Analysis of temperature distributions of interstitial hyperthermia using a hot water system

Interstitial hyperthermia is being increasingly used as an adjunct to brachytherapy in the treatment of implantable tumors. Of the several interstitial hyperthermia systems available, perhaps the simplest to use are the circulating hot water systems. An analysis of the thermal distributions obtained during our initial experience with interstitial hyperthermia using steel needles and the KHS-9 hot water system was therefore undertaken.

Between September 1988 and June 1991, 23 patients were treated with interstitial Iridium-192 high dose-rate brachytherapy immediately followed by interstitial hot water hyperthermia. A total of 32 implants were performed in these patients, of whom 14 presented with primary anal carcinomas, six with recurrent gynecological tumors, and three with subcutaneous metastases from malignant melanoma. All but the patients with anal cancers had failed in previously irradiated sites. One or two heat treatments were delivered to each tumor with the goal to reach and maintain an intratumoral temperature 42.5 degrees C over a period of 40 min. Temperature measurements were carried out by mapping three-point thermocouple probes along the track of one or two needles parallel to the implanted needles.

Minimum intratumoral temperatures exceeded 42.0 degrees C in 41%, 42.5 degrees C in 19%, 43.0 degrees C in 13%, and 44.0 degrees C in 3% of treatments. The average minimum, maximum, and mean intratumoral temperatures for all treatments were 41.7 degrees C, 43.5 degrees C, and 42.6 degrees C, respectively.

The temperature profiles obtained in this series compare favorable to those reported in literature for radiofrequency local current field systems and suggest the hot water device may be an alternative heating method. It is relatively simple to use, does not require shielding of the treatment room, and can easily be adapted to currently used brachytherapy systems. Further patient accrual and longer follow-up will be needed to assess the clinical results in terms of tumor response and duration of response.