Revisiting the safety limit in magnetic nanoparticle hyperthermia: insights from eddy current induced heating

Objective.Magnetic nanoparticle hyperthermia (MNH) emerges as a promising therapeutic strategy for cancer treatment, leveraging alternating magnetic fields (AMFs) to induce localized heating through magnetic nanoparticles. However, the interaction of AMFs with biological tissues leads to non-specific heating caused by eddy currents, triggering thermoregulatory responses and complex thermal gradients throughout the body of the patient. While previous studies have implemented the Atkinson-Brezovich limit to mitigate potential harm, recent research underscores discrepancies between this threshold and clinical outcomes, necessitating a re-evaluation of this safety limit. Therefore, in this study, through electromagnetic (EM) simulations, the complex interaction between AMFs and anatomical models was investigated.Approach.In particular, we considered a circular coil configuration placed at different positions along the craniocaudal axis of various anatomical human models. The excitation current was normalized, at different frequencies, to meet the basic restriction of local 10 g-averaged specific energy absorption rate (SAR) in the human models, as defined by the exposure guidelines of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and the standard IEC 60601-2-33 of the International Electrotechnical Commission (IEC).Main results.The resulting permissible magnetic field strength values, for the reference levels set by the ICNIRP 2020 guidelines, emerged to be up to approximately 1.4 and 3 times less than that defined in the Atkinson-Brezovich limit. The widely used limit was found to align more closely with the first level of controlled operating mode defined in the IEC 60601-2-33 standard.Significance.The results indicate that the permissible magnetic field amplitude during MNH treatment should be much lower than that in the Atkinson-Brezovich limit. This study offers valuable insights into the role of computational simulations in advancing the potential to establish a reliable metric for safety evaluation and monitoring within the clinical framework of MNH.