Utilization of a multilayer polyacrylamide phantom for evaluation of hyperthermia applicators

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Abstract
A muscle-stimulating material made of polyacrylamide gel (PAG) for testing various kinds of hyperthermia applicators was investigated. The permittivity and conductivity dispersion of PAG, as well as an internal wavelength and penetration depth, were in good agreement with those of actual muscle at frequencies between 500 MHz and 3 GHz. A single formula for PAG covering three ISM bands, most commonly used for hyperthermia, 433, 915 and 2450 MHz, is presented. The physical properties of the PAG phantom allow any desired form or shape to be moulded, including shapes conforming to the actual geometry of an interstitial or intracavitary applicator. Utilization of a multilayer phantom makes possible the generation of experimental three-dimensional specific absorption rate (SAR) distributions composed from several two-dimensional SAR images at different depths or radial distances from the applicator. Spatial resolution of 1 mm can be achieved. The two-dimensional SAR distributions at different depth values for commercial superficial applicator, an interstitial antenna and a new oesophageal applicator are presented.