Experimental investigation of an adaptive feedback algorithm for hot spot reduction in radio-frequency phased-array hyperthermia

Abstract

A computer-controlled adaptive phased array radiofrequency hyperthermia system for improved therapeutic tumor heating is experimentally investigated. Adaptive array feedback techniques are used to modify the electric-field in hyperthermia experiments with a homogeneous saline phantom target. A hyperthermia phased-array antenna system has been modified to implement adaptive nulling and adaptive focusing algorithms. The hyperthermia system is a ring phased-array antenna applicator with four independently controlled RF transmitter channels operating at a CW frequency of 100 MHz. The hyperthermia phased array is made adaptive by software modifications which invoke a gradient-search feedback algorithm that controls the amplitude and phase of each transmitter channel. The gradient-search algorithm implements the method of steepest descent for adaptive nulling (power minimization) and the method of steepest ascent for adaptive focusing (power maximization). The feedback signals are measured by electric-field short-dipole probe antennas. The measured data indicate that with an adaptive hyperthermia array it may be possible to maximize the applied electric field at a tumor position in a complex scattering target body and simultaneously minimize or reduce the electric field at target positions where undesired high-temperature regions (hot spots) occur.

Closed‐loop feedback control of phased‐array microwave heating using thermal measurements from magnetic resonance imaging

“…More than one probe may be necessary to ensure that healthy organs are not heated. Feedback control of microwave heating has been shown using this approach, but only at a single location (31)(32)(33)(34)(35). It is highly desirable to eliminate such invasive probes to prevent patient discomfort and possible medical complications.…”

Adaptive beam forming in time-domain

“…This paper focuses on the non-traditional beam forming in the time domain. The novelty of our approach is that the antenna array feeding is optimized directly in time domain so that the radiated energy is focused to a desired domain of space and vanishes in desired regions to meet the requirements of a biomedicine hyperthermia as specified in [5]. Such a scenario results in a multi-objective problem that is solved using a novel stochastic MultiObjective Self-Organizing Migrating Algorithm (MOSOMA) [6].…”

Variations of focal regions versus numbers and positions of sources in two-dimensional media

“…Besides positioning the primary hot spot in the target region, attention has to be paid to secondary hot spots which may be created in regions containing healthy tissue 13 . Paulsen et al 14 (page 158) observe that`it may be equally, if not more important, to utilize electromagnetic modelling to ® nd ways to diminish hot spots outside the immediate treatment ® eld as it is to identify methods of focusing power into the tumour volume' .…”