The position of the opposite flat applicator changes the SAR and thermal distributions of the RF capacitive intracavitary hyperthermia

The variations of the specific absorption rate (SAR) and thermal distributi on in the JSHO QA phantoms were investigated by radiofrequency (RF) capacit ive intracavitary hyperthermia (ICHT) applicator (AP-T01, Omron Electric Co ., Kyoto, Japan) with the changing position of the opposite flat applicator (15-cm in diameter). The thermal distribution was observed with the thermo graphic camera and the normalized SAR distribution was calculated with the thermal data that were measured with the thermocouple thermometers. The SAR and thermal distributions of AP-T01 significantly varied with the position of the opposite flat applicator. The slope of the normalized SAR became gr adual towards the side of the flat applicator. During the operating of a hi gh flow rate (1500 ml/min) cooling system, the region between AP-T01 and th e flat applicator was widely and rather homogeneously heated, except the ho t spot around the end of AP-T01. This hot spot may be due to the imbalance of cooling of AP-T01 and the warming-up of the electrode. These results sug gest that the RF capacitive ICHT using AP-T01 may be clinically effective o n the deep-seated tumours in the direction of either the end wall, such as cervical cancers, or the upper wall, such as prostatic cancers and the medi astinal metastatic lymph nodes, if an improvement of the cooling system is achieved.