Influence of Polyvinylidene Chloride Sheets on Temperature Distribution in Hyperthermia Treatment

In hyperthermia treatment for superficial tumors, covering the affected part is often required to avoid intolerable pain. Polyvinylidene chloride (PVDC) sheets have been used to protect the affected area; however, the influence of PVDC covering on the temperature distribution is still unclear. In this study, the temperature changes caused by PVDC covering in hyperthermia treatment using agar phantoms were evaluated. In warming experiments, 30-cmand 10-cm-diameter electrodes were applied for deep and superficial warming, respectively. To confirm the effect of covering, either half the top side or both phantom ends were covered with the PVDC sheets or dry gauzes. After warming with various covering conditions, the temperature distribution of the phantoms was observed with thermography. The temperature changes over time were also evaluated with a thermocouple thermometer set in the border region of the covering. In deep warming, the increase of heat was slightly inhibited by PVDC covering, which intensified in the uncovered area. This contrast was amplified in superficial warming. Compared with PVDC, covering with dry gauzes showed a significant decrease and increase of heat in the covered and uncovered areas, respectively. In the observation of the temperature changes over time, during deep warming, the PVDC covering lowered no more than -0.4°C and the gauze covering lowered no more than -1.4°C, compared to that without any covers, in 10 min. In superficial warming, the heat increase in the gauze covering reached +7.0°C in only 5 min. This report showed that partial covering under electrodes could decrease the heat in the covered area and increase in the uncovered area. Although the temperature changes were minimal in PVDC covering, certain conditions could amplify the remodeling of the temperature distribution. Considering such changes is required to safely perform hyperthermia treatment.