Optimising magnetic sentinel lymph node biopsy in an in vivo porcine model

Preclinical evaluation of polymer encapsulated carbon-based nano and microparticles for sentinel lymph node tattooing

Selective sentinel lymph node biopsy (SNLB) is the standard method for detecting regional metastases in breast cancer patients. Identifying affected axillary lymph nodes before neoadjuvant treatment is crucial, as such treatment may alter drainage pathways and lymph node morphology, hindering the identification of sentinel lymph nodes. The use of carbon-based tattooing on sentinel lymph nodes (SLN) has been employed as a permanent tattooing method in clinical studies of Targeted Axillary Dissection (TAD), aiding in the SLN identification during surgery. Our study introduces a new method of lymph node tattooing based on poly lactic-co-glycolic (PLGA) particles with encapsulated carbon. This strategy substantially improves tattooing efficiency over single carbon suspensions currently used in clinical studies. We synthesized and characterized carbon-loaded PLGA micro- and nanoparticles, experimentally assessing their biological impact on porcine lymph nodes. The effect of particles' size and concentration was evaluated over time (from 1 to 16 weeks). Light and electron microscopy studies were conducted to characterize the cellular effects induced by the presence of these particles. Our findings reveal that the diverse physicochemical parameters of the particles interact differently with the lymphatic tissue, influencing their biodistribution within the lymph nodes and the intensity of the inflammatory response.

Preclinical feasibility of robot-assisted sentinel lymph node biopsy using multi-modality magnetic and fluorescence guidance in the head and neck

BACKGROUND

Sentinel lymph node biopsy (SLNB) is a staging procedure dependent on accurate mapping of draining lymphatics via tracers. Robot-assisted SLNB enables access to multiple neck levels with a single incision and intraoperative fluorescence guidance to the SLN.

METHODS

Lymphatic mapping in swine was done using a magnetic tracer and fluorescent dye, injected into the tongue. MRI preoperatively mapped lymphatic spread of the magnetic tracer. Dissection was performed using a da Vinci Xi robot guided by fluorescence-imaging of the dye.

RESULTS

Robot-assisted SLNB was successfully performed in all animals (n = 5). A novel MRI protocol differentiated SLNs (n = 6) from lower echelon nodes (n = 11) based on flow progression. Fluorescence imaging provided valuable intraoperative guidance and correlated with magnetic-positive nodes.

CONCLUSIONS

This study demonstrates preclinical feasibility of a robot-assisted approach to SLNB using magnetic and fluorescent tracers in the head and neck, enabling both preoperative mapping and intraoperative guidance.

Exploratory Study of Superparamagnetic Iron Oxide Dose Optimization in Breast Cancer Sentinel Lymph Node Identification Using a Handheld Magnetic Probe and Iron Quantitation

Simple Summary

Sentinel lymph node biopsy (SLNB) using super magnetic iron oxide (SPIO) and magnetic probes is expected to be a simple and safe method of detecting cancerous lymph nodes without using radioisotopes (RIs). A multicenter trial of SLNB was conducted using a handheld magnetic probe and SPIO (Rizobist^®) and its non-inferiority with the conventional RI method. The quantity of iron in SLN was measured to examine the necessary dosage and administration method for sufficient SLN detection in the case of this test. Further, a clinical trial was conducted to determine the possibility of SLNB with a half-dose of SPIO (1.0 mL → 0.5 mL), and the resulting iron volume measured at that time was also examined. This study demonstrates that sufficient iron content reaches SLN even at an SPIO dose of 0.5 mL.

Abstract

This exploratory study compared doses of ferucarbotran, a superparamagnetic iron oxide nanoparticle, in sentinel lymph nodes (SLNs) and quantified the SLN iron load by dose and localization. Eighteen females aged ≥20 years scheduled for an SLN biopsy with node-negative breast cancer were divided into two equal groups and administered either 1 mL or 0.5 mL ferucarbotran. Iron content was evaluated with a handheld magnetometer and quantification device. The average iron content was 42.8 µg (range, 1.3–95.0; 0.15% of the injected dose) and 21.9 µg (1.1–71.0; 0.16%) in the 1-mL and 0.5-mL groups, respectively (p = 0.131). The iron content of the closest SLN compared to the second SLN was 53.0 vs. 10.0 µg (19% of the injected dose) and 34.8 vs. 4.1 µg (11.1%) for the 1-mL and 0.5-mL groups, respectively (p = 0.001 for both). The magnetic field was high in both groups (average 7.30 µT and 6.00 µT in the 1-mL and 0.5-mL groups, respectively) but was not statistically significant (p = 0.918). The magnetic field and iron content were correlated (overall SLNs, p = 0.02; 1-mL, p = 0.014; 0.5-mL, p = 0.010). A 0.5-mL dose was sufficient for SLN identification. Primary and secondary SLNs could be differentiated based on iron content. Handheld magnetometers could be used to assess the SLN iron content.

Optimization of SPIO Injection for Sentinel Lymph Node Dissection in a Rat Model

The magnetic technique, consisting of a magnetic tracer and a handheld magnetometer, is a promising alternative technique for sentinel lymph node dissection (SLND) and was shown to be non-inferior to the standard technique in terms of identification rates. In this study, injection characteristics (iron dose, dilution, time course and massaging) were evaluated to optimize magnetic tracer uptake in the sentinel lymph nodes (SLN) in a rat hindleg model. 202 successful SLNDs were performed. Iron uptake in the SLN is proportional (10% utilization rate) to the injection dose between 20 and 200 μg, showing a plateau uptake of 80 μg in the SLN around 1000 μg injection. Linear regression showed that time had a higher impact than dilution, on the SLN iron uptake. Massaging showed no significant change in iron uptake. The amount of residual iron at the injection site was also proportional to the injection dose without any plateau. Time was a significant factor for wash-out of residual iron. From these results, preoperative injection may be advantageous for SLN detection as well as reduction in residual iron at the injection site by potential decrease in required injection dose.

Optimization of SPIO Injection for Sentinel Lymph Node Dissection in a Rat Model

Simple Summary

In this study, the following injection characteristics were evaluated to optimize magnetic tracer uptake in the sentinel lymph nodes (SLN) in a rat hindleg model: (a) iron dose, (b) effect of dilution, (c) effect of injecting at different time courses and (d) effect of massaging the injection site. In conclusion, injection dose and time were primary factors for the SLN iron uptake. The result from this study will provide a background for magnetic procedures.

Abstract

The magnetic technique, consisting of a magnetic tracer and a handheld magnetometer, is a promising alternative technique for sentinel lymph node dissection (SLND) and was shown to be non-inferior to the standard technique in terms of identification rates. In this study, injection characteristics (iron dose, dilution, time course and massaging) were evaluated to optimize magnetic tracer uptake in the sentinel lymph nodes (SLN) in a rat hindleg model. 202 successful SLNDs were performed. Iron uptake in the SLN is proportional (10% utilization rate) to the injection dose between 20 and 200 μg, showing a plateau uptake of 80 μg in the SLN around 1000 μg injection. Linear regression showed that time had a higher impact than dilution, on the SLN iron uptake. Massaging showed no significant change in iron uptake. The amount of residual iron at the injection site was also proportional to the injection dose without any plateau. Time was a significant factor for wash-out of residual iron. From these results, preoperative injection may be advantageous for SLN detection as well as reduction in residual iron at the injection site by potential decrease in required injection dose.

Long-Term Outcome After Retro-Areolar Versus Peri-Tumoral Injection of Superparamagnetic Iron Oxide Nanoparticles (SPIO) for Sentinel Lymph Node Detection in Breast Cancer Surgery

BACKGROUND/OBJECTIVE

SPIO is effective in sentinel node (SN) detection. No nuclear medicine department is needed, and no allergic reactions have occurred. This study aimed to compare retro-areolar and peri-tumoral SPIO injections regarding skin staining, detection rates and number of SNs.

METHODS

Data on staining size, intensity and cosmetic outcome (0-5; 0 = no problem) were collected by telephone interviews with 258 women undergoing breast conservation. SN detection and the number of SNs were prospectively registered in 332 women.

RESULTS

After retro-areolar and peri-tumoral injections, 67.3% and 37.8% (p < 0.001) developed skin staining, with remaining staining in 46.2 vs. 9.4% after 36 months (p < 0.001). Initial mean size was 16.3 vs. 6.8 cm (p < 0.001) and after 36 months, 6.6 vs. 1.8 cm² (p < 0.001). At 75.1% of 738 interviews, staining was reported paler. After retro-areolar injections, cosmetic outcome scored worse for 2 years. The mean (median) scores were 1.3(0) vs. 0.5(0) points, and 0.2(0) vs. 0.1(0) points, at 12 and 36 months, respectively. Overall detection rates were 98.3% and 97.4% (p = 0.43) and the number of SNs 1.35 vs. 1.57 (p = 0.02) after retro-areolar and peri-tumoral injections. Injection, regardless of type, 1-27 days before surgery increased detection rates with SPIO, 98.0% vs. 94.2% (p = 0.06) ,and SN numbers, 1.56 vs. 1.27 (p = 0.003).

CONCLUSION

SPIO is effective and facilitates planning for surgery. Peri-tumoral injection reduced staining with a similar detection rate. Staining was not considered a cosmetic problem among most women. Injecting SPIO 1-27 days before surgery increased the detection rate by 3.8% and increased the number of SNs by 0.3.

Combined use of fluorescence with a magnetic tracer and dilution effect upon sentinel node localization in a murine model

Background

Sentinel node biopsy using radioisotope and blue dye remains a gold standard for axillary staging in breast cancer patients with low axillary burden. However, limitations in the use of radioisotopes have resulted in emergence of novel techniques. This is the first in vivo study to assess the feasibility of combining the two most common novel techniques of using a magnetic tracer and indocyanine green (ICG) fluorescence.

Materials and methods

A total of 48 mice were divided into eight groups. Groups 1 and 2, the co-localization groups, received an injection of magnetic tracers (Resovist^® and Sienna+^®, respectively) and ICG fluorescence; distilled water was used as the solvent of ICG. Groups 3 and 4, the diluted injection groups, received an injection of magnetic tracers (Resovist and Sienna+, respectively) and saline for dilution. Groups 5, 6, and 7, the control groups, received magnetic tracer (Resovist, Sienna+) and ICG alone, respectively. Fluorescent intensity assessment and iron quantification of excised popliteal lymph nodes were performed. Group 1', a co-localization group, received an injection of magnetic tracers (Resovist) and ICG' fluorescence: saline was used as the solvent for ICG.

Results

Lymphatic uptake of all tracers was confined to the popliteal nodes only, with co-localization confirmed in all cases and no significant difference in fluorescent intensity or iron content of ex vivo nodes between the groups (except for Group 1'). There was no impact of dilution on the iron content in the diluted Sienna+ group, but it significantly enhanced Resovist uptake (P=0.005). In addition, there was a significant difference in iron content (P=0.003) in Group 1'.

Conclusion

The combination of a magnetic tracer (Resovist or Sienna+) and ICG fluorescence is feasible for sentinel node biopsy and will potentially allow for precise transcutaneous node identification, in addition to accurate intraoperative assessment. This radioisotope-free "combined technique" warrants further assessment within a clinical trial.

The Nordic SentiMag trial: a comparison of super paramagnetic iron oxide (SPIO) nanoparticles versus Tc(99) and patent blue in the detection of sentinel node (SN) in patients with breast cancer and a meta-analysis of earlier studies

The aim of the study is to compare the efficacy of SPIO as a tracer in sentinel node biopsy (SNB) in breast cancer with Tc and patent blue in a multicentre prospective study and perform a meta-analysis of all published studies. It also aims to follow skin discoloration after SPIO injection and describe when and how it resolves. Totally 206 patients with early breast cancer were recruited. Tc and patent blue were administered in standard fashion. Patients were injected with SPIO (Sienna+) preoperatively. SNB was performed and detection rates were recorded for both methods. Skin discoloration was followed and documented postoperatively. Data extraction and subsequent meta-analysis of all previous studies were also performed. SN detection rates were similar between standard technique succeeded and SPIO both per patient (97.1 vs. 97.6 %, p = 0.76) as well as per node (91.3 vs. 93.3 %, p = 0.34), something which was not affected by the presence of malignancy. Concordance rates were also consistently high (98.0 % per patient and 95.9 % per node). Discoloring was present in 35.5 % of patients postoperatively, almost exclusively in breast conservation. It fades slowly and is still detectable in 8.6 % of patients after 15 months. Meta-analysis depicted similar detection rates (p = 0.71) and concordance rates (p = 0.82) per patient. However, it seems that SPIO is characterized by higher nodal retrieval (p < 0.001). SPIO is an effective method for the detection of SN in patients with breast cancer. It is comparable to the standard technique and seems to simplify logistics. Potential skin discoloration is something of consideration in patients planned for breast conservation.

Magnetic sentinel lymph node biopsy in a murine tumour model

The magnetic technique for sentinel node biopsy provides a radioisotope-free alternative for staging breast cancer. It requires refinement to reduce "residual iron content" at injection sites by maximising lymphatic uptake to prevent "void artefacts" on magnetic resonance imaging (MRI), which could adversely affect clinical use. The site and timing of injection of magnetic tracer was evaluated in a murine tumour model (right hind limb) in 24 wild type mice. Right-sided intratumoural and left sided subcutaneous injection of magnetic tracer and assessment of nodal iron uptake on MRI, surgical excision and histopathological grading at time frames up to 24 hours were performed. Rapid iron uptake on MRI, smaller "void artefacts"(P<0.001) and a significant increase in iron content with time were identified in the subcutaneous injection group (r=0.937; P<0.001).Subcutaneous injection and increasing delay between tracer injection and surgery is beneficial for lymphatic iron uptake.

FROM THE CLINICAL EDITOR

Sentinel lymph node biopsy (SLNB) has been the standard of care in breast cancer management for some time. Recent development has seen the introduction of magnetic tracer for SLNB. In this article, the authors investigated the refined use of magnetic tracer in determining the optimal timing of administration and the location of injection. The findings should provide more data on the future use of this new technique.