Interstitial thermoradiotherapy: review on technical and clinical aspects.

Interstitial hyperthermia (IHT) combined with brachycurietherapy (thermoradiotherapy) has gained increasing popularity among radiation oncologists due to its potential as an effective radio- and chemosensitizer. IHT offers considerable advantages over percutaneous methods: confined treatment volume, better sparing of normal tissue, accessibility of deeper tumors, more homogeneous therapeutic temperature distribution, and better control and evaluation of thermal parameters using extensive "thermal mapping" procedures. This article addresses technical principles and clinical applications of IHT methods, radiofrequency (RF), microwave (MW), and hot source (HS) hyperthermia. Clinical phase I/II studies have used IHT palliatively for primary advanced, persistent, or local recurrent tumors, which have responded poorly to conventional treatment. The preliminary clinical data on greater than 500 patients treated with interstitial thermoradiotherapy are extremely promising despite the broad variation among the different treatment approaches. The observed complete response (CR) rate in various clinical trials ranges between 11 and 74%. The differences between the various techniques are minor, with a CR of 57% for interstitial RF hyperthermia (169 of 299 patients) and 60% for interstitial MW hyperthermia (130 of 215 patients). Despite extensive pretreatment, the total observed compliation rate of 22% for RF hyperthermia (67 of 299) and 21% for MW hyperthermia (45 of 215) is acceptable. The prognostic treatment factors identified are tumor volume, applied radiation dose, sufficiently high minimum tumor temperatures, and good thermal parameters, i.e., good quality of the hyperthermia treatment sessions. Technical innovations may facilitate and improve clinical applications and should allow broad clinical implementations of IHT, e.g., intraoperative hyperthermia, and even intracavitary hyperthermia. From these experiences it would appear that IHT 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.