA: The Design, Evaluation and Clinical Translation of a Fluorinated Octreotide

The success of Lutathera™ ([¹⁷⁷Lu]Lu-DOTA-TATE) in the NETTER-1 clinical trial as a peptide receptor radionuclide therapy (PRRT) for somatostatin receptor expressing (SSTR) neuroendocrine tumours (NET) is likely to increase the demand for patient stratification by positron emission tomography (PET). The current gold standard of gallium-68 radiolabelled somatostatin analogues (e.g., [⁶⁸Ga]Ga-DOTA-TATE) works effectively, but access is constrained by the limited availability and scalability of gallium-68 radiopharmaceutical production. The aim of this review is three-fold: firstly, we discuss the peptide library design, biological evaluation and clinical translation of [¹⁸F]fluoroethyltriazole-βAG-TOCA ([¹⁸F]FET-βAG-TOCA), our fluorine-18 radiolabelled octreotide; secondly, to exemplify the potential of the 2-[¹⁸F]fluoroethylazide prosthetic group and copper-catalysed azide-alkyne cycloaddition (CuAAC) chemistry in accessing good manufacturing practice (GMP) compatible radiopharmaceuticals; thirdly, we aim to illustrate a framework for the translation of similarly radiolabelled peptides, in which in vivo pharmacokinetics drives candidate selection, supported by robust radiochemistry methodology and a route to GMP production. It is hoped that this review will continue to inspire the development and translation of fluorine-18 radiolabelled peptides into clinical studies for the benefit of patients.

Molecular Imaging in Pediatric Brain Tumors

In the last decade, several radiopharmaceuticals have been developed and investigated for imaging in vivo of pediatric brain tumors with the aim of exploring peculiar metabolic processes as glucose consumption, amino-acid metabolism, and protein synthesis with nuclear medicine techniques. Although the clinical shreds of evidence are limited, preliminary results are encouraging. In this review, we performed web-based and desktop research summarizing the most relevant findings of the literature published to date on this topic. Particular attention was given to the wide spectrum of nuclear medicine advances and trends in pediatric neurooncology and neurosurgery. Furthermore, the role of somatostatin receptor imaging through single-photon emission computed tomography (SPECT) and positron emission tomography (PET) probes, with reference to their potential therapeutic implications, was examined in the peculiar context. Preliminary results show that functional imaging in pediatric brain tumors might lead to significant improvements in terms of diagnostic accuracy and it could be of help in the management of the disease.

PET-Based Human Dosimetry of 68Ga-NODAGA-Exendin-4, a Tracer for β-Cell Imaging

⁶⁸Ga-NODAGA-exendin-4 is a promising tracer for β-cell imaging using PET/CT. Possible applications include preoperative visualization of insulinomas and discrimination between focal and diffuse forms of congenital hyperinsulinism. There is also a significant role for this tracer in extending our knowledge on the role of β-cell mass in the pathophysiology of type 1 and type 2 diabetes by enabling noninvasive quantification of tracer uptake as a measure for β-cell mass. Calculating radiation doses from this tracer is important to assess its safety for use in patients (including young children) with benign diseases and healthy individuals. Methods: Six patients with hyperinsulinemic hypoglycemia were included. After intravenous injection of 100 MBq of the tracer, 4 successive PET/CT scans were obtained at 30, 60, 120, and 240 min after injection. Tracer activity in the pancreas, kidneys, duodenum, and remainder of the body were determined, and time-integrated activity coefficients for the measured organs were calculated. OLINDA/EXM software, version 1.1, was applied to calculate radiation doses using the reference adult male and female models and to estimate radiation doses to children. Results: The mean total effective dose for adults was very low (0.71 ± 0.07 mSv for a standard injected dose of 100 MBq). The organ with the highest absorbed dose was the kidney (47.3 ± 10.2 mGy/100 MBq). The estimated effective dose was 2.32 ± 0.32 mSv for an injected dose of 20 MBq in newborns. This dose decreased to 0.77 ± 0.11 mSv/20 MBq for 1-y-old children and 0.59 ± 0.05 mSv for an injected dose of 30 MBq in 5-y-old children. Conclusion: Our human PET/CT-based dosimetric calculations show that the effective radiation doses from the novel tracer ⁶⁸Ga-NODAGA-exendin-4 are very low for adults and children. The doses are lower than reported for other polypeptide tracers such as somatostatin analogs (2.1–2.6 mSv/100 MBq) and are beneficial for application as a research tool, especially when repeated examinations are needed.

A Comprehensive Review of Non-Covalent Radiofluorination Approaches Using Aluminum [18F]fluoride: Will [18F]AlF Replace 68Ga for Metal Chelate Labeling?

Due to its ideal physical properties, fluorine-18 turns out to be a key radionuclide for positron emission tomography (PET) imaging, for both preclinical and clinical applications. However, usual biomolecules radiofluorination procedures require the formation of covalent bonds with fluorinated prosthetic groups. This drawback makes radiofluorination impractical for routine radiolabeling, gallium-68 appearing to be much more convenient for the labeling of chelator-bearing PET probes. In response to this limitation, a recent expansion of the 18F chemical toolbox gave aluminum [18F]fluoride chemistry a real prominence since the late 2000s. This approach is based on the formation of an [18F][AlF]2+ cation, complexed with a 9-membered cyclic chelator such as NOTA, NODA or their analogs. Allowing a one-step radiofluorination in an aqueous medium, this technique combines fluorine-18 and non-covalent radiolabeling with the advantage of being very easy to implement. Since its first reports, [18F]AlF radiolabeling approach has been applied to a wide variety of potential PET imaging vectors, whether of peptidic, proteic, or small molecule structure. Most of these [18F]AlF-labeled tracers showed promising preclinical results and have reached the clinical evaluation stage for some of them. The aim of this report is to provide a comprehensive overview of [18F]AlF labeling applications through a description of the various [18F]AlF-labeled conjugates, from their radiosynthesis to their evaluation as PET imaging agents.

Incremental value of 99mTc-HYNICTOC SPECT/CT over whole-body planar scintigraphy and SPECT in patients with neuroendocrine tumours

Aim: The aim of this study was to evaluate the additional value of 99mTc-HYNIC-TOC SPECT/CT over planar whole-body (WB) scintigraphy and SPECT alone in the detection and accurate localisation of neuroendocrine tumour (NET) lesions. Methods: This study included 65 patients with a definitive histological diagnosis of NET prior to scintigraphy. Planar WB scintigraphy, SPECT, and SPECT/CT images were acquired at 4 h postadministration of 670 MBq 99mTc-HYNIC- TOC. Additional SPECT images at 10 min after tracer administration were also acquired. Clinical and imaging follow-up findings were considered as the reference standards (minimum follow-up period, 15 months). Patient and lesion-based analyses of the efficacies of the imaging modalities were performed. Results: While 38 patients exhibited metastasis of NETs, 27 presented no evidence of metastasis. Upon patient- based analysis, the sensitivity and specificity of SPECT/CT were found to be 88.9 and 79.3 %, respectively. The diagnostic accuracies of WB scintigraphy, 4h-SPECT, and SPECT/CT were 72.3, 73.8, and 84.6 %o, respectively. The area under curve (AUC) value for SPECT/CT (0.84) was the highest, followed by those for 4h-SPECT (0.75) and WB scintigraphy (0.74). The accuracy and AUC values of SPECT/CT were significantly better compared to those of WB scintigraphy (p < 0.001), 10 min-SPECT (p < 0.001), and 4 h-SPECT (p = 0.001). The findings of SPECT/CT led to the change in treatment plan of 11 patients (16.9 %o). Conclusion: The sensitivity and diagnostic accuracy of SPECT/CT in the evaluation of NET lesions outperforms planar WB imaging or SPECT alone.

PET/CT to detect adverse reactions to metal debris in patients with metal-on-metal hip arthroplasty: an exploratory prospective study

Metal-on-metal (MoM) bearings in total hip arthroplasties and hip resurfacing arthroplasties have recently shown a new type of complication: adverse reactions to metal debris (ARMD). ARMD is characterized by local severe inflammation and tissue necrosis leading to implant failures. The gluteal muscle region is important for the patient outcome after revision surgery. This prospective positron emission tomography/computed tomography (PET/CT) study was undertaken to evaluate the characteristics of 2-deoxy-2-[¹⁸ F]fluoro-d-glucose ([¹⁸ F]FDG) and [⁶⁸ Ga]Gallium citrate ([⁶⁸ Ga]Citrate) PET/CT in ARMD patients. [¹⁸ F]FDG and [⁶⁸ Ga]Citrate PET/CT were performed in 18 hip arthroplasty patients: 12 ARMD patients (with 16 MoM hips) and six arthroplasty controls without ARMD. Tracer uptake was evaluated visually, and maximum standardized uptake (SUV_max ) was measured in the gluteal muscle region. ARMD severity was graded by metal artefact reduction sequence-magnetic resonance imaging (MARS-MRI). Periprosthetic [¹⁸ F]FDG uptake was observed in 15 of 16 hips, [⁶⁸ Ga]Citrate uptake in three of 16 hips, respectively. The distribution of tracer uptake resembled infection in three hips. In the gluteal muscle region, the SUV_max of [¹⁸ F]FDG was significantly greater in hips with moderate and severe ARMD compared with the controls (P = 0·009 for [¹⁸ F]FDG and P = 0·217 for [⁶⁸ Ga]Citrate). In patients who needed revision surgery, an intraoperative finding of gluteal muscle necrosis was associated with increased local SUV_max as detected by preoperative [¹⁸ F]FDG (P = 0·039), but not by [⁶⁸ Ga]Citrate (P = 0·301). In conclusion, the inflammatory reaction to metal debris in hip arthroplasty patients is best visualized with [¹⁸ F]FDG.

Radiological surveillance in multiple endocrine neoplasia type 1: a double-edged sword?

CONTEXT

Multiple endocrine neoplasia type 1 (MEN1) is a hereditary condition characterised by the predisposition to hyperplasia/tumours of endocrine glands. MEN1-related disease, moreover, malignancy related to MEN1, is increasingly responsible for death in up to two-thirds of patients. Although patients undergo radiological and biochemical surveillance, current recommendations for radiological monitoring are based on non-prospective data with little consensus or evidence demonstrating improved outcome from this approach. Here, we sought to determine whether cumulative radiation exposure as part of the recommended radiological screening programme posed a distinct risk in a cohort of patients with MEN1.

PATIENTS AND STUDY DESIGN

A retrospective review of 43 patients with MEN1 attending our institution between 2007 and 2015 was performed. Demographic and clinical information including phenotype was obtained for all patients. We also obtained details regarding all radiological procedures performed as part of MEN1 surveillance or disease localisation. An estimated effective radiation dose (ED) for each individual patient was calculated.

RESULTS

The mean ED for the total patient cohort was 121 mSv, and the estimated mean lifetime risk of cancer secondary to radiation exposure was 0.49%. Patients with malignant neuroendocrine tumours (NETS) had significantly higher ED levels compared to patients without metastatic disease (P < 0.0022).

CONCLUSIONS

In MEN1, radiological surveillance is associated with clinically significant exposure to ionising radiation. In patients with MEN1, multi-modality imaging strategies designed to minimise this exposure should be considered.

Clinical Translation of a Click-Labeled 18F-Octreotate Radioligand for Imaging Neuroendocrine Tumors

We conducted the first-in-human study of (18)F-fluoroethyl triazole [Tyr(3)] octreotate ((18)F-FET-βAG-TOCA) in patients with neuroendocrine tumors (NETs) to evaluate biodistribution, dosimetry, and safety. Despite advances in clinical imaging, detection and quantification of NET activity remains a challenge, with no universally accepted imaging standard.

METHODS

Nine patients were enrolled. Eight patients had sporadic NETs, and 1 had multiple endocrine neoplasia type 1 syndrome. Patients received 137-163 MBq (mean ± SD, 155.7 ± 8 MBq) of (18)F-FET-βAG-TOCA. Safety data were obtained during and 24 h after radioligand administration. Patients underwent detailed whole-body PET/CT multibed scanning over 4 h with sampling of venous bloods for radioactivity and radioactive metabolite quantification. Regions of interest were defined to derive individual and mean organ residence times; effective dose was calculated with OLINDA 1.1.

RESULTS

All patients tolerated (18)F-FET-βAG-TOCA with no adverse events. Over 60% parent radioligand was present in plasma at 60 min. High tumor (primary and metastases)-to-background contrast images were observed. Physiologic distribution was seen in the pituitary, salivary glands, thyroid, and spleen, with low background distribution in the liver, an organ in which metastases commonly occur. The organs receiving highest absorbed dose were the gallbladder, spleen, stomach, liver, kidneys, and bladder. The calculated effective dose over all subjects (mean ± SD) was 0.029 ± 0.004 mSv/MBq.

CONCLUSION

The favorable safety, imaging, and dosimetric profile makes (18)F-FET-βAG-TOCA a promising candidate radioligand for staging and management of NETs. Clinical studies in an expanded cohort are ongoing to clinically qualify this agent.

Direct comparison of (68)Ga-DOTA-TOC and (18)F-FDG PET/CT in the follow-up of patients with neuroendocrine tumour treated with the first full peptide receptor radionuclide therapy cycle

Purpose

To determine the value of ⁶⁸Ga-DOTA-TOC and ¹⁸F-FDG PET/CT for initial and follow-up evaluation of patients with neuroendocrine tumour (NET) treated with peptide receptor radionuclide therapy (PRRT).

Methods

We evaluated 66 patients who had histologically proven NET and underwent both PRRT and three combined ⁶⁸Ga-DOTA-TOC and ¹⁸F-FDG PET/CT studies. ⁶⁸Ga-DOTA-TOC PET/CT was performed before PRRT, 3 months after completion of PRRT and after a further 6 – 9 months. ¹⁸F-FDG PET/CT was done within 2 months of ⁶⁸Ga-DOTA-TOC PET/CT. Follow-up ranged from 11.8 to 80.0 months (mean 34.5 months).

Results

All patients were ⁶⁸Ga-DOTA-TOC PET-positive initially and at follow-up after the first full PRRT cycle. Overall, 62 of the 198 ¹⁸F-FDG PET studies (31 %) were true-positive in 38 of the 66 patients (58 %). Of the 66 patients, 28 (5 grade 1, 23 grade 2) were ¹⁸F-FDG-negative initially and during follow-up (group 1), 24 (5 grade 1, 13 grade 2, 6 grade 3) were ¹⁸F-FDG-positive initially and during follow-up (group 2), 9 patients (2 grade 1, 6 grade 2, 1 grade 3) were ¹⁸F-FDG-negative initially but ¹⁸F-FDG-positive during follow-up (group 3), and 5 patients (all grade 2) were ¹⁸F-FDG-positive initially but ¹⁸F-FDG-negative during follow-up (group 4).¹⁸F-FDG PET showed more and/or larger metastases than ⁶⁸Ga-DOTA-TOC PET in five patients of group 2 and four patients of group 3, all with progressive disease. In three patients with progressive disease who died during follow-up tumour SUVmax increased by 41 – 82 % from the first to the last follow-up investigation.

Conclusion

In NET patients, the presence of ¹⁸F-FDG-positive tumours correlates strongly with a higher risk of progression. Initially, patients with ¹⁸F-FDG-negative NET may show ¹⁸F-FDG-positive tumours during follow-up. Also patients with grade 1 and grade 2 NET may have ¹⁸F-FDG-positive tumours. Therefore, ¹⁸F-FDG PET/CT is a complementary tool to ⁶⁸Ga-DOTA-TOC PET/CT with clinical relevance for molecular investigation.

PET tracers for somatostatin receptor imaging of neuroendocrine tumors: current status and review of the literature

Neuroendocrine tumors have shown rising incidence mainly due to higher clinical awareness and better diagnostic tools over the last 30 years. Functional imaging of neuroendocrine tumors with PET tracers is an evolving field that is continuously refining the affinity of new tracers in the search for the perfect neuroendocrine tumor imaging tracer. (68)Ga-labeled tracers coupled to synthetic somatostatin analogs with differences in affinity for the five somatostatin receptor subtypes are now widely applied in Europe. Comparison of sensitivity between the most used tracers - (68)Ga-DOTA-Tyr3-octreotide, (68)Ga-DOTA-Tyr3-octreotate and (68)Ga-DOTA-l-Nal3-octreotide - shows little difference and expertise on the specific tracer used, and knowledge regarding physiological uptake might be more important than in vitro-proven differences in affinity. Using isotopes such as (18)F or (64)Cu might improve these PET tracers further.

Absorption, distribution and excretion of intravenously injected (68)Ge/ (68)Ga generator eluate in healthy rats, and estimation of human radiation dosimetry

Background

This study evaluated the absorption, distribution, and excretion of Gallium-68 (⁶⁸Ga) radionuclide after a single intravenous (i.v.) injection of ⁶⁸Ge/⁶⁸Ga generator eluate in healthy rats. Additionally, human radiation doses were estimated from the rat data.

Methods

Twenty-one female and 21 male Sprague-Dawley rats were i.v. injected with 47 ± 4 MBq of ⁶⁸Ge/⁶⁸Ga generator eluate, and the radioactivity of excised organs was measured using a gamma counter at 5, 30, 60, 120, or 180 min afterwards (n = 3–7 for each time point). The radioactivity concentration and plasma pharmacokinetic parameters were calculated. Subsequently, the estimates for human radiation dosimetry were determined. Additionally, 4 female and 5 male rats were positron emission tomography (PET) imaged for in vivo visualization of biodistribution.

Results

⁶⁸Ga radioactivity was cleared relatively slowly from blood circulation and excreted into the urine, with some retention in the liver and spleen. Notably, the ⁶⁸Ga radioactivity in female genital organs, i.e., the uterus and ovaries, was considerable higher compared with male genitals. Extrapolating from the female and male rat ⁶⁸Ga data, the estimated effective dose was 0.0308 mSv/MBq for a 57-kg woman and 0.0191 mSv/MBq for a 70-kg man.

Conclusions

The estimated human radiation burden of the ⁶⁸Ge/⁶⁸Ga generator eluate was slightly higher for females and similar for males as compared with somatostatin receptor ligands ⁶⁸Ga-DOTANOC, ⁶⁸Ga-DOTATOC, and ⁶⁸Ga-DOTATATE, which is probably due to the retention in the liver and spleen. Our results revealed some differences between female and male rat data, which, at least in part, may be explained by the small sample size.

Searching for primaries in patients with neuroendocrine tumors (NET) of unknown primary and clinically suspected NET: Evaluation of Ga-68 DOTATOC PET/CT and In-111 DTPA octreotide SPECT/CT

Background

To evaluate the clinical efficacy of In-111 DTPA octreotide SPECT/CT and Ga-68 DOTATOC PET/CT for detection of primary tumors in patients with either neuroendocrine tumor of unknown primary (NETUP) or clinically suspected primary NET (SNET).

Patients and methods.

A total of 123 patients were included from 2006 to 2009, 52 received Ga-68 DOTATOC PET/CT (NETUP, 33; SNET, 19) and 71 underwent In-111 DTPA octreotide SPECT/CT (50; 21). The standard of reference included histopathology or clinical verification based on follow-up examinations.

Results

In the NETUP group Ga-68 DOTATOC detected primaries in 15 patients (45.5%) and In-111 DTPA octreotide in 4 patients (8%) (p < 0.001); in the SNET group, only 2 primaries could be detected, all by Ga-68 DOTATOC. In patients with NETUP, primary tumors could be found significantly more often than in patients with SNET (p = 0.01). Out of these 21 patients 14 patients were operated.

Conclusion

Ga-68 DOTATOC PET/CT is preferable to In-111 DTPA octreotide SPECT/CT when searching for primary NETs in patients with NETUP but should be used with caution in patients with SNET.

Dosimetric measurements of (68)Ga-high affinity DOTATATE: twins in spirit - part III

PURPOSE

68Ga-labelled compounds are increasingly used for somatostatin-receptor scintigraphy because of their favourable biokinetic properties, a higher tumour-to-background contrast and higher diagnostic accuracy compared to the gamma-emitting tracer 111In-DTPA-octreotide. Recently, we have introduced the new tracer 68Ga-DOTA-3-iodo-Tyr3-Thr8-octreotide (68Ga-HA-DOTATATE). The present study demonstrates the biodistribution and radiation dosimetry of this tracer in humans.

PATIENTS, METHODS

Seven men were enrolled in this analysis. Every patient underwent a 20 min dynamic PET scan after intravenous injection of about 114 ± 9 MBq of 68Ga-HA-DOTATATE. This was followed by two whole-body scans at 30 min p. i. and 120 min p. i. Blood radioactivity concentration was determined non-invasively from a ROI drawn over the aorta. Urine was collected until the time of the last scan. Liver, spleen, kidneys and urinary bladder wall were included in the dosimetric estimation that was carried out with the software package OLINDA 1.0.

RESULTS

Physiological 68Ga-HA-DOTATATE uptake was observed in the pituitary gland, thyroid, salivary glands, liver, spleen, kidneys, urinary bladder, adrenals and intestine. Organs with the highest absorbed dose were spleen (0.26 ± 0.11 mSv/MBq), kidneys (0.14 ± 0.03 mSv/MBq) and liver (0.12 ± 0.02 mSv/MBq).The estimated effective dose was 0.024 ± 0.001 mSv/MBq.

CONCLUSION

Our study demonstrates biokinetics and radiation exposure of the 68Ga-labelled tracer HA-DOTATATE to be comparable to other 68Ga-labelled SSR analogues in clinical use.

Twins in spirit part II: DOTATATE and high-affinity DOTATATE--the clinical experience

PURPOSE

Over recent decades interest in diagnosis and treatment of neuroendocrine tumours (NET) has steadily grown. The basis for diagnosis and therapy of NET with radiolabelled somatostatin (hsst) analogues is the variable overexpression of hsst receptors (hsst1-5 receptors). We hypothesized that radiometal derivatives of DOTA-iodo-Tyr(3)-octreotide analogues might be excellent candidates for somatostatin receptor imaging. We therefore explored the diagnostic potential of (68)Ga-DOTA-iodo-Tyr(3)-octreotate [(68)Ga-DOTA,3-iodo-Tyr(3),Thr(8)]octreotide ((68)Ga-HA-DOTATATE; HA, high-affinity) compared to the established (68)Ga-DOTA-Tyr(3)-octreotate ((68)Ga-DOTATATE) in vivo.

METHODS

The study included 23 patients with known somatostatin receptor-positive metastases from NETs, thyroid cancer or glomus tumours who were investigated with both (68)Ga-HA-DOTATATE and (68)Ga-DOTATATE. A patient-based and a lesion-based comparative analysis was carried out of normal tissue distribution and lesion detectability in a qualitative and a semiquantitative manner.

RESULTS

(68)Ga-HA-DOTATATE and (68)Ga-DOTATATE showed comparable uptake in the liver (SUVmean 8.9 ± 2.2 vs. 9.3 ± 2.5, n.s.), renal cortex (SUVmean 13.3 ± 3.9 vs. 14.5 ± 3.7, n.s.) and spleen (SUVmean 24.0 ± 6.7 vs. 22.9 ± 7.3, n.s.). A somewhat higher pituitary uptake was found with (68)Ga-HA-DOTATATE (SUVmean 6.3 ± 1.8 vs. 5.4 ± 2.1, p < 0.05). On a lesion-by-lesion basis a total of 344 lesions were detected. (68)Ga-HA-DOTATATE demonstrated 328 lesions (95.3% of total lesions seen), and (68)Ga-DOTATATE demonstrated 332 lesions (96.4%). The mean SUVmax of all lesions was not significantly different between (68)Ga-HA-DOTATATE and (68)Ga-DOTATATE (17.8 ± 11.4 vs. 16.7 ± 10.7, n.s.).

CONCLUSION

Our analysis demonstrated very good concordance between (68)Ga-HA-DOTATATE and (68)Ga-DOTATATE PET data. As the availability and use of (68)Ga-HA-DOTATATE is not governed by patent restrictions it may be an attractive alternative to other (68)Ga-labelled hsst analogues.

PET and PET/CT with 68gallium-labeled somatostatin analogues in Non GEP-NETs Tumors

Somatostatin (SST) is a 28-amino-acid cyclic neuropeptide mainly secreted by neurons and endocrine cells. A major interest for SST receptors (SSTR) as target for in vivo diagnostic and therapeutic purposes was born since a series of stable synthetic SST-analouges PET became available, being the native somatostatin non feasible for clinical use due to the very low metabolic stability. The rationale for the employment of SST-analogues to image cancer is both based on the expression of SSTR by tumor and on the high affinity of these compounds for SSTR. The primary indication of SST-analogues imaging is for neuroendocrine tumors (NETs), which usually express a high density of SSTR, so they can be effectively targeted and visualized with radiolabeled SST-analogues in vivo. Particularly, SST-analogues imaging has been widely employed in gastroenteropancreatic (GEP) NETs. Nevertheless, a variety of tumors other than NETs expresses SSTR thus SST-analogues imaging can also be used in these tumors, particularly if treatment with radiolabeled therapeutic SST-analouges PET is being considered. The aim of this paper is to provide a concise overview of the role of positron emission tomography/computed tomography (PET/CT) with (68)Ga-radiolabeled SST-analouges PET in tumors other than GEP-NETs.

Comparison between F-18 fluorodeoxyglucose and Ga-68 DOTATOC in metastasized melanoma

PURPOSE

Somatostatin binding to somatostatin receptors (SSTRs) is known to have an antiproliferative effect in neuroendocrine tumours. Melanoma cells are derived from the neural crest and thus express SSTR. Treatment options in metastasized melanomas are limited. Therefore, we aimed to investigate whether there is a relevant uptake of the SSTR analogue DOTATOC in metastasized melanoma patients, which could be used for therapy with radiolabelled SSTR analogues.

MATERIALS AND METHODS

We investigated 18 patients (nine men and nine women; mean age 61 years) with metastasized melanoma using PET/CT, first with F-18 fluorodeoxyglucose ((18)F-FDG) and then with Ga-68 DOTATOC. The number of (18)F-FDG-positive or DOTATOC-positive lesions and the maximum standardized uptake value (SUV(max)) for an index lesion were determined for each patient.

RESULTS

DOTATOC could reveal metastatic lesions in 11 of 18 patients (61%). However, on a lesion-by-lesion basis only 59 of 263 (22%) (18)F-FDG-avid metastases were seen with DOTATOC. Further, DOTATOC uptake was only faint. The mean SUV(max) was 3.1 (range, 1.2-4.2) for DOTATOC, in contrast to 28.2 (range, 2.3-115) for (18)F-FDG.

CONCLUSION

Radiolabelled DOTATOC does not seem to be a promising agent for treatment of metastasized melanoma.

Repeatability of gallium-68 DOTATOC positron emission tomographic imaging in neuroendocrine tumors

OBJECTIVE

To evaluate the repeatability of gallium-68 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic (DOTA)-D-Phe1-Try3-octreotide (68Ga-DOTATOC) positron emission tomography (PET) in neuroendocrine tumors.

METHODS

Five patients with neuroendocrine tumors were imaged with 68Ga-DOTATOC PET twice within 5 days. Maximum and mean standardized uptake values (SUVmax and SUVmean) and kinetic parameters (K-Patlak and K-influx) of target lesions were measured. The repeatability of these measurements was investigated.

RESULTS

Forty-seven target lesions were identified on whole-body PET and 21 lesions on dynamic images. There was excellent repeatability with intraclass correlation coefficient of 0.99 for SUVmax, SUVmean, and K-Patlak, and 0.85 for K-influx. The median absolute percent differences and the interquartile ranges (IQR) between 2 scans for SUVmax and SUVmean were 7.4% (IQR, 14.1%) and 9.3% (IQR, 10.6%), respectively. The median absolute percent differences for K-Patlak and K-influx were 12.5% (IQR, 12.6%) and 29.9% (IQR, 22.4%), respectively. The SUVmax of target lesions did not differ by more than 25% between the 2 scans.

CONCLUSIONS

68Ga-DOTATOC PET imaging of neuroendocrine tumors is highly reproducible. A difference of more than 25% in SUVmax represents a change that is larger than the measurement error observed on repeated studies and should reflect a significant change in the biological character of the tumor.

Long-term evaluation of 'BARC 68Ge/68Ga generator' based on the nanoceria-polyacrylonitrile composite sorbent

This article describes the long-term evaluation of a nanoceria-polyacrylonitrile (CeO2-PAN) composite sorbent-based (68)Ge/(68)Ga generator reported. This generator used the new CeO2-PAN composite sorbent for preparation of the (68)Ge/(68)Ga generator. Since this sorbent has not been previously evaluated, a thorough long-term evaluation of the performance of the generator is necessary to ensure its applicability for clinical practice. The performance of the generator was evaluated in terms of (68)Ga yield, (68)Ge breakthrough, radioactive concentration of the (68)Ga solution, and suitability of the (68)Ga for the preparation of (68)Ga-labeled tracers. The (68)Ge/(68)Ga generator was able to provide a (68)Ga activity with consistent yields (>70%) and having acceptable radionuclidic (<10(-4)% of (68)Ge breakthrough), radiochemical, and chemical purities for an extended period of time. The eluted (68)GaCl3 is useful for the majority of the (68)Ga complexation chemistry.

Measured human dosimetry of 68Ga-DOTATATE

Measured human dosimetry of the (68)Ga-labeled synthetic somatostatin analog (68)Ga-DOTATATE has not been reported in the peer-reviewed literature. (68)Ga-DOTATATE is an investigational PET/CT imaging agent that binds with high affinity to somatostatin receptor subtype 2, found on many human cancers, most classically neuroendocrine tumors but also others. Reporting of measured dosimetry of (68)Ga-DOTATATE could be useful for investigations for diagnosis, staging, and restaging of somatostatin receptor-expressing tumors.

METHODS

We performed measured dosimetry with (68)Ga-DOTATATE PET/CT scanning in 6 volunteer human subjects as part of an Institutional Review Board-approved biodistribution investigation of the use of this radiopharmaceutical for possible future use in the diagnosis of indeterminate lung nodules or lung cancer. Five subjects were imaged at 3 time points, and 1 subject was imaged at 2 time points. Dosimetry was then measured for the whole body and for specific organs.

RESULTS

There were no observed adverse events to the radiopharmaceutical in the immediate or delayed time frames, with a follow-up of 1 y. One patient had stage IV non-small cell lung cancer and remains alive but with disease progressing on treatment. For the other 5 patients, it was ultimately proven that they had benign nodules. The measured dosimetry shows that the critical organ with (68)Ga-DOTATATE is the spleen, followed by the uroepithelium of the bladder, the kidneys, and the liver, in that order. Organ-specific and whole-body dosimetries for (68)Ga-DOTATATE were similar to but often slightly greater than those for (68)Ga-DOTATOC or (68)Ga-DOTANOC but less than those for (111)In-diethylenetriaminepentaacetic acid-octreotide.

CONCLUSION

No toxicity was observed in our 6 patients, and no adverse events occurred. The measured human dosimetry of (68)Ga-DOTATATE is similar to that of other (68)Ga-labeled somatostatin receptor analogs.

Radiation exposure to nuclear medicine personnel handling positron emitters from Ge-68/Ga-68 generator

Objective:

To measure the radiation exposure to nuclear medicine personnel during synthesis and injection to the patients of Ga-68 1,4,7,10-tetraazacyclododecane-N,N′,N″,N″′-tetraacetic acid (DOTA)-1-Nal³-octreotide (NOC)- (DOTA-NOC) using ring thermoluminescence dosimeters (TLDs).

Materials and Methods:

Synthesis of Ga-68 DOTA-NOC was done on a semi-automated system. Finger doses were measured during synthesis and injection of Ga-68 DOTA-NOC. The occupational workers wore TLDs at the base of ring finger of both hands. The finger doses of two radio chemists were measured during synthesis of Ga-68 DOTA-NOC while that of a physician during its injection to the patients.

Results:

Duration of the study was eight months and a total of 20 samples were prepared. During synthesis, the mean dose to base of left ring finger was 3.02 ± 1.01 mSv and to base of right ring finger was 1.96 ± 0.86 mSv. Mean dose to base of left ring finger was 1.26 ± 0.35 mSv while that to base of right ring finger was 1.03 ± 0.13 mSv during injection. The mean dose was observed to be higher during synthesis than injection. However, the difference was not significant (P = 0.27 and P = 0.18, respectively). Overall mean finger dose of left hand was 2.43 ± 1.21 mSv, whereas for the right hand the same was 1.65± 0.82 mSv.

Conclusion:

Finger doses to radio chemists during semi-automated synthesis of Ga-68 DOTA-NOC and that to the physician involved in injection of Ga-68 DOTA-NOC were found to be within permissible limits. Ring dosimeters must be worn for the safety of the nuclear medicine personnel involved in synthesis and injection of Ga-68 DOTA-NOC.

Dosimetry of [⁶⁸Ga]-labeled compounds

This review compiles and analyzes the available dosimetry data of [(68)Ga] labeled compounds. Dosimetry data are given for [(68)Ga]DOTA-NOC, TOC, TATE, and NODAGA-RGDyK. The number of PET-scans with [(68)Ga]DOTA-compounds for imaging neuroendocrine tumors is increasing because [(68)Ga] has a higher affinity to somatostatin receptors (SSTR) in comparison to comparable [(111)In]-compounds. In addition, the better image resolution of the PET images provides improved diagnostics. Despite its widespread use literature on dosimetry of [(68)Ga]-labeled radiopharmaceuticals is sparse. In some cases the description of the underlying methodology is missing or human data are gained from the extrapolation of animal experiments. More and better documented dosimetry data will further promote the use of these promising new agents.

High management impact of Ga-68 DOTATATE (GaTate) PET/CT for imaging neuroendocrine and other somatostatin expressing tumours

INTRODUCTION

Ga-68 DOTATATE (Ga-octreotate, GaTate) positron emission tomography (PET)/CT has multiple advantages compared with conventional and In-111 octreotide imaging for neuroendocrine tumours and other somatostatin-receptor expressing tumours. This study assesses the management impact of incremental diagnostic information obtained from this technique compared with conventional staging.

METHODS

Fifty-nine GaTate PET/CT studies were performed over an 18-month period (52 proven or suspected gastro-entero-pancreatic or bronchial neuroendocrine tumours and seven neural crest/mesenchymal tumours). A retrospective blinded review was performed on the number of abnormalities (1, 2-5 or >5) within defined regions with comparison to conventional imaging to assess incremental diagnostic information. Subsequent management impact (high, moderate or low) was determined by clinical review and follow up to assess pre-PET stage, treatment intent and post-PET management change.

RESULTS

Eighty-eight percent of GaTate studies were abnormal. Compared with conventional and In-111 octreotide imaging, additional information was provided by GaTate PET/CT in 68 and 83% of patients, respectively. Management impact was high (inter-modality change) in 47%, moderate (intra-modality change) in 10% and low in 41% (not assessable in 2%). High management impact included directing patients to curative surgery by identifying a primary site and directing patients with multiple metastases to systemic therapy.

CONCLUSION

GaTate PET/CT imaging provides additional diagnostic information in a high proportion of patients with consequent high management impact. GaTate PET/CT could replace (1)In-111 octreotide scintigraphy at centres where it is available given its superior accuracy, faster acquisition and lower radiation exposure. Rapid implementation could be achieved by allowing substitutional funding in the Medicare Benefit Schedule.

Whole-body distribution and radiation dosimetry of (68)Ga-NOTA-RGD, a positron emission tomography agent for angiogenesis imaging

(68)Ga labeled NOTA-RGD was a recently developed positron emission tomography (PET) radiotracer for the visualization of angiogenesis, and is regarded as a promising imaging agent for cancer and several other disorders. In this study, we investigated the whole-body distribution and radiation dosimetry of (68)Ga-NOTA-RGD in humans. Ten cancer patients (53.7 ± 13.5 years; 61.5 ± 7.4  kg) participated in this study. PET scans were performed using a PET/computed tomography (scanner in three-dimensional mode). After an intravenous injection of 172.4 ± 20.5  MBq of (68)Ga-NOTA-RGD, eight serial whole-body scans were performed during 90 minutes. Volumes of interest were drawn manually over the entire volumes of the urinary bladder, the gallbladder, heart, kidneys, liver, lungs, pancreas, spleen, and stomach. Time-activity curves were obtained from serial PET scan data. Residence times were calculated from areas under curve of time-activity curves and used as input to the OLINDA/EXM 1.1 software. The uptake of (68)Ga-NOTA-RGD was highest in the kidneys and urinary bladder. Radiation doses to kidneys and urinary bladder were 71.6 ± 28.4  μ Gy/MBq and 239.6 ± 56.6  μ Gy/MBq. Mean effective doses were 25.0 ± 4.4  μ Sv/MBq using International Commission of Radiation Protection (ICRP) publication 60 and 22.4 ± 3.8  μ Sv/MBq using ICRP publication 103 weighting factor. We evaluated the radiation dosimetry of (68)Ga labeled NOTA-RGD, which has an acceptable effective radiation dose.

Biokinetics and dosimetry of commonly used radiopharmaceuticals in diagnostic nuclear medicine - a review

PURPOSE

The impact on patients' health of radiopharmaceuticals in nuclear medicine diagnostics has not until now been evaluated systematically in a European context. Therefore, as part of the EU-funded Project PEDDOSE.NET ( www.peddose.net ), we review and summarize the current knowledge on biokinetics and dosimetry of commonly used diagnostic radiopharmaceuticals.

METHODS

A detailed literature search on published biokinetic and dosimetric data was performed mostly via PubMed ( www.ncbi.nlm.nih.gov/pubmed ). In principle the criteria for inclusion of data followed the EANM Dosimetry Committee guidance document on good clinical reporting.

RESULTS

Data on dosimetry and biokinetics can be difficult to find, are scattered in various journals and, especially in paediatric nuclear medicine, are very scarce. The data collection and calculation methods vary with respect to the time-points, bladder voiding, dose assessment after the last data point and the way the effective dose was calculated. In many studies the number of subjects included for obtaining biokinetic and dosimetry data was fewer than ten, and some of the biokinetic data were acquired more than 20 years ago.

CONCLUSION

It would be of interest to generate new data on biokinetics and dosimetry in diagnostic nuclear medicine using state-of-the-art equipment and more uniform dosimetry protocols. For easier public access to dosimetry data for diagnostic radiopharmaceuticals, a database containing these data should be created and maintained.

(68)Ga-labeled DOTA-peptides and (68)Ga-labeled radiopharmaceuticals for positron emission tomography: current status of research, clinical applications, and future perspectives

In this review we give an overview of current knowledge of (68)Ga-labeled pharmaceuticals, with focus on imaging receptor-mediated processes. A major advantage of a (68)Ge/(68)Ga generator is its continuous source of (68)Ga, independently from an on-site cyclotron. The increase in knowledge of purification and concentration of the eluate and the complex ligand chemistry has led to (68)Ga-labeled pharmaceuticals with major clinical impact. (68)Ga-labeled pharmaceuticals have the potential to cover all today's clinical options with (99m)Tc, with the concordant higher resolution of positron emission tomography (PET) in comparison with single photon emission computed tomography. (68)Ga-labeled analogs of octreotide, such as DOTATOC, DOTANOC, and DOTA-TATE, are in clinical application in nuclear medicine, and these analogs are now the most frequently applied of all (68)Ga-labeled pharmaceuticals. All the above-mentioned items in favor of successful application of (68)Ga-labeled radiopharmaceuticals for imaging in patients are strong arguments for the development of a (68)Ge/(68)Ga generator with Marketing Authorization and thus to provide pharmaceutical grade eluate. Moreover, now not one United States Food and Drug Administration-approved or European Medicines Agency-approved (68)Ga-radiopharmaceutical is available. As soon as these are achieved, a whole new radiopharmacy providing PET radiopharmaceuticals might develop.

Is there still a place for adrenal venous sampling in the diagnostic localization of pheochromocytoma?

Our objective is to outline the utility of adrenal venous sampling (AVS) with measurements of metanephrine to normetanephrine ratios for diagnostic localization of phaeochromocytoma in a patient with normal plasma levels of catecholamines. A 53-year-old-woman was referred for evaluation of recurrent pheochromocytoma following a right adrenalectomy 14 years earlier. Diagnosis of recurrent disease was established from elevations in plasma metanephrines with normal levels of catecholamines. Magnetic resonance imaging indicated two 1-2 cm masses in the right surgical bed and another 1-1.5 cm mass in the left adrenal. These masses were negative on (123)I-metaiodobenzylguanidine scintigraphy. There was no evidence of a hereditary syndrome. We, therefore, carried out two investigational approaches to identify the tumor masses. Hybrid positron emission tomography/computed tomography with (68)Ga-DOTATOC ((68)Ga-DOTATOC-PET/CT) confirmed the presence of recurrent disease in the right surgical bed and also suggested additional left adrenal involvement. Normal plasma catecholamines precluded the use of adrenal venous sampling (AVS) with catecholamine measurements. Hence, we performed AVS with measurements of plasma metanephrines, which were 4- to 7-fold higher in the left adrenal vein than in central venous plasma. We observed a reversal of the normally high metanephrine to normetanephrine ratio (mean value ± SD 5.28 ± 1.86; range 3.36-8.84, n = 13) to 0.73, establishing the presence of a left adrenal pheochromocytoma. Surgical pathology confirmed bilateral disease. This case highlights a scenario where a combination of (68)Ga-DOTATOC-PET/CT and AVS with measurement of the metanephrine to normetanephrine ratio was crucial for the preoperative assessment of a patient with bilateral pheochromocytoma.

[Quantification of immunohistochemical expression of somatostatin receptors in neuroendocrine tumors using 68Ga-DOTATATE PET/CT]

PURPOSE

The immunohistochemical expression of somatostatin receptor (SSTR) subtype 2 was compared to quantitative (68)Ga-DOTATATE PET in neuroendocrine tumors (NET).

MATERIAL AND METHODS

In 27 patients suffering from metastatic NET the expression of somatostatin receptors (SSTR, score 0-3) and the Ki-67 index were assessed. The immunohistochemical findings were compared with the (68)Ga-DOTATATE PET uptake in these tumors using the SUV(max) (standardized uptake value). Both values were compared with the Ki-67 proliferation index.

RESULTS

The SUV(max) in NET without SSTR expression was significantly lower compared to those with SSTR expression (p <0.05), even though 3 out of 5 NETs with a score of 0 showed a high uptake of (68)Ga-DOTATATE. The SUV(max) correlated significantly (r=0.40, p <0.05) with the score of immunohistochemical SSTR expression (negative, score 0, moderate, score 1 and high, scores 2 and 3). The Ki-67 index correlated inversely with the SSTR expression score (r=-0.42, p <0.05), but not significantly with the SUV(max) (r=-0.33, p=0.11).

CONCLUSION

(68)Ga-DOTATATE uptake was moderately correlated with the results of immunohistochemical SSTR analyses. However, SSTR negative NET may show high uptake of (68)Ga-DOTATATE.