Influence of dissolved gases in coupling waterbolus on superficial hyperthermia and evaluation of a water conditioning system with inline degassing

Purpose: A water conditioning system with inline degassing is presented for real time removal of the dissolved gases to improve heat delivery during superficial hyperthermia. Methodology: Coupled electromagnetic (EM) and thermal models are used to study the influence of air bubbles on the tissue specific absorption rate (SAR) and temperature distributions for a 915 MHzspiral antenna. The design and characterization of the water conditioning system with inline degassing, and evaluation on tissue phantoms are presented. Results: Perturbations in the simulated tissue SAR and temperature distributions for small air volume fractions in the bolus (1%-2%) were confirmed with phantom measurements. The water conditioning system maintained the bolus thickness and temperature within ±0.5% at a flow rate of 1 l min-1 and ±0.2 °Crespectively, and degassed the circulating water at an exponential rate with respect to time. The power coupled during phantom heating was more than 90% using the proposed system, and fluctuated between 31% and 90% for circulation of the predegassed water. Phantom heating experiments for the 39 °Cbolus recorded a 3 °Crise in temperature at 5mmdepth with inline degassing, and 1.9 °C-2.4 °Cwithout inline degassing. Conclusion: The inline bolus water degassing system is simple and cost effective, has shorter treatment pre-preparation time and could improve superficial hyperthermia treatment.