Magnetic nanoparticle hyperthermia: predictive model for temperature distribution

Abstract

Magnetic nanoparticle (mNP) hyperthermia is a promising adjuvant cancer therapy. mNP’s are delivered intravenously or directly into a tumor, and excited by applying an alternating magnetic field (AMF). The mNP’s are, in many cases, sequestered by cells and packed into endosomes. The proximity of the mNP’s has a strong influence on their ability to heat due to inter-particle magnetic interaction effects. This is an important point to take into account when modeling the mNP’s. Generally, more mNP heating can be achieved using higher magnetic field strengths. The factor which limits the maximum field strength applied to clinically relevant volumes of tissue is the heating caused by eddy currents, which are induced in the noncancerous tissue. A coupled electromagnetic and thermal model has been developed to predict dynamic thermal distributions during AMF treatment. The EM model is based on the method of auxiliary sources and the thermal modeling is based on the Pennes bioheat equation. The results of our phantom study are used to validate the model which takes into account nanoparticle heating, interaction effects, particle spatial distribution, particle size distribution, EM field distribution, and eddy current generation in a controlled environment. Preliminary in vivo data for model validation are also presented. Once fully developed and validated, the model will have applications in experimental design, AMF coil design, and treatment planning.

Magnetic nanoparticles with high specific absorption rate of electromagnetic energy at low field strength for hyperthermia therapy

“…The effects of magnetic dipolar interactions on the MNP hysteresis and heating efficiency have recently been studied intensively. [17][18][19][20][21][22][23][24][25][26][27]34,39,63 These studies have demonstrated a strong interaction effect between MNP aggregates and have attributed it to the observed MNP hysteresis. However, the detailed mechanism of the power loss in a MNPs assemblies, which exhibit particle-particle, particle-aggregate, and aggregate-aggregate strong and weak interactions, are not yet known.…”

“…30,31 These induced eddy currents can result in significant heating of normal tissue and impose limitations on the product of magnetic field strength and frequency (HÁf) for hyperthermia treatment. [32][33][34] The HÁf limitations that clinical test subjects were able to withstand for more than 1 h without major complications have been reported in four independent studies; 32,35-37 the limit varies from 4:5 Â 10 8 A=ðm sÞ or ð5:625 Â 10 6 Oe=sÞ to 8:5 Â 10 8 A=ðm sÞ or ð10:625 Â 10 6 Oe=sÞ and is summarized in Ref. 38.…”

Magnetic hyperthermia therapy for the treatment of glioblastoma: a review of the therapy’s history, efficacy and application in humans

“…The software can then calculate the expected heat distribution within the brain at various magnetic field amplitudes [64]. One group has validated a coupled electromagnetic and thermal model to predict dynamic and thermal distributions during AMF treatment [65]. Variables such as tissue density, specific heat of tissue, thermal conductivity of tissue, and metabolic heat generation rate were used in a variation of the BHTE equation.…”

Mitigation of eddy current heating during magnetic nanoparticle hyperthermia therapy

“…It is powered by a 25kW generator (Radyne Corp., Milwaukee, WI, USA), which drives 135–400kHz AC current through the coil, thus generating a 135–400kHz AMF [56]. The frequency used in the following experiments was 162kHz.…”