Additional hepatic 166Ho-radioembolization in patients with neuroendocrine tumours treated with 177Lu-DOTATATE; a single center, interventional, non-randomized, non-comparative, open label, phase II study (HEPAR PLUS trial)

Hepatic Radioembolization: A Multistep Theragnostic Procedure

This article provides a thorough overview of the practice and multistep approach of hepatic radioembolization. The current literature on hepatic radioembolization in primary or metastatic liver tumors as well as future perspectives are discussed.

Dose-effect relationships in neuroendocrine tumour liver metastases treated with [166Ho]-radioembolization

PURPOSE

Aim of this study was to investigate a dose-response relationship, dose-toxicity relationship, progression free survival (PFS) and overall survival (OS) in neuroendocrine tumour liver metastases (NELM) treated with holmium-166-microspheres radioembolization ([166Ho]-radioembolization).

MATERIALS AND METHODS

Single center, retrospective study included patients with NELM that received [166Ho]-radioembolization with post-treatment SPECT/CT and CECT or MRI imaging for 3 months follow-up. Post-treatment SPECT/CT was used to calculate tumour (Dt) and whole liver healthy tissue (Dh) absorbed dose. Clinical and laboratory toxicity was graded by Common Terminology Criteria for Adverse Events (CTCAE), version 5 at baseline and three-months follow-up. Response was determined according to RECIST 1.1. The tumour and healthy doses was correlated to lesion-based objective response and patient-based toxicity. Kaplan Meier analyses were performed for progression free survival (PFS) and overall survival (OS).

RESULTS

Twenty-seven treatments in 25 patients were included, with a total of 114 tumours. Median follow-up was 14 months (3 - 82 months). Mean Dt in non-responders was 68 Gy versus 118 Gy in responders, p = 0.01. ROC analysis determined 86 Gy to have the highest sensitivity and specificity, resp. 83% and 81%. Achieving a Dt of ≥ 120 Gy provided the highest likelihood of response (90%) for obtaining response. Sixteen patients had grade 1-2 clinical toxicity and only one patient grade 3. No clear healthy liver dose-toxicity relationship was found. The median PFS was 15 months (95% CI [10.2;19.8]) and median OS was not reached.

CONCLUSION

This study confirms the safety and efficacy of [166Ho]-radioembolization in NELM in a real-world setting. A clear dose-response relationship was demonstrated and future studies should aim at a Dt of ≥ 120 Gy, being predictive of response. No dose-toxicity relationship could be established.

Management of neuroendocrine tumor liver metastases

BACKGROUND

Neuroendocrine Tumors (NETs) are a group of tumors that arise from neuroendocrine cells, and are increasing in incidence worldwide. These tumors often metastasize to the liver, and management of these neuroendocrine tumor liver metastases (NELMs) requires a multi-disciplinary approach. We aim to provide a comprehensive update for treatment of NELMs.

METHODS

We completed a comprehensive systemic review of papers involving the diagnosis, treatment, and outcomes of NELMs. We identified 1612 records via Scopus database literature search. Two independent authors reviewed these records, with 318 meeting criteria for inclusion in the final systemic review.

RESULTS

Primary tumor resection with resection of liver metastases is the treatment of choice for patients with NELMs. Liver-directed therapies and liver transplantation can be considered for patients with unresectable liver metastases. Systemic medical therapy is used for managing tumor burden and symptoms caused by NELMs.

CONCLUSIONS

Advancement in liver-directed and targeted systemic therapies provide improved options for patients with unresectable tumors. Given the complexity of NELMs, management of NELMs necessitates multidisciplinary teams at comprehensive health centers.

Developments in interventional management of hepatic metastases from neuroendocrine tumours

Neuroendocrine tumours commonly metastasise to the liver, particularly those arising from the intestinal tract and pancreas. Whilst surgery offers the only approach with intent to cure, the vast majority of patients with neuroendocrine liver metastases are ineligible. Liver-directed interventional therapies seek to exploit the patho-anatomy of the blood supply of hepatic metastases to deliver therapy to liver deposits. This may involve percutaneous ablation, bland embolization, or the selective infusion of chemotherapeutics, targeted agents or radiolabelled embolic material. Retrospective case series evidence has characterised objective response rates, disease control rates, and longer-term outcomes associated with each approach. Recent advances in this field include ongoing comparative trials of different techniques, but more importantly, combinations of interventional liver-directed therapies and other systemic therapy in multimodal treatment concepts.

Automatic healthy liver segmentation for holmium-166 radioembolization dosimetry

BACKGROUND

For safe and effective holmium-166 (¹⁶⁶Ho) liver radioembolization, dosimetry is crucial and requires accurate healthy liver definition. The current clinical standard relies on manual segmentation and registration of a separately acquired contrast enhanced CT (CECT), a prone-to-error and time-consuming task. An alternative is offered by simultaneous imaging of ¹⁶⁶Ho and technetium-99m stannous-phytate accumulating in healthy liver cells (¹⁶⁶Ho-^99mTc dual-isotope protocol). This study compares healthy liver segmentation performed with an automatic method using ^99mTc images derived from a ¹⁶⁶Ho-^99mTc dual-isotope acquisition to the manual segmentation, focusing on healthy liver dosimetry and corresponding hepatotoxicity. Data from the prospective HEPAR PLuS study were used. Automatic healthy liver segmentation was obtained by thresholding the ^99mTc image (no registration step required). Manual segmentation was performed on CECT and then manually registered to the SPECT/CT and subsequently to the corresponding ¹⁶⁶Ho SPECT to compute absorbed dose in healthy liver.

RESULTS

Thirty-one patients (66 procedures) were assessed. Manual segmentation and registration took a median of 30 min per patient, while automatic segmentation was instantaneous. Mean ± standard deviation of healthy liver absorbed dose was 18 ± 7 Gy and 20 ± 8 Gy for manual and automatic segmentations, respectively. Mean difference ± coefficient of reproducibility between healthy liver absorbed doses using the automatic versus manual segmentation was 2 ± 6 Gy. No correlation was found between mean absorbed dose in the healthy liver and hepatotoxicity.

CONCLUSIONS

¹⁶⁶Ho-^99mTc dual-isotope protocol can automatically segment the healthy liver without hampering the ¹⁶⁶Ho dosimetry assessment.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT02067988. Registered 20 February 2014. https://clinicaltrials.gov/ct2/show/NCT02067988.

Clinical Results of Transarterial Radioembolization (TARE) with Holmium-166 Microspheres in the Multidisciplinary Oncologic Treatment of Patients with Primary and Secondary Liver Cancer

Holmium-166 microspheres are used for the transarterial radioembolization (TARE) treatment of primary and secondary liver cancers. In this study, its efficacy regarding local tumor control and integration into the oncological treatment sequence of the first 20 patients treated in our institution were examined. A total of twenty-nine ¹⁶⁶Ho-TARE procedures were performed to treat hepatocellular carcinoma (HCC, fourteen patients), metastatic colorectal cancer (mCRC, four patients), intrahepatic cholangiocarcinoma (ICC, one patient), and hemangioendothelioma of the liver (HE, one patient). In eight patients, ¹⁶⁶Ho-TARE was the initial oncologic treatment. In patients with HCC, the median treated-liver progression-free survival (PFS), overall PFS, and overall survival after ¹⁶⁶Ho-TARE were 10.3, 7.3, and 22.1 months; in patients with mCRC, these were 2.6, 2.9, and 20.6 months, respectively. Survival after ¹⁶⁶Ho-TARE in the patients with ICC and HE were 5.2 and 0.8 months, respectively. Two patients with HCC were bridged to liver transplantation, and one patient with mCRC was downstaged to curative surgery. In patients with HCC, a median treatment-free interval of 7.3 months was achieved. In line with previous publications, ¹⁶⁶Ho-TARE was a feasible treatment option in patients with liver tumors, with favorable clinical outcomes in the majority of cases. It was able to achieve treatment-free intervals, served as bridging-to-transplant, and did not prevent subsequent therapies.

Advances in Radionuclides and Radiolabelled Peptides for Cancer Therapeutics

Radiopharmaceutical therapy, which can detect and treat tumours simultaneously, was introduced more than 80 years ago, and it has changed medical strategies with respect to cancer. Many radioactive radionuclides have been developed, and functional, molecularly modified radiolabelled peptides have been used to produce biomolecules and therapeutics that are vastly utilised in the field of radio medicine. Since the 1990s, they have smoothly transitioned into clinical application, and as of today, a wide variety of radiolabelled radionuclide derivatives have been examined and evaluated in various studies. Advanced technologies, such as conjugation of functional peptides or incorporation of radionuclides into chelating ligands, have been developed for advanced radiopharmaceutical cancer therapy. New radiolabelled conjugates for targeted radiotherapy have been designed to deliver radiation directly to cancer cells with improved specificity and minimal damage to the surrounding normal tissue. The development of new theragnostic radionuclides, which can be used for both imaging and therapy purposes, allows for more precise targeting and monitoring of the treatment response. The increased use of peptide receptor radionuclide therapy (PRRT) is also important in the targeting of specific receptors which are overexpressed in cancer cells. In this review, we provide insights into the development of radionuclides and functional radiolabelled peptides, give a brief background, and describe their transition into clinical application.

Peptide Receptor Radionuclide Therapy

The concept of using a targeting molecule labeled with a diagnostic radionuclide for using positron emission tomography or single photon emission computed tomography imaging with the potential to demonstrate that tumoricidal radiation can be delivered to tumoral sites by administration of the same or a similar targeting molecule labeled with a therapeutic radionuclide termed "theranostics." Peptide receptor radionuclide therapy (PRRT) with radiolabeled somatostatin analogs (SSAs) is a well-established second/third-line theranostic treatment for somatostatin receptor-positive well-differentiated (neuro-)endocrine neoplasms (NENs). PRRT with 177Lu-DOTATATE was approved by the regulatory authorities in 2017 and 2018 for selected patients with low-grade well-differentiated gastroenteropancreatic (GEP) NENs. It improves progression-free survival as well as quality of life of GEP NEN patients. Favorable symptomatic and biochemical responses using PRRT with 177Lu-DOTATATE have also been reported in patients with functioning metastatic GEP NENs like metastatic insulinomas, Verner Morrison syndromes (VIPomas), glucagonomas, and gastrinomas and patients with carcinoid syndrome. This therapy might also become a valuable therapeutic option for inoperable low-grade bronchopulmonary NENs, inoperable or progressive pheochromocytomas and paragangliomas, and medullary thyroid carcinomas. First-line PRRT with 177Lu-DOTATATE and combinations of this therapy with cytotoxic drugs are currently under investigation. New radiolabeled somatostatin receptor ligands include SSAs coupled with alpha radiation emitting radionuclides and somatostatin receptor antagonists coupled with radionuclides.

The Evolving Role of Radioembolization in the Treatment of Neuroendocrine Liver Metastases

Simple Summary

This review provides basic insights into radioembolization, also known as selective internal radiation therapy, in patients suffering from neuroendocrine liver metastases. Radioembolization is a treatment that uses radioactive beads that are implanted intra-arterially to locally irradiate liver tumors. The available literature on radioembolization in neuroendocrine liver metastases show promising results in terms of efficacy and toxicity and will be discussed in more detail. However, data in the field of NELM need clarification, and this review also discusses the caveats, challenges and new insights when considering radioembolization in neuroendocrine liver metastases.

Abstract

At diagnosis, 21–50% of neuroendocrine tumors already have distant metastases, of which the liver is most commonly affected. Unfortunately, the presence of neuroendocrine liver metastases (NELM) is the most incriminating factor for survival. At NELM diagnosis, 60–70% of patients suffer from bilobar multifocal disease, making them ineligible for surgical resection. With limited systemic options, a clinical need for liver-directed treatments exists. Trans-arterial (bland) embolization, chemoembolization and radioembolization have been increasingly used in the treatment of NELM. In recent years, radioembolization (also known as selective internal radiation therapy) has gained attention due to promising tumor reductive results, limited toxicities and increasing scientific evidence. This review provides basic insights into radioembolization as a technique, a summary of available literature on radioembolization in NELM, and discusses caveats, challenges and new insights when considering radioembolization in NELM.

166Holmium-99mTechnetium dual-isotope imaging: scatter compensation and automatic healthy-liver segmentation for 166Holmium radioembolization dosimetry

Background

Partition modeling allows personalized activity calculation for holmium-166 (¹⁶⁶Ho) radioembolization. However, it requires the definition of tumor and non-tumorous liver, by segmentation and registration of a separately acquired CT, which is time-consuming and prone to error. A protocol including ¹⁶⁶Ho-scout, for treatment simulation, and technetium-99m (^99mTc) stannous phytate for healthy-liver delineation was proposed. This study assessed the accuracy of automatic healthy-liver segmentation using ^99mTc images derived from a phantom experiment. In addition, together with data from a patient study, the effect of different ^99mTc activities on the ¹⁶⁶Ho-scout images was investigated. To reproduce a typical scout procedure, the liver compartment, including two tumors, of an anthropomorphic phantom was filled with 250 MBq of ¹⁶⁶Ho-chloride, with a tumor to non-tumorous liver activity concentration ratio of 10. Eight SPECT/CT scans were acquired, with varying levels of ^99mTc added to the non-tumorous liver compartment (ranging from 25 to 126 MBq). For comparison, forty-two scans were performed in presence of only ^99mTc from 8 to 240 MBq. ^99mTc image quality was assessed by cold-sphere (tumor) contrast recovery coefficients. Automatic healthy-liver segmentation, obtained by thresholding ^99mTc images, was evaluated by recovered volume and Sørensen–Dice index. The impact of ^99mTc on ¹⁶⁶Ho images and the role of the downscatter correction were evaluated on phantom scans and twenty-six patients’ scans by considering the reconstructed ¹⁶⁶Ho count density in the healthy-liver.

Results

All ^99mTc image reconstructions were found to be independent of the ¹⁶⁶Ho activity present during the acquisition. In addition, cold-sphere contrast recovery coefficients were independent of ^99mTc activity. The segmented healthy-liver volume was recovered fully, independent of ^99mTc activity as well. The reconstructed ¹⁶⁶Ho count density was not influenced by ^99mTc activity, as long as an adequate downscatter correction was applied.

Conclusion

The ^99mTc image reconstructions of the phantom scans all performed equally well for the purpose of automatic healthy-liver segmentation, for activities down to 8 MBq. Furthermore, ^99mTc could be injected up to at least 126 MBq without compromising ¹⁶⁶Ho image quality.

Clinical trials The clinical study mentioned is registered with Clinicaltrials.gov (NCT02067988) on February 20, 2014.

Predictive Factors for Resistant Disease with Medical/Radiologic/Liver-Directed Anti-Tumor Treatments in Patients with Advanced Pancreatic Neuroendocrine Neoplasms: Recent Advances and Controversies

Simple Summary

Tumor resistance, both primary and acquired, is leading to increased complexity in the nonsurgical treatment of patients with advanced panNENs, which would be greatly helped by reliable prognostic/predictive factors. The importance in identifying resistance is being contributed to by the increased array of possible treatments available for treating resistant advanced disease; the variable clinical course as well as response to any given treatment approach of patients within one staging or grading system, the advances in imaging which are providing increasing promising results/parameters that correlate with grading/outcome/resistance, the increased understanding of the molecular pathogenesis providing promising prognostic markers, all of which can contribute to selecting the best treatment to overcome resistance disease. Several factors have been identified that have prognostic/predictive value for identifying development resistant disease and affecting overall survival (OS)/PFS with various nonsurgical treatments of patients with advanced panNENs. Prognostic factors identified for patients with advanced panNENs for both OS/PFSs include various clinically-related factors (clinical, laboratory/biological markers, imaging, treatment-related factors), pathological factors (histological, classification, grading) and molecular factors. Particularly important prognostic factors for the different treatment modalities studies are the recent grading systems. Most prognostic factors for each treatment modality for OS/PFS are not specific for a given treatment option. These advances have generated several controversies and new unanswered questions, particularly those related to their possible role in predicting the possible sequence of different anti-tumor treatments in patients with different presentations. Each of these areas is reviewed in this paper.

Abstract

Purpose: Recent advances in the diagnosis, management and nonsurgical treatment of patients with advanced pancreatic neuroendocrine neoplasms (panNENs) have led to an emerging need for sensitive and useful prognostic factors for predicting responses/survival. Areas covered: The predictive value of a number of reported prognostic factors including clinically-related factors (clinical/laboratory/imaging/treatment-related factors), pathological factors (histological/classification/grading), and molecular factors, on therapeutic outcomes of anti-tumor medical therapies with molecular targeting agents (everolimus/sunitinib/somatostatin analogues), chemotherapy, radiological therapy with peptide receptor radionuclide therapy, or liver-directed therapies (embolization/chemoembolization/radio-embolization (SIRTs)) are reviewed. Recent findings in each of these areas, as well as remaining controversies and uncertainties, are discussed in detail, particularly from the viewpoint of treatment sequencing. Conclusions: The recent increase in the number of available therapeutic agents for the nonsurgical treatment of patients with advanced panNENs have raised the importance of prognostic factors predictive for therapeutic outcomes of each treatment option. The establishment of sensitive and useful prognostic markers will have a significant impact on optimal treatment selection, as well as in tailoring the therapeutic sequence, and for maximizing the survival benefit of each individual patient. In the paper, the progress in this area, as well as the controversies/uncertainties, are reviewed.

Inflammatory markers and long term hematotoxicity of holmium-166-radioembolization in liver-dominant metastatic neuroendocrine tumors after initial peptide receptor radionuclide therapy

PURPOSE

In patients with neuroendocrine tumor liver metastases, additional tumor reduction can be achieved by sequential treatment with [166Ho]-radioembolization after peptide receptor radionuclide therapy (PRRT). The aim of this study was to analyze hematotoxicity profiles, (i.e. lymphocyte and neutrophile toxicity) and the prognostic value of neutrophil-to-lymphocyte ratio (NLR) and thrombocyte-to-lymphocyte ratio (TLR).

METHODS

All patients included in the prospective HEPAR PLuS study were included in this study. Blood testing was performed at baseline (before radioembolization) and at regular intervals during 1-year follow-up. Radiological response was assessed at 3, 6, 9, and 12 months according to RECIST 1.1. Logistic regression was used to analyze the prognostic value of NLR and TLR on response.

RESULTS

Thirty-one patients were included in the toxicity analysis; thirty were included in the response analysis. Three weeks after radioembolization, a significant decrease in lymphocyte count (mean change - 0.26 × 109/L) was observed. Ten patients (32.2%) experienced grade 3-4 lymphocyte toxicity. This normalized at 6 weeks and 3 months after treatment, while after 6 months a significant increase in lymphocyte count was observed. An increase in NLR and TLR at 3 weeks, compared to baseline, significantly predicted response at 3 months (AUC = 0.841 and AUC = 0.839, respectively) and at 6 months (AUC = 0.779 and AUC = 0.765). No significant relation with survival was found.

CONCLUSIONS

Toxicity after sequential treatment with PRRT and [166Ho]-radioembolization is limited and temporary, while significant additional benefit can be expected. Change in NLR and TLR at 3-weeks follow-up may be valuable early predictors of response. Trial registration ClinicalTrials.gov, NCT02067988. Registered 20 February 2014, https://clinicaltrials.gov/ct2/show/record/NCT02067988 .

Peptide receptor radionuclide therapy with [177Lu]Lu-DOTA-TATE

This continuing education aims to present in a clear and easy-to-understand way, the biology of neuroendocrine tumors (NETs), the characteristics of somatostatin receptors, the selection of patients for radiolabelled peptide therapy (PRRT), the inclusion criteria to benefit from treatment with the minimum possible adverse effects, the administration protocol, follow-up and response evaluation. The functional imaging studies necessary to explore the biology of the tumor and to individualize the treatment are also carried out, and constitute the cornerstone for the development of teragnosis. Clinical trials are being developed to better define the position of PRRT within the broad therapeutic options, and among the future perspectives, there are several lines of research to improve the objective response rate and survival with PRRT, focused on the development of new agonists and somatostatin receptor antagonists, new radionuclides and radiosensitizing combination therapies. In conclusion, PRRT is a great therapeutic, well-tolerated and safe tool with generally mild and self-limited acute side effects, that must be sequenced at the best moment of the evolution of the disease of patients with NET. Candidate patients for PRRT should always be evaluated by a multidisciplinary clinical committee.

Theragnostics in primary and secondary liver tumors: the need for a personalized approach

Primary and secondary hepatic tumors have a dramatic impact in oncology. Despite many advances in diagnosis and therapy, the management of hepatic malignancies is still challenging, ranging from various loco-regional approaches to system therapies. In this scenario, theragnostic approaches, based on the administration of a radiopharmaceuticals' pair, the first labeled with a radionuclide suitable for the diagnostic phase and the second one bound to radionuclide emitting particles for therapy, is gaining more and more importance. Selective internal radiation therapy (SIRT) with microspheres labeled with ⁹⁰Y or ¹⁶⁶Ho is widely used as a loco-regional treatment for primary and secondary hepatic tumors. While ¹⁶⁶Ho presents both gamma and beta emission and can be therefore considered a real "theragnostic" agent, for ⁹⁰Y-microspheres theragnostic approach is realized at the diagnostic phase through the utilization of macroaggregates of human albumin, labeled with ^99mTc as "biosimilar" agent respect to microspheres. The aim of the present review was to cover theragnostic applications of ⁹⁰Y/¹⁶⁶Ho-labeled microspheres in clinical practice. Furthermore, we report the preliminary data concerning the potential role of some emerging theragnostic biomarkers for hepatocellular carcinoma, such as glypican-3 (GPC3) and prostate specific membrane antigen (PSMA).

Prophylactic Peripheral Blood Stem Cell Collection in Patients with Extensive Bone-Marrow Infiltration of Neuroendocrine Tumours Prior to Peptide Receptor Radionuclide Therapy with 177Lu-DOTATATE

Peptide receptor radionuclide therapy (PRRT) of metastatic neuroendocrine tumors (NET) can be successfully repeated but may eventually be dose-limited. Since ¹⁷⁷Lu-DOTATATE dose limitation may come from hematological rather than renal function, hematological peripheral blood stem cell backup might be desirable. Here, we report our initial experience of peripheral blood stem-cell collection (PBSC) in patients with treatment-related cytopenia and therefore high risk of bone-marrow failure. Five patients with diffuse bone-marrow infiltration of NET and relevant myelosuppression (≥grade 2) received PBSC before one PRRT cycle with ¹⁷⁷Lu-DOTATATE (7.6 ± 0.8 GBq/cycle). Standard stem-cell mobilization with Granulocyte-colony stimulating factor (G-CSF) was applied, and successful PBSC was defined as a collection of >2 × 10⁶/kg CD34+ cells. In case of initial failure, Plerixafor was administered in addition to G-CSF prior to apheresis. PBSC was successfully performed in all patients with no adverse events. Median cumulative activity was 44.8 GBq (range, 21.3-62.4). Three patients had been previously treated with PRRT, two of which needed the addition of Plerixafor for stem-cell mobilization. Only one of five patients required autologous peripheral blood stem-cell transplantation during the median follow up time of 28 months. PBSC collection seems to be feasible in NET with bone-marrow involvement and might be worth considering as a backup strategy prior to PRRT, in order to overcome dose-limiting bone-marrow toxicity.

Somatostatin receptor radionuclide therapy in neuroendocrine tumors

Peptide receptor radionuclide therapy (PRRT) using 177Lu-DOTATATE has been approved for the treatment of gastroenteropancreatic NETs. An understanding of benefits and risks is important for the appropriate implementation of this therapy. This review summarizes study data supporting the use of radiolabeled somatostatin analogs for the treatment of advanced NETs and highlights risks, including potential toxicities in specific populations. Key ongoing clinical trials, including randomized studies, are designed to better define the position of PRRT within the broader therapeutic landscape. Preclinical and early-phase human studies are focused on the development of novel somatostatin-receptor agonists and antagonists, new radionuclides, and radiosensitizing combination therapies.

Liver Embolisation for Patients with Neuroendocrine Neoplasms: Systematic Review

BACKGROUND

Liver embolisation is one of the treatment options available for patients diagnosed with neuro-endocrine neoplasms (NEN). It is still uncertain whether the benefits of the various types of embolisation treatments truly outweigh the complications in NENs. This systematic review assesses the available data relating to liver embolisation in patients with NENs.

METHODS

Eligible studies (identified using MEDLINE-PubMed) were those reporting data on NEN patients who had undergone any type of liver embolisation. The primary end points were best radiological response and symptomatic response; secondary end-points included progression-free survival (PFS), overall survival (OS) and toxicity.

RESULTS

Of 598 studies screened, 101 were eligible: 16 were prospective (15.8%). The eligible studies included a total of 5,545 NEN patients, with a median of 39 patients per study (range 5-214). Pooled rate of partial response was 36.6% (38.9% achieved stable disease) and 55.2% of patients had a symptomatic response to therapy when pooled data were analysed. The median PFS and OS were 18.4 months (95% CI 15.5-21.2) and 40.7 months (95% CI 35.2-46.2) respectively. The most common toxicities were found to be abdominal pain (48.8%) and nausea (48.1%). Outcome did not significantly vary depending on the type of embolisation performed.

CONCLUSION

Liver embolisation provides adequate symptom relief for patients with carcinoid syndrome and is also able to reach partial response in a significant proportion of patients and a reasonable PFS. Quality of studies was limited, highlighting the need of further prospective studies to confirm the most suitable form of liver embolisation in NENs.

Evaluation of the Safety and Feasibility of Same-Day Holmium-166 -Radioembolization Simulation and Treatment of Hepatic Metastases

PURPOSE

To evaluate the safety and feasibility of same-day treatment, including the simulation procedure for assessment of intrahepatic and extrahepatic distribution of the microspheres, with holmium-166 (¹⁶⁶Ho)-radioembolization.

MATERIALS AND METHODS

This was a secondary analysis of patients included in the 4 prospective studies (HEPAR I, HEPAR II, HEPAR PLuS, and SIM) on ¹⁶⁶Ho-radioembolization. The technical success rate of the same-day treatment protocol, defined as the number of patients who completed the same-day treatment, was measured. Total in-room time, duration of the scout procedure, time to imaging, and duration of the treatment procedure were recorded. Reasons for discontinuation or adjustment of treatment were identified. Adverse events that occurred during the treatment day were recorded.

RESULTS

One hundred five of 120 scheduled patients completed the same-day treatment with ¹⁶⁶Ho-radioembolization (success rate, 88%). After the simulation procedure, treatment was cancelled in 15 patients because of extrahepatic deposition (n = 8), suboptimal tumor targeting (n = 1), unanticipated vascular anatomy (n = 5), and dissection (n = 1). In another 14 patients, the treatment plan was adjusted. The median total procedure time (ie, simulation, imaging, and treatment) was 6:39 hours:minutes (range, 3:58-9:17 hours:minutes). Back pain was a major same-day treatment-related complaint (n = 28).

CONCLUSION

¹⁶⁶Ho-radioembolization as a same-day treatment procedure is feasible in most selected patients, although treatment was adjusted in 12% of patients and cancelled in 12% of patients. This approach might be beneficial for a select patient population, such as patients needing a radiation segmentectomy.

The North American Neuroendocrine Tumor Society Consensus Guidelines for Surveillance and Medical Management of Pancreatic Neuroendocrine Tumors

This article is the result of the North American Neuroendocrine Tumor Society consensus conference on the medical management of pancreatic neuroendocrine tumors from July 19 to 20, 2018. The guidelines panel consisted of medical oncologists, pathologists, gastroenterologists, endocrinologists, and radiologists. The panel reviewed a series of questions regarding the medical management of patients with pancreatic neuroendocrine tumors as well as questions regarding surveillance after resection. The available literature was reviewed for each of the question and panel members voted on controversial topics, and the recommendations were included in a document circulated to all panel members for a final approval.

Quantitative 166Ho-microspheres SPECT derived from a dual-isotope acquisition with 99mTc-colloid is clinically feasible

Purpose

Accurate dosimetry is essential in radioembolization. To this purpose, an automatic protocol for healthy liver dosimetry based on dual isotope (DI) SPECT imaging, combining holmium-166 (¹⁶⁶Ho)-microspheres, and technetium-99 m (^99mTc)-colloid was developed: ¹⁶⁶Ho-microspheres used as scout and therapeutic particles, and ^99mTc-colloid to identify the healthy liver. DI SPECT allows for an automatic and accurate estimation of absorbed doses, introducing true personalized dosimetry. However, photon crosstalk between isotopes can compromise image quality. This study investigates the effect of ^99mTc downscatter on ¹⁶⁶Ho dosimetry, by comparing ¹⁶⁶Ho-SPECT reconstructions of patient scans acquired before (¹⁶⁶Ho-only) and after additional administration of ^99mTc-colloid (¹⁶⁶Ho-DI).

Methods

The ¹⁶⁶Ho-only and ¹⁶⁶Ho-DI scans were performed in short succession by injecting ^99mTc-colloid on the scanner table. To compensate for ^99mTc downscatter, its influence was accounted for in the DI image reconstruction using energy window-based scatter correction methods. The qualitative assessment was performed by independent blinded comparison by two nuclear medicine physicians assessing 65 pairs of SPECT/CT. Inter-observer agreement was tested by Cohen’s kappa coefficient. For the quantitative analysis, two volumes of interest within the liver, VOI_TUMOR, and VOI_HEALTHY were manually delineated on the ¹⁶⁶Ho-only reconstruction and transferred to the co-registered ¹⁶⁶Ho-DI reconstruction. Absorbed dose within the resulting VOIs, and in the lungs (VOI_LUNGS), was calculated based on the administered therapeutic activity.

Results

The qualitative assessment showed no distinct clinical preference for either ¹⁶⁶Ho-only or ¹⁶⁶Ho-DI SPECT (kappa = 0.093). Quantitative analysis indicated that the mean absorbed dose difference between ¹⁶⁶Ho-DI and ¹⁶⁶Ho-only was − 2.00 ± 2.84 Gy (median 27 Gy; p value < 0.00001), − 5.27 ± 8.99 Gy (median 116 Gy; p value = 0.00035), and 0.80 ± 1.08 Gy (median 3 Gy; p value < 0.00001) for VOI_HEALTHY, VOI_TUMOR, and VOI_LUNGS, respectively. The corresponding Pearson’s correlation coefficient between ¹⁶⁶Ho-only and ¹⁶⁶Ho-DI for absorbed dose was 0.97, 0.99, and 0.82, respectively.

Conclusion

The DI protocol enables automatic dosimetry with undiminished image quality and accuracy.

Clinical trials

The clinical study mentioned is registered with Clinicaltrials.gov (NCT02067988) on 20 February 2014.

Simultaneous 166Ho/99mTc dual-isotope SPECT with Monte Carlo-based downscatter correction for automatic liver dosimetry in radioembolization

Background

Intrahepatic dosimetry is paramount to optimize radioembolization treatment accuracy using radioactive holmium-166 microspheres (¹⁶⁶Ho). This requires a practical protocol that combines quantitative imaging of microsphere distribution with automated and robust delineation of the volumes of interest. To this end, we propose a dual isotope single photon emission computed tomography (SPECT) protocol based on ¹⁶⁶Ho therapeutic microspheres and technetium-99 m (^99mTc) stannous phytate, which accumulates in healthy liver tissue. This protocol may allow accurate and automatic estimation of tumor-absorbed dose and healthy liver-absorbed dose. The current study focuses on a Monte Carlo-based reconstruction framework that inherently corrects for scatter crosstalk between the ¹⁶⁶Ho and ^99mTc imaging. To demonstrate the feasibility of the method, it is evaluated with realistic phantom experiments and patient data.

Methods

The Utrecht Monte Carlo System (UMCS) was extended to include detailed modeling of crosstalk interactions between ^99mTc and ¹⁶⁶Ho. First, ^99mTc images were reconstructed including energy window-based corrections for ¹⁶⁶Ho downscatter. Next, ^99mTc downscatter in the 81-keV ¹⁶⁶Ho window was Monte Carlo simulated to allow quantitative reconstruction of the ¹⁶⁶Ho images. The accuracy of the ^99mTc-downscatter modeling was evaluated by comparing measurements with simulations. In addition, the ratio between ^99mTc and ¹⁶⁶Ho yielding the best ¹⁶⁶Ho dose estimates was established and the quantitative accuracy was reported.

Results

Given the same level of activity, ^99mTc contributes twice as many counts to the 81-keV window than ¹⁶⁶Ho, and four times as many counts to the 140-keV window, applying a ¹⁶⁶Ho/^99mTc ratio of 5:1 yielded a high accuracy in both ¹⁶⁶Ho and ^99mTc reconstruction. Phantom experiments revealed that the accuracy of quantitative ¹⁶⁶Ho activity recovery was reduced by 10% due to the presence of ^99mTc. Twenty iterations (8 subsets) of the SPECT/CT reconstructions were considered feasible for clinical practice. Applicability of the proposed protocol was shown in a proof-of-concept case.

Conclusion

A novel ¹⁶⁶Ho/^99mTc dual-isotope protocol for automatic dosimetry compensates accurately for downscatter and allows for the addition of ^99mTc without compromising ¹⁶⁶Ho SPECT image quality.

Additional holmium-166 radioembolisation after lutetium-177-dotatate in patients with neuroendocrine tumour liver metastases (HEPAR PLuS): a single-centre, single-arm, open-label, phase 2 study

BACKGROUND

In patients with metastatic neuroendocrine neoplasms, the liver is the most commonly affected organ and a crucial factor for prognosis and survival. Peptide receptor radionuclide therapy can prolong progression-free survival in these patients. Additional treatment of liver disease might further improve outcomes. We aimed to investigate the safety and efficacy of additional holmium-166 (¹⁶⁶Ho) radioembolisation after peptide receptor radionuclide therapy in patients with metastatic liver neuroendocrine neoplasms.

METHODS

The Holmium Embolization Particles for Arterial Radiotherapy Plus ¹⁷⁷Lu-Dotatate in Salvage Neuroendocrine Tumour Patients (HEPAR PLuS) study was a single-centre, phase 2 study done at the University Medical Center Utrecht (Utrecht, Netherlands). Patients, aged at least 18 years, with histologically proven grade 1 or 2 neuroendocrine neoplasms of all origins, an Eastern Cooperative Oncology Group performance status of 0-2, and three or more measurable liver metastases according to Response Evaluation Criteria In Solid Tumors (RECIST) version 1.1 criteria received ¹⁶⁶Ho-radioembolisation within 20 weeks after four cycles of peptide receptor radionuclide therapy (lutetium-177-dotatate [¹⁷⁷Lu-dotatate]). The primary endpoint was objective liver tumour response in the treated liver volume, defined as complete response (disappearance of all lesions) or partial response (≥30% decrease in the sum of the longest diameters of the target lesions, compared with baseline measurements), according to RECIST 1.1, analysed per protocol at 3 months. Safety was assessed in all patients who received treatment. This study is registered with ClinicalTrials.gov, NCT02067988. Recruitment is completed and long-term follow-up is ongoing.

FINDINGS

From Oct 15, 2014, to Sept 12, 2018, 34 patients were assessed for eligibility. 31 patients received treatment and 30 (97%) patients were available for primary endpoint assessment and completed 6 months of follow-up. Three (9%) patients were excluded at screening and one (3%) patient was treated and died before the primary endpoint and was replaced. According to the per-protocol analysis 13 (43%; 95% CI 26-63) of 30 patients achieved an objective response in the treated volume. The most frequently reported Common Terminology Criteria for Adverse Events (CTCAE) grade 3-4 clinical and laboratory toxicities within 6 months included abdominal pain (three [10%] of 31 patients), increased γ-glutamyl transpeptidase (16 [54%]), and lymphocytopenia (seven [23%]). One (3%) fatal treatment-related serious adverse event occurred (radioembolisation-induced liver disease). Two (6%) patients had serious adverse events deemed to be unrelated to treatment (gastric ulcer and perforated cholecystitis).

INTERPRETATION

¹⁶⁶Ho-radioembolisation, as an adjunct to peptide receptor radionuclide therapy in patients with neuroendocrine neoplasm liver metastases, is safe and efficacious. Radioembolisation can be considered in patients with bulky liver disease, including after peptide receptor radionuclide therapy. A future randomised, controlled study should investigate the added benefit of this treatment on progression-free survival.

FUNDING

None.

The various therapeutic applications of the medical isotope holmium-166: a narrative review

Over the years, a broad spectrum of applications of the radionuclide holmium-166 as a medical isotope has been established. The isotope holmium-166 is attractive as it emits high-energy beta radiation which can be used for a therapeutic effect and gamma radiation which can be used for nuclear imaging purposes. Furthermore, holmium-165 can be visualized by MRI because of its paramagnetic properties and by CT because of its high density. Since holmium-165 has a natural abundance of 100%, the only by-product is metastable holmium-166 and no costly chemical purification steps are necessary for production of nuclear reactor derived holmium-166. Several compounds labelled with holmium-166 are now used in patients, such Ho¹⁶⁶-labelled microspheres for liver malignancies, Ho¹⁶⁶-labelled chitosan for hepatocellular carcinoma (HCC) and [¹⁶⁶Ho]Ho DOTMP for bone metastases. The outcomes in patients are very promising, making this isotope more and more interesting for applications in interventional oncology. Both drugs as well as medical devices labelled with radioactive holmium are used for internal radiotherapy. One of the treatment possibilities is direct intratumoural treatment, in which the radioactive compound is injected with a needle directly into the tumour. Numerous other applications have been developed, like patches for treatment of skin cancer and holmium labelled antibodies and peptides. The second major application that is currently clinically applied is selective internal radiation therapy (SIRT, also called radioembolization), a novel treatment option for liver malignancies. This review discusses medical drugs and medical devices based on the therapeutic radionuclide holmium-166.

Holmium-166 Microsphere Radioembolization of Hepatic Malignancies

Holmium microspheres have recently become available in the European market as the third type of microspheres for radioembolization of unresectable liver malignancies. Holmium microspheres come with a dedicated administration system, and since these microspheres contain holmium-166 (¹⁶⁶Ho) instead of yttrium-90, unique dosing and imaging possibilities have become available as well. In addition, a scout dose of ¹⁶⁶Ho microspheres (Conformité Européenne mark is now granted and not pending anymore) can be used instead of ^99mTc-macroaggragated albumin during the preparatory angiography procedure. So far, two prospective phase I and phase II clinical studies have been performed on ¹⁶⁶Ho radioembolization in a population of liver metastases from mixed origins. These studies showed that a mean whole-liver dose of 60 Gy is safe and induces tumor response. Ongoing trials investigate the effect of ¹⁶⁶Ho radioembolization in patients with neuroendocrine tumor metastases, hepatocellular carcinoma, and colorectal cancer metastases. Data derived from these studies will be used to refine the dosing schedule of 60 Gy to the whole liver and determine the optimal level of activity for each patient. This paper discusses several basics and provides an overview of relevant dosing aspects, technical aspects of performing holmium radioembolization, as well as a summary of completed and ongoing clinical studies and the upcoming developments regarding these microspheres.