On the Optimal Matching Medium and the Working Frequency in Deep Pelvic Hyperthermia

A necessary step when designing electromagnetic-based medical devices is the choice of an optimal matching medium, standing between the patient and the phased array applicator, and the operating frequency. This is crucial to improve the efficiency both from a technical and clinical points of view. In this paper, we propose a new approach, based on the propagation theory, to support the selection of the matching medium properties and the working frequency in a robust way by accounting for patient body shape and properties variability. The case of adjuvant hyperthermia treatment administered to patient with tumors in the pelvic region has been used as a numerical assessment in both 2D and 3D patient specific models. For this case, the proposed approach suggests an optimal range of working frequencies (130MHz < f < 500MHz) and of matching material properties (ϵb < 20), wherein one can select the working conditions depending on the trade-off between penetration and focal spot dimensions as well as other specific requirements. Results have been compared to the working frequencies used by commercial applicators and using demineralized water as matching material. In conclusion, this work assesses the proposed approach in its general-purpose mathematical formulation, thus, paving the way for its wide application.