Hyperthermia properties of gold fiducial markers

Purpose. The combination of Radiotherapy and Magnetic Fluid Hyperthermia (MFH) is gaining importance since it may offer new strategies for several oncological pathologies. In MFH magnetic nanoparticles are injected directly into the tumour and, under the action of an externally applied alternating magnetic field HAC, they generate an amount of heat proportional to the field. Metallic materials implanted within 40 cm from the tumour heat up during MFH treatment and are removed. The aim of this work is to investigate the hyperthermia properties of the fiducial markers employed in Image Guided Radiation Therapy (IGRT) and to study the physics mechanisms of the observed macroscopic effects. Methods and materials. Hydrogel matrix samples were prepared and used as tissue mimicking materials. Different types of gold fiducial markers used in IGRT procedures were positioned in gel samples, considering various geometric configurations simulating the actual position of the markers in the clinical practice. Hyperthermic properties of gold fiducial markers were studied varying the field amplitude HAC from 7 to 17 kA/m and the frequency from 100 to 1000 kHz. During the stimulation, an optical fiber based sensor enables the measurement of the temperature in a point of the hydrogel samples. Beside these temperature measurement, a high-resolution thermal camera was used to map the temperature distribution over the samples. Results. Preliminary results attested an increase of the temperature in the gel matrices as effect of the heating of the gold fiducial markers under a suitable magnetic stimulation. Hyperthermic effects were also significant in the typical experimental conditions (2 < HAC < 15 kA/m and f = 100 kHz) employed at present in MFH clinical trials. Conclusion. The results of this study highlight the need to carefully evaluate the presence and location of gold fiducial markers in patients undergoing MFH treatments, in order to prevent damage to health tissues surrounding the lesions.