Theoretical Evaluation on the Thermal Effects of Extracellular Hyperthermia and Intracellular Hyperthermia

Although not currently a routine cancer treatment therapy, hyperthermia is developing rather rapidly as an alternative way as part of conventional treatment for some cancers. This treatment takes advantage of the high sensitivity of tumor cell to heat. Up to now, a variety of heating methods have been established to induce temperature rises either locally in target tissue region, or over the whole body. Among them, magnetic nano-particles offer some attractive possibilities in tumor hyperthermia, which have controllable sizes ranging from a few nanometers up to tens of nanometers. The magnetic nano-particles can be made to resonantly respond to a time-varying electromagnetic (EM) field, with advantageous results related to the transfer of energy from the exciting field to the nano-particles. This heat then efficiently conducts into the surrounding diseased cells and tissues. A major concern involved in magnetic nano-hyperthermia is about the controversy that whether intracellular hyperthermia is superior to extracellular hyperthermia [1]. The potential of time-varying EM heating effects in a scale length smaller than the biological cell diameter was first addressed by Gordon et al. and termed as “intracellular hyperthermia” [2]. Since experimental validation of the thermal effects of intracellular hyperthermia is still not feasible with the current experimental technique, this problem has been studied theoretically. However, different researchers have suggested different results, and the controversy still goes on [1–3]. In order to understand the exact micro-mechanisms of EM heating involved in intracellular hyperthermia and extracellular hyperthermia, an energy analysis is presented in this study to simulate the corresponding heat transfer problems thus involved. Different from intracellular hyperthermia, the main characteristic of the extracellular hyperthermia is to heat up the target tissue by EM energy absorption only in the extracellular medium. A series of numerical calculations for both intracellular hyperthermia and extracellular hyperthermia are performed. The results will answer the question from the heat transfer mechanism whether intracellular hyperthermia is superior to extracellular hyperthermia in the thermal sense.