Magnetic sentinel lymph node biopsy and localization properties of a magnetic tracer in an in vivo porcine model

Abstract

The standard for the treatment of early non-palpable breast cancers is wide local excision directed by wire-guided localization and sentinel lymph node biopsy (SLNB). This has drawbacks technically and due to reliance upon radioisotopes. We evaluated the use of a magnetic tracer for its localization capabilities and concurrent performance of SLNB using a handheld magnetometer in a porcine model as a novel alternative to the current standard. Ethical approval by the IRCAD Ethics Review Board, Strasbourg (France) was received. A magnetic tracer was injected in varying volumes (0.1-5 mL) subcutaneously into the areolar of the left and right 3rd inguinal mammary glands in 16 mini-pigs. After 4 h magnetometer counts were taken at the injection sites and in the groins. The magnetometer was used to localize any in vivo signal from the draining inguinal lymph nodes. Magnetic SLNB followed by excision of the injection site was performed. The iron content of sentinel lymph nodes (SLNs) were graded and quantified. All excised specimens were weighed and volumes were calculated. Univariate analyses were performed to evaluate correlation. Magnetic SLNB was successful in all mini-pigs. There was a significant correlation (r = 0.86; p < 0.01) between magnetometer counts and iron content of SLNs. Grading of SLNs on both H&E and Perl's staining correlated significantly with the iron content (p = 0.001; p = 0.003) and magnetometer counts (p < 0.001; p = 0.004). The peak counts corresponded to the original magnetic tracer injection sites 4 h after injection in all cases. The mean volume and weight of excised injection site specimens was 2.9 cm(3) (SD 0.81) and 3.1 g (SD 0.85), respectively. Injection of ≥0.5 mL magnetic tracer was associated with significantly greater volume (p = 0.05) and weight of excision specimens (p = 0.01). SLNB and localization can be performed in vivo using a magnetic tracer. This could provide a viable alternative for lesion localization and concurrent SLNB in the treatment of non-palpable breast cancer.

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

“…This study confirmed a significant correlation between the handheld magnetometer counts and the iron content of ex vivo SLNs as recorded on VSM measurements. The Pearson's Correlation (r) of 0.82 (Fig.2) was in keeping with our previous study in which r=0.86, [20] reaffirming the ability of handheld magnetometers to quantify iron content in-vivo.…”

“…It has been shown that the iron content within SLNs after interstitial magnetic tracer injection is predominately distributed within the subcapsular space and sinuses of the lymph nodes. [14,20] Our results suggest that the porcine SLNs have a saturation limit for the iron content distributed within them. Once this saturation point is exceeded the iron is passed on to the next echelon SLN, which once its saturation point is exceeded will similarly result in passage to the next nodes.…”

“…Based upon data accrued from our previous feasibility study [20] a power calculation was performed to determine sample size. We conducted a two-sided test (alpha=0.05) expecting a difference of 50 g (SD: 30) in iron content readings between different volumes of tracer.…”

“…This model was used to successfully demonstrate the feasibility of magnetic SLNB using 16 mini-pigs and 32 SLNB procedures. [20] Anninga and Ahmed et al [20] identified a significant correlation between magnetometer counts and the magnetic tracer content of ex vivo SLNs and the significant association between the grading of ex vivo SLNs for their tracer content and magnetometer counts. [20] This model had therefore been validated for the purpose of magnetic SLNB.…”

“…[20] Anninga and Ahmed et al [20] identified a significant correlation between magnetometer counts and the magnetic tracer content of ex vivo SLNs and the significant association between the grading of ex vivo SLNs for their tracer content and magnetometer counts. [20] This model had therefore been validated for the purpose of magnetic SLNB. Based upon our previous experience, it was possible to determine an adequate sample size via power analysis to identify the optimal volume of magnetic tracer required to ensure maximal SLN tracer uptake and therefore optimise clinical SLN identification and potentially reduce false negative rates using the magnetic technique.…”