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Optimisation of the magnetic procedure to detect the sentinel lymph node in breast cancer patients

Winkelhorst, E.W. (2020) Optimisation of the magnetic procedure to detect the sentinel lymph node in breast cancer patients.

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Abstract:Investigation whether tumour cells are metastasized to lymph nodes is necessary for appropriate treatment of breast cancer patients. If no suspected lymph nodes can be found during clinical examination, sentinel lymph node biopsies (SLNBs) are performed using radioactive tracers and blue dye. However, this procedure has major disadvantages in use because of short half-lives of radioactive tracers and strict guidelines for working with radioactivity. To overcome these limitations, magnetic SLNB procedures using superparamagnetic iron oxide nanoparticles (SPIOs) have been developed. Initial studies showed detection rates of the sentinel node (SN) non-inferior to conventional SLNBs. However, high SPIOs doses induced artefacts on postoperative magnetic resonance imaging’s (MRIs). Therefore, a pilot study using low SPIOs doses, named the LowMag trial, has been performed. Surgeons expressed that it was difficult and sometimes impossible to magnetically detect the SN. Therefore, the aim of this thesis was to investigate how to improve magnetic detection of SNs using the Sentimag magnetometer and low dose SPIOs. First, we performed phantom studies to determine the correlation between the number of counts detected with the magnetometer and the iron dose. Subsequently, we performed retrospective analyses using data from the LowMag trial and two prior breast cancer studies, the SentiMag trial and MagSNOLL trial. These studies used respectively an intratumoural SPIOs injection containing 1.1 mg iron, a periareolair SPIOs injection containing 56 mg iron, and an intratumoural SPIOs injection containing 2.8-14 mg iron. We compared the iron content in SNs. In addition, we investigated whether the iron content in SNs correlated with the time interval between injection and surgery, and following personal factors: age, body mass index (BMI), breast size, tumour size, and tumour location. Subsequently, for ten patients, the iron content in the SN after a peritumoural injection has been examined. For eight of them, the injected iron dose was increased to 4.4 mg iron. The results of these ten patients were compared to the iron content in the SN after an intratumoural injection from prior LowMag trial results. In addition, we compared this magnetic SLNB with conventional SLNB regarding detectability of the SN. At last, for five patients, we evaluated the presence of SPIOs induced artefacts on postoperative MRIs of the breast made six weeks after surgery. We found a correlation between the detected number of counts and iron dose for a fixed position of the SPIOs to the magnetometer. In addition, we showed that the distance between SPIOs and the magnetometer strongly affects the detected number of counts. We found a significant difference in iron content in the SN between the LowMag trial and SentiMag trial (p=.000), and no significant difference between the LowMag trial and MagSNOLL trial (p=.705). Furthermore, no significant correlation was seen between iron content in the SN and age (p=.241), BMI (p=.314), breast size (p=.770), tumour size (p=.609), tumour location (p=.065), and time interval (p=.433). In addition, we found no significant difference between the iron content in the SN using intratumoural or peritumoural injections (p=.723). SNs were 7 magnetically detectable in 50% of the procedures, whereas all SNs were detectable using the conventional procedure (n=10). The surgeons agreed that it was easy to magnetically locate the SN in 80% of the procedures in which it was possible to magnetically detect the SN. It was easy to locate the SN using the conventional SLNB procedure in all procedures. At last, no void artefacts induced by remaining SPIOs in the breast were visible in all postoperative MRIs. We confirmed that it is difficult to magnetically detect the SN during the LowMag trial, since the SN was magnetically detected in 50% of the procedures (n=10). A promising finding is that surgeons agreed that it was easy to locate SNs using the magnetic SLNB procedure in 80% of the procedures in which it was possible to magnetically detect the SN. Furthermore, we found that postoperative MRIs showed good assessable images of breast tissue, without SPIOs induced artefacts after a peritumoural SPIOs injection. In addition, we found no significant correlation between personal factors and iron content in SNs, which suggests that SPIOs injection procedures do not have to be person specific. For implementation in conventional care, detection rates of magnetic SLNBs using a low dose SPIOs have to be further increased. The possibility to magnetically detect the SN is mainly affected by the following three factors: the size and dose of the magnetic tracer, the technique of the magnetometer, and the experience and understanding of the surgeon.
Item Type:Essay (Master)
Faculty:TNW: Science and Technology
Subject:33 physics, 44 medicine
Programme:Technical Medicine MSc (60033)
Link to this item:https://purl.utwente.nl/essays/83532
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