Sentinel Node Imaging and Radioguided Surgery in the Era of SPECT/CT and PET/CT: Toward New Interventional Nuclear Medicine Strategies

Molecular image-guided surgery in gynaecological cancer: where do we stand?

PURPOSE

The aim of this review is to give an overview of the current status of molecular image-guided surgery in gynaecological malignancies, from both clinical and technological points of view.

METHODS

A narrative approach was taken to describe the relevant literature, focusing on clinical applications of molecular image-guided surgery in gynaecology, preoperative imaging as surgical roadmap, and intraoperative devices.

RESULTS

The most common clinical application in gynaecology is sentinel node biopsy (SNB). Other promising approaches are receptor-target modalities and occult lesion localisation. Preoperative SPECT/CT and PET/CT permit a roadmap for adequate surgical planning. Intraoperative detection modalities span from 1D probes to 2D portable cameras and 3D freehand imaging.

CONCLUSION

After successful application of radio-guided SNB and SPECT, innovation is leaning towards hybrid modalities, such as hybrid tracer and fusion of imaging approaches including SPECT/CT and PET/CT. Robotic surgery, as well as augmented reality and virtual reality techniques, is leading to application of these innovative technologies to the clinical setting, guiding surgeons towards a precise, personalised, and minimally invasive approach.

New EAU/ASCO guideline recommendations on sentinel node biopsy for penile cancer and remaining challenges from a nuclear medicine perspective

INTRODUCTION

The European Association of Urology (EAU) and the American Society of Clinical Oncology (ASCO) recently issued updated guidelines on penile cancer, emphasising dynamic sentinel node biopsy (DSNB) as the preferred method for surgical staging among patients with invasive penile tumours and no palpable inguinal lymphadenopathy. This paper outlines the rationale behind this new recommendation and describes remaining challenges, as well as strategies for promoting DSNB worldwide.

MAIN TEXT

DSNB offers high diagnostic accuracy with the lowest postoperative complications compared to open or minimally invasive inguinal lymph node dissection (ILND), prompting its preference in the new guidelines. Nevertheless, despite its advantages, there are challenges hampering the widespread adoption of DSNB. This includes the false-negative rate associated with DSNB and the potential negative impact on patient outcome. To address this issue, improvements should be made in several areas, including refining the timing and interpretation of the lymphoscintigraphy and the single photon emission computed tomography/computed tomography images. In addition, the quantity of tracer employed and choice of the injection site for the radiopharmaceutical should be optimised. Finally, limiting the removal of nodes without tracer activity during surgery may help minimise complication rates.

CONCLUSION

Over the years, DSNB has evolved significantly, related to the dedicated efforts and innovations in nuclear medicine and subsequent clinical studies validating its efficacy. It is now strongly recommended for surgical staging among selected penile cancer patients. To optimise DSNB further, multidisciplinary collaborative research is required to improve SN identification for better diagnostic accuracy and fewer complications.

The Rise of Molecular Image-Guided Robotic Surgery

Following early acceptance by urologists, the use of surgical robotic platforms is rapidly spreading to other surgical fields. This empowerment of surgical perception via robotic advances occurs in parallel to developments in intraoperative molecular imaging. Convergence of these efforts creates a logical incentive to advance the decades-old image-guided robotics paradigm. This yields new radioguided surgery strategies set to optimally exploit the symbiosis between the growing clinical translation of robotics and molecular imaging. These strategies intend to advance surgical precision by increasing dexterity and optimizing surgical decision-making. In this state-of-the-art review, topic-related developments in chemistry (tracer development) and engineering (medical device development) are discussed, and future scientific robotic growth markets for molecular imaging are presented.

Near-infrared fluorescence lymph node template region dissection plus backup lymphadenectomy in open radical cystectomy for bladder cancer using an innovative handheld device: A single center experience

BACKGROUND

The extent of pelvic lymphadenectomy (PLND) as part of radical cystectomy (RC) for bladder cancer (BC) remains unclear. Sentinel-based and lymphangiographic approaches could lead to reduced morbidity without sacrificing oncologic safety.

OBJECTIVE

To evaluate the feasibility and diagnostic value of fluorescence-guided template sentinel region dissection (FTD) using a handheld near-infrared fluorescence (NIRF) camera in open radical cystectomy.

DESIGN, SETTING, AND PARTICIPANTS

After peritumoral cystoscopic injection of indocyanine green (ICG) 21 patients underwent open RC with FTD due to BC between June 2019 and June 2021. Intraoperatively, the FIS-00 Hamamatsu Photonics® NIRF camera was used to identify and resect fluorescent template sentinel regions (FTRs) followed by extended pelvic lymphadenectomy (ePLND) as oncological back-up.

OUTCOME MEASUREMENT AND STATISTICAL ANALYSIS

Descriptive analysis of positive and negative results per template region.

RESULTS AND LIMITATIONS

FTRs were identified in all 21 cases. Median time (range) from ICG injection to fluorescence detection was 75 (55-125) minutes. On average (SD), 33.4 (9.6) lymph nodes were dissected per patient. Considering template regions as the basis of analysis, 67 (38.3%) of 175 resected regions were NIRF-positive, with 13 (7.4%) regions harboring lymph node metastases. We found no metastatic lymph nodes in NIRF-negative template regions. Outside the standard template, two NIRF-positive benign nodes were identified.

CONCLUSION

The concept of NIRF-guided FTD proved for this group all lymph node metastases to be found in NIRF-positive template regions. Pending validation in a larger collective, resection of approximately 40% of standard regions may be sufficient and may result in less morbidity.

Innovations in dedicated PET instrumentation: from the operating room to specimen imaging

This review casts a spotlight on intraoperative positron emission tomography (PET) scanners and the distinctive challenges they confront. Specifically, these systems contend with the necessity of partial coverage geometry, essential for ensuring adequate access to the patient. This inherently leans them towards limited-angle PET imaging, bringing along its array of reconstruction and geometrical sensitivity challenges. Compounding this, the need for real-time imaging in navigation systems mandates rapid acquisition and reconstruction times. For these systems, the emphasis is on dependable PET image reconstruction (without significant artefacts) while rapid processing takes precedence over the spatial resolution of the system. In contrast, specimen PET imagers are unburdened by the geometrical sensitivity challenges, thanks to their ability to leverage full coverage PET imaging geometries. For these devices, the focus shifts: high spatial resolution imaging takes precedence over rapid image reconstruction. This review concurrently probes into the technical complexities of both intraoperative and specimen PET imaging, shedding light on their recent designs, inherent challenges, and technological advancements.

The realization of medical devices for precision surgery - development and implementation of 'stop-and-go' imaging technologies

INTRODUCTION

Surgery and biomedical imaging encompass a big share of the medical-device market. The ever-mounting demand for precision surgery has driven the integration of these two into the field of image-guided surgery. A key-question herein is how imaging modalities can guide the surgical decision-making process. Through performance-based design, chemists, engineers, and doctors need to build a bridge between imaging technologies and surgical challenges.

AREAS-COVERED

This perspective article highlights the complementary nature between the technological design of an image-guidance modality and the type of procedure performed. The specific roles of the involved professionals, imaging technologies, and surgical indications are addressed.

EXPERT-OPINION

Molecular-image-guided surgery has the potential to advance pre-, intra- and post-operative tissue characterization. To achieve this, surgeons need the access to well-designed indication-specific chemical-agents and detection modalities. Hereby, some technologies stimulate exploration ('go'), while others stimulate caution ('stop'). However, failing to adequately address the indication-specific needs rises the risk of incorrect tool employment and sub-optimal surgical performance. Therefore, besides the availability of new technologies, market growth is highly dependent on the practical nature and impact on real-life clinical care. While urology currently takes the lead in the widespread implementation of image-guidance technologies, the topic is generic and its popularity spreads rapidly within surgical oncology.

Continuous innovation in precision radio-guided surgery

Since its origins, nuclear medicine has faced technological changes that led to modifying operating modes and adapting protocols. In the field of radioguided surgery, the incorporation of preoperative scintigraphic imaging and intraoperative detection with the gamma probe provided a definitive boost to sentinel lymph node biopsy to become a standard procedure for melanoma and breast cancer. The various technological innovations and consequent adaptation of protocols come together in the coexistence of the disruptive and the gradual. As obvious examples we have the introduction of SPECT/CT in the preoperative field and Drop-in probes in the intraoperative field. Other innovative aspects with possible application in radio-guided surgery are based on the application of artificial intelligence, navigation and telecare.

Clinical practice consensus for the diagnosis and management of melanoma in Taiwan

Melanoma is rare in Taiwan. Asian melanoma is distinct from Western melanoma because acral and mucosal melanoma accounts for the majority of melanoma cases, leading to distinct tumor behaviors and genetic profiling. With consideration of the clinical guidelines in Western countries, Taiwanese experts developed a local clinical practice consensus guideline. This consensus includes diagnosis, staging, and surgical and systemic treatment, based only on clinical evidence, local epidemiology, and available resources evaluated by experts in Taiwan. This consensus emphasizes the importance of surgical management, particularly for sentinel lymph node biopsies. In addition, molecular testing for BRAF is mandatory for patients before systemic treatment. Furthermore, immunotherapy and targeted therapy are prioritized for systemic treatment. This consensus aimed to assist clinicians in Taiwan in diagnosing and treating patients according to available evidence.

Dual-radionuclide in vivo imaging of micro-metastasis and lymph tract with submillimetre resolution

Multi-radionuclide in vivo imaging with submillimetre resolution can be a potent tool for biomedical research. While high-resolution radionuclide imaging faces challenges in sensitivity, multi-radionuclide imaging encounters difficulty due to radiation contamination, stemming from crosstalk between radionuclides and Compton scattering. Addressing these challenges simultaneously is imperative for multi-radionuclide high-resolution imaging. To tackle this, we developed a high-spatial-resolution and high-energy-resolution small animal single-photon emission computed tomography (SPECT) scanner, named CdTe-DSD SPECT-I. We first assessed the feasibility of multi-tracer SPECT imaging of submillimetre targets. Using the CdTe-DSD SPECT-I, we performed SPECT imaging of submillimetre zeolite spheres absorbed with 125I- and subsequently imaged 125I-accumulated spheroids of 200-400 µm in size within an hour, achieving clear and quantitative images. Furthermore, dual-radionuclide phantom imaging revealed a distinct image of the submillimetre sphere absorbed with 125I- immersed in a 99mTc-pertechnetate solution, and provided a fair quantification of each radionuclide. Lastly, in vivo imaging was conducted on a cancer-bearing mouse with lymph node micro-metastasis using dual-tracers. The results displayed dual-tracer images of lymph tract by 99mTc-phytic acid and the submillimetre metastatic lesion by 125I-, shown to align with the immunofluorescence image.

Role of Nuclear Sentinel Lymph Node Mapping Compared to New Alternative Imaging Methods

With the emergence of sentinel node technology, many patients can be staged histopathologically using lymphatic mapping and selective lymphadenectomy. Structural imaging by using US, CT and MR permits precise measurement of lymph node volume, which is strongly associated with neoplastic involvement. Sentinel lymph node detection has been an ideal field of application for nuclear medicine because anatomical data fails to represent the close connections between the lymphatic system and regional lymph nodes, or, more specifically, to identify the first draining lymph node. Hybrid imaging has demonstrated higher accuracy than standard imaging in SLN visualization on images, but it did not change in terms of surgical detection. New alternatives without ionizing radiations are emerging now from "non-radiological" fields, such as ophthalmology and dermatology, where fluorescence or opto-acoustic imaging, for example, are widely used. In this paper, we will analyze the advantages and limits of the main innovative methods in sentinel lymph node detection, including innovations in lymphoscintigraphy techniques that persist as the gold standard to date.

Radioguided Occult Lesion Localization for Gynecologic Tumor Relapses: Development of a Technique

PURPOSE OF THE REPORT

Excision of peritoneal or nodal isolated recurrences frequently involves performing a surgery on a previously operated area, which is more difficult to achieve with minimally invasive approaches. Our aim was to describe the technical aspects, feasibility, and complications derived from the application of the radioguided occult lesions localization (ROLL) in gynecologic oncology recurrence excision.

PATIENTS AND METHODS

All consecutive patients bearing localized relapses of a gynecologic tumor that were considered candidates for surgical excision were assessed to undergo a ROLL procedure. Radiotracer (99mTc-albumin macroaggregate) injection of the lesions was performed by ultrasonography or CT guidance. Relapses were localized using a gamma probe by minimally invasive surgery when located in the abdomen, or percutaneously when located in the groin. Intraoperative and early (up to postoperative day 30) complications were prospectively recorded.

RESULTS

A total of 8 patients underwent the procedure. The median age was 59 years (range, 35-87 years). Four patients had abdominal relapses, whereas 4 patients presented groin relapses. The mean operative time was 120 minutes (range, 30-190 minutes), whereas the median estimated blood loss was 5 mL (range, 0-150 mL). All the targeted lesions were successfully removed. No intraoperative complications were reported. One postoperative complication (inguinal lymphocele) was recorded.

CONCLUSIONS

ROLL surgery constitutes a new approach for isolated recurrences in gynecological tumors.

A Drop-in Gamma Probe for Minimally Invasive Sentinel Lymph Node Dissection in Prostate Cancer: Preclinical Evaluation and Interim Results From a Multicenter Clinical Trial

PURPOSE

This study evaluated the performance of a drop-in gamma probe for prostate cancer (PCa) sentinel lymph node dissection (SLND) in a pelvic phantom, porcine model, and in PCa patients as part of an ongoing prospective multicenter clinical trial.

METHODS

Two design variants of the drop-in gamma probe (SENSEI; Lightpoint Medical Ltd) were assessed in the pelvic phantom, and the preferred design was evaluated in a porcine model with clinically representative volumes and 99mTc activities. In the clinical trial, radical prostatectomy, SLND, and extended pelvic lymph node dissection were performed the day after 99mTc-nanocolloid injection and imaging. Sentinel lymph nodes (SLNs) were detected with the drop-in probe and a rigid laparoscopic gamma probe (RLGP). An interim analysis was performed after 10 patients were recruited.

RESULTS

The narrow field of view probe design outperformed the wide field of view design in the pelvic phantom (detection rate, 100% vs 50%). In the porcine model, all activity concentrations could be successfully detected. The drop-in gamma probe successfully detected SLNs in all 10 patients (detection rate, 100%). Two of the SLNs identified by the drop-in gamma probe could not be found with the RLGP. No false-negative cases and no adverse events related to the SLND procedure or the drop-in gamma probe occurred.

CONCLUSION

The drop-in gamma probe meets the usability and performance requirements for SLND in PCa and provides performance advantages over the RLGP. The final clinical study results will confirm the performance of the technique across multiple sites.

Development of scalable lymphatic system in the 4D XCAT phantom: Application to quantitative evaluation of lymphoma PET segmentations

BACKGROUND

Digital anthropomorphic phantoms, such as the 4D extended cardiac-torso (XCAT) phantom, are actively used to develop, optimize, and evaluate a variety of imaging applications, allowing for realistic patient modeling and knowledge of ground truth. The XCAT phantom defines the activity and attenuation for a simulated patient, which includes a complete set of organs, muscle, bone, and soft tissue, while also accounting for cardiac and respiratory motion. However, the XCAT phantom does not currently include the lymphatic system, critical for evaluating medical imaging tasks such as sentinel node detection, node density measurement, and radiation dosimetry.

PURPOSE

In this study, we aimed to develop a scalable lymphatic system in the XCAT phantom, to facilitate improved research of the lymphatic system in medical imaging. Using this scalable lymphatic system, we modeled the lymph node conglomerate pathology that is characteristically observed in primary mediastinal B-cell lymphoma (PMBCL). As an extended application, we evaluated positron emission tomography (PET) image quantification of metabolic tumor volume (MTV) and total lesion glycolysis (TLG) of these simulated lymphomas, though the phantoms may be applied to other imaging modalities and study design paradigms (e.g., image quality, detection).

METHODS

A template model for the lymphatic system was developed based on anatomical data from the Visible Human Project of the National Library of Medicine. The segmented nodes and vessels were fit with non-uniform rational basis spline surfaces, and multichannel large deformation diffeomorphic metric mapping was used to propagate the template to different XCAT anatomies. To model conglomerates observed in PMBCL, lymph nodes were enlarged, converged within the mediastinum, and tracer concentration was increased. We used the phantoms as inputs to a PET simulation tool, which generated images using ordered subsets expectation maximization reconstruction with 2-8 mm Gaussian filters. Fixed thresholding (FT) and gradient segmentation were used to determine MTV and TLG. Percent bias (%Bias) and coefficient of variation (COV) were computed as measures of accuracy and precision, respectively, for each MTV and TLG measurement.

RESULTS

Using the methodology described above, we introduced a scalable lymphatic system in the XCAT phantom, which allows for the radioactivity and attenuation ground truth to be generated in 116 ± 2.5 s using a 2.3 GHz processor. Within the Rhinoceros interface, lymph node anatomy and function were modified to create a cohort of 10 phantoms with lymph node conglomerates. Using the lymphoma phantoms to evaluate PET quantification of MTV, mean %Bias values were -9.3%, -41.3%, and 20.9%, while COV values were 4.08%, 7.6%, and 3.4% using 25% FT, 40% FT, and gradient segmentations, respectively. Comparatively for TLG, mean %Bias values were -27.4%, -45.8%, and -16.0%, while COV values were 1.9%, 5.7%, and 1.4%, for the 25% FT, 40% FT, and gradient segmentations, respectively.

CONCLUSIONS

In this work, we upgraded the XCAT phantom to include a lymphatic system, comprised of a network of 276 scalable lymph nodes and corresponding vessels. As an application, we created a cohort of phantoms with lymph node conglomerates to evaluate lymphoma quantification in PET imaging, which highlights an important application of this work.

Value-assessment of computer-assisted navigation strategies during percutaneous needle placement

Purpose

Navigational strategies create a scenario whereby percutaneous needle-based interventions of the liver can be guided using both pre-interventional 3D imaging datasets and dynamic interventional ultrasound (US). To score how such technologies impact the needle placement process, we performed kinematic analysis on different user groups.

Methods

Using a custom biopsy phantom, three consecutive exercises were performed by both novices and experts (n = 26). The exercise came in three options: (1) US-guidance, (2) US-guidance with pre-interventional image-registration (US + Reg) and (3) US-guidance with pre-interventional image-registration and needle-navigation (US + Reg + Nav). The traveled paths of the needle were digitized in 3D. Using custom software algorithms, kinematic metrics were extracted and related to dexterity, decision making indices to obtain overall performance scores (PS).

Results

Kinematic analysis helped quantifying the visual assessment of the needle trajectories. Compared to US-guidance, novices yielded most improvements using Reg (PSavg(US) = 0.43 vs. PSavg(US+Reg) = 0.57 vs. PSavg(US+Reg+Nav) = 0.51). Interestingly, the expert group yielded a reversed trend (PSavg(US) = 0.71 vs PSavg(US+Reg) = 0.58 vs PSavg(US+Reg+Nav) = 0.59).

Conclusion

Digitizing the movement trajectory allowed us to objectively assess the impact of needle-navigation strategies on percutaneous procedures. In particular, our findings suggest that these advanced technologies have a positive impact on the kinematics derived performance of novices.

Current use and potential role of radioguided surgery in brain tumours

Purpose

The aim of this mini-review is to discuss the possible role of radioguided surgery in brain tumours and, in particular, in gliomas.

Methods

A research in the PubMed/Medline database was carried out to identify relevant studies evaluating radioguided surgery in brain tumours.

Results

Radioguided surgery results using gamma (γ)-emitting tracers and γ-detection probes were summarised. Most importantly, the review included preliminary findings with novel approaches, particularly those relying on the use of beta (β)−emitting isotopes and a dedicated β probe.

Conclusion

Although few data are available in the current literature, the use of β probes could be useful to accurately identify surgical margins in brain tumours. Nevertheless, further in vivo studies are required.

Interventional nuclear medicine's contribution to molecularly targeted precision surgery

The surgical approach to different pathologies, not only oncological, has evolved. As Veronesi's group has coined very graphically, we are moving from "maximum tolerable treatments to minimum effective treatments" and this journey cannot be carried out in any other way than through a multidisciplinary and multimodality approach. Multidisciplinary, because collaboration between surgeons, oncologists, radiologists, nuclear physicians, pathologists, and all those involved in patient follow-up is necessary, and multimodality, because we must move towards precision surgery tailored to each patient in which, on the part of Nuclear Medicine, hybrid imaging (SPECT/CT and PET/CT), bimodal tracers, the use of new allies such as ultrasound or our own adaptation to robotic surgery have a great deal to say. A wide range of possibilities is built on the solid foundation of preoperative scintigraphy, which makes it possible to identify the target tissues and whose knowledge prior to surgery allows the necessary surgical approach to be considered for each patient.

The Importance of SPECT/CT in Preoperative Localization of Sentinel Lymph Nodes in 2 Patients With Acral Melanoma in the Foot

ABSTRACT

A 68-year-old woman with melanoma in the left heel underwent sentinel node lymphoscintigraphy and radioguided biopsy. The sentinel node lymphoscintigraphy with SPECT/CT detected 3 foci of increased activity in the popliteal fossa and inguinal region. When coregistered to CT, the sentinel node was localized in the inguinal region, and the popliteal foci were considered tracer retention in lymphatic vessel. In another patient with melanoma in the foot, sentinel node lymphoscintigraphy detected 3 foci of increased activity in the popliteal fossa and inguinal region, which were all identified to be nodal uptake in SPECT/CT. The sentinel node was finally localized in popliteal fossa in this patient.

Sentinel Lymph Node Biopsy in Prostate Cancer Using the SENSEI® Drop-In Gamma Probe

ABSTRACT

Minimally invasive surgery in the form of laparoscopic and robot-assisted procedures has been widely adopted in the field of prostate cancer. When performing minimally invasive radioguided surgery, conventional rigid laparoscopic gamma probes have limited maneuverability and control due to their form factor, which may hinder detection of radiotracer-avid lesions in anatomically challenging areas. A drop-in gamma probe has been developed to address these limitations. Our group report on the first clinical use of this probe (SENSEI®) as part of an ongoing prospective, international, multicenter clinical trial in primary prostate cancer patients undergoing 99mTc-nanocolloid sentinel lymph node biopsy.

A novel targeted multifunctional nanoplatform for visual chemo-hyperthermia synergy therapy on metastatic lymph nodes via lymphatic delivery

Background

Distant metastasis to vital organs is the major contributor to breast cancer mortality, and regional lymph node metastasis is an important facilitator of distant metastasis and recurrence in this cancer. The early diagnosis and precise treatment of lymph node metastasis are crucial for staging and prognosis in breast cancer. Herein, we report a visualized precision medicine nanoplatform of metastatic lymph nodes for ultrasonic/photoacoustic (US/PA) dual modal imaging-guided in situ targeted hyperthermia-combined chemotherapy.

Results

Carbon nanoparticles (CNs), approved by the China Food and Drug Administration, were loaded with docetaxel and rationally combined with anti-hypoxia-inducible factor 1α antibody-modified poly (lactic-co-glycolic acid) (PLGA) nanoparticles to achieve the combination of passive targeting at the lymph nodes and intracellular targeting at HIF 1α factor. The accumulation and retention of nanoparticles in metastatic lymph nodes via lymphatic delivery were enhanced. Docetaxel could be effectively offloaded by CNs that have active carbon nanoparticles, and the PLGA membrane prevented drug leakage. The nanoparticles exhibited excellent photothermal performance with a photothermal conversion efficiency of 28.9%, killing tumor cells in metastatic lymph nodes through hyperthermia. In vitro and in vivo systematic evaluations revealed that hyperpyrexia triggered the rupture of nanoparticles caused by the phase transition of perfluorohexane, resulting in docetaxel release for achieving in situ hyperthermia-combined chemotherapy.

Conclusions

The laser-triggered highly efficient in situ chemotherapy nanosystem achieves targeted synergistic chemo-hyperthermia treatment of metastatic lymph nodes, and lymphatic delivery represents a strategy to avoid additional injury caused by drugs entering the blood circulation.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-01186-8.

Early Institutional Experience of Dual Tracer and Single-Photon Emission Computed-Tomography/Computed-Tomography Mapping for Sentinel Node Biopsy: A Report of Two Early-Stage Breast Cancer

Intraoperative sentinel lymph node mapping (SLNM) with methylene blue dye (MBD) tracer has been the recommended method to detect SLN in early-stage breast cancer patients in low-resource settings. However, the use of MBD alone is hampered by the high false-negative rate; thus, it requires coupling with other mapping methods if the appropriate infrastructure and services are available. In this article, we present two prospective cases detailing our initial experience using the gold-standard dual tracer technique (DTT: MBD and 99mTc-nanocolloid radioisotope) in combination with hybrid single-photon emission computed-tomography/computed-tomography (SPECT/CT) preoperative mapping for image-guided SLN biopsy (SLNB). Overall, both studies were successful in identifying the SLNs, which aided in mapping the possible anatomical spread of the disease.

Physiological models for in vivo imaging and targeting the lymphatic system: Nanoparticles and extracellular vesicles

Imaging of the lymphatic vasculature has gained great attention in various fields, not only because lymphatic vessels act as a key draining system in the body, but also for their implication in autoimmune diseases, organ transplant, inflammation and cancer. Thus, neolymphangiogenesis, or the generation of new lymphatics, is typically an early event in the development of multiple tumor types, particularly in aggressive ones such as malignant melanoma. Still, the understanding of how lymphatic endothelial cells get activated at distal (pre)metastatic niches and their impact on therapy is still unclear. Addressing these questions is of particular interest in the case of immune modulators, because endothelial cells may favor or halt inflammatory processes depending on the cellular context. Therefore, there is great interest in visualizing the lymphatic vasculature in vivo. Here, we review imaging tools and mouse models used to analyze the lymphatic vasculature during tumor progression. We also discuss therapeutic approaches based on nanomedicines to target the lymphatic system and the potential use of extracellular vesicles to track and target sentinel lymph nodes. Finally, we summarize main pre-clinical models developed to visualize the lymphatic vasculature in vivo, discussing their applications with a particular focus in metastatic melanoma.

PET- and SPECT-based navigation strategies to advance procedural accuracy in interventional radiology and image-guided surgery

INTRODUCTION

Nuclear medicine has a crucial role in interventional strategies where a combination between the increasing use of targeted radiotracers and intraprocedural detection modalities enable novel, but often complex, targeted procedures in both the fields of interventional radiology and surgery. 3D navigation approaches could assist the interventional radiologist or surgeon in such complex procedures.

EVIDENCE ACQUISITION

This review aimed to provide a comprehensive overview of the current application of computer-assisted navigation strategies based on nuclear imaging to assist in interventional radiology and image-guided surgery. This work starts with a brief overview of the typical navigation workflow from a technical perspective, which is followed by the different clinical applications organized based on their anatomical organ of interest.

EVIDENCE SYNTHESIS

Although many studies have proven the feasibility of PET- and SPECT-based navigation strategies for various clinical applications in both interventional radiology and surgery, the strategies are spread widely in both navigation workflows and clinical indications, evaluated in small patient groups. Hence, no golden standard has yet been established.

CONCLUSIONS

Despite that the clinical outcome is yet to be determined in large patient cohorts, navigation seems to be a promising technology to translate nuclear medicine findings, provided by PET- and SPECT-based molecular imaging, to the intervention and operating room. Interventional Nuclear Medicine (iNM) has an exciting future to come using both PET- and SPECT-based navigation.

Contemporary update of SPECT tracers and novelties in radioguided surgery: a perspective based on urology

Recent technical advances and implementation of novel radiotracers have further increased the potential of radioguided surgery for a broad variety of malignancies. Indeed, the possibilities for future applications of novel radiotracers in diverse oncological strategies has become more promising than ever. This literature review aims to provide a contemporary update on a selected group of radiotracers and evaluates the usability of radioguided surgery and sentinel node procedures, focusing on most promising advances. For example, the impact of targeted radiotracers on prostate specific membrane antigen (PSMA), CD206 receptor-targeted agents (^99mTc-tilmanocept), and hybrid tracers adding fluorescence to radioguidance (ICG-^99mTc-nanocolloid) as well as targeting hypoxia-induced carbonic anhydrase IX (CAIX) will be covered. Furthermore, future outlooks on the implementation of gold nanoparticles (AuNP's), but also technical advances in improved radiotracer detection by hybrid gamma devices will be discussed.