Stability of temperatures during hyperthermia treatments

Abstract

Attempts to develop a dosimetry for hyperthermia treatments have been limited by problems such as the inability of hyperthermia delivery systems to produce desired temperature distributions and the complexity of modelling complete temperature distributions. However, dosimetric modelling could be simplified if spatial temperature distributions were temporally stable after the treatment's initial heat-up period. In this study, therefore, temporal stability of spatial distributions was examined quantitatively. Hyperthermia was induced electromagnetically. Treatment parameters were documented on surface transparencies. These parameters were kept as constant as possible during treatments, and were reproduced as closely as possible from treatment to treatment Manual thermometer translation devices facilitated temperature scanning along interstitial catheters. Intra-treatment spatial temperature profiles T(r) of the same catheter were plotted together to characterize each treatment. Time-averaged T(r) of different treatments were plotted together to show inter-treatment variations. Standard deviations s`<sub>T</sub> of temperature from average temperature after heat-up were calculated from 302 T(r) obtained from 57 treatments of eight humans and three canines. Over periods of 30–60 min each, the average s`_T of all points scanned was ± 0.8°C, an order of magnitude less than intratumoral spatial variations of temperature. We conclude that procedures for reproducing treatment parameters led to a desirable extent of temporal stability of temperature during hyperthermia.