Magnetic hyperthermia for tumour reduction (Vol. 44 No. 6)

Magnetic hyperthermia is the process by which cycling magnetic nanoparticles in an alternating magnetic field leads to heat dissipation. It is a very attractive approach for the treatment of cancer because it generates no side effects unlike more conventional therapies such as radiotherapy or chemotherapy. The development of this therapy has been hampered by the lack of a clear understanding of the physical mechanisms leading heat generation. At the present time it is not possible for clinicians to be given details of the dosage and field conditions required for a given therapeutic outcome.

There are three mechanisms by which exposing magnetic nanoparticles to a cycling field can generate heat: susceptibility loss, hysteresis loss and viscous heating. We have found that these mechanisms are highly particle size dependent as shown schematically in the figure and will also depend upon the degree of aggregation of the particles. In experiments of magnetic nanoparticles of different sizes dispersed in solvents of varying viscosities, hysteresis heating has been shown to be the dominant mechanism. Although the contribution arising from viscous heating is significant its effects are uncontrollable and will not occur in vivo due to the high viscosity of tumour tissue.