Rotationally Adjustable Hyperthermia Applicators: A Computational Comparative Study of Circular and Linear Array Applicators

Abstract

Microwave breast hyperthermia (MH) aims to increase the temperature at the tumor location with minimal change in the healthy tissue. To this end, the specific absorption rate (SAR) inside the breast is optimized. The choice of the MH applicator design is important for a superior energy focus on the target. Although hyperthermia treatment planning (HTP) changes for every patient, the MH applicator is required to be effective for different breast models and tumor types. The linear applicator (LA) is one of the previously proposed applicator designs with linearly arranged antennas; however, it suffers from low focusing ability in certain breast regions due to its unsymmetrical geometrical features. In this paper, we propose to radially adjust the LA to obtain alternative excitation schemes without actually changing the applicator. Antipodal Vivaldi antennas were utilized, and the antenna excitations were optimized with particle swarm optimization (PSO). The comparison of the rotated and the fixed linear applicator, between 12-antenna circular and linear applicators, and finally, between a 24-antenna circular applicator are provided. Within the 12 rotation angles and two target locations that were analyzed, the 135° axially rotated linear applicator gave a 35% to 84% higher target-to-breast SAR ratio (TBRS) and a 21% to 28% higher target-to-breast temperature ratio (TBRT) than the fixed linear applicator. For the deep-seated target, the 135° rotated linear applicator had an 80% higher TBRS and a 59% higher TBRT than the 12-antenna circular applicator, while the results were comparable to the 24-antenna circular applicator.

Comparison of Microwave Hyperthermia Applicator Designs with Fora Dipole and Connected Array

“…To facilitate design comparison, the target centers were set on the positive x-axis, between (0, 0, 0) and (39, 0, 0) mm with increments of (1, 0, 0) mm. Keeping the target locations fixed, each applicator was axially rotated around the origin [ 11 ] and the was analyzed. For the circular and the linear applicators, the positions shown in Figure 3 a,c gave the individual best performance.…”

“…Particle Swarm Optimization was used to optimize the antenna excitation parameters, i.e., the phase and the power of the individual antenna feed. PSO has previously been used as an optimization technique in HT [ 11 , 16 , 18 , 19 ]. It is a fast optimization technique, and it enables multi-parameter optimization and multi-objective cost functions.…”

“…Linearly distributed applicator ( ) designs have also been proposed [ 8 , 9 , 10 ]; however, their practice has not been appealing because it has low coverage due to non-symmetrical geometry. In a recent study, the physical rotation of the linear array has been proposed to better align with the target, and thus enhance the focusing performance [ 11 ]. Furthermore, a formation of a hemispherical hyperthermia chamber deploying an antenna array around the breast has been shown to realize selective heating of a tumor in a sample [ 12 , 13 , 14 ].…”

“…This enables almost continuous current flow among the different FORA elements, thus realizing the continuous current sheet proposed by Wheeler [ 22 ]. The earlier works of the authors are related to wide-band Vivaldi antennas, tailored especially for imaging applications [ 8 , 10 , 11 ]. In this work, FORA dipole provides the narrow-band application, while FORA—connected array provides the conformal and wide-band characteristic that can be used in a future wearable hyperthermia device application.…”

Fresnel-Zone Focused Antenna Arrays: Tolerance Analysis for Biomedical Applications

“…Just as an example, Fresnel-zone focusing is of crucial importance in the framework of microwave hyperthermia applications [24] [25]. Here, the field concentration is required into a specific (focal) point where the treatment should be applied, while leaving untouched the surrounding tissues, thus guaranteeing health safety [26]. The Fresnel zone can be also relevant for biomedical implants, using microwaves to recharge [27]- [30].…”