Feasibility and analysis of thermal parameters for the whole-body-hyperthermia system IRATHERM-2000.

Abstract

The infrared system IRATHERM-2000, with water-filtered infrared A wavelength underwent 20 treatments of whole body hyperthermia in conjunction with chemotherapy. In all the sessions, the aimed systemic temperature (41.8 degrees C, maximum 42.0 degrees C) could be achieved and maintained for 60 min. Due to increasing clinical experience, the unnegligible local toxicity, exhibited as heat-induced superficial lesions, and neurotoxicity, could be reduced during the course of the study. Data from three other series accomplished at the von Ardenne Clinic, totalling 120 heat sessions, were available and included for a comparative analysis. Analysis of the toxicity shows that a correlation exists between thermal side-effects and heat-up periods (until steady-state), maximum temperatures, and superficial thermal doses. The time needed to reach the plateau seems to correlate with fluid loss, which, thus, indirectly influences toxicity, and most importantly the initial power level. The typical heat-up time in such a standard set-up amounts to 100-150 min, for a temperature rise from 37.5 to 42.0 degrees C. Evaluation of the energy balance reveals a highly patient-specific range for the reactive evaporation in the IRATHERM system, resulting in a power (heat) loss of up to 1400 W via sweat production of approximately 2 l/h. In order to counterbalance this effect, an accordingly high infrared power, ranging from 1200-1500 W, needs to be delivered, resulting in a significant thermal skin exposition. Concepts used to reduce the heat loss by reactive evaporation include prevention of convection by appropriate sealing of the heating chamber and increasing the humidity by a nebulizer. For the more trained user, the heat-up time can be considerably shortened, particularly, in the introductory phase of the heating process, by employing higher, but still tolerable, patient-specific power levels. However, such a strategy requires, due to higher risks, close monitoring of skin temperatures together with a considerable amount of clinical experience. The results of the IRATHERM pilot study were compared, not only with previous groups where the IRATHERM was applied, but also with results of various other investigators where the Enthermics Radiant Heat Device was employed. In the authors' opinion, improved understanding of the mechanisms and crucial parameters underlying whole body hyperthermia, will enable a controllable and tolerable therapy through proficient contribution to equipment and methods.