Background: design and construction of a hyperthermia applicator for targeted heating of advanced carcinomas in the head and neck region.

Materials and Methods: parameters studies using high-resolution 3D electromagnetic (EM) simulations were performed to guide the design of the applicator setup. Investigated parameters were: operating frequency, number of sources, position of sources and antenna design. A laboratory prototype was build and its performance was tested in a neck-mimicking muscle phantom. With this setup we investigated the power absorption (PA) patterns obtainable and the possibilities for steering this pattern. Next a clinical prototype was build. With this clinical prototype we performed comfort tests by healthy volunteers and investigated the shape and corresponding influences of the waterbolus on the PA pattern.

Results: By laboratory prototype measurements and subsequently measurements with the clinical prototype, we established that a central focus in the neck can be obtained with the applicator. This focus can be steered in all directions (x,y,z). The location of the maximum power absorption in the phantom is measured close to the desired point of focus (accuracy ~5mm). Analysis of the obtained PA distributions in the clinical prototype for central and extreme steering setting revealed that an ellipsoidal focus is obtained with a half power length of 3.5cm in radial direction (x,y) and 8-10cm in axial direction (z). The comfort tests with healthy volunteers reveal that the applicator provides sufficient comfort to maintain in treatment position for an hour: the normal hyperthermia treatment time. By treatment planning with EM simulations we showed that the focus can effectively be steered towards the target region. And by implementing an automated optimisation routine we expect to be able to further reduce hotspots in normal tissue.

Conclusion: a site-specific applicator was designed that enables a good control of the power absorption pattern. The feasibility of heating in the neck with this applicator will be tested under clinical conditions during a phase I study.