Quality assurance in various radiative hyperthermia systems applying a phantom with LED matrix

The Amsterdam phantom with LED-matrix is applied as an instrument in testing the performance of four types of radiative deep-body hyperthermia systems, which are in clinical use in Germany and The Netherlands. The devices tested were Essen's BSD-1000, Berlin's BSD-2000, Utrecht's Coaxial TEM applicator and Amsterdam's Four-waveguide-array. Photographs were taken of the matrix of dipoles loaded with light-emitting diodes (LED) to visualize the distribution of the RF power deposition or specific absorption rate (SAR) in the aperture midplane. The utility of the phantom with LED matrix for various types of radiative hyperthermia systems is demonstrated. Within this preliminary study, the influence of important parameters on the SAR-pattern in the aperture midplane was demonstrated. After corrections on the phase relation of the applicators a central focus in the SAR distribution could be realized in all systems and could also be moved in any direction. The patterns of the central focus changed in its absolute values and its proportions depending on the relative relations of phase and amplitude of the lateral applicators with respect to the top and bottom applicator. Frequency dependency was recognized for the central focus of the BSD-1000 as well as for the irradiation pattern of a single applicator for the BSD-2000. In the Coaxial TEM applicator it was demonstrated that the dimension of the open water bolus influenced the absolute value of SAR in the aperture midplane.