The design of a clinical deep-body hyperthermia system based on the 'coaxial TEM' applicator is presented. The 'coaxial TEM' applicator produces a radiative circumferential RF field, and the adjustable aperture width of this applicator allows the optimization of field dimensions and penetration depth. A new type of open water bolus, in which the patient is almost freely floating, avoids physical stresses on the patient, provides an optimal coupling of the EM energy into the patient, and may limit aberrant heating. A convenient patient position is possible with this system and discomfort is expected to be minimal. Preliminary phantom experiments with the clinical applicator resulted in typical SAR distributions of a radiative circumferential field applicator with the central interference at maximum.