RF hyperthermia array modelling; validation by means of measured EM-field distributions

Abstract

The accuracy of a hyperthermia treatment simulation determines its role in prospective treatment planning and dosimetry for the individual patient. Of importance are (1) the accuracy of the numerical simulation method, and (2) the numerical description of the hyperthermia treatment system. The accuracy of the numerical method is generally determined by analysis of a problem that is analytically solvable. The validity of the description of the hyperthermia system is to be investigated by comparison of the simulated and measured EM-field amplitude and phase of the clinical operational hyperthermia system. In this paper, the numerical description of the AMC-4 waveguide phased array for which treatment planning is performed by the Weak Form of the Conjugate Gradient FFT method is investigated. The accuracy of the description is analysed for four set-ups, varying the bolus size and the number of waveguides attached to a phantom. The comparison of experimental and numerical data has demonstrated the ability of the Weak Formulation of the Conjugate Gradient FFT method to predict the EM-field of the AMC-4 waveguide array hyperthermia system, including effects due to bolus size variations. However, based on the comparison of the measured EM-field distributions and those obtained from simulations, the accuracy of the planning system is found to be insufficient for quantitative SAR dosimetry for individual patients. Qualitative SAR dosimetry can be applied in cases where the accuracy is of minor importance, e.g. for the retrospective analysis of problematic hyperthermia treatments. Prospective applications of the treatment planning system include the (qualitative) determination/simulation of a set of starting points giving a 'close to optimal' amplitude and phase setting, the prediction of possible problem areas and the analysis of the performance of new/improved hyperthermia devices.

Thermal Therapy, Part 2: Hyperthermia Techniques

“…Two outstanding challenges in EM phased-array hyperthermia are (1) to selectively elevate the temperature in the cancerous tissue without excessively elevating the temperature of the surrounding healthy tissues in the presence of electrical and thermodynamic inhomogeneities, and (2) to react to unexpected changes in the patient positioning and physiology (e.g., sudden change in blood flow in the tumor) that can significantly impact the quality of the delivered treatment. 192,193 Significant research progress has been obtained recently in heating devices appropriate for deep hyperthermia including ultrasonic arrays, [194][195][196][197][198][199][200][201][202][203][204][205][206][207][208] RF arrays, 105,[209][210][211][212][213][214][215][216] and microwave arrays. 39,137,191,192,193, Petrovich et al 240 have reported the results of a 14-institution trial conducted in the United States that employed the annular phased array system for regional hyperthermia production in 353 patients with advanced, recurrent, or persistent deep-seated tumors.…”

Delineation of potential hot spots for hyperthermia treatment planning optimisation

“…The EM-field in the patient generated by the four (N ¼ 4) individual applicators of the hyperthermia treatment apparatus at our institute is calculated by the CGFFT method [10]. This method has been described elsewhere [11,12].…”

Fem Modeling for Performance Evaluation of an Electromagnetic Oncology Deep Hyperthermia Applicator When Using Monopole, Inverted T, and Plate Antennas

“…Some waveguides used as hyperthermia applicators are the ridged waveguides, [6] the AMC-4 array [7] and the two tilted waveguide [8]; however, all of them are fed by monopole antennas [1,[6][7][8]. There are performance studies of monopoles proposed for ISM-band applications, which have been used in the design of feeders for microwave antennas [9,10].…”