The current role of interstitial thermo-radiotherapy.

Internal methods of thermotherapy such as interstitial, endocavitary and perfusional hyperthermia in combination with high- (HDR) or low-dose rate (LDR) brachytherapy have gained increasing interest among oncologists due to the known radio- and chemosensitizing potential of heat. Interstitial techniques offer several advantages over percutaneous heating techniques: confined treatment volume with improved sparing of normal tissue; accessibility of deeper tumors in various sites; more homogeneous distribution of therapeutic temperatures; and better control and evaluation of thermal parameters, when using extensive "thermal mapping" procedures. Currently several promising techniques are investigated such as radiofrequency (RF), microwave (MW) and hot source (HS) techniques. In phase 1 to 2 studies interstitial hyperthermia (IHT) has been mostly applied in the head and neck and brain, the chest wall, the pelvic region and the extremities for primary advanced, persistent or local recurrent tumors, which have responded poorly to conventional treatment approaches. Preliminary data on 600 patients treated with interstitial thermo-radiotherapy (IHT-IRT) are extremely promising despite broad variations among the technical and clinical treatment parameters. The tumor response rate in various clinical trials ranges between 11% and 74% CR, and with respect of extensive pre-treatment approaches, the overall complication rate of 20% appears acceptable. So far several prognostic treatment factors have been identified: tumor volume; radiation dose; high minimum tumor temperatures and sufficiently good thermal quality of the hyperthermia treatment. Future technical innovations should broaden clinical implementations of interventional hyperthermia such as intraoperative hyperthermia and intracavitary hyperthermia. It would appear from these experiences, that interstitial hyperthermia is an effective and safe treatment modality, especially when combined with radiotherapy for tumor palliation. Prospective randomized multicentric studies have already been initiated to investigate its role in palliative and adjuvant tumor therapy.