Tumor cells and tumors can be effectively killed by thermal stress, also called hyperthermia [1]. This promising approach has already been tested in clinical studies. There, a lack of the ability to homogeneously deposit cytotoxic temperatures in the tumor area to reach all tumor cells led to unsatisfactory results. Hyperthermia can be optimized by using magnetic fluids, like for example iron oxide magnetic nanoparticles (MNP), which are deposited directly in the tumor, and which produce heat when placed inside of an alternating magnetic field (AMF). Up to date, intratumoral injection of the magnetic material is the state-of-the-art because it readily leads to sufficient amounts of magnetic material to induce hyperthermic temperatures above 43 °C in the tumor. However, after intratumoral injection naturally the magnetic material will be heterogeneously distributed, leading to intratumoral temperature gradients. Especially regions of temperature underdosage, where the temperatures are in the sublethal range, pose a problem to therapeutic efficiency because surviving cells can form a new tumor.

A thorough characterization of intratumoral MNP distribution could enhance the effects of hyperthermia by the identification of regions where MNP are absent and should be re-injected. Furthermore in regions where MNP are close to non-tumor tissue or spine, very high temperatures could be avoided.