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Electromagnetic Heating of Breast Tumors in Interventional Radiology: In Vitro and in Vivo Studies in Human Cadavers and Mice¹

¹ From the Institutes of Diagnostic and Interventional Radiology (I.H., W.A.K.) and Animal Research (H.S.), Clinics of Friederich Schiller University Jena, Bachstrasse 18, D-07740 Jena, Germany; and the Institute of Physical High Technology, Jena, Germany (W.A., R. Hergt, R. Hiergeist). From the 1999 RSNA scientific assembly. Received November 28, 1999; revision requested January 11, 2000; final revision received May 30; accepted June 9. Address correspondence to W.A.K. (e-mail: Werner.Kaiser@med.uni-jena.de).

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 (T) as a function of the magnetite mass increased linearly up to 28 mg; at higher masses, a saturation of T was observed at nearly 88°C. The dependence of T on magnetic field amplitude (H) revealed a third-order power law: T = 0.26°C/(kA/m)³ · H³, with r² = 0.95. A mean temperature of 71°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.

Index terms: Animals • Breast neoplasms, therapeutic radiology, 00.1299 • Breast neoplasms, therapy, 00.1299 • Neoplasms, experimental studies, 00.1299

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