111In-pentetreotide scintigraphy: procedure guidelines for tumour imaging

Quantitative analysis of phantom studies of 111In and 68Ga imaging of neuroendocrine tumours

Background

Nuclear medicine imaging of neuroendocrine tumours is performed either by SPECT/CT imaging, using ¹¹¹In-octreotide or by PET/CT imaging using ⁶⁸Ga-radiolabelled somatostatin analogs. These imaging techniques will give different image quality and different detection thresholds for tumours, depending on size and activity uptake. The aim was to evaluate the image quality for ¹¹¹In-SPECT and ⁶⁸Ga-PET imaging, i.e. the smallest volume possible to visualize for different source-to-background activity ratios. The accuracy of quantification of lesion volume and activity was also investigated to develop an objective evaluation for radionuclide therapy eligibility.

The phantom study was performed using the NEMA IEC Body Phantom with six hot spheres having inner diameters of 10, 13, 17, 22, 28, and 37 mm, filled with either ⁶⁸Ga or ¹¹¹In with sphere-to-background ratios (SBRs) of no background activity, 5:1, 2.5:1, and 1.25:1. Activity ratios of 1.25:1 and 2.5:1 are clinically found for lesions close to the liver and spleen. Clinical acquisition and reconstruction protocols were applied. Line profiles were drawn to evaluate the smallest detectable volume within a given SBR. Recovery curves based on threshold-based VOIs, threshold-based VOIs adapted to the background and CT-based ROIs were obtained for all SBRs and sphere diameters, allowing for quantification.

Results

The 10-mm sphere was not possible to detect in SPECT images. It was detectable in PET images for SBRs of 2.5:1 and higher. In a background corresponding to the activity uptake in the liver, spheres larger than 22–37 mm were detectable in the ¹¹¹In-SPECT images and spheres larger than 13–22 mm were detectable in the ⁶⁸Ga-PET images. The maximum activity concentration was accurately quantified for spheres larger than 22 mm in the PET images; however, the quantification was impaired by sphere size and background activity.

Conclusions

It was not possible to detect the 10-mm sphere in any of the SPECT images. In a background corresponding to the activity uptake in the liver, spheres larger than approximately 30 mm were visible in the ¹¹¹In-SPECT images and spheres larger than approximately 17 mm were visible in the ⁶⁸Ga-PET images. Sphere diameter and background activity strongly affect the possibility of a correct quantification.

EANM 2012 guidelines for radionuclide imaging of phaeochromocytoma and paraganglioma

PURPOSE

Radionuclide imaging of phaeochromocytomas (PCCs) and paragangliomas (PGLs) involves various functional imaging techniques and approaches for accurate diagnosis, staging and tumour characterization. The purpose of the present guidelines is to assist nuclear medicine practitioners in performing, interpreting and reporting the results of the currently available SPECT and PET imaging approaches. These guidelines are intended to present information specifically adapted to European practice.

METHODS

Guidelines from related fields, issued by the European Association of Nuclear Medicine and the Society of Nuclear Medicine, were taken into consideration and are partially integrated within this text. The same was applied to the relevant literature, and the final result was discussed with leading experts involved in the management of patients with PCC/PGL. The information provided should be viewed in the context of local conditions, laws and regulations.

CONCLUSION

Although several radionuclide imaging modalities are considered herein, considerable focus is given to PET imaging which offers high sensitivity targeted molecular imaging approaches.

Review of functional/anatomical imaging in oncology

Patient management in oncology increasingly relies on imaging for diagnosis, response assessment, and follow-up. The clinical availability of combined functional/anatomical imaging modalities, which integrate the benefits of visualizing tumor biology with those of high-resolution structural imaging, revolutionized clinical management of oncologic patients. Conventional high-resolution anatomical imaging modalities such as computed tomography (CT) and MRI excel at providing details on lesion location, size, morphology, and structural changes to adjacent tissues; however, these modalities provide little insight into tumor physiology. With the increasing focus on molecularly targeted therapies, imaging radiolabeled compounds with PET and single-photon emission tomography (SPECT) is often carried out to provide insight into a tumor's biological functions and its surrounding microenvironment. Despite their high sensitivity and specificity, PET and SPECT alone are substantially limited by low spatial resolution and inability to provide anatomical detail. Integrating SPECT or PET with a modality capable of providing these (i.e. CT or MR) maximizes their separate strengths and provides anatomical localization of physiological processes with detailed visualization of a tumor's structure. The availability of multimodality (hybrid) imaging with PET/CT, SPECT/CT, and PET/MR improves our ability to characterize lesions and affect treatment decisions and patient management. We have just begun to exploit the truly synergistic capabilities of multimodality imaging. Continued advances in the development of instrumentation and imaging agents will improve our ability to noninvasively characterize disease processes. This review will discuss the evolution of hybrid imaging technology and provide examples of its current and potential future clinical uses.

[PET-CT for neuroendocrine tumors and nuclear medicine therapy options]

Neuroendocrine tumors (NET) are defined by biochemical characteristics and structures which can be specifically addressed by radioligands for diagnostic imaging as well as radionuclide therapy in nuclear medicine. Somatostatin receptor imaging has been shown to be an important part of the diagnostic process in the management of NET for a long time. In recent years a number of tracers enabling PET-based imaging of somatostatin receptors and amine precursor uptake have been developed. By combining the specific functional information of the PET signal with anatomical information by CT imaging using PET-CT hybrid scanners, primary tumors and metastases can be detected with high resolution and high sensitivity. Compared with conventional indium-111 octreotide scintigraphy PET-CT has a higher resolution and also a lower radiation exposure. In addition, quantification of the tracer uptake allows therapy monitoring. By labelling with therapeutic beta-emitters, such as lutetium-177 or yttrium-90, a systemic internal radiotherapy with somotostatin analogues (peptide radionuclide radiation therapy, PRRT) can be provided as a therapeutic option for patients with unresectable and metastasized neuroendocrine tumors.

Adsorption of metallic radionuclides on plastic phantom walls

Metal radionuclide solutions at neutral pH adhere to plastic containers. Adsorption of radionuclides on the walls of phantoms leads to a nonuniform activity distribution, which could adversely affect imaging studies, as well as phantom-based validations of absorbed dose calculations used in radioimmunotherapy, requiring accurate knowledge of the underlying activity distribution. In the work reported here, the authors determined the degree of metal chelation required to minimize metallic radionuclide oxide formation and adsorption on phantom walls in order to yield more reliable experimental data for validating image-based dosimetry. Using hollow spherical plastic phantoms, the authors evaluated three different radionuclides, I-131, In-111, and Y-90, in solutions containing three different concentrations of the chelator, ethylenediaminetetraacetate (EDTA). Adsorption to plastic walls was determined using microSPECT imaging and/or by counting aliquots of solutions. Reconstructed images and measurements of I-131 activity showed that it was uniformly distributed within all spheres; however, images of In-111 in 0.25-microM EDTA indicated that the activity concentration near the wall was much higher than that in the middle of the sphere. The decrease in activity concentration near the center of the spheres was approximately 47%. Y-90 in 0.25-microM EDTA behaved similarly; the activity concentration of Y-90 decreased by 46%. For an In-111 or Y-90 radioactivity concentration of 0.74 MBq/mL, a 2.5-microM EDTA solution was required to achieve a uniform distribution, suggesting that, under our experimental conditions, approximately 700 EDTA molecules were required for each radiometal atom to prevent precipitation and adsorption on poly(methylmethacrylate). For certain radiometals, e.g., In-111 or Y-90, adequate chelation is essential to achieve uniform activity concentration values and homogeneous distribution within the phantom compartments.

Chronic bronchitis mimicking metastases from thyroid medullary carcinoma demonstrated by indium-111 pentetreotide scintigraphy

We present a case of medullary thyroid carcinoma (MTC) with pulmonary symptoms, elevated calcitonin and CEA levels. Both [¹¹¹In]pentetreotide (Octreoscan) scintigraphy and 2-deoxy-2-[¹⁸F]fluoro-d-glucose positron emission tomography/computed tomography (FDG-PET/CT) scan revealed mild increased uptake of radionuclides in the upper lobe of the right lung compatible with metastases. Histopathological analysis showed it to be chronic bronchitis. The patient was followed without any treatment. Three months later, no pathological uptake on [¹¹¹In]pentetreotide (Octreoscan) was observed. False positive [¹¹¹In]pentetreotide uptake in the lungs was likely related to acute exacervation of the chronic bronchitis.

Indium-111–Pentetreotide Scintigraphy and Somatostatin Receptor Subtype 2 Expression: New Prognostic Factors for Malignant Well-Differentiated Endocrine Tumors

Purpose

Well-differentiated metastatic endocrine carcinomas are difficult to manage because of variable disease outcome. New prognostic factors are required. These tumors overexpress somatostatin receptors (sst), implying the use of somatostatin analogs for tumor localization by somatostatin receptor scintigraphy using indium-111–pentetreotide (111In-pentetreotide) and for medical treatment. The aim of the present study was to evaluate the correlation between 111In-pentetreotide scintigraphy, sst receptor expression, and prognosis.

Patients and Methods

Between 1994 and 2002, 48 consecutive patients with well-differentiated endocrine carcinomas and a negative 111In-pentetreotide scintigraphy were retrospectively paired according to sex, age, and tumor localization with 50 patients with well-differentiated endocrine carcinomas and a positive tracer uptake at 111In-pentetreotide scintigraphy. Overall survival and expression of sst1 to sst5 receptors by immunohistochemistry were assessed.

Results

The lack of tracer uptake at the 111In-pentetreotide scintigraphy seemed to be a poor prognostic factor (P = .007) for overall survival by Kaplan-Meier test and in multivariate analysis; age and absence of clinical secretory syndrome also seemed to be poor prognostic factors. The tracer uptake (positive 111In-pentetreotide scintigraphy) correlated with the tumor expression of somatostatin receptor sst2 (P < .001) but not with that of sst1, sst3, sst4, or sst5. In a bivariate analysis, lack of sst2 expression also significantly correlated with poor prognosis.

Conclusion

We demonstrate the prognostic value of 111In-pentetreotide scintigraphy in well-differentiated malignant endocrine tumors. In these tumors, sst2 somatostatin receptor expression correlates with both tracer uptake and a better prognosis.