The joint IAEA, EANM, and SNMMI practical guidance on peptide receptor radionuclide therapy (PRRNT) in neuroendocrine tumours

MIB-1 Index-Stratified Assessment of Dual-Tracer PET/CT with 68Ga-DOTATATE and 18F-FDG and Multimodality Anatomic Imaging in Metastatic Neuroendocrine Tumors of Unknown Primary in a PRRT Workup Setting

Our aim was to comparatively assess dual-tracer PET/CT (⁶⁸Ga-DOTATATE and ¹⁸F-FDG) and multimodality anatomic imaging in studying metastatic neuroendocrine tumors (NETs) of unknown primary (CUP-NETs) scheduled for peptide receptor radionuclide therapy for divergence of tracer uptake on dual-tracer PET/CT, detection of primary, and overall lesion detection vis-a-vis tumor proliferation index (MIB-1/Ki-67). Methods: Fifty-one patients with CUP-NETs (25 men, 26 women; age, 22-74 y), histopathologically proven and thoroughly investigated with conventional imaging modalities (ultrasonography, CT/contrast-enhanced CT, MRI, and endoscopic ultrasound, wherever applicable), were retrospectively analyzed. Patients were primarily referred for deciding on feasibility of peptide receptor radionuclide therapy (except 2 patients), and all had undergone ⁶⁸Ga-DOTATATE and ¹⁸F-FDG PET/CT as part of pretreatment workup. The sites of metastases included liver, lung/mediastinum, skeleton, abdominal nodes, and other soft-tissue sites. Patients were divided into 5 groups on the basis of MIB-1/Ki-67 index on a 5-point scale: group I (1%-5%) (n = 35), group II (6%-10%) (n = 8), group III (11%-15%) (n = 4), group IV (16%-20%) (n = 2), and group V (>20%) (n = 2). Semiquantitative analysis of tracer uptake was undertaken by SUV_max of metastatic lesions and the primary (when detected). The SUV_max values were studied over increasing MIB-1/Ki-67 index. The detection sensitivity of ⁶⁸Ga-DOTATATE for primary and metastatic lesions was assessed and compared with other imaging modalities including ¹⁸F-FDG PET/CT. Results: Unknown primary was detected on ⁶⁸Ga-DOTATATE in 31 of 51 patients, resulting in sensitivity of 60.78% whereas overall lesion detection sensitivity was 96.87%. The overall lesion detection sensitivities (individual groupwise from group I to group V) were 97.75%, 87.5%, 100%, 100%, and 66.67%, respectively. As MIB-1/Ki-67 index increased, ⁶⁸Ga-DOTATATE uptake decreased in metastatic and primary lesions (mean SUV_max, 43.5 and 22.68 g/dL in group I to 22.54 and 16.83 g/dL in group V, respectively), whereas ¹⁸F-FDG uptake showed a gradual rise (mean SUV_max, 3.66 and 2.86 g/dL in group I to 7.53 and 9.58 g/dL in group V, respectively). There was a corresponding decrease in the ⁶⁸Ga-DOTATATE-to-¹⁸F-FDG uptake ratio with increasing MIB-1/Ki-67 index (from 11.89 in group I to 2.99 in group V). Conclusion: In CUP-NETs, the pattern of uptake on dual-tracer PET (⁶⁸Ga-DOTATATE and ¹⁸F-FDG) correlates well with tumor proliferation index with a few outliers; combined dual-tracer PET/CT with MIB-1/Ki-67 index would aid in better whole-body assessment of tumor biology in CUP-NETs.

Peptide Receptor Radionuclide Therapy Outcomes in a North American Cohort With Metastatic Well-Differentiated Neuroendocrine Tumors

OBJECTIVES

The objective of this study was to describe the outcomes of patients in the University of Iowa Neuroendocrine Tumor (NET) Database treated with peptide receptor radionuclide therapy (PRRT).

METHODS

One hundred thirty-five patients from the University of Iowa NET Database who received PRRT were analyzed, their characteristics were described, and survival was calculated.

RESULTS

The median age at diagnosis was 51 years, and 64% were men. The primary tumor was located in the small bowel (SBNET) in 37.8%, in the pancreas (PNET) in 26.0%, in the lung in 13.3%, in unknown primary in 9.6%, and in other sites in 13.3%. A radiographic response of any magnitude was observed in 65.8%, 11.1% had a mixed response, and 15.4% showed progression. The overall survival (OS) from the first PRRT was 40 months, and the median time to progression was 23.9 months. Higher pretreatment chromogranin A and pancreastatin levels predicted inferior OS.

CONCLUSIONS

Peptide receptor radionuclide therapy resulted in a relatively long OS and time to progression in heavily pretreated North American patients with advanced NETs. Elevated pretreatment chromogranin A and pancreastatin predicted shorter OS after therapy. Peptide receptor radionuclide therapy is a valuable treatment option in patients with advanced NETs, especially SBNETS.

Peptide receptor radionuclide therapy in the management of gastrointestinal neuroendocrine tumors: efficacy profile, safety, and quality of life

Peptide receptor radionuclide therapy (PRRT), developed over the last two decades, is carried out using radiopharmaceuticals such as 90Y-DOTA-Tyr3-octreotide and 177Lu-DOTA-Tyr3-octreotate (177Lu-Dotatate). These radiocompounds are obtained by labeling a synthetic somatostatin analog with a β-emitting radioisotope. The compounds differ from each other in terms of their energetic features (due to the radionuclide) and peptide receptor affinity (due to the analog) but share the common characteristic of binding specific membrane somatostatin receptors that are (generally) overexpressed in neuroendocrine neoplasms (NENs) and their metastases. NENs are tumors arising from diffuse neuroendocrine system cells that are classified according to grading based on Ki67 percentage values (Grades 1 and 2 are classed as neuroendocrine tumors [NETs]) and to the anatomical site of occurrence (in this paper, we only deal with gastroenteropancreatic [GEP]-NETs, which account for 60%–70% of all NENs). They are also characterized by specific symptoms such as diarrhea and flushing (30% of cases). Despite substantial experience gained in the area of PRRT and its demonstrable effects in terms of efficacy, safety, and improvement in quality of life, these compounds are still not registered (registration of 177Lu-Dotatate for the treatment of midgut NETs is expected soon). Thus, PRRT can only be used in experimental protocols. We provide an overview of the work of leading groups with wide-ranging experience and continuity in data publication in the area of GEP-NET PRRT and report our own personal experience of using different dosage schedules based on the presence of kidney and bone marrow risk factors. Our results on the retreatment of patients previously administered 90Y-DOTA-Tyr3-octreotide with a low dosage of 177Lu-Dotatate are also included. A comment on potential future developments of PRRT in GEP-NETs is provided.

Guidelines for the management of neuroendocrine tumours by the Brazilian gastrointestinal tumour group

Neuroendocrine tumours are a heterogeneous group of diseases with a significant variety of diagnostic tests and treatment modalities. Guidelines were developed by North American and European groups to recommend their best management. However, local particularities and relativisms found worldwide led us to create Brazilian guidelines. Our consensus considered the best feasible strategies in an environment involving more limited resources. We believe that our recommendations may be extended to other countries with similar economic standards.

Accuracy and precision assessment for activity quantification in individualized dosimetry of 177Lu-DOTATATE therapy

Background

In order to obtain a reliable ¹⁷⁷Lu-DOTATATE therapy dosimetry, it is crucial to acquire accurate and precise activity measurements with the radionuclide calibrator, the SPECT/CT camera, and the NaI(Tl) well counter. The aim of this study was to determine, in a clinical context, the accuracy and the precision of their activity quantification over a range of activities and time.

Ninety-three ¹⁷⁷Lu sources from the manufacturer were measured in the radionuclide calibrator over 2.5 years to evaluate its calibration accuracy and precision compared to the manufacturer’s value. A NEMA 2012/IEC 2008 phantom was filled with a ¹⁷⁷Lu activity concentration sphere-to-background ratio of five. It was acquired with the SPECT/CT camera to determine the reconstruction parameters offering the best compromise between partial volume effect and signal-to-noise ratio. The calibration factor was computed accordingly. The calibration quality was monitored over 2.5 years with 33 phantom acquisitions with activities ranging from 7040 to 0.6 MBq. Home-made sources were used to calibrate the well counter. Its reliability was evaluated with activities ranging from 150 to 0.2 kBq measured 34 times over 2.5 years.

Results

For the radionuclide calibrator, median [interquartile range] for the error on activity measurement was −0.99 [1.31] %. The optimal SPECT reconstruction parameters were obtained with 16 iterations, 16 subsets and a 12-mm Gaussian post-filter. The calibration factor was 9.87 cps/MBq with an error of −1.05 [2.12] %. The well counter was calibrated with 31.5 cps/kBq, and the error was evaluated to −12.89 [16.55] %.

Conclusions

The accuracy and the precision of activity quantification using dedicated quality control were found to be sufficient for use in dosimetry implemented in clinical routine. The proposed methodology could be implemented in other centres to obtain reproducible ¹⁷⁷Lu-based treatment dosimetry.

188Re(V) Nitrido Radiopharmaceuticals for Radionuclide Therapy

The favorable nuclear properties of rhenium-188 for therapeutic application are described, together with new methods for the preparation of high yield and stable ¹⁸⁸Re radiopharmaceuticals characterized by the presence of the nitride rhenium core in their final chemical structure. ¹⁸⁸Re is readily available from an ¹⁸⁸W/¹⁸⁸Re generator system and a parallelism between the general synthetic procedures applied for the preparation of nitride technetium-99m and rhenium-188 theranostics radiopharmaceuticals is reported. Although some differences between the chemical characteristics of the two metallic nitrido fragments are highlighted, it is apparent that the same general procedures developed for the labelling of biologically active molecules with technetium-99m can be applied to rhenium-188 with minor modification. The availability of these chemical strategies, that allow the obtainment, in very high yield and in physiological condition, of ¹⁸⁸Re radiopharmaceuticals, gives a new attractive prospective to employ this radionuclide for therapeutic applications.

ENETS Consensus Guidelines for the Standards of Care in Neuroendocrine Neoplasia: Peptide Receptor Radionuclide Therapy with Radiolabeled Somatostatin Analogues

The purpose of these guidelines is to assist physicians caring for patients with neuroendocrine neoplasia in considering eligibility criteria for peptide receptor radionuclide therapy (PRRT) and in defining the minimum requirements for PRRT. It is not these guidelines' aim to give recommendations on the use of specific radiolabelled somatostatin analogues for PRRT as different analogues are being used, and their availability is governed by varying international regulations. However, a recent randomized controlled trial, NETTER-1, has provided evidence that may establish ¹⁷⁷Lu-DOTA-octreotate (LutaThera®) as the first widely approved agent. It also makes recommendations on what minimal patient, tumour, and treatment outcome characteristics should be reported for PRRT to facilitate robust comparisons between studies.

Metabolic Bone Disease in the Context of Metastatic Neuroendocrine Tumor: Differentiation from Skeletal Metastasis, the Molecular PET-CT Imaging Features, and Exploring the Possible Etiopathologies Including Parathyroid Adenoma (MEN1) and Paraneoplastic Humoral Hypercalcemia of Malignancy Due to PTHrP Hypersecretion

Three cases of metabolic bone disease in the setting of metastatic neuroendocrine tumor (NET) are illustrated with associated etiopathologies.  One of these cases harbored mixed lesions in the form of vertebral metastasis (biopsy proven) while the other skeletal lesions were caused due to metabolic bone disease related to multiple parathyroid adenomas. While the metastatic lesion was positive on 68Ga-DOTATATE positron emission tomography-computed tomography (PET-CT), the lesions of metabolic bone disease were negative and the 18F-fluoride PET-CT demonstrated the features of metabolic bone scan. Similar picture of metabolic bone disease [18-sodium fluoride (18NaF)/68Ga-DOTATATE mismatch] was documented in the other two patients, while fluorodeoxyglucose (FDG)-PET-CT was variably positive, primarily showing tracer uptake in the metabolic skeletal lesions of the patient with hypersecretion of parathyroid hormone-related protein (PTHrP) by the underlying tumor. Discordance between 18NaF PET-CT and 68Ga-DOTATATE PET-CT serves as a good marker for identification of metabolic bone disease and diagnosing such a clinical entity. In a patient of NET with metabolic bone disease and hypercalcemia, thus, two causes need to be considered: (i) Coexisting parathyroid adenoma in multiple endocrine neoplasia type I (MEN-I) syndrome and (ii) humoral hypercalcemia of malignancy (HHM) related to hypersecretion of PTHrP by the tumor. The correct diagnosis of metabolic bone disease in metastatic NET can alter the management substantially. Interestingly, peptide receptor radionuclide therapy (PRRT) can emerge as a very promising treatment modality in patients of metabolic bone disease caused by HHM in the setting of NET.

Effectiveness of radiolabelled somatostatin analogues (90Y-DOTATOC and 177Lu-DOTATATE) in patients with metastatic neuroendocrine tumours: a single centre experience in Mexico

OBJECTIVE

To determine the effectiveness of therapy with the radiolabelled somatostatin analogues, ⁹⁰Y-DOTATOC and ¹⁷⁷Lu-DOTATATE, in the treatment of metastatic neuroendocrine tumours with progression to first-line treatment.

MATERIAL AND METHODS

A study was conducted on 30 patients diagnosed with neuroendocrine tumours (gastroenteropancreatic, bronchopulmonary, MEN2A, MEN2B, phaeochromocytoma, and paraganglioma) with metastatic disease diagnosed by the pathology department, with progression to first-line treatment, and recruited from December 2014 to February 2016. Efficacy was analysed using computed tomography (CT) according RECIST 1.1 criteria, and the molecular changes using the SUVmax of PET/CT with ⁶⁸Ga-DOTATOC. Safety was carried out with a renal scan with ^99mTc-MAG3.

RESULTS

The 30 patients received a total of 49 cycles ⁹⁰Y-DOTATOC (21 doses) and ¹⁷⁷ Lu-DOTATATE (28 doses), with a mean of 1.5 cycles per patient. Of these, 17 (56.7%) showed a partial morphological response, 22 (73.3%) molecular and biochemical response, and 23 (76.6%) clinical response. One patient died during the median follow-up of 13 months. The median overall survival from diagnosis was 54 months (95% CI; 31.18-76.81), and median progression-free survival was 32 months (95% CI; 15.00-48.99).

CONCLUSION

Therapy with ⁹⁰Y-DOTATOC and ¹⁷⁷Lu-DOTATATE is a promising therapy for patients with well and moderately differentiated neuroendocrine tumours. The efficacy is better the larger the number of cycles administered, inversely proportional to the number of metastases (<10), and is associated with the level of uptake according to the SUVmax by the metastases, regardless of metabolically active tumour volume.

Molecular Imaging of Gastroenteropancreatic Neuroendocrine Tumors: Current Status and Future Directions

Through diagnostic imaging and peptide receptor radionuclide therapy, nuclear medicine has earned a major role in gastroenteropancreatic neuroendocrine tumors (GEP NETs). GEP NETs are diagnosed fortuitously or on the basis of symptoms or hormonal syndrome. The functional tumor characteristics shown by radionuclide imaging allow for more accurate staging and treatment selection. Tumor grade helps determine which tracer should be selected. In the past, ¹¹¹In-pentetreotide has been successful in well-differentiated (G1 and G2) tumors. However, PET/CT imaging with novel somatostatin analogs (e.g., ⁶⁸Ga-DOTATOC, ⁶⁸Ga-DOTATATE, ⁶⁸Ga-DOTANOC, and ⁶⁴Cu-DOTATATE) now offers improved sensitivity. ¹⁸F-fluorodihydroxyphenylalanine (¹⁸F-FDOPA) is another interesting radiopharmaceutical. ¹⁸F-FDOPA sensitivity is influenced by a tumor's capacity to take up, decarboxylate, and store amine precursors. ¹⁸F-FDOPA sensitivities are highest in ileal NETs and may also be helpful in insulinomas. A high uptake of ¹⁸F-FDG with a low uptake of somatostatin analog usually indicates poorly differentiated tumors (G3). Starting from these principles, this article discusses theranostic approaches to GEP NETs, taking into account both primary and metastatic lesions.

Parametric Net Influx Rate Images of 68Ga-DOTATOC and 68Ga-DOTATATE: Quantitative Accuracy and Improved Image Contrast

⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE are radiolabeled somatostatin analogs used for the diagnosis of somatostatin receptor-expressing neuroendocrine tumors (NETs), and SUV measurements are suggested for treatment monitoring. However, changes in net influx rate (K_i) may better reflect treatment effects than those of the SUV, and accordingly there is a need to compute parametric images showing K_i at the voxel level. The aim of this study was to evaluate parametric methods for computation of parametric K_i images by comparison to volume of interest (VOI)-based methods and to assess image contrast in terms of tumor-to-liver ratio. Methods: Ten patients with metastatic NETs underwent a 45-min dynamic PET examination followed by whole-body PET/CT at 1 h after injection of ⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE on consecutive days. Parametric K_i images were computed using a basis function method (BFM) implementation of the 2-tissue-irreversible-compartment model and the Patlak method using a descending aorta image-derived input function, and mean tumor K_i values were determined for 50% isocontour VOIs and compared with K_i values based on nonlinear regression (NLR) of the whole-VOI time-activity curve. A subsample of healthy liver was delineated in the whole-body and K_i images, and tumor-to-liver ratios were calculated to evaluate image contrast. Correlation (R²) and agreement between VOI-based and parametric K_i values were assessed using regression and Bland-Altman analysis. Results: The R² between NLR-based and parametric image-based (BFM) tumor K_i values was 0.98 (slope, 0.81) and 0.97 (slope, 0.88) for ⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE, respectively. For Patlak analysis, the R² between NLR-based and parametric-based (Patlak) tumor K_i was 0.95 (slope, 0.71) and 0.92 (slope, 0.74) for ⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE, respectively. There was no bias between NLR and parametric-based K_i values. Tumor-to-liver contrast was 1.6 and 2.0 times higher in the parametric BFM K_i images and 2.3 and 3.0 times in the Patlak images than in the whole-body images for ⁶⁸Ga-DOTATOC and ⁶⁸Ga-DOTATATE, respectively. Conclusion: A high R² and agreement between NLR- and parametric-based K_i values was found, showing that K_i images are quantitatively accurate. In addition, tumor-to-liver contrast was superior in the parametric K_i images compared with whole-body images for both ⁶⁸Ga-DOTATOC and ⁶⁸Ga DOTATATE.

Use of 177Lu-dotatate in the treatment of iodine refractory thyroid carcinomas

In a patient with a differentiated thyroid cancer the standard treatment protocol to be followed is surgery, ablation of thyroid remnants with ¹³¹Iodine (¹³¹I), and TSH suppression. However, the treatment with ¹³¹I is not effective in some cases, and it no longer becomes a therapeutic option due to cell de-differentiation with loss of ¹³¹I uptake. Systemic treatment can be used as other options, although patients are not always responsive; thus, the disease may progress and therapeutic options may run out. Endocrine tumours may express somatostatin receptors,and this characteristic has been used, not only for diagnosis, but also for their treatment through somatostatin analogue labelling with radioactive isotopes. This was the case of a patient suffering from iodine-refractory follicular thyroid carcinoma, with somatostatin receptors expression, treated with ¹⁷⁷Lu-DOTATATE, showing an excellent clinical and analytical response.

Long-term follow-up and role of FDG PET in advanced pancreatic neuroendocrine patients treated with 177Lu-D OTATATE

PURPOSE

Lu-DOTATATE (Lu-PRRT) is a valid therapeutic option in differentiated pancreatic neuroendocrine tumors (P-NETs). FDG PET seems to be an important prognostic factor in P-NETs. We evaluated the efficacy of Lu-PRRT and the role of FDG PET in 60 patients with advanced P-NETs.

METHODS

From March 2008 to June 2011, 60 consecutive patients with P-NETs were enrolled in the study. Follow-up lasted until March 2016. Eligible patients were treated with two different total cumulative activities (18.5 or 27.8 GBq in 5 cycles every 6-8 weeks), according to kidney and bone marrow parameters.

RESULTS

Twenty-eight patients received a mean full activity (FA) of 25.9 GBq and 32 a mean reduced activity (RA) of 18.5 GBq. The disease control rate (DCR), defined as the sum of CR+PR+SD was 85.7 % in the FA group and 78.1 % in the RA group. Median progression-free survival (mPFS) was 53.4 months in the FA group and 21.7 months in the RA group (P = 0.353). Median overall survival (mOS) was not reached (nr) in FA patients and was 63.8 months in the RA group (P = 0.007). Fifty-five patients underwent an FDG PET scan before Lu-PRRT, 32 (58 %) showing an increased FDG uptake in tumor sites. mPFS was 21.1 months in FDG PET-positive patients and 68.7 months in the FDG PET-negative group (P < 0.0002), regardless of the total activity administered.

CONCLUSION

Both FA and RA are active in patients undergoing Lu-PRRT. However, an FA of 27.8 GBq of Lu-PRRT prolongs PFS and OS compared to an RA of 18.5 GBq. Our results indicate that FDG PET is an independent prognostic factor in this patient setting.

Summary of emerging personalized medicine in neuroendocrine tumors: are we on track?

Neuroendocrine tumors (NETs) comprise a heterogeneous group of malignancies, with differences in prognosis and effective therapies. Traditionally, NETs have been characterized by tumor grade, site of primary tumor, functional status, and presence of underlying familial syndrome. However, increased feasibility and utilization of next-generation sequencing and other methodologies have revealed new genomic and epigenetic aberrations. In the last decade, treatment options available for metastatic well-differentiated gastroenteropancreatic (GEP) NETs have expanded, with approval of antiangiogenic and mTOR-directed targeted therapies, and our armamentarium of active therapies is likely to further increase. Cytotoxic therapies also are an important option for pancreatic NETs, and MGMT promoter methylation and protein expression may be an important biomarker for efficacy of alkylating agents. Peptide receptor radioligand therapy is an emerging treatment that uses functional imaging to personalize dosimetry to the tumor and avoid nephrotoxicity. Nevertheless, there is a critical need for further biomarkers, particularly multianalyte biomarkers, to aid in prognostication and predict efficacy of therapies.

Lutetium 177-DOTA-TATE therapy for esthesioneuroblastoma: A case report

Esthesioneuroblastoma (ENB), also known as olfactory neuroblastoma, is a rare malignant tumor that accounts for 3% of all tumors of the nasal cavity. The incidence of ENB is 0.4 cases per million in the general population, and the most common symptoms are nasal obstruction and epistaxis. Previous studies have indicated the presence of somatostatin receptors in this tumor type. Common treatment strategies for ENB include resection and adjuvant radiotherapy and/or chemotherapy (combined treatment); however, the rate of recurrence is high. Treatment of neuroendocrine tumors using radionuclides bound to somatostatin analogues is well established in clinical practice. However, a standard and effective therapeutic approach has not been reported for ENB. The current study described the case of a 74-year-old female with numerous recurrences of ENB following multiple treatments and without possibility of resection. The patient was treated with the radiolabeled-somatostatin analogue, ¹⁷⁷Lutetium-DOTA-octreotate (¹⁷⁷Lu-DOTA-TATE), which successfully controlled the disease. This suggests that ¹⁷⁷Lu-DOTA-TATE is a potential treatment for ENB and may represent an effective alternative and novel therapeutic strategy for this disease.

Radiolabeled enzyme inhibitors and binding agents targeting PSMA: Effective theranostic tools for imaging and therapy of prostate cancer

Because of the broad incidence, morbidity and mortality associated with prostate-derived cancer, the development of more effective new technologies continues to be an important goal for the accurate detection and treatment of localized prostate cancer, lymphatic involvement and metastases. Prostate-specific membrane antigen (PSMA; Glycoprotein II) is expressed in high levels on prostate-derived cells and is an important target for visualization and treatment of prostate cancer. Radiolabeled peptide targeting technologies have rapidly evolved over the last decade and have focused on the successful development of radiolabeled small molecules that act as inhibitors to the binding of the N-acetyl-l-aspartyl-l-glutamate (NAAG) substrate to the PSMA molecule. A number of radiolabeled PSMA inhibitors have been described in the literature and labeled with SPECT, PET and therapeutic radionuclides. Clinical studies with these agents have demonstrated the improved potential of PSMA-targeted PET imaging agents to detect metastatic prostate cancer in comparison with conventional imaging technologies. Although many of these agents have been evaluated in humans, by far the most extensive clinical literature has described use of the ⁶⁸Ga and ¹⁷⁷Lu agents. This review describes the design and development of these agents, with a focus on the broad clinical introduction of PSMA targeting motifs labeled with ⁶⁸Ga for PET-CT imaging and ¹⁷⁷Lu for therapy. In particular, because of availability from the long-lived ⁶⁸Ge (T_1/2=270days)/⁶⁸Ga (T_1/2=68min) generator system and increasing availability of PET-CT, the ⁶⁸Ga-labeled PSMA targeted agent is receiving widespread interest and is one of the fastest growing radiopharmaceuticals for PET-CT imaging.

Growth hormone–secreting macroadenoma of the pituitary gland successfully treated with the radiolabeled somatostatin analog 90Y-DOTATATE: case report

Pituitary tumors causing acromegaly are usually macroadenomas at the time of diagnosis, and they can grow aggressively, infiltrating surrounding tissues. Difficulty in achieving complete tumor removal at surgery can lead toward a strong tendency for recurrence, making it necessary to consider a means of treatment other than those currently used such as somatostatin analogs (SSAs), growth hormone (GH) receptor antagonist, surgical removal, and radiotherapy. The purpose of this paper is to describe a patient diagnosed with an aggressive, giant GH-secreting tumor refractory to medical therapy but ultimately treated with the radiolabeled somatostatin analog 90Y-DOTATATE.

A 26-year-old male with an invasive macroadenoma of the pituitary gland (5.6 × 2.5 × 3.6 cm) and biochemically confirmed acromegaly underwent 2 partial tumor resections: the first used the transsphenoidal approach and the second used the transcranial method. The patient received SSAs pre- and postoperatively. Because of the progression in pituitary tumor size, he underwent classic irradiation of the tumor (50 Gy). One and a half years later, the patient presented with clinically and biochemically active disease, and the tumor size was still 52 mm in diameter (height). Two neurosurgeons disqualified him from further surgical procedures. After confirming the presence of somatostatin receptors in the pituitary tumor by using 68Ga-DOTATATE PET/CT, we treated the patient 4 times with an SSA bound with 90Y-DOTATATE. After this treatment, the patient attained partial biochemical remission and a reduction in the tumor mass for the first time.

Treatment with an SSA bound with 90Y-DOTATATE may be a promising option for some aggressive GH-secreting pituitary adenomas when other methods have failed.

Design and Fabrication of Kidney Phantoms for Internal Radiation Dosimetry Using 3D Printing Technology

Currently, the validation of multimodal quantitative imaging and absorbed dose measurements is impeded by the lack of suitable, commercially available anthropomorphic phantoms of variable sizes and shapes. To demonstrate the potential of 3-dimensional (3D) printing techniques for quantitative SPECT/CT imaging, a set of kidney dosimetry phantoms and their spherical counterparts was designed and manufactured with a fused-deposition-modeling 3D printer. Nuclide-dependent SPECT/CT calibration factors were determined to assess the accuracy of quantitative imaging for internal renal dosimetry.

METHODS

A set of 4 single-compartment kidney phantoms with filling volumes between 8 and 123 mL was designed on the basis of the outer kidney dimensions provided by MIRD pamphlet 19. After the phantoms had been printed, SPECT/CT acquisitions of 3 radionuclides (^99mTc, ¹⁷⁷Lu, and ¹³¹I) were obtained and calibration constants determined for each radionuclide-volume combination. A set of additionally manufactured spheres matching the kidney volumes was also examined to assess the influence of phantom shape and size on the calibration constants.

RESULTS

A set of refillable, waterproof, and chemically stable kidneys and spheres was successfully manufactured. Average calibration factors for ^99mTc, ¹⁷⁷Lu, and ¹³¹I were obtained in a large source measured in air. For the largest phantom (122.9 mL), the volumes of interest had to be enlarged by 1.2 mm for ^99mTc, 2.5 mm for ¹⁷⁷Lu, and 4.9 mm for ¹³¹I in all directions to obtain calibration factors comparable to the reference. Although partial-volume effects were observed for decreasing phantom volumes (percentage difference of up to 9.8% for the smallest volume [8.6 mL]), the difference between corresponding sphere-kidney pairs was small (<1.1% for all volumes).

CONCLUSION

3D printing is a promising prototyping technique for geometry-specific calibration of SPECT/CT systems. Although the underlying radionuclide and the related collimator have a major influence on the calibration, no relevant differences between kidney-shaped and spherically shaped uniform-activity phantoms were observed. With comparably low costs and submillimeter resolution, 3D printing techniques hold the potential for manufacturing individualized anthropomorphic phantoms in many clinical applications in nuclear medicine.

Myelotoxicity of Peptide Receptor Radionuclide Therapy of Neuroendocrine Tumors: A Decade of Experience

AIM

This review of the literature, and the authors' own decade of experience with lutetium-177-octreotate-capecitabine±temozolomide peptide receptor radionuclide therapy (PRRT)-chemotherapy of GEPNETs, analyses the risk of both short- and long-term hematotoxicity.

BACKGROUND

Myelodysplastic syndrome (MDS) and acute leukemia (AL) have been associated with PRRT in heavily pretreated patients with a history of exposure to alkylating agents. Commenced 15 years ago, PRRT is now becoming established as first- and second-line therapy for gastroentero pancreatic neuroendocrine tumors (GEPNETs), and early treatment minimizes myelotoxicity, which is the most significant potential adverse event following PRRT.

RESULTS

Sixteen key articles involving primary research were identified. A total of 2225 patients were treated (2104 treated with PRRT monotherapy and 121 with PRRT combined with chemotherapy). The average age of patients in these studies ranged from 53 to 64 years with median duration of follow-up ranging from 6 to 62 months. Short-term myelotoxicity was observed in 221 patients (10%), occurring in 213 of 2104 patients treated with PRRT monotherapy and 8 of 121 patients treated with PRRT combined with chemotherapy. Acute toxicity manifested as modest self-limited grade 3/4 toxicity (CTCAE or WHO), most often affecting platelets during the first cycle of treatment. Toxicity manifesting early was easily managed with dose modification or therapy cessation and was ameliorated by appropriate patient selection. MDS/AL was a rare stochastic event occurring in 32 (1.4%) patients. Where bone marrow biopsy was performed, cases of MDS displayed cytogenetic abnormalities, consistent with secondary MDS. Factors associated with myelotoxicity included age >70 years, impaired renal function, baseline cytopenias, prior number of therapies, prior chemotherapy (alkylating agents), and prior radiotherapy.

CONCLUSION

Early therapy with PRRT-containing regimens improves outcomes, minimizes myelotoxicity, and renders the risk of MDS and AL negligible.

Calcitonin-secreting pancreatic neuroendocrine tumors: a case report and review of the literature

OBJECTIVE

We report the presentation and novel therapy of a calcitonin-secreting pancreatic neuroendocrine tumor (PNET) and review the literature on this unusual neoplasm.

METHODS

We cite the history of a 38-year-old male who presented with fatigue, weight loss, and diarrhea and was found to have a pancreatic head mass on cross-sectional imaging, as well as liver metastases.

RESULTS

The patient's laboratory evaluation was notable for a >100-fold elevation of the peptide hormone calcitonin in serum. As calcitonin is typically secreted by thyroid C-cells, hypercalcitoninemia is considered a marker for medullary thyroid cancer (MTC) or C-cell hyperplasia, but it may be present in several physiologic or pathologic conditions or may be ectopically secreted in rare PNETs. An octreotide scan confirmed the presence of somatostatin (SST) receptors on the pancreatic mass and liver metastases, leading to the diagnosis of a calcitonin-secreting PNET. We initiated treatment with long-acting SST analogs and peptide receptor radionuclide therapy (90Yttrium-DOTATOC) and achieved disease regression while maintaining a high quality of life.

CONCLUSION

Functional PNETs that secrete calcitonin are exceedingly rare, but they are important to consider in the differential diagnosis of nonthyroid-mediated hypercalcitonemia or pancreatic tumors that present with diarrhea, as the management differs markedly from both MTC and other pancreatic malignancies.

The Influence of Early Measurements Onto the Estimated Kidney Dose in [(177)Lu][DOTA(0),Tyr(3)]Octreotate Peptide Receptor Radiotherapy of Neuroendocrine Tumors

PURPOSE

Multiple measurements have been required to estimate the radiation dose to the kidneys resulting from [(177)Lu]DOTATATE therapy for neuroendocrine tumors. The aim of this study was to investigate the influence of early time-point measurement in the renal dose calculation.

PROCEDURES

Anterior/posterior whole-body planar scintigraphy images were acquired at approx. 1, 24, 48, and 72 h after administration of [(177)Lu]DOTATATE. Furthermore, we acquired planar 1-bed dynamic recordings in 12 frames (5 min each) during the first hour. We assessed kidney exposure with a three-phase model consisting of a linear increase to the maximum within the initial minutes p.i., followed a bi-exponential decline. This three-phase-model served as reference for evaluating accuracy of dose estimates in 105 kidneys calculated by conventional mono-exponential fitting of the final three and four whole-body images.

RESULTS

Mean effective half-life times for the reference model were 25.8 ± 12.0 min and 63.9 ± 17.6 h, predicting a mean renal dose of 5.7 ± 2.1 Gy. The effective half-life time was 46.3 ± 15.4 h for the last four and 63.3 ± 17.0 h for the last three data points. The mean start of the first whole-body measurement was 1.2 ± 0.1 h p.i. The ratio of fast to slow phases was 28.1 ± 23.9% at this time point, which caused a mean absolute percentage dose deviation of 12.4% for four data points, compared to 3.1% for three data points. At a mean time of 2.4 h p.i. (max 5.1 h), the ratio of fast to slow phase declined below 5%.

CONCLUSIONS

Kinetic analysis of renal uptake using dynamic planar scans from the first hour after injection revealed a fast and a slow washout phase. Although the fast phase did not contribute substantially to the estimated renal dose, it could influence planar measurements performed within the first hours. We found that the presence of two clearance phases can hamper accurate dose estimation based on a single-phase model, resulting in approximately 12.4% dose underestimation, thus potentially resulting in overtreatment. In the absence of dynamic initial recordings, the first dosimetry measurements should therefore be obtained later than 3-5 h after [(177)Lu]DOTATATE injection. Omitting the early whole-body image reduced the dose estimation error to 3.1%.

177Lu-OPS201 targeting somatostatin receptors: in vivo biodistribution and dosimetry in a pig model

Background

¹⁷⁷Lu is used in peptide receptor radionuclide therapies for the treatment of neuroendocrine tumors. Based on the recent literature, SST2 antagonists are superior to agonists in tumor uptake. The compound OPS201 is the novel somatostatin antagonist showing the highest SST2 affinity. The aim of this study was to measure the in vivo biodistribution and dosimetry of ¹⁷⁷Lu-OPS201 in five anesthetized Danish Landrace pigs as an appropriate substitute for humans to quantitatively assess the absorbed doses for future clinical applications.

Results

¹⁷⁷Lu-OPS201 was obtained with a specific activity ranging from 10 to 17 MBq/μg. Prior to administration, the radiochemical purity was measured as s > 99.7 % in all cases. After injection, fast clearance of the compound from the blood stream was observed. Less than 5 % of the injected activity was presented in blood 10 min after injection. A series of SPECT/CT and whole-body scans conducted until 10 days after intravenous injection showed uptake mostly in the liver, spine, and kidneys. There was no visible uptake in the spleen. Blood samples were taken to determine the time-activity curve in the blood. Time-activity curves and time-integrated activity coefficients were calculated for the organs showing visible uptake. Based on these data, the absorbed organ dose coefficients for a 70-kg patient were calculated with OLINDA/EXM. For humans after an injection of 5 GBq ¹⁷⁷Lu-OPS201, the highest predicted absorbed doses are obtained for the kidneys (13.7 Gy), the osteogenic cells (3.9 Gy), the urinary bladder wall (1.8 Gy), and the liver (1.0 Gy). No metabolites of ¹⁷⁷Lu-OPS201 were found by radio HPLC analysis. None of the absorbed doses calculated will exceed organ toxicity levels.

Conclusions

The ¹⁷⁷Lu-OPS201 was well tolerated and caused no abnormal physiological or behavioral signs. In vivo distributions and absorbed doses of pigs are comparable to those observed in other publications. According to the biodistribution data in pigs, presented in this work, the expected radiation exposure in humans will be within the acceptable range.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-016-0204-9) contains supplementary material, which is available to authorized users.

Complexation of Bi3+, Ac3+, Y3+, Lu3+, La3+ and Eu3+ with benzo-diaza-crown ether with carboxylic pendant arms

Polyaminopolycarboxylates are attractive ligands for binding cationic radionuclides for synthesis of radiopharmaceuticals with target delivery to tumor cells. Nowadays beta emitting Y−90 and Lu−177 are used as therapeutic agents, while Ac−225 and Bi−213 are considered as perspective for alpha therapy. In the present study new data on complexation of Y3+, Lu3+, Ac3+ and Bi3+ with 2,2’-(15-formyl-2,3,5,6,8,9,11,12-octahydrobenzo [b][1,4,10,7,13]trioxadiazacyclopentadecine-4,10- diyl)diacetic acid are presented. For ligand and complexes characterization potentiometric titration, solvent extraction, chromatography and solubility techniques were applied. The highest values of stability constants within the range of log K = 5.8 – 7.5 were found for Ac3+ and REE. Fast complex formation is established which is beneficial for practical applications in radiopharmaceutical synthesis.

Pitfalls and Limitations of SPECT, PET, and Therapeutic Radiopharmaceuticals

Radiopharmaceuticals are widely accepted to be a very safe class of drugs, with very few adverse reactions and unexpected biodistributions. However, problems can arise because of technical issues in manufacture or reconstitution, patient preparation, or drug administration. This review presents highlights of issues that have arisen in the newer classes of radiopharmaceuticals in the last 20 years and expands the scope of the previous report to include PET and therapeutic radiopharmaceuticals. Variations in the "quality" of the eluate of a (99)Mo/(99m)Tc generator remain a major issue. Several of the newer (99m)Tc tracers require a heating step in preparation that can also lead to unacceptably low radiochemical purity. Radiolytic breakdown can be a problem with all classes of radiopharmaceuticals. Many of the newer radiopharmaceuticals localize by receptor- or transporter-mediated processes and thus can be affected by other drugs, making patient preparation more important than ever. Therapeutic radiopharmaceuticals may require coadministration of radioprotectant regimens, such as the use of lysine-arginine infusions with radiopeptide therapy. Extravasation can have serious consequences with therapeutic radiopharmaceuticals. Adverse reactions to newer radiopharmaceuticals remain rare, though may increase because of coadministration of agents such as contrast media. However, there is known to be underreporting of minor adverse reactions. Knowledge of the pitfalls that can occur with radiopharmaceuticals is important in the interpretation of nuclear medicine images and optimal patient care.

Cerenkov and radioluminescence imaging of brain tumor specimens during neurosurgery

We presented the first example of Cerenkov luminescence imaging (CLI) and radioluminescence imaging (RLI) of human tumor specimens. A patient with a brain meningioma localized in the left parietal region was injected with 166 MBq of 90Y-DOTATOC the day before neurosurgery. The specimens of the tumor removed during surgery were imaged using both CLI and RLI using an optical imager prototype developed in our laboratory. The system is based on a cooled electron multiplied charge coupled device coupled with an f ∕0.95 17-mm C-mount lens. We showed for the first time the possibility of obtaining CLI and RLI images of fresh human brain tumor specimens removed during neurosurgery.

Update on management of midgut neuroendocrine tumors

Midgut neuroendocrine tumors are typically indolent but can be fatal when advanced. They can also cause significant morbidity due to the characteristic carcinoid syndrome. Somatostatin analogs continue to be the mainstay of treatment given their antiproliferative properties, as well as inhibitory effects on hormones that cause carcinoid syndrome. There have been several recent advances in the systemic therapy of these tumors including consolidation of somatostatin analogs as the cornerstone of therapy, completion of pivotal trials with mTOR inhibitors, and the establishment of novel approaches including peptide receptor radionuclide therapy and oral inhibitors of peripheral tryptophan hydroxylase in tumor and symptom control, respectively. In this review article, the recent advances are summarized and an updated approach to management is proposed.

Correlation and discordance of tumour proliferation index and molecular imaging characteristics and their implications for treatment decisions and outcome pertaining to peptide receptor radionuclide therapy in patients with advanced neuroendocrine tumour: developing a personalized model

This communication critically illustrates the molecular imaging features and correlates them with the histopathological characteristics (focussing primarily on Ki-67 or MiB1 index) of neuroendocrine tumours (NETs), their implications for important treatment decision-making, and their response to peptide receptor radionuclide therapy. Such multiparametric analysis of functional imaging (along with conventional size, site-specific and stage-specific morphological assessment and histopathology) is crucial for developing a personalized model for the treatment of advanced and metastatic NET and to fine-tune the multimodal therapies, including the combination regimens. Illustrations with case examples have been made with respect to (a) concordant and (b) discordant tumour proliferation index and functional imaging features, (c) the variable molecular imaging parameters at the intermediate MiB1 indices, including (d) outliers with respect to their MiB1 index, and (e) interlesional heterogeneity between primary and metastatic sites in the same individual as demonstrated by molecular imaging features and its possible implications for therapeutic strategy. In each case, the treatment outcome has been described that would aid in better understanding of the potential usefulness of functional imaging in managing patients with NETs on an individual basis.

Effectiveness and side-effects of peptide receptor radionuclide therapy for neuroendocrine neoplasms in Germany: A multi-institutional registry study with prospective follow-up

BACKGROUND

Monocentric and retrospective studies indicate effectiveness of peptide receptor radionuclide therapy targeting somatostatin receptors of neuroendocrine neoplasms. We assessed overall and progression-free survival and adverse events of peptide receptor radionuclide therapy by a multi-institutional, board certified registry with prospective follow-up in five centres in Germany.

METHODS

A total of 450 patients were included and followed for a mean of 24.4 months. Most patients had progressive low- or intermediate grade neuroendocrine neoplasms and 73% were pretreated with at least one therapy. Primary neuroendocrine neoplasms were mainly derived of pancreas (38%), small bowel (30%), unknown primary (19%) or bronchial system (4%). Patients were treated with Lutetium-177 in 54%, with Yttrium-90 in 17% and with both radionuclides in 29%. Overall and progression-free survival was determined with Kaplan-Meier curves and uni-variate log rank test Cox models.

FINDINGS

Median overall survival of all patients was 59 (95% confidence interval [CI] 49-68.9) months. Overall survival was significantly inferior in the patients treated with Yttrium-90 solely (hazard ratio, 3.22; 95% CI, 1.83-5.64) compared to any peptide receptor radionuclide therapy with Lutetium-177. Grade II (hazard ratio, 2.06; 95% CI, 0.79-5.32) and grade III (hazard ratio, 4.22; 95% CI, 1.41-12.06) neuroendocrine neoplasms had significantly worse overall survival than grade I neuroendocrine neoplasms. Patients with small neuroendocrine neoplasms of small bowel had significantly increased survival (hazard ratio, 0.39; 95% CI, 0.18-0.87) compared to neuroendocrine neoplasms of other locations. Median progression-free survival was 41 (35.9-46.1) months and significantly inferior in patients treated with Yttrium solely (hazard ratio, 2.7; 95% CI, 1.71-4.55). Complete remission was observed in 5.6% of patients, 22.4% had a partial remission, 47.3% were stable and 4% were progressive as best response. Adverse events of bone marrow and kidney function higher than grade III occurred in 0.2-1.5% of patients.

INTERPRETATION

These results indicate that peptide receptor radionuclide therapy is a highly effective therapy for patients with low to intermediate grade neuroendocrine neoplasms with minor adverse events.

New Developments in the Treatment of Neuroendocrine Tumours - RADIANT-4, NETTER-1 and Telotristat Etiprate

Neuroendocrine tumours (NETs) are a heterogeneous group of neoplasms whose incidence has increased significantly in recent years, and whose optimal management remains controversial. We report the latest innovations in their management, in particular the results of three trials concerning the use of the mammalian target of rapamycin (mTOR) inhibitor, everolimus, in non-functional NETs of lung/ gastrointestinal (GI) origin, the first randomised trial of radiolabelled 177Lu-DOTATATE in patients with mid-gut NETs, and the use of the 5-HT synthesis inhibitor, telotristat etiprate, in patients with the carcinoid syndrome.

[(177)Lu-DOTA](0)-D-Phe(1)-Tyr(3)-Octreotide ((177)Lu-DOTATOC) For Peptide Receptor Radiotherapy in Patients with Advanced Neuroendocrine Tumours: A Phase-II Study

PURPOSE

To characterise efficacy and safety of (177)Lu-DOTATOC as agent for peptide receptor radiotherapy (PRRT) of advanced neuroendocrine tumours (NET).

PATIENTS AND METHODS

Fifty-six subjects with metastasized and progressive NET (50% gastroenteral, 26.8% pancreatic, 23.2% other primary sites) treated consecutively with (177)Lu-DOTATOC were analysed retrospectively. Subjects were administered (177)Lu-DOTATOC (mean 2.1 cycles; range 1-4) as 7.0GBq (median) doses at three-monthly intervals. Efficacy was analysed using CT and/or MRI according to RECIST 1.1 criteria and results were stratified for the number of administered cycles and the primary tumour origin.

RESULTS

In the total NET population (A), median progression-free (PFS) and overall survival (OS) were 17.4 and 34.2 months, respectively, assessed in a follow-up time (mean ± SD) of 16.1 ± 12.4 months. In patients receiving more than one cycle, mean follow-up time was 22.4 ± 11.0 months for all NETs (B) and PFS was 32.0 months for all NETs (B), 34.5 months for GEP-NET (C), and 11.9 months for other NETs (D). Objective response rates (Complete/Partial Responses) were 33.9%, 40.6%, 54.2%, and 0% for A, B, C, and D groups, respectively, while disease control rates in the same were 66.1%, 93.8%, 100%, and 75%. Complete responses (16.1%, 18.8% and 25.0% for groups A, B and C) were high, 78% of which were maintained throughout the follow up. There were no serious adverse events. One case of self-limiting grade 3 myelotoxicity was reported. Although 20% of patients had mild renal insufficiency at baseline, there was no evidence of exacerbated or de novo renal toxicity after treatment.

CONCLUSION

(177)Lu-DOTATOC is a novel agent for PRRT with major potential to induce objective tumour responses and sustained disease control in progressive neuroendocrine tumours, even when administered in moderate activities. The observed safety profile suggests a particularly favourable therapeutic index, including in patients with impaired bone marrow or renal function, which reflects a uniquely low uptake of (177)Lu-DOTATOC by normal organs.

Prospective Study of 68Ga-DOTATATE Positron Emission Tomography/Computed Tomography for Detecting Gastro-Entero-Pancreatic Neuroendocrine Tumors and Unknown Primary Sites

PURPOSE

Gastro-entero-pancreatic neuroendocrine tumors (GEPNETs) are increasing in incidence, and accurate staging is important for selecting the appropriate treatment. (68)Ga-DOTATATE imaging is a promising approach for detecting GEPNETs and could help in selecting optimal therapeutic strategies. The aim of this study was to prospectively determine the clinical utility of (68)Ga-DOTATATE positron emission tomography (PET)/computed tomography (CT) in detecting unknown primary and metastatic GEPNETs.

PATIENTS AND METHODS

One hundred thirty-one patients were enrolled in a prospective study of patients undergoing (68)Ga-DOTATATE PET/CT, (111)In-pentetreotide single-photon emission computed tomography (SPECT)/CT and multiphasic CT scan, and/or magnetic resonance imaging in a blinded fashion with comprehensive biochemical testing. The primary outcome measure was the detection of lesions by each imaging study.

RESULTS

(68)Ga-DOTATATE PET/CT imaging detected 95.1% of lesions (95% CI, 92.4% to 96.8%) with an average maximum standardized uptake value of 65.4 ± 47 (range, 6.9 to 244), anatomic imaging detected 45.3% of lesions (95% CI, 37.9% to 52.9%), and (111)In-pentetreotide SPECT/CT detected 30.9% of lesions (95% CI, 25.0% to 37.5%), with a significant difference between imaging modalities (P < .001). In four of 14 patients (28.6%), (68)Ga-DOTATATE PET/CT found a previously unknown primary tumor, and detected primary GEPNET, lymph node, and distant metastases correctly in 72 of 113 lesions (63.7%) when compared with histopathology, with 22.1% and 38.9% detected by using (111)In-pentetreotide SPECT/CT and anatomic imaging, respectively. On the basis of findings with (68)Ga-DOTATATE PET/CT, 43 of 131 patients (32.8%) had a change in management recommendation. In patients with carcinoid symptoms but negative biochemical testing, (68)Ga-DOTATATE PET/CT detected lesions in 65.2% of patients, 40% of which were detected neither by anatomic imaging nor by (111)In-pentetreotide SPECT/CT.

CONCLUSION

(68)Ga-DOTATATE PET/CT imaging provides important information for accurate staging of GEPNETs and selection of appropriate treatment interventions even in the absence of biochemical evidence of disease in symptomatic patients.

Human Anti-Oxidation Protein A1M--A Potential Kidney Protection Agent in Peptide Receptor Radionuclide Therapy

Peptide receptor radionuclide therapy (PRRT) has been in clinical use for 15 years to treat metastatic neuroendocrine tumors. PRRT is limited by reabsorption and retention of the administered radiolabeled somatostatin analogues in the proximal tubule. Consequently, it is essential to develop and employ methods to protect the kidneys during PRRT. Today, infusion of positively charged amino acids is the standard method of kidney protection. Other methods, such as administration of amifostine, are still under evaluation and show promising results. α₁-microglobulin (A1M) is a reductase and radical scavenging protein ubiquitously present in plasma and extravascular tissue. Human A1M has antioxidation properties and has been shown to prevent radiation-induced in vitro cell damage and protect non-irradiated surrounding cells. It has recently been shown in mice that exogenously infused A1M and the somatostatin analogue octreotide are co-localized in proximal tubules of the kidney after intravenous infusion. In this review we describe the current situation of kidney protection during PRRT, discuss the necessity and implications of more precise dosimetry and present A1M as a new, potential candidate for renal protection during PRRT and related targeted radionuclide therapies.

Optimized Peptide Amount and Activity for ⁹⁰Y-Labeled DOTATATE Therapy

In peptide receptor radionuclide therapy with (90)Y-labeled DOTATATE, the kidney absorbed dose limits the maximum amount of total activity that can be safely administered in many patients. A higher tumor-to-kidney absorbed dose ratio might be achieved by optimizing the amount of injected peptide and activity, as recent studies have shown different degrees of receptor saturation for normal tissue and tumor. The aim of this work was to develop and implement a modeling method for treatment planning to determine the optimal combination of peptide amount and pertaining therapeutic activity for each patient.

METHODS

A whole-body physiologically based pharmacokinetic (PBPK) model was developed. General physiologic parameters were taken from the literature. Individual model parameters were fitted to a series (n= 12) of planar γ-camera and serum measurements ((111)In-DOTATATE) of patients with meningioma or neuroendocrine tumors (NETs). Using the PBPK model and the individually estimated parameters, we determined the tumor, liver, spleen, and red marrow biologically effective doses (BEDs) for a maximal kidney BED (20 Gy2.5) for different peptide amounts and activities. The optimal combination of peptide amount and activity for maximal tumor BED, considering the additional constraint of a red marrow BED less than 1 Gy15, was individually quantified.

RESULTS

The PBPK model describes the biokinetic data well considering the criteria of visual inspection, the coefficients of determination, the relative standard errors (<50%), and the correlation of the parameters (<0.8). All fitted parameters were in a physiologically reasonable range but varied considerably between patients, especially tumor perfusion (meningioma, 0.1-1 mL·g(-1)·min(-1), and NETs, 0.02-1 mL·g(-1)·min(-1)) and receptor density (meningioma, 5-34 nmol·L(-1), and NETs, 7-35 nmol·L(-1)). Using the proposed method, we identified the optimal amount and pertaining activity to be 76 ± 46 nmol (118 ± 71 μg) and 4.2 ± 1.8 GBq for meningioma and 87 ± 50 nmol (135 ± 78 μg) and 5.1 ± 2.8 GBq for NET patients.

CONCLUSION

The presented work suggests that to achieve higher efficacy and safety for (90)Y-DOATATE therapy, both the administered amount of peptide and the activity should be optimized in treatment planning using the proposed method. This approach could also be adapted for therapy with other peptides.

First-in-Human Experience of CXCR4-Directed Endoradiotherapy with 177Lu- and 90Y-Labeled Pentixather in Advanced-Stage Multiple Myeloma with Extensive Intra- and Extramedullary Disease

Chemokine receptor 4 (CXCR4) is a key factor for tumor growth and metastasis in several types of human cancer. Based on promising experiences with a radiolabeled CXCR4 ligand ((68)Ga-pentixafor) for diagnostic receptor targeting, (177)Lu- and (90)Y-pentixather were recently developed as endoradiotherapeutic vectors. Here, we summarize the first-in-human experience in 3 heavily pretreated patients with intramedullary and extensive extramedullary manifestations of multiple myeloma undergoing CXCR4-directed endoradiotherapy.

METHODS

CXCR4 target expression was demonstrated by baseline (68)Ga-pentixafor PET. Each treatment was approved by the clinical ethics committee. Pretherapeutic (177)Lu-pentixather dosimetry was performed before (177)Lu-pentixather or (90)Y-pentixather treatment. Subsequently, patients underwent additional chemotherapy and autologous stem cell transplantation for bone marrow rescue.

RESULTS

A remarkable therapeutic effect was visualized in 2 patients, who showed a significant reduction in (18)F-FDG uptake.

CONCLUSION

CXCR4-targeted radiotherapy with pentixather appears to be a promising novel treatment option in combination with cytotoxic chemotherapy and autologous stem cell transplantation, especially for patients with advanced multiple myeloma.

SPECT- and PET-based patient-tailored treatment in neuroendocrine tumors: a comprehensive multidisciplinary team approach

The overexpression of somatostatin receptors on the tumor cell surface of neuroendocrine tumors (NETs) detected by multimodal functional imaging modalities such as SPECT and PET tracers constitutes a therapeutic option using targeting radiolabeled compounds. We will introduce the theranostic concept in general, explain in more detail its development in NETs, and discuss available SPECT and PET tracers regarding their potential for diagnostic imaging, visualization of target expression, and treatment tailoring. Moreover, we will discuss the currently available peptide receptor radionuclide therapy principles and compare them to previously published studies. Finally, we will discuss which new concepts will most likely influence the theranostic treatment approach in NETs in the future.

Therapeutic radionuclides in nuclear medicine: current and future prospects

The potential use of radionuclides in therapy has been recognized for many decades. A number of radionuclides, such as iodine-131 ((131)I), phosphorous-32 ((32)P), strontium-90 ((90)Sr), and yttrium-90 ((90)Y), have been used successfully for the treatment of many benign and malignant disorders. Recently, the rapid growth of this branch of nuclear medicine has been stimulated by the introduction of a number of new radionuclides and radiopharmaceuticals for the treatment of metastatic bone pain and neuroendocrine and other malignant or non-malignant tumours. Today, the field of radionuclide therapy is enjoying an exciting phase and is poised for greater growth and development in the coming years. For example, in Asia, the high prevalence of thyroid and liver diseases has prompted many novel developments and clinical trials using targeted radionuclide therapy. This paper reviews the characteristics and clinical applications of the commonly available therapeutic radionuclides, as well as the problems and issues involved in translating novel radionuclides into clinical therapies.