Assessment of the performance characteristics of a prototype 12-element capacitive contact flexible microstrip applicator (CFMA-12) for superficial hyperthermia

Abstract

The electrical performance of the CFMA-12 operating at 433 MHz is assessed under laboratory conditions using a RF network analyser. From measurements of the scattering parameters of the CFMA-12 on both a multi-layered muscle- and fat/muscle-equivalent phantom, the optimal water bolus thickness, at which the transfer of the energy to the phantom configuration is maximal, is determined to be approximately 1 cm. The SAR distribution of the CFMA-12 in a multi-layered muscle-equivalent phantom is characterized using Schottky diode sheets and a TVS-600 IR camera. From the SAR measurements using the Schottky diode sheets it is shown that the contribution of the E(x) component to the SAR (SAR(x)) is maximal 7% of the contribution of the E(y)component to the SAR (SAR(y)) at different layers in both phantom configurations. The complete SAR distribution (SAR(tot)) at different depths is measured using the power pulse technique. From these measurements, it can be seen that SAR(y)at a depth of 0 cm in the muscle-equivalent phantom represents up to 80% of SAR(tot). At 1 and 2 cm depth, SAR(y) is up to 95% of SAR(tot). Therefore, in homogeneous muscle-equivalent phantoms, E(y) is the largest E-field component and measurement of SAR(y) distribution is sufficient to characterize SAR-steering performance of the CFMA-12. SAR steering measurements at 1 cm depth in the muscle-equivalent phantom show that the SAR maximum varies by 40% (1 SD) around the average value of 38.8 W kg(-1) (range 10-65 W kg(-1)) between single antenna elements. The effective fieldsize (E(50)) varies by 14% (1 SD) around the average value of 19.1 cm(2).

Evaluation of a dual-arm Archimedean spiral array for microwave hyperthermia

“…They also tend to be simpler and less expensive to fabricate. Several microstrip antenna designs, such as the MicrostripMicroslot applicator [11] and the Contact Flexible Microstrip Applicator (CFMA) [12][13][14][15] have exhibited favourable characteristics for use in hyperthermia treatments such as light-weight, an EFS approaching the outer dimensions of the radiating aperture and the ability to form antenna arrays for increased heating area. The largest microstrip array applicator to date is the Conformal Microwave Array (CMA) [2,3,[16][17][18][19][20] which utilizes an array of Dual Concentric Conductor (DCC) antennae [17,[21][22][23][24][25][26][27][28][29] formed from thin, multilayer flexible PCB material.…”

Performance evaluation of a conformal thermal monitoring sheet sensor array for measurement of surface temperature distributions during superficial hyperthermia treatments

“…Efforts thus far have been aimed at evaluating the prototype TMS for use in monitoring and control of surface temperature distributions under multi-element array microwave hyperthermia applicators like the 16-element Microtherm and 32-element CMA applicator developed for treatments of chest wall recurrence of breast cancer [1,5,32,33]. This thermometry approach should be equally useful for superficial hyperthermia induced with numerous other multielement array microwave applicators [9,13,14,16,34,35]. Clinical evaluations of these multi-element applicators have demonstrated the ability to deliver adjustable heating patterns to large surface areas over highly contoured portions of the anatomy if sufficient feedback information is available to guide power adjustments [1,5].…”

“…Commercially available multi-element array devices in the USA include the Sonotherm 1000 (Labthermics Technologies, Champaign, IL) 4 Â 4 array 3.4 MHz ultrasound heating device and the Microtherm 1000 (Labthermics Technologies, Champaign, IL) 4 Â 4 planar array 915 MHz microwave heating device for treating superficial tissue regions below the skin [5][6][7][8]. Multi-element array devices in clinical use today in Europe include custom sized arrays of 433 MHz current sheet applicators (CSA) [9], lucite cone applicators (LCA) [10][11][12], and the contact flexible microstrip applicator (CFMA) [13,14]. Another approach that has been used successfully in the clinic involves computer controlled mechanical rotation of one or two scanning spiral microstrip antennas over surface disease [15].…”

Quality assurance guidelines for superficial hyperthermia clinical trials

“…Multi-element array applicator: Alternatively a heat applicator can be constructed with a fixed spatial array of independently controlled heating elements, such as spiral microstrip [26–28], conformal microwave array (CMA) [30–33], Microtherm 1000 planar array [35] applicators, or a fixed array of ultrasound apertures, such as four and sixteen element devices [60, 61]. …”