Surgical Guidance in Prostate Cancer: “From Molecule to Man” Translations

Delphi consensus project on prostate-specific membrane antigen (PSMA)-targeted surgery-outcomes from an international multidisciplinary panel

PURPOSE

Prostate-specific membrane antigen (PSMA) is increasingly considered as a molecular target to achieve precision surgery for prostate cancer. A Delphi consensus was conducted to explore expert views in this emerging field and to identify knowledge and evidence gaps as well as unmet research needs that may help change practice and improve oncological outcomes for patients.

METHODS

One hundred and five statements (scored by a 9-point Likert scale) were distributed through SurveyMonkey®. Following evaluation, a consecutive second round was performed to evaluate consensus (16 statements; 89% response rate). Consensus was defined using the disagreement index, assessed by the research and development project/University of California, Los Angeles appropriateness method.

RESULTS

Eighty-six panel participants (72.1% clinician, 8.1% industry, 15.1% scientists, and 4.7% other) participated, most with a urological background (57.0%), followed by nuclear medicine (22.1%). Consensus was obtained on the following: (1) The diagnostic PSMA-ligand PET/CT should ideally be taken < 1 month before surgery, 1-3 months is acceptable; (2) a 16-20-h interval between injection of the tracer and surgery seems to be preferred; (3) PSMA targeting is most valuable for identification of nodal metastases; (4) gamma, fluorescence, and hybrid imaging are the preferred guidance technologies; and (5) randomized controlled clinical trials are required to define oncological value. Regarding surgical margin assessment, the view on the value of PSMA-targeted surgery was neutral or inconclusive. A high rate of "cannot answer" responses indicates further study is necessary to address knowledge gaps (e.g., Cerenkov or beta-emissions).

CONCLUSIONS

This Delphi consensus provides guidance for clinicians and researchers that implement or develop PSMA-targeted surgery technologies. Ultimately, however, the consensus should be backed by randomized clinical trial data before it may be implemented within the guidelines.

Feasibility of fluorescence imaging at microdosing using a hybrid PSMA tracer during robot-assisted radical prostatectomy in a large animal model

Background

With the rise of prostate-specific membrane antigen (PSMA) radioguided surgery, which is performed using a microdosing regime, demand for visual target confirmation via fluorescence guidance is growing. While proven very effective for radiotracers, microdosing approaches the detection limit for fluorescence imaging. Thus, utility will be highly dependent on the tracer performance, the sensitivity of the fluorescence camera used, and the degree of background signal. Using a porcine model the ability to perform robot-assisted radical prostatectomy under fluorescence guidance using the bimodal or rather hybrid PSMA tracer (^99mTc-EuK-(SO₃)Cy5-mas₃) was studied, while employing the tracer in a microdosing regime. This was followed by ex vivo evaluation in surgical specimens obtained from prostate cancer patients.

Results

T_{50% blood} and T_{50% urine} were reached at 85 min and 390 min, in, respectively, blood and urine. Surgical fluorescence imaging allowed visualization of the prostate gland based on the basal PSMA-expression in porcine prostate. Together, in vivo visualization of the prostate and urinary excretion suggests at least an interval of > 7 h between tracer administration and surgery. Confocal microscopy of excised tissues confirmed tracer uptake in kidney and prostate, which was confirmed with PSMA IHC. No fluorescence was detected in other excised tissues. Tumor identification based on ex vivo fluorescence imaging of human prostate cancer specimens correlated with PSMA IHC.

Conclusion

Intraoperative PSMA-mediated fluorescence imaging with a microdosing approach was shown to be feasible. Furthermore, EuK‐(SO₃)Cy5‐mas₃ allowed tumor identification in human prostate samples, underlining the translational potential of this novel tracer.

Trial registration Approval for use of biological material for research purposes was provided by the Translational Research Board of the Netherlands Cancer Institute-Antoni van Leeuwenhoek hospital (NKI-AvL) under reference IRBm19-273 (22/10/2019).

Towards Complete Tumor Resection: Novel Dual-Modality Probes for Improved Image-Guided Surgery of GRPR-Expressing Prostate Cancer

Nuclear and optical dual-modality probes can be of great assistance in prostate cancer localization, providing the means for both preoperative nuclear imaging and intraoperative surgical guidance. We developed a series of probes based on the backbone of the established GRPR-targeting radiotracer NeoB. The inverse electron demand of the Diels–Alder reaction was used to integrate the sulfo-cyanine 5 dye. Indium-111 radiolabeling, stability studies and a competition binding assay were carried out. Pilot biodistribution and imaging studies were performed in PC-3 tumor-bearing mice, using the best two dual-labeled probes. The dual-modality probes were radiolabeled with a high yield (>92%), were proven to be hydrophilic and demonstrated high stability in mouse serum (>94% intact labeled ligand at 4 h). The binding affinity for the GRPR was in the nanomolar range (21.9–118.7 nM). SPECT/CT images at 2 h p.i. clearly visualized the tumor xenograft and biodistribution studies, after scanning confirmed the high tumor uptake (8.47 ± 0.46%ID/g and 6.90 ± 0.81%ID/g for probe [111In]In-12 and [111In]In-15, respectively). Receptor specificity was illustrated with blocking studies, and co-localization of the radioactive and fluorescent signal was verified by ex vivo fluorescent imaging. Although optimal tumor-to-blood and tumor-to-kidney ratios might not yet have been reached due to the prolonged blood circulation, our probes are promising candidates for the preoperative and intraoperative visualization of GRPR-positive prostate cancer.

Radiolabeled PSMA Inhibitors

PSMA has shown to be a promising target for diagnosis and therapy (theranostics) of prostate cancer. We have reviewed developments in the field of radio- and fluorescence-guided surgery and targeted photodynamic therapy as well as multitargeting PSMA inhibitors also addressing albumin, GRPr and integrin αvβ3. An overview of the regulatory status of PSMA-targeting radiopharmaceuticals in the USA and Europe is also provided. Technical and quality aspects of PSMA-targeting radiopharmaceuticals are described and new emerging radiolabeling strategies are discussed. Furthermore, insights are given into the production, application and potential of alternatives beyond the commonly used radionuclides for radiolabeling PSMA inhibitors. An additional refinement of radiopharmaceuticals is required in order to further improve dose-limiting factors, such as nephrotoxicity and salivary gland uptake during endoradiotherapy. The improvement of patient treatment achieved by the advantageous combination of radionuclide therapy with alternative therapies is also a special focus of this review.

Synthesis and in vitro preliminary evaluation of prostate-specific membrane antigen targeted upconversion nanoparticles as a first step towards radio/fluorescence-guided surgery of prostate cancer

Over the last decade, upconversion nanoparticles (UCNP) have been widely investigated in nanomedicine due to their high potential as imaging agents in the near-infrared (NIR) optical window of biological tissues. Here, we successfully develop active targeted UCNP as potential probes for dual NIR-NIR fluorescence and radioactive-guided surgery of prostate-specific membrane antigen (PSMA)(+) prostate cancers. We designed a one-pot thermolysis synthesis method to obtain oleic acid-coated spherical NaYF4:Yb,Tm@NaYF4 core/shell UCNP with narrow particle size distribution (30.0 ± 0.1 nm, as estimated by SAXS analysis) and efficient upconversion luminescence. Polyethylene glycol (PEG) ligands bearing different anchoring groups (phosphate, bis- and tetra-phosphonate-based) were synthesized and used to hydrophilize the UCNP. DLS studies led to the selection of a tetra-phosphonate PEG(2000) ligand affording water-dispersible UCNP with sustained colloidal stability in several aqueous media. PSMA-targeting ligands (i.e., glutamate-urea-lysine derivatives called KuEs) and fluorescent or radiolabelled prosthetic groups were grafted onto the UCNP surface by strain-promoted azide-alkyne cycloaddition (SPAAC). These UCNP, coated with 10 or 100% surface density of KuE ligands, did not induce cytotoxicity over 24 h incubation in LNCaP-Luc or PC3-Luc prostate cancer cell lines or in human fibroblasts for any of the concentrations evaluated. Competitive binding assays and flow cytometry demonstrated the excellent affinity of UCNP@KuE for PSMA-positive LNCaP-Luc cells compared with non-targeted UCNP@CO2H. Furthermore, the binding of UCNP@KuE to prostate tumour cells was positively correlated with the surface density of PSMA-targeting ligands and maintained after 125I-radiolabelling. Finally, a preliminary biodistribution study in LNCaP-Luc-bearing mice demonstrated the radiochemical stability of non-targeted [125I]UCNP paving the way for future in vivo assessments.

The role of fluorescent and hybrid tracers in radioguided surgery in urogenital malignancies

The increasing availability of new imaging technologies and tracers has enhanced the application of nuclear molecular imaging in urogenital interventions. In this context, preoperative nuclear imaging and radioactivity-based intraoperative surgical guidance have become important tools for the identification and anatomical allocation of tumor lesions and/or suspected lymph nodes. Fluorescence guidance can provide visual identification of the preoperatively defined lesions during surgery. However, the added value of fluorescence guidance is still mostly unknown. This review provides an overview of the role of fluorescence imaging in radioguided surgery in urogenital malignancies. The sentinel node (SN) biopsy procedure using hybrid tracers (radioactive and fluorescent component) serves as a prominent example for in-depth evaluation of the complementary value of radio- and fluorescence guidance. The first large patient cohort and long-term follow-up studies show: 1) improvement in the SN identification rate compared to blue dye; 2) improved detection of cancer-positive SNs; and 3) hints towards a positive effect on (biochemical) recurrence rates compared to extended lymph node dissection. The hybrid tracer approach also highlights the necessity of a preoperative roadmap in preventing incomplete resection. Recent developments focus on receptor-targeted approaches that allow intraoperative identification of tumor tissue. Here radioguidance is still leading, but fluorescent and hybrid tracers are also finding their way into the clinic. Emerging multiwavelength approaches that allow concomitant visualization of different anatomical features within the surgical field may provide the next step towards even more refined procedures.

A DROP-IN beta probe for robot-assisted 68Ga-PSMA radioguided surgery: first ex vivo technology evaluation using prostate cancer specimens

BACKGROUND

Recently, a flexible DROP-IN gamma-probe was introduced for robot-assisted radioguided surgery, using traditional low-energy SPECT-isotopes. In parallel, a novel approach to achieve sensitive radioguidance using beta-emitting PET isotopes has been proposed. Integration of these two concepts would allow to exploit the use of PET tracers during robot-assisted tumor-receptor-targeted. In this study, we have engineered and validated the performance of a novel DROP-IN beta particle (DROP-INβ) detector.

METHODS

Seven prostate cancer patients with PSMA-PET positive tumors received an additional intraoperative injection of ~ 70 MBq 68Ga-PSMA-11, followed by robot-assisted prostatectomy and extended pelvic lymph node dissection. The surgical specimens from these procedures were used to validate the performance of our DROP-INβ probe prototype, which merged a scintillating detector with a housing optimized for a 12-mm trocar and prograsp instruments.

RESULTS

After optimization of the detector and probe housing via Monte Carlo simulations, the resulting DROP-INβ probe prototype was tested in a robotic setting. In the ex vivo setting, the probe-positioned by the robot-was able to identify 68Ga-PSMA-11 containing hot-spots in the surgical specimens: signal-to-background (S/B) was > 5 when pathology confirmed that the tumor was located < 1 mm below the specimen surface. 68Ga-PSMA-11 containing (and PET positive) lymph nodes, as found in two patients, were also confirmed with the DROP-INβ probe (S/B > 3). The rotational freedom of the DROP-IN design and the ability to manipulate the probe with the prograsp tool allowed the surgeon to perform autonomous beta-tracing.

CONCLUSIONS

This study demonstrates the feasibility of beta-radioguided surgery in a robotic context by means of a DROP-INβ detector. When translated to an in vivo setting in the future, this technique could provide a valuable tool in detecting tumor remnants on the prostate surface and in confirmation of PSMA-PET positive lymph nodes.

Image-Guided Surgery: Are We Getting the Most Out of Small-Molecule Prostate-Specific-Membrane-Antigen-Targeted Tracers?

Expressed on virtually all prostate cancers and their metastases, the transmembrane protein prostate-specific membrane antigen (PSMA) provides a valuable target for the imaging of prostate cancer. Not only does PSMA provide a target for noninvasive diagnostic imaging, e.g., PSMA-positron emission tomography (PSMA-PET), it can also be used to guide surgical resections of PSMA-positive lesions. The latter characteristic has led to the development of a plethora of PSMA-targeted tracers, i.e., radiolabeled, fluorescent, or hybrid. With image-guided surgery applications in mind, this review discusses these compounds based on clinical need. Here, the focus is on the chemical aspects (e.g., imaging label, spacer moiety, and targeting vector) and their impact on in vitro and in vivo tracer characteristics (e.g., affinity, tumor uptake, and clearance pattern).

Hybrid Tracers Based on Cyanine Backbones Targeting Prostate-Specific Membrane Antigen: Tuning Pharmacokinetic Properties and Exploring Dye-Protein Interaction

Prostate cancer surgery is currently being revolutionized by the use of prostate-specific membrane antigen (PSMA)-targeted radiotracers, for example, ^99mTc-labeled PSMA tracer analogs for radioguided surgery. The purpose of this study was to develop a second-generation ^99mTc-labeled PSMA-targeted tracer incorporating a fluorescent dye. Methods: Several PSMA-targeted hybrid tracers were synthesized: glutamic acid-urea-lysine (EuK)-Cy5-mas₃, EuK-(SO₃)Cy5-mas₃, EuK-Cy5(SO₃)-mas₃, EuK-(Ar)Cy5-mas₃, and EuK-Cy5(Ar)-mas₃; the Cy5 dye acts as a functional backbone between the EuK targeting vector and the 2-mercaptoacetyl-seryl-seryl-seryl (mas₃) chelate to study the dye's interaction with PSMA's amphipathic entrance funnel. The compounds were evaluated for their photophysical and chemical properties and PSMA affinity. After radiolabeling with ^99mTc, we performed in vivo SPECT imaging, biodistribution, and fluorescence imaging on BALB/c nude mice with orthotopically transplanted PC346C tumors. Results: The dye composition influenced the photophysical properties (brightness range 0.3-1.5 × 10⁴ M^-1 × cm^-1), plasma protein interactions (range 85.0% ± 2.3%-90.7% ± 1.3% bound to serum, range 76% ± 0%-89% ± 6% stability in serum), PSMA affinity (half-maximal inhibitory concentration [IC₅₀] range 19.2 ± 5.8-175.3 ± 61.1 nM) and in vivo characteristics (tumor-to-prostate and tumor-to-muscle ratios range 0.02 ± 0.00-154.73 ± 28.48 and 0.46 ± 0.28-5,157.50 ± 949.17, respectively; renal, splenic, and salivary retention). Even though all tracer analogs allowed tumor identification with SPECT and fluorescence imaging, ^99mTc-EuK-(SO₃)Cy5-mas₃ had the most promising properties (e.g., half-maximal inhibitory concentration, 19.2 ± 5.8, tumor-to-muscle ratio, 5,157.50 ± 949.17). Conclusion: Our findings demonstrate the intrinsic integration of a fluorophore in the pharmacophore in PSMA-targeted small-molecule tracers. In this design, having 1 sulfonate on the indole moiety adjacent to EuK (^99mTc-EuK-(SO₃)Cy5-mas₃) yielded the most promising tracer candidate for imaging of PSMA.

High-resolution imaging and single-cell analysis via laser ablation-inductively coupled plasma-mass spectrometry for the determination of membranous receptor expression levels in breast cancer cell lines using receptor-specific hybrid tracers

This work evaluates the possibility of placement of high-resolution imaging and single-cell analysis via laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) within precision medicine by assessing the suitability of LA-ICP-MS as a micro-analytical technique for the localization and quantification of membranous receptors in heterogeneous cell samples that express both the membrane-bound receptors C-X-C chemokine receptor type 4 (CXCR4) and epidermal growth factor receptor (EGFR). Staining of the breast cancer cell lines MDA-MB-231 X4 and MDA-MB-468 was achieved using receptor-specific hybrid tracers, containing both a fluorophore and a DTPA single-lanthanide chelate. Prior to LA-ICP-MS imaging, fluorescence confocal microscopy (FCM) imaging was performed to localize the receptors, hereby enabling direct comparison. Based on the different expression levels of CXCR4 and EGFR, a distinction could be made between the cell lines using both imaging modalities. Furthermore, FCM and LA-ICP-MS demonstrated complementary characteristics, as a more distinct discrimination could be made between both cell lines based on the EGFR-targeting hybrid tracer via LA-ICP-MS, due to the intrinsic CXCR4-related green fluorescent protein (GFP) signal present in the MDA-MB-231 X4 cells. Employing state-of-the-art LA-ICP-MS instrumentation in bidirectional area scanning mode for sub-cellular imaging of MDA-MB-231 X4 cells enabled the specific binding of the CXCR4-targeting hybrid tracer to the cell membrane to be clearly demonstrated. The stretching of cells over the glass substrate led to a considerably higher signal response for pixels at the cell edges, relative to the more central pixels. The determination of the expression levels of CXCR4 and EGFR for the MDA-MB-468 cell line was performed using LA-ICP-MS single-cell analysis (sc-LA-ICP-MS) and external calibration, based on the quantitative ablation of Ho-spiked dried gelatin droplet standards. Additionally, a second calibration approach was applied based on spot ablation of highly homogeneous dried gelatin gels in combination with the determination of the ablated volume using atomic force microscopy (AFM) and yielded results which were in good agreement with the expression levels determined via flow cytometry (FC) and mass cytometry (MC). Hybrid tracers enable a direct comparison between (i) FCM and LA-ICP-MS imaging for the evaluation of the microscopic binding pattern and between (ii) FC, MC and sc-LA-ICP-MS for the quantification of receptor expression levels in single cells.

Synthesis and Preclinical Characterization of the PSMA-Targeted Hybrid Tracer PSMA-I&F for Nuclear and Fluorescence Imaging of Prostate Cancer

The prostate-specific membrane antigen (PSMA)–targeted radiotracers ⁶⁸Ga/¹⁷⁷Lu-PSMA-I&T and ^99mTc-PSMA-I&S (for imaging and surgery) are currently successfully used for clinical PET imaging, radionuclide therapy, and radioguided surgery of metastatic prostate cancer. To additionally exploit the high sensitivity and spatial resolution of fluorescence imaging for improved surgical guidance, a PSMA-I&T–based hybrid tracer, PSMA-I&F (DOTAGA-k(Sulfo-Cy5)-y-nal-k-Sub-KuE), has been developed and evaluated. Methods: The in vitro PSMA-targeting efficiency of PSMA-I&F, the reference PSMA-I&T, and their corresponding ^natGa-/⁶⁸Ga- and ^natLu/¹⁷⁷Lu counterparts was determined in LNCaP cells via competitive binding assays (IC₅₀) and dual-tracer radioligand and fluorescence internalization studies. Biodistribution and small-animal PET imaging studies were performed in CB17 SCID and LNCaP xenograft–bearing SHO mice, respectively, and complemented by intraoperative far-red fluorescence imaging using a clinical laparoscope. Additionally, fully automated serial cryosectioning and fluorescence imaging of 1 tumor-bearing animal as well as PSMA immunohistochemistry and fluorescence microscopy of organ cryosections (tumor, kidney, spleen) were also performed. Results: Compared with the parent PSMA-I&T analogs, the PSMA affinities of PSMA-I&F and its ^natGa-/^natLu-complexes remained high and unaffected by dye conjugation (7.9 < IC₅₀ < 10.5 nM for all ligands). The same was observed for the internalization of ⁶⁸Ga- and ¹⁷⁷Lu-PSMA-I&F. In vivo, blood clearance of ⁶⁸Ga- and ¹⁷⁷Lu-PSMA-I&F was only slightly delayed by high plasma protein binding (94%–95%), and very low accumulation in nontarget organs was observed already at 1 h after injection. Dynamic PET imaging confirmed PSMA-specific (as demonstrated by coinjection of 2-PMPA) uptake into the LNCaP xenograft (4.5% ± 1.8 percentage injected dose per gram) and the kidneys (106% ± 23 percentage injected dose per gram). Tumor-to-background ratios of 2.1, 5.2, 9.6, and 9.6 for blood, liver, intestines, and muscle, respectively, at 1 h after injection led to excellent imaging contrast in ⁶⁸Ga-PSMA-I&F PET and in intraoperative fluorescence imaging. Furthermore, fluorescence imaging of tissue cryosections allowed high-resolution visualization of intraorgan PSMA-I&F distribution in vivo and its correlation with PSMA expression as determined by immunohistochemistry. Conclusion: Thus, with its high PSMA-targeting efficiency and favorable pharmacokinetic profile, ⁶⁸Ga/¹⁷⁷Lu-PSMA-I&F serves as an excellent proof-of-concept compound for the general feasibility of PSMA-I&T–based hybrid imaging. The PSMA-I&T scaffold represents a versatile PSMA-targeted lead structure, allowing relatively straightforward adaptation to the different structural requirements of dedicated nuclear or hybrid imaging agents.

Hybrid Imaging Labels: Providing the Link Between Mass Spectrometry-Based Molecular Pathology and Theranostics

Background: Development of theranostic concepts that include inductively coupled plasma mass spectrometry (ICP-MS) and laser ablation ICP-MS (LA-ICP-MS) imaging can be hindered by the lack of a direct comparison to more standardly used methods for in vitro and in vivo evaluation; e.g. fluorescence or nuclear medicine. In this study a bimodal (or rather, hybrid) tracer that contains both a fluorescent dye and a chelate was used to evaluate the existence of a direct link between mass spectrometry (MS) and in vitro and in vivo molecular imaging findings using fluorescence and radioisotopes. At the same time, the hybrid label was used to determine whether the use of a single isotope label would allow for MS-based diagnostics.

Methods: A hybrid label that contained both a DTPA chelate (that was coordinated with either ¹⁶⁵Ho or ¹¹¹In) and a Cy5 fluorescent dye was coupled to the chemokine receptor 4 (CXCR4) targeting peptide Ac-TZ14011 (hybrid-Cy5-Ac-TZ4011). This receptor targeting tracer was used to 1) validate the efficacy of (¹⁶⁵Ho-based) mass-cytometry in determining the receptor affinity via comparison with fluorescence-based flow cytometry (Cy5), 2) evaluate the microscopic binding pattern of the tracer in tumor cells using both fluorescence confocal imaging (Cy5) and LA-ICP-MS-imaging (¹⁶⁵Ho), 3) compare in vivo biodistribution patterns obtained with ICP-MS (¹⁶⁵Ho) and radiodetection (¹¹¹In) after intravenous administration of hybrid-Cy5-Ac-TZ4011 in tumor-bearing mice. Finally, LA-ICP-MS-imaging (¹⁶⁵Ho) was linked to fluorescence-based analysis of excised tissue samples (Cy5).

Results: Analysis with both mass-cytometry and flow cytometry revealed a similar receptor affinity, respectively 352 ± 141 nM and 245 ± 65 nM (p = 0.08), but with a much lower detection sensitivity for the first modality. In vitro LA-ICP-MS imaging (¹⁶⁵Ho) enabled clear discrimination between CXCR4 positive and negative cells, but fluorescence microscopy was required to determine the intracellular distribution. In vivo biodistribution patterns obtained with ICP-MS (¹⁶⁵Ho) and radiodetection (¹¹¹In) of the hybrid peptide were shown to be similar. Assessment of tracer distribution in excised tissues revealed the location of tracer uptake with both LA-ICP-MS-imaging and fluorescence imaging.

Conclusion: Lanthanide-isotope chelation expands the scope of fluorescent/radioactive hybrid tracers to include MS-based analytical tools such as mass-cytometry, ICP-MS and LA-ICP-MS imaging in molecular pathology. In contradiction to common expectations, MS detection using a single chelate imaging agent was shown to be feasible, enabling a direct link between nuclear medicine-based imaging and theranostic methods.

Multispectral Fluorescence Imaging During Robot-assisted Laparoscopic Sentinel Node Biopsy: A First Step Towards a Fluorescence-based Anatomic Roadmap

BACKGROUND

During (robot-assisted) sentinel node (SN) biopsy procedures, intraoperative fluorescence imaging can be used to enhance radioguided SN excision. For this combined pre- and intraoperative SN identification was realized using the hybrid SN tracer, indocyanine green-^99mTc-nanocolloid. Combining this dedicated SN tracer with a lymphangiographic tracer such as fluorescein may further enhance the accuracy of SN biopsy.

OBJECTIVE

Clinical evaluation of a multispectral fluorescence guided surgery approach using the dedicated SN tracer ICG-^99mTc-nanocolloid, the lymphangiographic tracer fluorescein, and a commercially available fluorescence laparoscope.

DESIGN, SETTING, AND PARTICIPANTS

Pilot study in ten patients with prostate cancer. Following ICG-^99mTc-nanocolloid administration and preoperative lymphoscintigraphy and single-photon emission computed tomograpy imaging, the number and location of SNs were determined. Fluorescein was injected intraprostatically immediately after the patient was anesthetized. A multispectral fluorescence laparoscope was used intraoperatively to identify both fluorescent signatures.

SURGICAL PROCEDURE

Multispectral fluorescence imaging during robot-assisted radical prostatectomy with extended pelvic lymph node dissection and SN biopsy.

MEASUREMENTS

(1) Number and location of preoperatively identified SNs. (2) Number and location of SNs intraoperatively identified via ICG-^99mTc-nanocolloid imaging. (3) Rate of intraoperative lymphatic duct identification via fluorescein imaging. (4) Tumor status of excised (sentinel) lymph node(s). (5) Postoperative complications and follow-up.

RESULTS AND LIMITATIONS

Near-infrared fluorescence imaging of ICG-^99mTc-nanocolloid visualized 85.3% of the SNs. In 8/10 patients, fluorescein imaging allowed bright and accurate identification of lymphatic ducts, although higher background staining and tracer washout were observed. The main limitation is the small patient population.

CONCLUSION

Our findings indicate that a lymphangiographic tracer can provide additional information during SN biopsy based on ICG-^99mTc-nanocolloid. The study suggests that multispectral fluorescence image-guided surgery is clinically feasible.

PATIENT SUMMARY

We evaluated the concept of surgical fluorescence guidance using differently colored dyes that visualize complementary features. In the future this concept may provide better guidance towards diseased tissue while sparing healthy tissue, and could thus improve functional and oncologic outcomes.

Hybrid surgical guidance based on the integration of radionuclear and optical technologies

With the evolution of imaging technologies and tracers, the applications for nuclear molecular imaging are growing rapidly. For example, nuclear medicine is increasingly being used to guide surgical resections in complex anatomical locations. Here, a future workflow is envisioned that uses a combination of pre-operative diagnostics, navigation and intraoperative guidance. Radioguidance can provide means for pre-operative and intraoperative identification of "hot" lesions, forming the basis of a virtual data set that can be used for navigation. Luminescence guidance has shown great potential in the intraoperative setting by providing optical feedback, in some cases even in real time. Both of these techniques have distinct drawbacks, which include inaccuracy in areas that contain a background signal (radioactivity) or a limited degree of signal penetration (luminescence). We, and others, have reasoned that hybrid/multimodal approaches that integrate the use of these complementary modalities may help overcome their individual weaknesses. Ultimately, this will lead to advancement of the field of interventional molecular imaging/image-guided surgery. In this review, an overview of clinically applied hybrid surgical guidance technologies is given, whereby the focus is placed on tracers and hardware.