[Magnetic thermotherapy of breast tumors: an experimental therapeutic approach]. / Magnetische Thermotherapie von Tumoren der Brust: ein experimenteller Therapieansatz.

The therapeutic strategy for breast cancer is changing, especially for early tumor stages with good prognosis. One potential minimally invasive therapy modality consists in the accumulation of a well-tolerated magnetic material (iron oxides, particularly magnetite) in the target tissue. By applying an alternating magnetic field, energy is selectively absorbed and induces harmful heating of the tumor. The present review deals with the essential conditions and parameters as studied in vitro and in vivo in animal experiments. Extrapolations to the clinical situation are discussed, in particular, the heating potential of the magnetic material, the selection of the magnetic field parameters, the occurrence of eddy currents, the generation of localized heating spots and the expected temperature rises and their effects on the tumor area.

[In vitro imaging of magnetite particles]. / Bildgebende Darstellung von Magnetiten in vitro.

PURPOSE: To find an optimal imaging modality for the assessment of magnetite agglomerations used as the heating sources during magnetic thermoablation of tumors. METHODS: 1 to 107 mg of coated (starch) magnetite particles were directly administered to an in vitro tumor model (swine lymph nodes) and investigated immediately (radiography) or after being embedded within a 4 % agar-phantom (sonography). T1-weighted MR images (TR = 400 ms, TE = 14 ms) were acquired from lymph nodes containing 0.5 to 25 mg magnetite. RESULTS: All investigated magnetite masses were qualitatively detectable by radiography. Sonographically, only mass agglomerations containing 107 mg magnetite were appropriately discernible. MRT images revealed distinct susceptibility artifacts. CONCLUSIONS: Based on the investigated imaging modalities, radiography is the method of choice for assessment of magnetite agglomerations using relevant dosages for magnetic thermoablation of tumors.

Electromagnetic heating of breast tumors in interventional radiology: in vitro and in vivo studies in human cadavers and mice.

PURPOSE: To assess relevant parameters for the minimally invasive elimination of breast tumors by using a selective application of magnetite and exposure of the breast to an alternating magnetic field. MATERIALS AND METHODS: The specific absorption rate (SAR) of different magnetite samples was determined calorimetrically. Temperature elevations based on magnetite mass (7-112 mg) and magnetic field amplitude (1.2-6.5 kA/m frequency, 400 kHz) were investigated by using human breast tissue. Parameter combinations (21 mg +/- 9 [SD], 242-second magnetic field exposure, 6.5-kA/m amplitude) were tested in 10 immunodeficient mice bearing human adenocarcinomas (MX-1 cells). Histologic sections of heated tumor tissue were analyzed. RESULTS: SAR data of different magnetite particle types ranged from 3 to 211 W/g. Temperature elevation (DeltaT) as a function of the magnetite mass increased linearly up to 28 mg; at higher masses, a saturation of DeltaT was observed at nearly 88 degrees C. The dependence of DeltaT on magnetic field amplitude (H) revealed a third-order power law: DeltaT = 0.26 degrees C/(kA/m)(3). H(3), with r(2) = 0.95. A mean temperature of 71 degrees C +/- 8 was recorded in the tumor region at the end of magnetic field exposure of the mice. Typical macroscopic findings included tumor shrinkage after heating. Histologically nuclear degenerations were observed in heated malignant cells. CONCLUSION: Magnetic heating of breast tumors is a promising technique for future interventional radiologic treatments.