Objective. Circulating Tumor Cells (CTCs) carry crucial informationrelated to the spreading and proliferation of tumors, especially at early stages of the disease. Despite the huge clinical potential held by CTCs in cancer therapy, capture and detection of these cells from the patient’s peripheral blood system is rather challenging since CTCs are extremely rare cells. The objective of this paper is, based on Monte Carlo simulations, to propose the detection of immunomagnetically labelled tumor cells by micro-X-ray fluorescence (μ-XRF). Approach. The simulations were carried out with the Monte Carlo N-Particle, version 6.2, (MCNP6.2) code. The model simulates 20μm cancer cell lines and 10μm circulating tumor cells (CTCs) tagged with Fe3O4@SiO2 spherical nanoparticles of diameters 25nm, 60nm and 110nm. A 17.5 keV monochromatic, micro-focused X-ray beam of diameter 15μm, impinges on cancer cells immersed in a phosphate-buffered saline (PBS) solution. The simulations also include a polymeric sample holder and a silicon drift detector (SDD) with a beryllium window and silver collimator. Main Results. The results show the dependence of the signal intensity (Fe Kα line) on cell and nanoparticle sizes. Samples containing two and three CTCs were also simulated in particular geometrical configurations. It is presented how the inter-cell distances and cell positions relative to the incident X-ray beam affect the signal. In addition, within the parameters used in the simulations, μ- XRF method provides a minimum detection limit of 9.4 pg of Fe, which corresponds to detecting a single 10μm CTC labeled with 110nm Fe3O4@SiO2 nanoparticles at 6.3% binding. Significance. The μ-XRF based method proposed in this paper for detecting CTCs, combined with immunomagnetic nanoparticles (NPs), has the potential to be innovative in the field of liquid biopsy.
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