Experimental and computational evaluation of capacitive hyperthermia

Objective Hyperthermia as an enhancer of radio- and/or chemotherapy has been confirmed by various trials. Quite a few positive randomized trials have been carried out with capacitive hyperthermia systems (CHS), even though specific absorption rates (SAR) in deep regions are known to be inferior to the established annular-phased array techniques. Due to a lack of systematic SAR measurements for current capacitive technology, we performed phantom measurements in combination with simulation studies. Materials and Methods According to the current guidelines, homogeneous and inhomogeneous agarose phantoms were manufactured for the commercial CHS Celsius42. Temperature/time curves were registered, and specific absorption rate (SAR) profiles and distributions were derived using the temperature gradient method. We implemented models for electrodes and phantom setups for simulation studies using Sim4Life. Results For a standard total power of 200 W, we measured effective SAR until depths of 6-8 cm in a homogeneous phantom, which indicates fair heating conditions for tumor diseases in superficial and intermediate depths. A fat layer of 1 cm strongly weakens the SAR, but 10-20 W/kg are still achieved in intermediate to deep regions (2-10 cm). In the phantom setup with integrated bone, we measured low SAR of 5-10 W/kg in the cancellous bone. Our simulations could fairly describe the measured SAR distributions, but predict tendentially higher SAR than measured. Additional simulations suggest that we would achieve higher SAR with vital fatty tissue and bone metastases in clinical situations. Conclusion Capacitive systems are suitable to heat superficial and medium-deep tumors as well as some bone metastases, and CHS application is feasible for a specific class of patients with pelvic and abdominal tumors. These findings are consistent with positive clinical studies.

Automated summary

Objective hyperthermia has been confirmed as an enhancer of radio- and/or chemotherapy through various trials, with positive results from capacitive hyperthermia systems (CHS) observed despite lower specific absorption rates (SAR) in deep regions compared to established techniques. Phantom measurements and simulations for commercial CHS Celsius42 showed effective SAR reaching depths of 6-8 cm in a homogeneous phantom and 10-20 W/kg achieved in intermediate to deep regions despite the presence of a fat layer. The application of CHS is feasible for certain pelvic and abdominal tumor patients, as well as for heating superficial and medium-deep tumors and some bone metastases.