Prospects for radiofrequency hyperthermia applicator research. I -- Pre-optimised prototypes of endocavitary applicators with matching interfaces for prostate hyperplasia and cancer treatments

Inconsistency is observed in comparing assessment data of applicators for endocavitary hyperthermia (EHT) with microwaves (MW) and radiofrequency (RF) obtained using the standard method of inserting bare applicators in phantom tissues. MW antennae exhibit overall average penetration depths of approximately 6 mm, excluding hot spots. RF radiators exhibit penetration depths of not more than approximately 3 mm, a value too low considering the superior penetration of the RF plane wave radiation. Assuming that a mismatch at the RF radiator--tissue interface is causing the poor energy transfer of RF energy, we developed new RF radiators with controlled dielectric matching interfaces for evaluating the potential of RF radiation in EHT and in interstitial hyperthermia (IHT) treatments. We designed, developed and assessed 27.12 MHz, 8 mm OD inductive and capacitive devices of novel and existing designs, each provided an optimised bi-layer matching interface. The assessment results reveal features such as customisable length and shape, independence of insertion depth, uncritical air gap, longitudinal heating uniformity, outstanding penetration depths (19--20 mm) and high SAR gradients at both radiator ends -- i.e. prostatic urethra ends -- for added safety. These data clear the way for the development of pre-optimised EHT inductive and capacitive RF applicators. Evidence of positive effects of high near-fields density in cavity microenvironments is given. Such devices show potential for more effective prostatic hyperplasia treatments and for improving the feasibility of more adequate treatment planning and thermal dosimetry of interstitial and transurethral hyperthermia treatments of prostate carcinoma.</.