From the Angio Suite to the γ-Camera: Vascular Mapping and 99mTc-MAA Hepatic Perfusion Imaging Before Liver Radioembolization—A Comprehensive Pictorial Review

Voxel-Based Dosimetry as a Means for Treatment Personalisation in Radioembolization: A Systematic Review

INTRODUCTION

Radionuclide therapy including 90Y radioembolization is an established form of brachytherapy for treatment of malignancy including hepatocellular carcinoma. Currently, there are several methods available to estimate patient absorbed dose, including voxel-based dosimetry, that can achieve a level of personalisation in the planning and outcome assessments of radioembolization. Despite the advantages of voxel-based dosimetry, it remains a relatively new concept in radioembolization. This study evaluates if voxel-based dosimetry was associated with improved treatment efficacy in radioembolization planning.

METHODS

A systematic review was conducted by searching relevant databases (Medline Ovid, PubMed, Embase Ovid, CINAHL Complete, Cochrane Library, CENTRAL, Australian New Zealand Clinical Trials Registry, ClinicalTrials.gov, WHO International Trials Registry, Google Scholar) for literature regarding voxel-based dosimetry in radioembolization.

RESULTS

A total of 41 papers were included for this systematic review. Review of these studies revealed that voxel-based dosimetry can benefit numerous aspects of radioembolization in radionuclide therapy including predicting tumour response, toxicity and patient survival. Numerous studies also indicated that voxel-based dosimetry in radioembolization is a more accurate approach in establishing a dose-effect relationship in targeted radionuclide therapy when compared to other methods. Despite these promising findings, these studies did not investigate or comment on the accuracy of voxel-based dosimetry.

CONCLUSION

The evidence from this review highlights that voxel-based dosimetry can improve treatment efficacy in radioembolization planning. However, further studies are required to validate the accuracy and feasibility of voxel-based dosimetry in clinical practice.

99mTc/90Y radiolabeled biodegradable gel microspheres for lung shutting fraction assessment and radioembolization in hepatocellular carcinoma theranostics

Transarterial radioembolization (TARE) is a well-established clinical therapy for the treatment of patients with intermediate to advanced hepatocellular carcinoma (HCC) or those who are ineligible for radical treatment. However, commercialized radioactive microspheres still have some issues, such as high density, complicated preparation, non-biodegradability. Furthermore, the use of different radioactive microspheres during TARE and lung shunt fraction assessment has led to inconsistencies in biodistribution in certain cases. This study employed biodegradable hyaluronic acid (HA) as the backbone and modified with bisphosphonate and methacrylic acid to prepare biodegradable gel microspheres (HAMS) using the water-in-oil emulsification and photo-crosslinking for labeling the diagnostic radionuclide of 99mTc and therapeutic radionuclide of 90Y. Both 99mTc radiolabeled HAMS (99mTc-HAMS) and radiolabeled 90Y-HAMS (90Y-HAMS) were highly efficient in radiolabeling and exhibited excellent radiostability in vitro and in vivo. 99mTc-HAMS are highly effective in assessing the LSF, while 90Y-HAMS, administered though TARE, are effective in inhibiting the growth of in situ HCC without any side effects. Both 99mTc-HAMS and 90Y-HAMS have promising clinical applications in HCC theranostics.

Hepatopulmonary Shunt Ratio Verification Model for Transarterial Radioembolization

INTRODUCTION

The most important toxicity of transarterial radioembolization therapy applied in liver malignancies is radiation pneumonitis and fibrosis due to hepatopulmonary shunt of Yttrium-90 (90Y) microspheres. Currently, Technetium-99m macroaggregated albumin (99mTc-MAA) scintigraphic images are used to estimate lung shunt fraction (LSF) before treatment. The aim of this study was to create a phantom to calculate exact LFS rates according to 99mTc activities in the phantom and to compare these rates with LSF values calculated from scintigraphic images.

MATERIALS AND METHODS

A 3D-printed lung and liver phantom containing two liver tumors was developed from Polylactic Acid (PLA) material, which is similar to the normal-sized human body in terms of texture and density. Actual %LSFs were calculated by filling phantoms and tumors with 99mTc radionuclide. After the phantoms were placed in the water tank made of plexiglass material, planar, SPECT, and SPECT/CT images were obtained. The actual LSF ratio calculated from the activity amounts filled into the phantom was used for the verification of the quantification of scintigraphic images and the results obtained by the Simplicity90YTM method.

RESULTS

In our experimental model, LSFs calculated from 99mTc activities filled into the lungs, normal liver, small tumor, and large tumor were found to be 0%, 6.2%, 10.8%, and 16.9%. According to these actual LSF values, LSF values were calculated from planar, SPECT/CT (without attenuation correction), and SPECT/CT (with both attenuation and scatter correction) scintigraphic images of the phantom. In each scintigraphy, doses were calculated for lung, small tumor, large tumor, normal liver, and Simplicity90YTM. The doses calculated from planar and SPECT/CT (NoAC+NoSC) images were found to be higher than the actual doses. The doses calculated from SPECT/CT (with AC+with SC) images and Simplicity90YTM were found to be closer to the real dose values.

CONCLUSION

LSF is critical in dosimetry calculations of 90Y microsphere therapy. The newly introduced hepatopulmonary shunt phantom in this study is suitable for LSF verification for all models/brands of SPECT and SPECT/CT devices.

Microspheres as a Carrier System for Therapeutic Embolization Procedures: Achievements and Advances

The targeted delivery of anti-cancer drugs and isotopes is one of the most pursued goals in anti-cancer therapy. One of the prime examples of such an application is the intra-arterial injection of microspheres containing cytostatic drugs or radioisotopes during hepatic embolization procedures. Therapy based on the application of microspheres revolves around vascular occlusion, complemented with local therapy in the form of trans-arterial chemoembolization (TACE) or radioembolization (TARE). The broadest implementation of these embolization strategies currently lies within the treatment of untreatable hepatocellular cancer (HCC) and metastatic colorectal cancer. This review aims to describe the state-of-the-art TACE and TARE technologies investigated in the clinical setting for HCC and addresses current trials and new developments. In addition, chemical properties and advancements in microsphere carrier systems are evaluated, and possible improvements in embolization therapy based on the modification of and functionalization with therapeutical loads are explored.

Hepatic Artery Infusion Pumps: A Surgical Toolkit for Intraoperative Decision-Making and Management of Hepatic Artery Infusion-Specific Complications

BACKGROUND

Hepatic artery infusion (HAI) is a liver-directed therapy that delivers high-dose chemotherapy to the liver through the hepatic arterial system for colorectal liver metastases and intrahepatic cholangiocarcinoma. Utilization of HAI is rapidly expanding worldwide.

OBJECTIVE AND METHODS

This review describes the conduct of HAI pump implantation, with focus on common technical pitfalls and their associated solutions. Perioperative identification and management of common postoperative complications is also described.

RESULTS

HAI therapy is most commonly performed with the surgical implantation of a subcutaneous pump, and placement of its catheter into the hepatic arterial system for inline flow of pump chemotherapy directly to the liver. Intraoperative challenges and abnormal hepatic perfusion can arise due to aberrant anatomy, vascular disease, technical or patient factors. However, solutions to prevent or overcome technical pitfalls are present for the majority of cases. Postoperative HAI-specific complications arise in 22% to 28% of patients in the form of pump pocket (8%-18%), catheter (10%-26%), vascular (5%-10%), or biliary (2%-8%) complications. The majority of patients can be rescued from these complications with early identification and aggressive intervention to continue to deliver safe and effective HAI therapy.

CONCLUSIONS

This HAI toolkit provides the HAI team a reference to manage commonly encountered HAI-specific perioperative obstacles and complications. Overcoming these challenges is critical to ensure safe and effective pump implantation and delivery of HAI therapy, and key to successful implementation of new programs and expansion of HAI to patients who may benefit from such a highly specialized treatment strategy.

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

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.

Unusual Radiotracer Deposition to the Forearm After Intrahepatic Injection of 99mTc-Macroaggregated Albumin Using a Transradial Approach

ABSTRACT

Arterial mapping and 99mTc-macroaggregated albumin (99mTc-MAA) hepatic perfusion imaging are routinely performed before 90Y radioembolization of hepatic tumors. These procedures serve multiple purposes, including an anatomical survey of hepatic arterial anatomy, interrogating expected microsphere distribution to avoid nontargeted embolization during therapy, and evaluating for possible hepatopulmonary shunting. We present a case where 99mTc-MAA planar images revealed unexpected soft tissue uptake within the left forearm, an unexpected complication that may result from residual 99mTc-MAA in the catheter being expelled as the catheter is removed, which is particularly important to avoid during the 90Y radioembolization procedure given the risk for associated radionecrosis.

Standardizing SPECT/CT dosimetry following radioembolization with yttrium-90 microspheres

Background

Multiple post-treatment dosimetry methods are currently under investigation for Yttrium-90 (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{90}\hbox {Y}$$\end{document}90Y) radioembolization. Within each methodology, a variety of dosimetric inputs exists that affect the final dose estimates. Understanding their effects is essential to facilitating proper dose analysis and crucial in the eventual standardization of radioembolization dosimetry. The purpose of this study is to investigate the dose differences due to different self-calibrations and mass density assignments in the non-compartmental and local deposition methods. A practical mean correction method was introduced that permits dosimetry in images where the quality is compromised by patient motion and partial volume effects.

Methods

Twenty-one patients underwent \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{90}\hbox {Y}$$\end{document}90Y radioembolization and were imaged with SPECT/CT. Five different self-calibrations (FOV, Body, OAR, Liverlung, and Liver) were implemented and dosimetrically compared. The non-compartmental and local deposition method were used to perform dosimetry based on either nominal- or CT calibration-based mass densities. A mean correction method was derived assuming homogeneous densities. Cumulative dose volume histograms, linear regressions, boxplots, and Bland Altman plots were utilized for analysis.

Results

Up to 270% weighted dose difference was found between self-calibrations with mean dose differences up to 50 Gy in the liver and 23 Gy in the lungs. Between the local deposition and non-compartmental methods, the liver and lung had dose differences within 0.71 Gy and 20 Gy, respectively. The local deposition method’s nominal and CT calibration-based mass density implementations dosimetric metrics were within 1.4% in the liver and 24% in the lungs. The mean lung doses calculated with the CT method were shown to be inflated. The mean correction method demonstrated that the corrected mean doses were greater by up to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim 5$$\end{document}∼5 Gy in the liver and lower by up to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim 12$$\end{document}∼12 Gy in the lungs.

Conclusions

The OAR calibration may be utilized as a potentially more accurate and precise self-calibration. The non-compartmental method was found more comparable to the local deposition method in organs that were more homogeneous in mass densities. Due to the potential for inflated lung mean doses, the non-compartmental and local deposition method implemented with nominal mass densities is recommended for more consistent dosimetric results. If patient motion and partial volume effects are present in the liver, our practical correction method will calculate more representative doses in images suboptimal for dosimetry.

Current Approach to Planning Angiography and MAA Administration

Transarterial radioembolization of primary and secondary hepatic malignancies utilizing yttrium-90 microspheres is a commonly performed treatment by interventional radiologists. Traditionally performed as a two-part procedure, a diagnostic angiography is performed 1 to 3 weeks prior to treatment with the injection of technetium-99m-macroaggregated albumin followed by planar scintigraphy in the nuclear medicine department. Careful attention must be paid to the details during the diagnostic angiography to ensure the delivery of a safe and optimal dose to the diseased liver and to minimize radiation-induced damage to both unaffected liver and adjacent structures. In this article, we will review the steps and considerations that must be made during the angiography planning and discuss current and future areas of research.

Treatment response assessment following transarterial radioembolization for hepatocellular carcinoma

Transarterial radioembolization with yttrium-90 microspheres is an established therapy for hepatocellular carcinoma. Post-procedural imaging is important for the assessment of both treatment response and procedural complications. A variety of challenging treatment-specific imaging phenomena complicate imaging assessment, such as changes in tumoral size, tumoral and peritumoral enhancement, and extrahepatic complications. A review of the procedural steps, emerging variations, and timelines for post-treatment tumoral and extra-tumoral imaging changes are presented, which may aid the reporting radiologist in the interpretation of post-procedural imaging. Furthermore, a description of post-procedural complications and their significance is provided.

Hepatic Arterial Infusion Pumps: What the Radiologist Needs to Know

Hepatic arterial infusion (HAI) entails the surgical implantation of a subcutaneous pump to deliver chemotherapeutic agents directly to the liver in the setting of primary or secondary liver cancer. The purpose of HAI chemotherapy is to maximize hepatic drug concentrations while minimizing systemic toxicity, facilitating more effective treatment. HAI is used in combination with systemic chemotherapy and can be considered in several clinical scenarios, including adjuvant therapy, conversion of unresectable disease to resectable disease, and unresectable disease. Radiologists are key members of the multidisciplinary team involved in the selection and management of these patients with complex liver disease. As these devices begin to be used at more sites across the country, radiologists should become familiar with the guiding principles behind pump placement, expected imaging appearances of these devices, and potential associated complications. The authors provide an overview of HAI therapy, with a focus on the key imaging findings associated with this treatment that radiologists may encounter. ^©RSNA, 2021.

Tumor-to-Normal Ratio Relationship between Planning Technetium-99 Macroaggregated Albumin and Posttherapy Yttrium-90 Bremsstrahlung SPECT/CT

PURPOSE

To quantify the relationship of the tumor-to-normal ratio (TNR) attained from the technetium-99m macroaggregated albumin (MAA) and posttreatment yttrium-90 bremsstrahlung (Y90-Brem) single-photon emission computerized tomography (SPECT)/computer tomography (CT) studies in patients with hepatocellular carcinoma (HCC) treated with glass microspheres.

MATERIALS AND METHODS

Retrospectively, a total of 190 consecutive patients with HCC who underwent 204 MAA and Y90-Brem SPECT/CT for glass microsphere Y90 radiation segmentectomy (Y90-RS) or lobar treatment (Y90-RLT) between 2013 and 2018 were included. Semi-automated regions-of-interests were drawn around the targeted tumor and nontumoral liver tissue on the SPECT/CT studies. TNR values from MAA and Y90-Brem SPECT/CT were compared using paired t-tests, Pearson correlation, and median with interquartile ranges (IQR).

RESULTS

The mean TNR for MAA and Y90-Brem SPECT/CT was 2.96 ± 1.86 (median, 2.64; IQR, 2.50) and 2.29 ± 1.10 (median, 2.06; IQR, 1.05), respectively (P < .0001). The mean Y90-RLT TNR was 2.88 ± 1.67 (median, 2.59; IQR, 0.83) and 2.17 ± 0.89 (median, 1.98; IQR, 0.81) for MAA and Y90-Brem SPECT/CT, respectively (P < .0001). The mean Y90-RS TNR was 3.02 ± 2.01 (median, 2.87; IQR, 3.01) and 2.39 ± 1.25 (median, 2.11; IQR, 1.28) for MAA and Y90-Brem SPECT/CT, respectively (P = .0003). TNR attained from MAA and Y90 SPECT/CT studies showed a moderate correlation in a positive linear fashion for the overall (r = 0.54; P < .001), Y90-RLT (r = 0.66, P < .001), and Y90-RS cohorts (r = 0.48, P < .001).

CONCLUSIONS

The TNR attained from Y90-Brem SPECT/CT is often underestimated, positively correlated, and less variable than that attained from MAA SPECT/CT.

Factors affecting the response to Y-90 microsphere therapy in the cholangiocarcinoma patients

OBJECTIVE

The aim of this study was to assess the early therapy response in patients with unresectable CCA who received Y-90 microsphere therapy for CCA and define the factors related to therapy response.

MATERIALS AND METHODS

Data of 19 patients [extrahepatic (n: 6) and intrahepatic (n: 13)] who received 24 sessions of Y-90 microsphere therapy [glass (n: 13) and resin (n: 11)] were retrospectively evaluated. Tumor load, tumor size, therapy response evaluation by RECIST1.1 criteria (n: 13), tumor lesion glycolysis (TLG), metabolic tumor volume (MTV), and metabolic therapy responses were evaluated (n: 8) using PERCIST1.0 criteria.

RESULTS

No significant relation was found between therapy response and tumor localization, treated liver lobe, type of Y90 microspheres, the presence of previous therapies, perfusion pattern on hepatic artery perfusion scintigraphy, or patient demographics. The mean overall survival (OS) was 11.9 ± 2.3 months and was similar after both resin and glass Y90 microspheres; however, it was longer RECIST responders (p: 0.005). MTV and TLG values significantly decreased after therapy, and ΔMTV (- 45.4% ± 12.1) was found to be positively correlated with OS. No statistical difference was found between iCCA and eCCA, in terms of OS and response to therapy. Although not quantitatively displayed, better-perfused areas on HAPS images had a better metabolic response and less perfused areas were prone to local recurrences.

CONCLUSIONS

Both resin and glass microsphere therapy can be applied safely to iCCA and eCCA patients. Early therapy response can be evaluated with both RECIST and PERCIST criteria. Both anatomical and metabolic therapy response evaluations give complementary information.

Expected and Unexpected Imaging Findings after 90Y Transarterial Radioembolization for Liver Tumors

Transarterial radioembolization (TARE), also called radioembolization or selective internal radiation therapy, is an interventional radiology technique used to treat primary liver tumors and liver metastases. The aim of this therapy is to deliver tumoricidal doses of radiation to liver tumors while selecting a safe radiation dose limit for nontumoral liver and lung tissue. Hence, correct treatment planning is essential to obtaining good results. However, this treatment invariably results in some degree of irradiation of normal liver parenchyma, inducing different radiologic findings that may affect follow-up image interpretation. When evaluating treatment response, the treated area size, tumor necrosis, devascularization, and changes seen at functional MRI must be taken into account. Unlike with other interventional procedures, with TARE, it can take several months for the tumor response to become evident. Ideally, responding lesions will show reduced size and decreased enhancement 3-6 months after treatment. In addition, during follow-up, there are many imaging findings related to the procedure itself (eg, peritumoral edema, inflammation, ring enhancement, hepatic fibrosis, and capsular retraction) that can make image interpretation and response evaluation difficult. Possible complications, either hepatic or extrahepatic, also can occur and include biliary injuries, hepatic abscess, radioembolization-induced liver disease, and radiation pneumonitis or dermatitis. A complete understanding of these possible posttreatment changes is essential for correct radiologic interpretations during the follow-up of patients who have undergone TARE. ^©RSNA, 2019.

Tc-99m sulfur colloid SPECT-CT and assessment of functional liver reserve after Y90 radioembolization: A case report

INTRODUCTION

Quantitative assessment is an essential tool in determining the proportion of liver to be reserved before lobectomy. Technetium-99 m sulfur colloid single-photon emission computed tomography (Tc-99 m SC SPECT-CT) can help in the quantitative assessment of functioning liver tissues and percentage of liver reserve before segmentectomy and lobectomy Matesan et al. (2017), Bowen et al. (2016) and Lam et al. (2013).

PRESENTATION OF CASE

A 64-year-old man with alcoholic cirrhosis was admitted to our hospital with a 15 × 10 x 13 cm bilobar HCC. Y90 radioembolization was utilized to downstage the liver tumor. On follow-up CT scan of the liver after radiotherapy, the HCC was much reduced to 6.5 cm in size but still viable with elevated alpha fetoprotein ([AFP] from 225 to 381 to 959 ng/mL). Resection was considered. Constitutional indocyanine green retention at 15 min (ICG-R-15) was 22%. We introduced the Tc-99 m SC SPECT-CT scan in order to assess the percentage liver function of each lobe. It showed minimal uptake in the remaining functioning right lobe with a hypertrophic left lobe to whole liver uptake ratio of 87.1%. This finding gave us confidence to perform right hepatectomy.

DISCUSSION

We used Tc-99 m SC SPECT-CT to estimate the normal functional liver reserve after Y90 radioembolization of a hepatocellular carcinoma (HCC). To our understanding, it is the first case report using Tc-99 m SC to predict the percentage of functional liver reserve after yttrium-90 (Y90) radioembolization.

CONCLUSION

Tc-99 m SC SPECT-CT is a novel helper used to assess the differential liver function after Y90 radioembolization of HCC and before segmentectomy and lobectomy of the liver.

Anatomy of the hepatic arteries and their extrahepatic branches in the human liver: A cadaveric study

BACKGROUND

To describe the hepatic arterial anatomy in detail, tracing the individual hepatic arteries from their origin, extrahepatic course, branching to their segmental territorial supply as applicable to the vascular mapping for hepatic endovascular procedures.

METHODS

The study was conducted on 100 formalin fixed adult cadaveric livers. The hepatic arterial anatomy was dissected from the origin of hepatic arteries up to their segmental branching.

RESULTS

The origin of hepatic arteries was standard in 72% and aberrant in 28% livers. In livers with standard origin, extrahepatic branching of the main hepatic artery was close to the hepatic hilum in 48% and was in the lower part of the hepatoduodenal ligament in 24% livers. The pattern of extrahepatic branching in each type was three and five respectively. Aberrant arterial anatomy was broadly categorized into three groups. The mapping of segmental arterial vascularization of individual hepatic arteries in each type was also done.

CONCLUSIONS

In the present study, an attempt was made to systematically describe the complex hepatic arterial anatomy in a clinically applicable fashion. High variability was seen in the hepatic arterial anatomy at each level, a lot of which could not be included in the current classification systems. The information provided is an important prerequisite for performing accurate intra-arterial hepatic interventions.

Delivery of selective internal radiation therapy complicated by variant hepatic vascular anatomy

“Difficult vascular anatomy” is a challenge for Interventional Radiologists especially in liver directed therapies such as trans arterial radio embolization.

Trans arterial radio embolization is a long and difficult procedure in which the basic knowledge of hepatic and gastro-enteric vascularization, with its high degree of variations, is very important in order to correctly administer the therapeutic drug selectively.

In this report, we present a case of an atypical patient affected by an unresectable hepatocellular carcinoma, candidate for Radio-embolization treatment.

His vascular anatomy was very difficult to manage, but the Interventional Radiologist was not only able to go over the “difficult anatomy,” but also to take advantage of it.

Radioembolization of Hepatocellular Carcinoma with Built-In Dosimetry: First in vivo Results with Uniformly-Sized, Biodegradable Microspheres Labeled with 188Re

A common form of treatment for patients with hepatocellular carcinoma (HCC) is transarterial radioembolization (TARE) with non-degradable glass or resin microspheres (MS) labeled with ⁹⁰Y (⁹⁰Y-MS). To further simplify the dosimetry calculations in the clinical setting, to have more control over the particle size and to change the permanent embolization to a temporary one, we developed uniformly-sized, biodegradable ¹⁸⁸Re-labeled MS (¹⁸⁸Re-MS) as a new and easily imageable TARE agent.

Methods: MS made of poly(L-lactic acid) were produced in a flow focusing microchip. The MS were labeled with ¹⁸⁸Re using a customized kit. An orthotopic HCC animal model was developed in male Sprague Dawley rats by injecting N1-S1 cells directly into the liver using ultrasound guidance. A suspension of ¹⁸⁸Re-MS was administered via hepatic intra-arterial catheterization 2 weeks post-inoculation of the N1-S1 cells. The rats were imaged by SPECT 1, 24, 48, and 72 h post-radioembolization.

Results: The spherical ¹⁸⁸Re-MS had a diameter of 41.8 ± 6.0 µm (CV = 14.5%). The site and the depth of the injection of N1-S1 cells were controlled by visualization of the liver in sonograms. Single 0.5 g tumors were grown in all rats. ¹⁸⁸Re-MS accumulated in the liver with no deposition in the lungs. ¹⁸⁸Re decays to stable ¹⁸⁸Os by emission of β^¯ particles with similar energy to those emitted by ⁹⁰Y while simultaneously emitting γ photons, which were imaged directly by single photon computed tomography (SPECT). Using Monte Carlo methods, the dose to the tumors was calculated to be 3-6 times larger than to the healthy liver tissue.

Conclusions:¹⁸⁸Re-MS have the potential to become the next generation of β^¯-emitting MS for TARE. Future work revolves around the investigation of the therapeutic potential of ¹⁸⁸Re-MS in a large-scale, long-term preclinical study as well as the evaluation of the clinical outcomes of using ¹⁸⁸Re-MS with different sizes, from 20 to 50 µm.

In vivo stability of supramolecular host-guest complexes monitored by dual-isotope multiplexing in a pre-targeting model of experimental liver radioembolization

INTRODUCTION

Cyclodextrin (CD)-based supramolecular interactions have been proposed as nanocarriers for drug delivery. We previously explored the use of these supramolecular interactions to perform targeted hepatic radioembolization. In a two-step procedure the appropriate location of the diagnostic pre-targeting vector can first be confirmed, after which the therapeutic vector will be targeted through multivalent host-guest interactions. Such a procedure would prevent therapeutic errors that come from a mismatch between diagnostic and therapeutic procedures. In the current study we explored the use of dual-isotope imaging to assess the in vivo stability of the formed complex and individual components.

METHODS

Dual-isotope imaging of the host and guest vectors was performed after labeling of the pre-targeted guest vector, being adamantane (Ad) functionalized macro-aggregated albumin (MAA) particles, with technetium-99 m (99mTc-MAA-Ad). The host vector, Cy50.5CD9PIBMA39, was labeled with indium-111 (111In-Cy50.5CD9PIBMA39). The in situ stability of both the individual vectors and the resulting [MAA-Ad-111In-Cy50.5CD9PIBMA39] complexes was studied over 44 h at 37 °C in a serum protein-containing buffer. In vivo, the host vector 111In-Cy50.5CD9PIBMA39 was administered two hours after local deposition of 99mTc-MAA-Ad in mice. Dual-isotope SPECT imaging and quantitative biodistribution studies were performed between 2 and 44 h post intravenous host vector administration.

RESULTS

The individual vectors portrayed <5% dissociation of the radioisotope over the course of 20 h. Dissociation of [MAA-Ad-111In-Cy50.5CD9PIBMA39] complexes remained within a 10-20% range after incubation in serum. In vivo dual-isotope SPECT imaging of host-guest interactions revealed co-localization of the tracer components. Quantitative assessment of the biodistribution revealed that the hepatic accumulation of the host vector nearly doubled between 2 h and 44 h post-injection (from 14.9 ± 6.1%ID/g to 26.2 ± 2.1%ID/g).

CONCLUSIONS

Assessment of intra-hepatic host-guest complexation was successfully achieved using dual isotope multiplexing, underlining the complex stability that was found in situ (up to 44 h in serum). Overall, the results obtained in this study highlight the potential of supramolecular chemistry as a versatile platform that could advance the field of nanomedicine.

Imaging Evaluation Following 90Y Radioembolization of Liver Tumors: What Radiologists Should Know

Radioembolization using beta-emitting yttrium-90 microspheres is being increasingly used for the treatment of primary and metastatic liver cancers. It is a form of intra-arterial brachytherapy which delivers intense radiation to liver tumors with little embolic effect; this mode of action results in unique post-treatment imaging findings. It is important to understand these imaging findings to avoid misinterpretation of tumor response and to determine further management of the disease. Herein, we discuss the current concepts for assessing tumor response, common post-treatment imaging features, and associated complications following radioembolization.

Biodistribution of 99mTc-MAA on SPECT/CT performed for 90Y radioembolization therapy planning: a pictorial review

Purpose

To evaluate the frequency of 99mTc-MAA uptake in extrahepatic organs during 90Y radioembolization therapy planning.

Methods

This retrospective case series of 70 subjects who underwent 99mTc-MAA hepatic artery perfusion studies between January 2014 and July 2016 for 90Y radioembolization therapy planning at our institution involved direct image review for all subjects, with endpoints recorded: lung shunt fraction, extrahepatic radiotracer uptake, time from MAA injection to imaging.

Results

Combined planar and SPECT/CT imaging findings in the 70 subjects demonstrated lung shunt fraction measurements of less than 10% in 53 (76%) subjects and greater than 10% in 17 (24%) subjects. All patients demonstrated renal cortical uptake, 23 (33%) demonstrated salivary gland uptake, 23 (33%) demonstrated thyroid uptake, and 32 (46%) demonstrated gastric mucosal uptake, with significant overlap between these groups. The range of elapsed times between MAA injection and initial imaging was 41-138 min, with a mean of 92 min. There was no correlation between time to imaging and the presence of extrahepatic radiotracer uptake at any site.

Conclusions

During hepatic artery perfusion scanning for 90Y radioembolization therapy planning, extrahepatic uptake is common, particularly in the kidney, salivary gland, thyroid and gastric mucosa, and is hypothesized to result from breakdown of 99mTc-MAA over time. Given the breakdown to smaller aggregates and ultimately pertechnetate, this should not be a contraindication to actual Y-90 microsphere therapy. Although we found no correlation between time to imaging and extrahepatic uptake, most of our injection to imaging times were relatively short.

Highlights of articles published in annals of nuclear medicine 2016

This article is the first installment of highlights of selected articles published during 2016 in the Annals of Nuclear Medicine, an official peer-reviewed journal of the Japanese Society of Nuclear Medicine. A companion article highlighting selected articles published during 2016 in the European Journal of Nuclear Medicine and Molecular Imaging, which is the official peer-reviewed journal of the European Association of Nuclear Medicine, will also appear in the Annals Nuclear Medicine. This new initiative by the respective journals will continue as an annual endeavor and is anticipated to not only enhance the scientific collaboration between Europe and Japan but also facilitate global partnership in the field of nuclear medicine and molecular imaging.

Targeted Radionuclide Therapy: An Evolution Toward Precision Cancer Treatment

OBJECTIVE

This article reviews recent developments in targeted radionuclide therapy (TRT) approaches directed to malignant liver lesions, bone metastases, neuroendocrine tumors, and castrate-resistant metastatic prostate cancer and discusses challenges and opportunities in this field.

CONCLUSION

TRT has been employed since the first radioiodine thyroid treatment almost 75 years ago. Progress in the understanding of the complex underlying biology of cancer and advances in radiochemistry science, multimodal imaging techniques including the concept of "see and treat" within the framework of theranostics, and universal traction with the notion of precision medicine have all contributed to a resurgence of TRT.

Radionuclides in oncology clinical practice – review of the literature

Radionuclide therapy is a promising type of targeted therapy for cancer and its use is becoming more common in several types of malignant tumors.

99mTc-Macroaggregated Albumin SPECT/CT Perfusion Imaging of Omental Extrahepatic Vascularization

The authors present a case of omental perfusion by an extrahepatic branch of the right hepatic artery depicted during pre-embolization planning with 99mTc-macroaggregated albumin SPECT/CT imaging. This omental scintigraphic finding corresponds to an extrahepatic branch of the right hepatic artery demonstrated by selective angiography and related CT angiography. The authors would like to add the omentum to the previously reported sites of extrahepatic vascularization encountered during the hepatic pre-embolization imaging.

A review of 3D image-based dosimetry, technical considerations and emerging perspectives in 90Y microsphere therapy

Yttrium-90 radioembolization (⁹⁰Y-RE) is a well-established therapy for the treatment of hepatocellular carcinoma (HCC) and also of metastatic liver deposits from other malignancies. Nuclear Medicine and Cath Lab diagnostic imaging takes a pivotal role in the success of the treatment, and in order to fully exploit the efficacy of the technique and provide reliable quantitative dosimetry that are related to clinical endpoints in the era of personalized medicine, technical challenges in imaging need to be overcome. In this paper, the extensive literature of current ⁹⁰Y-RE techniques and challenges facing it in terms of quantification and dosimetry are reviewed, with a focus on the current generation of 3D dosimetry techniques. Finally, new emerging techniques are reviewed which seek to overcome these challenges, such as high-resolution imaging, novel surgical procedures and the use of other radiopharmaceuticals for therapy and pre-therapeutic planning.

Systematic evaluation of tumoral 99mTc-MAA uptake using SPECT and SPECT/CT in 502 patients before 90Y radioembolization

The aim of this study was to evaluate the (99m)Tc-macroaggregated albumin ((99m)Tc-MAA) uptake of primary and secondary liver tumors in a large patient cohort before (90)Y radioembolization.

METHODS

We included 502 patients during the years 2005-2013 (55% male; mean age, 62 ± 11 y), who were examined with (99m)Tc-MAA SPECT or SPECT/CT before planned radioembolization. The patients had colorectal cancer (CRC; n = 195, 38.8%), neuroendocrine tumors (NET; n = 77, 15.3%), mammary cancer (MAM; n = 68, 13.5%), hepatocellular carcinoma (HCC; n = 59, 11.8%), cholangiocellular carcinoma (CCC; n = 40, 8.0%), or urologic tumors (URO; n = 14, 2.8%). SPECT with coregistered contrast-enhanced CT or MR imaging and SPECT/CT images of these patients were analyzed using dedicated software with regard to the (99m)Tc-MAA uptake of the liver tumors. Regions of interest were drawn around the lesions manually and quantified the uptake of up to 3 lesions per patient and also adjacent healthy liver tissue without evidence of tumor. We quantified maximum and mean counts per pixel and calculated tumor-to-background ratio (TBR). Data are reported as mean ± SD. Lesion uptake was classified as being homogeneously high (grade 1), heterogeneously high (grade 2), equal to that of the liver (grade 3), or low (grade 4).

RESULTS

Grade 1 uptake was seen in 230 of 1,008 lesions (with the highest rates in sarcoma [47%], MAM [37%], and NET [32%]), grade 2 in 706 lesions (with the highest rates in CRC [77%], HCC [75%], and CCC [74%]), grade 4 in 57 lesions (with the highest rates in pancreatic cancer [17%], sarcoma [SAR] [13%], and MAM [8%]), and grade 3 in only 15 lesions. In quantitative analysis, the mean TBRmax of all lesions was 4.8 ± 4.1 (range, 0.2-50.1), with the highest values in HCC (6.0 ± 4.7; range, 1.4-21.6), NET (5.4 ± 4.9; range, 0.8-43.0), pancreatic cancer (4.0 ± 2.8; range, 0.9-12.2), and CCC (4.7 ± 2.9; range, 0.9-11.6), and the lowest values in SAR (3.5 ± 1.8; range, 0.8-2.7) and MAM (3.6 ± 2.2; range, 0.9-11.6). The mean TBRmean was 1.9 ± 1.0 (range, 0.1-7.2), with the highest values in NET (2.2 ± 1.2; range, 0.2-7.2), HCC (2.1 ± 1.2; range, 0.3-6.3), and CCC (2.0 ± 1.0; range, 0.2-6.3) and the lowest values in MAM (1.7 ± 0.8; range, 0.2-4.1), CRC (1.8 ± 0.9; range, 0.4-6.6), and SAR (1.7 ± 1.1; range, 0.3-3.9).

CONCLUSION

The (99m)Tc-MAA uptake of different tumor entities shows a wide variation, with generally highest values for NET, HCC, and CCC and lowest values for MAM, CRC, and SAR. However, the variation of uptake within the different tumor entities is high.

Vascular targeting of nanocarriers: perplexing aspects of the seemingly straightforward paradigm

Targeted nanomedicine holds promise to find clinical use in many medical areas. Endothelial cells that line the luminal surface of blood vessels represent a key target for treatment of inflammation, ischemia, thrombosis, stroke, and other neurological, cardiovascular, pulmonary, and oncological conditions. In other cases, the endothelium is a barrier for tissue penetration or a victim of adverse effects. Several endothelial surface markers including peptidases (e.g., ACE, APP, and APN) and adhesion molecules (e.g., ICAM-1 and PECAM) have been identified as key targets. Binding of nanocarriers to these molecules enables drug targeting and subsequent penetration into or across the endothelium, offering therapeutic effects that are unattainable by their nontargeted counterparts. We analyze diverse aspects of endothelial nanomedicine including (i) circulation and targeting of carriers with diverse geometries, (ii) multivalent interactions of carrier with endothelium, (iii) anchoring to multiple determinants, (iv) accessibility of binding sites and cellular response to their engagement, (v) role of cell phenotype and microenvironment in targeting, (vi) optimization of targeting by lowering carrier avidity, (vii) endocytosis of multivalent carriers via molecules not implicated in internalization of their ligands, and (viii) modulation of cellular uptake and trafficking by selection of specific epitopes on the target determinant, carrier geometry, and hydrodynamic factors. Refinement of these aspects and improving our understanding of vascular biology and pathology is likely to enable the clinical translation of vascular endothelial targeting of nanocarriers.

Identifying aberrant hepatic arteries prior to intra-arterial radioembolization

PURPOSE

Failing to identify aberrant hepatic arteries before radioembolization (RE) may compromise its treatment efficacy due to inadequate biodistribution of radioactive microspheres. The purpose of this study was to evaluate how often aberrant hepatic arteries were identified correctly in clinical practice, with computed tomography (CT), and during angiography in patients with liver tumors who received a workup for RE.

METHODS

The presence and vascularization pattern of aberrant (i.e., accessory and replaced) hepatic arteries was assessed on triphasic liver CT in 110 patients. Subsequently, radiological reports on CT and angiographic procedures were reviewed to determine whether aberrant hepatic arteries were identified correctly in clinical practice. The intrahepatic biodistribution of (99m)Tc-MAA and radioactive microspheres was assessed on SPECT/CT and PET/CT in all patients with unidentified aberrant hepatic arteries.

RESULTS

Thirty-seven of 110 patients (34%) had aberrant hepatic arteries. In 18 of 37 (49%) patients, the aberrant hepatic arteries were correctly identified on CT and in 32 of 37 (86%) during angiography. Aberrant right hepatic arteries were identified more frequently than aberrant left hepatic arteries on CT (54 vs. 44%) and during angiography (100 vs. 69%, p = 0.007). In five patients (14%), an aberrant left hepatic artery remained unidentified, resulting in a lack of (99m)Tc-MAA and (90)Y activity in the segmental territory of the unidentified aberrant hepatic arteries.

CONCLUSIONS

Aberrant left hepatic arteries were the most common unidentified aberrant hepatic arteries, resulting in incomplete radiation coverage. We formulated a practical approach to identify aberrant hepatic arteries correctly before RE.

The role of SPECT/CT in radioembolization of liver tumours

Radioembolization (RE) with (90)Y microspheres is a promising catheter-based therapeutic option for patients with unresectable primary and metastatic liver tumours. Its rationale arises from the dual blood supply of liver tissue through the hepatic artery and the portal vein. Metastatic hepatic tumours measuring >3 mm derive 80 - 100 % of their blood supply from the arterial rather than the portal hepatic circulation. Typically, an angiographic evaluation combined with (99m)Tc-macroaggregated albumin ((99m)Tc-MAA) scan precedes therapy to map the tumour feeding vessels as well as to avoid the inadvertent deposition of microspheres in organs other than the liver. Prior to administration of (99m)Tc-MAA, prophylactic coil embolization of the gastroduodenal artery is recommended to avoid extrahepatic deposition of the microspheres. SPECT/CT allows direct correlation of anatomic and functional information in patients with unresectable liver disease. SPECT/CT is recommended to assess intrahepatic distribution as well as extrahepatic gastrointestinal uptake in these patients. Pretherapeutic SPECT/CT is an important component of treatment planning including catheter positioning and dose finding. A post-therapy bremsstrahlung (BS) scan should follow RE to verify the distribution of the administered tracer. BS SPECT/CT imaging enables better localization and definition of intrahepatic and possible extrahepatic sphere distribution and to a certain degree allows posttreatment dosimetry. In this paper we address the usefulness and significance of SPECT/CT in therapy planning and therapy monitoring of RE.

Feasibility of temporary protective embolization of normal liver tissue using degradable starch microspheres during radioembolization of liver tumours

PURPOSE

To describe a new approach to protect nontarget healthy liver tissue using degradable starch microspheres (DSM) as a short-term embolizate during radioembolization of liver tumours with (90)Y microspheres.

METHODS

Between December 2011 and July 2012 radioembolization was performed in 54 patients. Five of these patients (three women, two men; mean age 67 years) underwent protective temporary embolization using DSM (EmboCept® S) of normal liver tissue that could not be excluded from the area treated by radioembolization through catheter repositioning. Clinical symptoms, laboratory findings, preinterventional imaging, and (99m)Tc-MAA and bremsstrahlung SPECT/CT, as well as baseline and follow-up imaging with (18)F-FDG PET/CT and MRI, were evaluated in relation to the technical and clinical success of the protective embolization.

RESULTS

Temporary embolization of arteries supplying normal liver tissue using DSM was technically successful in all five patients. (99m)Tc-MAA SPECT/CT performed in the first two patients after DSM injection showed no increased pulmonary shunting compared to the MAA test injection without DSM. Bremsstrahlung SPECT/CT after radioembolization demonstrated satisfactory irradiation of the tumour and successful protection of normal liver tissue. There were only mild hepatotoxic effects (grade 1) on laboratory follow-up examinations, and no adverse events associated with DSM embolization or radioembolization were recorded.

CONCLUSION

Temporary embolization with DSM before radioembolization is feasible and can effectively protect areas of normal liver tissue from irradiation and avoid permanent embolization if other methods such as catheter repositioning are not possible due to the location of the metastases.