68Ga-DOTATOC versus 68Ga-DOTATATE PET/CT in functional imaging of neuroendocrine tumors

Design of CGMP production of 18F- and 68Ga-radiopharmaceuticals

Objective. Radiopharmaceutical production process must adhere to current good manufacturing process (CGMP) compliance to ensure the quality of precursor, prodrug (active pharmaceutical ingredient, API), and the final drug product that meet acceptance criteria. We aimed to develop an automated system for production of CGMP grade of PET radiopharmaceuticals. Methods. The hardware and software of the automated synthesizer that fit in the hot cell under cGMP requirement were developed. Examples of production yield and purity for ⁶⁸Ga-DOTATATE and ¹⁸F-FDG at CGMP facility were optimized. Analytical assays and acceptance criteria for cGMP grade of ⁶⁸Ga-DOTATATE and ¹⁸F-FDG were established. Results. CGMP facility for the production of PET radiopharmaceuticals has been established. Radio-TLC and HPLC analyses of ⁶⁸Ga-DOTATATE and ¹⁸F-FDG showed that the radiochemical purity was 92% and 96%, respectively. The products were sterile and pyrogenic-free. Conclusion. CGMP compliance of radiopharmaceuticals has been reviewed. ⁶⁸Ga-DOTATATE and ¹⁸F-FDG were synthesized with high radiochemical yield under CGMP process.

(68)Ga-DOTATATE PET/CT in the evaluation of patients with neuroendocrine metastatic carcinoma of unknown origin

OBJECTIVE

There is little evidence regarding the role of (68)Ga-DOTATATE PET/CT for the identification of primary tumors in patients with metastatic neuroendocrine carcinoma of unknown primary. The aim of this study is to assess the value of this technique in the mentioned clinical scenario.

METHODS

We retrospectively studied twenty-nine patients (mean age 59.5 ± 10.6 years; female 17) with pathologically proven neuroendocrine metastases. In all cases conventional imaging was negative for primary tumor identification. (68)Ga-DOTATATE PET/CT was performed with a mean dose of 104.2 ± 18.8 MBq, using a 64-slice PET/CT with time-of-flight correction. A team of an experienced radiologist and a nuclear medicine physician evaluated the images. The maximum SUV (SUVm) was measured in all abnormal foci. Histopathology (when available) and/or clinical follow-up with correlative imaging was considered as reference standard.

RESULTS

(68)Ga-DOTATATE PET/CT identified the primary tumor in 17/29 (59%) patients in the following locations: pancreas (n = 7), ileum (n = 7), duodenum (n = 1), colon (n = 1) and stomach (n = 1). In this population a significant correlation was found between SUVm of primary tumor and metastases (r = 0.815, P < 0.0001). Furthermore, additional sites of unsuspected metastases were demonstrated in 9 patients of this group and in 6 patients in whom no primary tumor was localized, mainly in lymph nodes and mesentery. Pathology confirmation was obtained in 7 patients who underwent surgery, whereas in the remaining 10 patients, correlative imaging and follow-up confirmed primary tumor localization.

CONCLUSIONS

(68)Ga-DOTATATE PET/CT is a clinically useful imaging technique for the localization of primary tumors in patients with neuroendocrine metastatic carcinoma of unknown origin with the potential of having a significant impact in patient management and therapy planning.

Diagnostic role of Gallium-68 DOTATOC and Gallium-68 DOTATATE PET in patients with neuroendocrine tumors: a meta-analysis

BACKGROUND

Gallium-68 somatostatin receptor positron emission tomography (PET) has been used in the diagnosis of neuroendocrine tumors (NETs). The compounds often used in molecular imaging of NETs with PET are 68Ga-DOTATOC, 68Ga-DOTATATE, and 68Ga-DOTANOC. There is varying affinity to different somatostatin receptors.

PURPOSE

To systematically review and perform a meta-analysis of published data regarding the diagnostic role of 68Ga-DOTATOC and 68Ga-DOTATATE PET in the diagnosis of NETs.

MATERIAL AND METHODS

A comprehensive literature search of studies published through 30 April 2013 regarding 68Ga-DOTATOC and 68Ga-DOTATATE PET in the diagnosis of NETs was performed using the PubMed/MEDLINE, Embase, and Scopus databases. Pooled sensitivity and specificity of 68Ga-DOTATOC and 68Ga-DOTATATE PET in the diagnosis of NETs were calculated. The area under the receiver-operating characteristic (ROC) curve was calculated to measure the accuracy of 68Ga-DOTATOC and 68Ga-DOTATATE PET in the diagnosis of NETs.

RESULTS

Ten studies comprising 416 patients with NETs were included in this meta-analysis. The pooled sensitivity of 68Ga-DOTATOC and 68Ga-DOTATATE PET in the diagnosis of NETs calculated on a per-patient-based analysis was 93% (95% confidence interval [CI] 89-96%) and 96% (95% CI 91-99%). The pooled specificity of 68Ga-DOTATOC and 68Ga-DOTATATE PET in diagnosing NETs was 85% (95% CI 74-93%) and 100% (95% CI 82-100%). The area under the ROC curve of 68Ga-DOTATOC and 68Ga-DOTATATE PET was 0.96 and 0.98, respectively, on a per-patient-based analysis.

CONCLUSION

The molecular imaging agents 68Ga-DOTATOC and 68Ga-DOTATATE demonstrated high sensitivity and specificity in the diagnosis of NETs on PET scan. Although both are accurate tools in the diagnosis of NETs, 68Ga-DOTATATE PET may be more sensitive and specific than 68Ga-DOTATOC PET scan.

The use of gallium-68 labeled somatostatin receptors in PET/CT imaging

68Ga-DOTA-SSTRTs PET/CT has become the most promising noninvasive procedure to study well-differentiated NET. Although the excellent diagnostic accuracy of the procedure is well known, its use is limited to specialized centers in Europe as parts of clinical trials. Literature reports confirm the superiority of 68Ga-DOTA-SSTRTs PET/CT for the assessment of well-differentiated NET over morphologic imaging procedures, SRS, and even PET/CT using metabolic radiotracers. 68Ga-DOTA-SSTRTs provide good visualization of NET lesions at both the primary and the metastatic sites (node, bone, liver, and unusual localizations). The advantages of their use over metabolic tracers (18F-DOPA, 18F-FDG) are not only limited to a better overall detection rate but also to the fact that they also provide data on SSTR expression on target lesions, resulting a fundamental procedure before starting therapy with either hot or cold somatostatin analogues. Moreover, they can be used also in centers without an on-site cyclotron. To interpret 68Ga-DOTA-SSTRTs images correctly, it is crucial to understand the tracer’s biodistribution as well as the conditions that may alter tracer uptake. Considering that SSTR are expressed on activated lymphocytes, all areas of inflammation show 68Ga-DOTA-SSTRTs uptake. Areas of increased uptake in frequent sites of inflammation (eg, thyroid, mediastinal nodes, inguinal nodes, and nodes adjacent to areas of recent surgery/trauma) should be interpreted with care. A detailed clinical history with particular attention to concomitant disorders (eg, sarcoidosis, chronic gastritis, chronic thryoiditis) and recent invasive procedures or trauma may often help image interpretation. The presence of uptake in the head of the pancreas should always be carefully evaluated because it may often be benign. Otherwise, because the pancreas is also a frequent site of NET onset, particular attention should be devoted to the evaluation of the uptake pattern (diffuse more likely to be benign) and to the comparison with other imaging techniques.

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.

Neuroendocrine tumours: the role of imaging for diagnosis and therapy

In patients with neuroendocrine tumours (NETs), a combination of morphological imaging and nuclear medicine techniques is mandatory for primary tumour visualization, staging and evaluation of somatostatin receptor status. CT and MRI are well-suited for discerning small lesions that might escape detection by single photon emission tomography (SPECT) or PET, as well as for assessing the local invasiveness of the tumour or the response to therapy. Somatostatin receptor imaging, by (111)In-pentetreotide scintigraphy or PET with (68)Ga-labelled somatostatin analogues, frequently identifies additional lesions that are not visible on CT or MRI scans. Currently, somatostatin receptor scintigraphy with (111)In-pentetreotide is the more frequently available of the two techniques to determine somatostatin receptor expression and is needed to select patients for peptide receptor radionuclide therapy. In the future, because of its higher sensitivity, PET with (68)Ga-labelled somatostatin analogues is expected to replace somatostatin receptor scintigraphy. Whereas (18)F-FDG-PET is only used in high-grade neuroendocrine cancers, PET-CT with (18)F-dihydroxy-L-phenylalanine or (11)C-5-hydroxy-L-tryptophan is a useful problem-solving tool and could be considered for the evaluation of therapy response in the future. This article reviews the role of imaging for the diagnosis and management of intestinal and pancreatic NETs. Response evaluation and controversies in NET imaging will also be discussed.

Gallium-68 DOTATOC PET/CT in vivo characterization of somatostatin receptor expression in the prostate

AIM

The aim was to investigate somatostatin receptor (sstr) expression in normal prostate by determining the maximum standardized uptake value (SUVmax) of (68)Ga-DOTATOC PET/CT in neuroendocrine tumor (NET) patients, without NET involvement of the prostate gland, for establishing the reference standard.

METHODS

Sixty-four NET patients underwent (68)Ga-DOTATOC PET/CT. SUVmax of the prostate gland, normal liver, testes, and gluteus muscles were evaluated. The prostate gland size was measured. Statistical analysis was performed using dedicated software (SPSS13).

RESULTS

Mean/median (68)Ga-DOTATOC SUVmax values were as follows: normal prostate 2.6 ± 0.0, slightly enlarged prostate 4.2 ± 1.6, prostatic hypertrophy 4.9 ± 1.6, prostatic hyperplasia 5.0 ± 1.5, prostate cancer 9.5 ± 2.1, normal liver 7.3 ± 1.8, testes 1.8 ± 0.5, and gluteus 1.0 ± 0.2. The normal prostate gland had three times less sstr expression than normal liver tissue. Strong correlation was found between patient age and sstr expression in prostate/prostate size. No significant difference existed in sstr expression between prostatic hypertrophy and hyperplasia. Much higher sstr expression was found in prostatic cancer compared with normal prostate.

CONCLUSION

(68)Ga-DOTATOC PET/CT defines the baseline sstr uptake in prostate not affected by NET (significantly lower than in the liver). Higher values were established in prostatic hyperplasia and hypertrophy. Only concomitant prostate cancer was associated with higher SUVmax in comparison with non-neoplastic liver.

Predictive value of 68Ga-DOTANOC PET/CT in patients with suspicion of neuroendocrine tumors: is its routine use justified?

OBJECTIVE

The objective of this study was to evaluate the predictive value of Ga-DOTANOC PET/CT in patients with suspected neuroendocrine tumor (NET).

METHODS

Data of 164 patients (mean age, 42.5 ± 17.3 years; 54.8% male) who underwent Ga-DOTANOC PET/CT for suspected NET were retrospectively analyzed. Neuroendocrine tumor was suspected based on clinical features (n = 94) and/or raised biochemical markers (n = 83, serum chromogranin A, gastrin, serum/urinary catecholamines, insulin/C-peptide, and 5-hydroxytrytophan/5-hydroxyindoleacetic acid) and/or imaging findings (n = 93). PET/CT images were reviewed by 2 experienced nuclear medicine physicians, and any nonphysiological Ga-DOTANOC uptake was taken as positive for NET. Histopathology (n = 55) and clinical/imaging follow-up (n = 109; median, 11 months) was used as reference standard.

RESULTS

Based on the reference standard, 97 of 164 patients had NET. Ga-DOTANOC PET/CT was positive for NET in 101 and negative in 63 patients. Primary tumor was demonstrated in 90 patients (commonest site-pancreas) and metastasis in 30 (commonest site-liver). PET/CT was true positive in 92 patients, true negative in 58, false positive in 9, and false negative in 5. The overall sensitivity was 94.8%, specificity was 86.5%, positive predictive value was 91%, negative predictive value was 92%, and accuracy was 91.4%. The accuracy of PET-CT in patients with clinical features of NET was 90.4%, with raised biochemical markers was 86.7%, and with imaging findings suggestive of NET was 93.5%. No difference was seen in the accuracy in patients with or without clinical symptoms (P = 0.794), raised versus those with normal/unknown biochemical markers (P = 0.094), and suggestive imaging versus those with negative/unavailable imaging (P = 0.420).

CONCLUSIONS

Ga-DOTANOC PET-CT shows high positive and negative predictive values in patients with suspected NET and can be routinely used for this purpose.

Quantitative and qualitative intrapatient comparison of 68Ga-DOTATOC and 68Ga-DOTATATE: net uptake rate for accurate quantification

Quantitative imaging and dosimetry are crucial for individualized treatment during peptide receptor radionuclide therapy (PRRT). (177)Lu-DOTATATE and (68)Ga-DOTATOC/(68)Ga-DOTATATE are used, respectively, for PRRT and PET examinations targeting somatostatin receptors (SSTRs) in patients affected by neuroendocrine tumors. The aim of the study was to quantitatively and qualitatively compare the performance of (68)Ga-DOTATOC and (68)Ga-DOTATATE in the context of subsequent PRRT with (177)Lu-DOTATATE under standardized conditions in the same patient as well as to investigate the sufficiency of standardized uptake value (SUV) for estimation of SSTR expression.

METHODS

Ten patients with metastatic neuroendocrine tumors underwent one 45-min dynamic and 3 whole-body PET/CT examinations at 1, 2, and 3 h after injection with both tracers. The number of detected lesions, SUVs in lesions and normal tissue, total functional tumor volume, and SSTR volume (functional tumor volume multiplied by mean SUV) were investigated for each time point. Net uptake rate (Ki) was calculated according to the Patlak method for 3 tumors per patient.

RESULTS

There were no significant differences in lesion count, lesion SUV, Ki, functional tumor volume, or SSTR volume between (68)Ga-DOTATOC and (68)Ga-DOTATATE at any time point. The detection rate was similar, although with differences for single lesions in occasional patients. For healthy organs, marginally higher uptake of (68)Ga-DOTATATE was observed in kidneys, bone marrow, and liver at 1 h. (68)Ga-DOTATOC uptake was higher in mediastinal blood pool at the 1-h time point (P = 0.018). The tumor-to-liver ratio was marginally higher for (68)Ga-DOTATOC at the 3-h time point (P = 0.037). Blood clearance was fast and similar for both tracers. SUV did not correlate with Ki linearly and achieved saturation for a Ki of greater than 0.2 mL/cm(3)/min, corresponding to an SUV of more than 25.

CONCLUSION

(68)Ga-DOTATOC and (68)Ga-DOTATATE are suited equally well for staging and patient selection for PRRT with (177)Lu-DOTATATE. However, the slight difference in the healthy organ distribution and excretion may render (68)Ga-DOTATATE preferable. SUV did not correlate linearly with Ki and thus may not reflect the SSTR density accurately at its higher values, whereas Ki might be the outcome measure of choice for quantification of SSTR density and assessment of treatment outcome.

Prospective of ⁶⁸Ga-radiopharmaceutical development

Positron Emission Tomography (PET) experienced accelerated development and has become an established method for medical research and clinical routine diagnostics on patient individualized basis. Development and availability of new radiopharmaceuticals specific for particular diseases is one of the driving forces of the expansion of clinical PET. The future development of the ⁶⁸Ga-radiopharmaceuticals must be put in the context of several aspects such as role of PET in nuclear medicine, unmet medical needs, identification of new biomarkers, targets and corresponding ligands, production and availability of ⁶⁸Ga, automation of the radiopharmaceutical production, progress of positron emission tomography technologies and image analysis methodologies for improved quantitation accuracy, PET radiopharmaceutical regulations as well as advances in radiopharmaceutical chemistry. The review presents the prospects of the ⁶⁸Ga-based radiopharmaceutical development on the basis of the current status of these aspects as well as wide range and variety of imaging agents.

Free somatostatin receptor fraction predicts the antiproliferative effect of octreotide in a neuroendocrine tumor model: implications for dose optimization

Somatostatin receptors (SSTR) are highly expressed in well-differentiated neuroendocrine tumors (NET). Octreotide, an SSTR agonist, has been used to suppress the production of vasoactive hormones and relieve symptoms of hormone hypersecretion with functional NETs. In a clinical trial, an empiric dose of octreotide treatment prolonged time to tumor progression in patients with small bowel neuroendocrine (carcinoid) tumors, irrespective of symptom status. However, there has yet to be a dose optimization study across the patient population, and methods are currently lacking to optimize dosing of octreotide therapy on an individual basis. Multiple factors such as total tumor burden, receptor expression levels, and nontarget organ metabolism/excretion may contribute to a variation in SSTR octreotide occupancy with a given dose among different patients. In this study, we report the development of an imaging method to measure surface SSTR expression and occupancy level using the PET radiotracer (68)Ga-DOTATOC. In an animal model, SSTR occupancy by octreotide was assessed quantitatively with (68)Ga-DOTATOC PET, with the finding that increased occupancy resulted in decreased tumor proliferation rate. The results suggested that quantitative SSTR imaging during octreotide therapy has the potential to determine the fractional receptor occupancy in NETs, thereby allowing octreotide dosing to be optimized readily in individual patients. Clinical trials validating this approach are warranted.

Somatostatin receptor-based molecular imaging and therapy for neuroendocrine tumors

Neuroendocrine tumors (NETs) are tumors originated from neuroendocrine cells in the body. The localization and the detection of the extent of NETs are important for diagnosis and treatment, which should be individualized according to the tumor type, burden, and symptoms. Molecular imaging of NETs with high sensitivity and specificity is achieved by nuclear medicine method using single photon-emitting and positron-emitting radiopharmaceuticals. Somatostatin receptor imaging (SRI) using SPECT or PET as a whole-body imaging technique has become a crucial part of the management of NETs. The radiotherapy with somatostatin analogues labeled with therapeutic beta emitters, such as lutetium-177 or yttrium-90, has been proved to be an option of therapy for patients with unresectable and metastasized NETs. Molecular imaging can deliver an important message to improve the outcome for patients with NETs by earlier diagnosis, better choice of the therapeutic method, and evaluation of the therapeutic response.

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.

Somatostatin receptor PET/CT in neuroendocrine tumours: update on systematic review and meta-analysis

PURPOSE

Neuroendocrine tumours (NET) are uncommon and may be localized in many different places in the body. Traditional imaging has mainly been performed with CT and somatostatin receptor scintigraphy (SRS). Recently, it has become possible to use somatostatin receptor PET/CT (SMSR PET) instead, which might improve diagnostic quality. To evaluate the diagnostic quality of SMSR PET we performed a meta-analysis as an update of a previous study published in 2012.

METHODS

A literature search was performed searching MEDLINE, Embase and five other databases with a combination of the expressions "PET", "positron emission tomography", "neuroendocrine" and "NET". The search was updated to 31 December 2012. Studies were selected which evaluated the sensitivity and specificity of SMSR PET for NET in the thorax or abdomen with a study size of at least eight patients. The methodological quality of the included studies was evaluated with QUADAS-2.

RESULTS

Eight studies fulfilled the inclusion criteria and were selected for final analysis, and 14 articles from a previous meta-analysis were added for a total of 22 articles. A total of 2,105 patients were included in the studies, an increase from 567 in the previous meta-analysis. The pooled sensitivity was 93 % (95 % CI 91 - 94 %) and specificity 96 % (95 % CI 95 - 98 %). The area under the summary ROC curve was 0.98 (95 % CI 0.95 - 1.0). In the previous meta-analysis the pooled sensitivity was 93 % (95 % CI 91 - 95 %) and specificity 91 % (95 % CI 82 - 97 %).

CONCLUSION

SMSR PET has good diagnostic performance for evaluation of NET in the thorax and abdomen, better than SRS which has been the previous standard method. This meta-analysis gives further support for switching to SMSR PET.

Staging of neuroendocrine tumours: comparison of [⁶⁸Ga]DOTATOC multiphase PET/CT and whole-body MRI

Purpose: In patients with a neuroendocrine tumour (NET), the extent of disease strongly influences the outcome and multidisciplinary therapeutic management. Thus, systematic analysis of the diagnostic performance of the existing staging modalities is necessary. The aim of this study was to compare the diagnostic performance of 2 whole-body imaging modalities, [⁶⁸Ga]DOTATOC positron emission tomography (PET)/computed tomography (CT) and magnetic resonance imaging (MRI) in patients with NET with regard to possible impact on treatment decisions. Materials and methods: [⁶⁸Ga]DOTATOC-PET/CT and whole-body magnetic resonance imaging (wbMRI) were performed on 51 patients (25 females, 26 males, mean age 57 years) with histologically proven NET and suspicion of metastatic spread within a mean interval of 2.4 days (range 0–28 days). PET/CT was performed after intravenous administration of 150 MBq [⁶⁸Ga]DOTATOC. The CT protocol comprised multiphase contrast-enhanced imaging. The MRI protocol consisted of standard sequences before and after intravenous contrast administration at 1.5 T. Each modality (PET, CT, PET/CT, wbMRI) was evaluated independently by 2 experienced readers. Consensus decision based on correlation of all imaging data, histologic and surgical findings and clinical follow-up was established as the standard of reference. Lesion-based and patient-based analysis was performed. Detection rates and accuracy were compared using the McNemar test. P values <0.05 were considered significant. The impact of whole-body imaging on the treatment decision was evaluated by the interdisciplinary tumour board of our institution. Results: 593 metastatic lesions were detected in 41 of 51 (80%) patients with NET (lung 54, liver 266, bone 131, lymph node 99, other 43). One hundred and twenty PET-negative lesions were detected by CT or MRI. Of all 593 lesions detected, PET identified 381 (64%) true-positive lesions, CT 482 (81%), PET/CT 545 (92%) and wbMRI 540 (91%). Comparison of lesion-based detection rates between PET/CT and wbMRI revealed significantly higher sensitivity of PET/CT for metastatic lymph nodes (100% vs 73%; P < 0.0001) and pulmonary lesions (100% vs 87%; P = 0.0233), whereas wbMRI had significantly higher detection rates for liver (99% vs 92%; P < 0.0001) and bone lesions (96% vs 82%; P < 0.0001). Of all 593 lesions, 22 were found only in PET, 11 only in CT and 47 only in wbMRI. The patient-based overall assessment of the metastatic status of the patient showed comparable sensitivity of PET/CT and MRI with slightly higher accuracy of PET/CT. Patient-based analysis of metastatic organ involvement revealed significantly higher accuracy of PET/CT for bone and lymph node metastases (100% vs 88%; P = 0.0412 and 98% vs 78%; P = 0.0044) and for the overall comparison (99% vs 89%; P < 0.0001). The imaging results influenced the treatment decision in 30 patients (59%) with comparable information from PET/CT and wbMRI in 30 patients, additional relevant information from PET/CT in 16 patients and from wbMRI in 7 patients. Conclusion: PET/CT and wbMRI showed comparable overall lesion-based detection rates for metastatic involvement in NET but significantly differed in organ-based detection rates with superiority of PET/CT for lymph node and pulmonary lesions and of wbMRI for liver and bone metastases. Patient-based analysis revealed superiority of PET/CT for NET staging. Individual treatment strategies benefit from complementary information from PET/CT and MRI.

Comparison of 68Ga-DOTANOC and 68Ga-DOTATATE PET/CT within patients with gastroenteropancreatic neuroendocrine tumors

Somatostatin receptor PET tracers such as [(68)Ga-DOTA,1-Nal(3)]-octreotide ((68)Ga-DOTANOC) and [(68)Ga-DOTA,Tyr(3)]-octreotate ((68)Ga-DOTATATE) have shown promising results in patients with neuroendocrine tumors, with a higher lesion detection rate than is achieved with (18)F-fluorodihydroxyphenyl-l-alanine PET, somatostatin receptor SPECT, CT, or MR imaging. (68)Ga-DOTANOC has high affinity for somatostatin receptor subtypes 2, 3, and 5 (sst2,3,5). It has a wider receptor binding profile than (68)Ga-DOTATATE, which is sst2-selective. The wider receptor binding profile might be advantageous for imaging because neuroendocrine tumors express different subtypes of somatostatin receptors. The goal of this study was to prospectively compare (68)Ga-DOTANOC and (68)Ga-DOTATATE PET/CT in the same patients with gastroenteropancreatic neuroendocrine tumors (GEP-NETs) and to evaluate the clinical impact of (68)Ga-DOTANOC PET/CT.

METHODS

Eighteen patients with biopsy-proven GEP-NETs were evaluated with (68)Ga-DOTANOC and (68)Ga-DOTATATE using a randomized crossover design. Labeling of DOTANOC and DOTATATE with (68)Ga was standardized using a fully automated synthesis device. PET/CT findings were compared with 3-phase CT scans and in some patients with MR imaging, (18)F-FDG PET/CT, and histology. Uptake in organs and tumor lesions was quantified and compared by calculation of maximum standardized uptake values (SUVmax) using volume computer-assisted reading.

RESULTS

Histology revealed low-grade GEP-NETs (G1) in 4 patients, intermediate grade (G2) in 7, and high grade (G3) in 7. (68)Ga-DOTANOC and (68)Ga-DOTATATE were false-negative in only 1 of 18 patients. In total, 248 lesions were confirmed by cross-sectional and PET imaging. The lesion-based sensitivity of (68)Ga-DOTANOC PET was 93.5%, compared with 85.5% for (68)Ga-DOTATATE PET (P = 0.005). The better performance of (68)Ga-DOTANOC PET is attributed mainly to the significantly higher detection rate of liver metastases rather than tumor differentiation grade. Multivariate analysis revealed significantly higher SUVmax in G1 tumors than in G3 tumors (P = 0.009). This finding was less pronounced with (68)Ga-DOTANOC (P > 0.001). Altogether, (68)Ga-DOTANOC changed treatment in 3 of 18 patients (17%).

CONCLUSION

The sst2,3,5-specific radiotracer (68)Ga-DOTANOC detected significantly more lesions than the sst2-specific radiotracer (68)Ga-DOTATATE in our patients with GEP-NETs. The clinical relevance of this finding has to be proven in larger studies.

Clinical applications of Gallium-68

Gallium-68 is a positron-emitting radioisotope that is produced from a (68)Ge/(68)Ga generator. As such it is conveniently used, decoupling radiopharmacies from the need for a cyclotron on site. Gallium-68-labeled peptides have been recognized as a new class of radiopharmaceuticals showing fast target localization and blood clearance. (68)Ga-DOTATOC, (8)Ga-DOTATATE, (68)Ga-DOTANOC, are the most prominent radiopharmaceuticals currently in use for imaging and differentiating lesions of various somatostatin receptor subtypes, overexpressed in many neuroendocrine tumors. There has been a tremendous increase in the number of clinical studies with (68)Ga over the past few years around the world, including within the United States. An estimated ∼10,000 scans are being performed yearly in Europe at about 100 centers utilizing (68)Ga-labeled somatostatin analogs within clinical trials. Two academic sites within the US have also begun to undertake human studies. This review will focus on the clinical experience of selected, well-established and recently applied (68)Ga-labeled imaging agents used in nuclear medicine.

Hepatocellular carcinoma and gastroenteropancreatic neuroendocrine tumors: potential role of other positron emission tomography radiotracers

18F-Fluorodeoxyglucose avidity for gastroenteropancreatic neuroendocrine tumors and hepatocellular carcinoma is variable, depending on the underlying tumor biology. Experience with non-fluorodeoxyglucose (FDG) tracers (eg, 18F-labeled amine precursors l-dihydroxyphenylalanine and 68Ga-DOTA-peptides for gastroenteropancreatic neuroendocrine tumors and radiolabeled acetate or choline for hepatocellular carcinoma) is evolving and expanding rapidly. This article reviews the role of FDG and non-FDG radiotracers in the imaging evaluation of patients with gastroenteropancreatic neuroendocrine tumors or hepatocellular carcinoma.

Differential uptake of (68)Ga-DOTATOC and (68)Ga-DOTATATE in PET/CT of gastroenteropancreatic neuroendocrine tumors

PURPOSE

Abundant expression of somatostatin receptors (sst) is a characteristic of neuroendocrine tumors (NET). Thus, radiolabeled somatostatin analogs have emerged as important tools for both in vivo diagnosis and therapy of NET. The two compounds most often used in functional imaging with positron emission tomography (PET) are (68)Ga-DOTATATE and (68)Ga-DOTATOC. Both analogs share a quite similar sst binding profile. However, the in vitro affinity of (68)Ga-DOTATATE in binding the sst subtype 2 (sst2) is approximately tenfold higher than that of (68)Ga-DOTATOC. This difference may affect their efficiency in detection of NET lesions, as sst2 is the predominant receptor subtype on gastroenteropancreatic NET. We thus compared the diagnostic value of PET/CT with both radiolabeled somatostatin analogs ((68)Ga-DOTATATE and (68)Ga-DOTATOC) in the same patients with gastroenteropancreatic NET.

PATIENTS AND METHODS

Twenty-seven patients with metastatic gastroenteropancreatic NET underwent (68)Ga-DOTATOC and (68)Ga-DOTATATE PET/CT as part of the workup before prospective peptide receptor radionuclide therapy (PRRT). The performance of both imaging methods was analyzed and compared for detection of individual lesions per patient and for eight defined body regions. A region was regarded as positive if at least one lesion was detected in that region. In addition, radiopeptide uptake in terms of the maximal standardized uptake value (SUV(max)) was compared for concordant lesions and renal parenchyma.

RESULTS

Fifty-one regions were found positive with both (68)Ga-DOTATATE and (68)Ga-DOTATOC. Overall, however, significantly fewer lesions were detected with (68)Ga-DOTATATE in comparison with (68)Ga-DOTATOC (174 versus 179, p < 0.05). Mean (68)Ga-DOTATATE SUV(max) across all lesions was significantly lower compared with (68)Ga-DOTATOC (16.9 ± 6.8 versus 22.1 ± 12.0, p < 0.01). Mean SUV(max) for renal parenchyma was not significantly different between (68)Ga-DOTATATE and (68)Ga-DOTATOC (12.6 ± 2.6 versus 12.6 ± 2.7).

CONCLUSIONS

(68)Ga-DOTATOC and (68)Ga-DOTATATE possess similar diagnostic accuracy for detection of gastroenteropancreatic NET lesions (with a potential advantage of (68)Ga-DOTATOC) despite their evident difference in affinity for sst2. Quite unexpectedly, maximal uptake of (68)Ga-DOTATOC tended to be higher than its (68)Ga-DOTATATE counterpart. However, tumor uptake shows high inter- and intraindividual variance with unpredictable preference of one radiopeptide. Thus, our data encourage the application of different sst ligands to enable personalized imaging and therapy of gastroenteropancreatic NET with optimal targeting of tumor receptors.

Radiological and nuclear medicine imaging of gastroenteropancreatic neuroendocrine tumours

Neuroendocrine tumours (NETs) comprise a heterogeneous group of neoplasms with very varying clinical expression. A functioning NET, for instance in the pancreas, may be very small and yet give rise to severe endocrine symptoms whereas a patient with a small bowel tumour may present with diffuse symptoms and disseminated disease with a palpable bulky liver. Imaging of NETs is therefore challenging and the imaging needs in the various patients are diverse. The basic modalities for NET imaging are computed tomography (CT) or magnetic resonance imaging (MRI) in combination with somatostatin receptor imaging (SMI) by scintigraphy with 111In-labelled octreotide (OctreoScan) or more recently by positron emission tomography (PET) with 68Ga-labelled somatostatin analogues. In this review these various morphological and functional imaging modalities and important methodological aspects are described. Imaging requirements for the various types of NETs are discussed and typical image findings are illustrated.

Diagnostic performance of Gallium-68 somatostatin receptor PET and PET/CT in patients with thoracic and gastroenteropancreatic neuroendocrine tumours: a meta-analysis

Gallium-68 somatostatin receptor (SMSR) positron emission tomography (PET) and positron emission tomography/computed tomography (PET/CT) are valuable diagnostic tools for patients with neuroendocrine tumours (NETs). To date, a meta-analysis about the diagnostic accuracy of these imaging methods is lacking. Aim of our study is to meta-analyse published data about the diagnostic performance of SMSR PET or PET/CT in patients with thoracic and/or gastroenteropancreatic (GEP) NETs. A comprehensive computer literature search of studies published in PubMed/MEDLINE, Scopus and Embase databases through October 2011 and regarding SMSR PET or PET/CT in patients with NETs was carried out. Only studies in which SMSR PET or PET/CT were performed in patients with thoracic and/or GEP NETs were selected (medullary thyroid tumours and neural crest derived tumours were excluded from the analysis). Pooled sensitivity, pooled specificity and area under the ROC curve were calculated to measure the diagnostic accuracy of SMSR PET and PET/CT in NETs.

RESULTS

Sixteen studies comprising 567 patients were included in this meta-analysis. The pooled sensitivity and specificity of SMSR PET or PET/CT in detecting NETs were 93% (95% confidence interval [95% CI]: 91-95%) and 91% (95% CI: 82-97%), respectively, on a per patient-based analysis. The area under the ROC curve was 0.96. In patients with suspicious thoracic and/or GEP NETs, SMSR PET and PET/CT demonstrated high sensitivity and specificity. These accurate techniques should be considered as first-line diagnostic imaging methods in patients with suspicious thoracic and/or GEP NETs.

Clinical PET of neuroendocrine tumors using 64Cu-DOTATATE: first-in-humans study

The use of positron emitter-labeled compounds for somatostatin receptor imaging (SRI) has become attractive because of the prospect of improved spatial resolution, accelerated imaging procedures, and the ability to quantify tissue radioactivity concentrations. This paper provides results from first-in-humans use of (64)Cu-DOTATATE, an avidly binding somatostatin receptor ligand linked to a radioisotope with intermediate half-life and favorable positron energy (half-life, 12.7 h; maximum positron energy, 0.653 MeV).

METHODS

In a prospective setup, 14 patients with a history of neuroendocrine tumors underwent both PET/CT with (64)Cu-DOTATATE and SPECT/CT with our current routine imaging agent (111)In-diethylenetriaminepentaacetic acid-octreotide. After intravenous injection of 193-232 MBq of (64)Cu-DOTATATE, whole-body PET scans were acquired at 1 h (n = 14), 3 h (n = 12), and 24 h (n = 5) after administration. Tissue radioactivity concentrations for normal organs and lesions were quantified, and standardized uptake values were calculated for the early (1 h) and delayed (3 h) scans. Using the data for 5 patients, we assessed the radiation dose with OLINDA/EXM software. Furthermore, the clinical performance of (64)Cu-DOTATATE with respect to lesion detection was compared with conventional SRI.

RESULTS

SRI with (64)Cu-DOTATATE produced images of excellent quality and high spatial resolution. Images were characterized by high and stable tumor-to-background ratios over an imaging time window of at least 3 h. Compared with conventional scintigraphy, (64)Cu-DOTATATE PET identified additional lesions in 6 of 14 patients (43%). In 5 patients, lesions were localized in organs and organ systems not previously known as metastatic sites, including the early-stage detection of a secondary neuroendocrine tumor in a patient with a known mutation in the multiple endocrine neoplasia type I gene. All major additional findings seen only on PET could be confirmed on the basis of a clinical follow-up interval of 18 mo. Calculated radiation dose estimates yielded an effective dose of 6.3 mSv for an injected activity of 200 MBq of (64)Cu-DOTATATE, with the liver being the organ with the highest absorbed radiation dose (0.16 mGy/MBq).

CONCLUSION

This first-in-humans study supports the clinical use of (64)Cu-DOTATATE for SRI with excellent imaging quality, reduced radiation burden, and increased lesion detection rate when compared with (111)In-diethylenetriaminepentaacetic acid-octreotide.

PET SUV correlates with radionuclide uptake in peptide receptor therapy in meningioma

PURPOSE

To investigate whether the tumour uptake of radionuclide in peptide receptor radionuclide therapy (PRRT) of meningioma can be predicted by a PET scan with (68)Ga-labelled somatostatin analogue.

METHODS

In this pilot trial, 11 meningioma patients with a PET scan indicating somatostatin receptor expression received PRRT with 7.4 GBq (177)Lu-DOTATOC or (177)Lu-DOTATATE, followed by external beam radiotherapy. A second PET scan was scheduled for 3 months after therapy. During PRRT, multiple whole-body scans and a SPECT/CT scan of the head and neck region were acquired and used to determine the kinetics and dose in the voxel with the highest radionuclide uptake within the tumour. Maximum voxel dose and retention of activity 1 h after administration in PRRT were compared to the maximum standardized uptake values (SUV(max)) in the meningiomas from the PET scans before and after therapy.

RESULTS

The median SUV(max) in the meningiomas was 13.7 (range 4.3 to 68.7), and the maximum fractional radionuclide uptake in voxels of size 0.11 cm³ was a median of 23.4 × 10(-6) (range 0.4 × 10(-6) to 68.3 × 10(-6)). A strong correlation was observed between SUV(max) and the PRRT radionuclide tumour retention in the voxels with the highest uptake (Spearman's rank test, P < 0.01). Excluding one patient who showed large differences in biokinetics between PET and PRRT and another patient with incomplete data, linear regression analysis indicated significant correlations between SUV(max) and the therapeutic uptake (r = 0.95) and between SUV(max) and the maximum voxel dose from PRRT (r = 0.76). Observed absolute deviations from the values expected from regression were a median of 5.6 × 10(-6) (maximum 9.3 × 10(-6)) for the voxel fractional radionuclide uptake and 0.40 Gy per GBq (maximum 0.85 Gy per GBq) (177)Lu for the voxel dose from PRRT.

CONCLUSION

PET with (68)Ga-labelled somatostatin analogues allows the pretherapeutic assessment of tumour radionuclide uptake in PRRT of meningioma and an estimate of the achievable dose.