Two-Layer FEM Analysis of Nanoparticle Heterogeneity in Magnetic Hyperthermia

Abstract

The clinical efficacy of magnetic nanoparticle hyperthermia (MNH) is critically dependent on the spatial distribution of iron-oxide nanoparticles (NPs) within the tumor, but most simulation studies still assume a uniform intratumoral concentration. In this work, a compact two-layer three-dimensional finite-element model was constructed in COMSOL Multiphysics 6.4 to compare a uniformly loaded tumor (Case U: NP volume fraction vNP = 0.004 in both core and rim) against a heterogeneously loaded tumor in which the rim contains seven times more nanoparticles than the core (Case H: vNP,core = 0.001, vNP,rim = 0.007). The Pennes bioheat equation was solved with the built-in Biological Tissue feature on a tumor consisting of two concentric spheres (core radius 2 mm, total tumor radius 4 mm) embedded in a 16 mm cubic phantom of normal tissue. Both cases received the same total nanoparticle mass and the same heat-source coefficient; the only difference was the spatial distribution. After 500 s of heating, the uniform case reached a tumor-center temperature of 39.94 °C while the heterogeneous case reached only 37.77 °C, a deficit of 2.17 K (5.4 %) at the very location where viable tumor cells are typically most numerous. Conversely, the tumor edge temperature was 1.08 K higher in Case H. Normal-tissue temperature 2 mm beyond the tumor surface remained at 37.18 °C in both cases, confirming thermal safety. These results provide a transparent, compact demonstration that intratumoral nanoparticle heterogeneity can shift heating away from the tumor core and toward the rim, with direct implications for treatment planning in clinical MNH.