1 Perspectives of Tumour Therapy by Local Ultrasonic Hyperthermia and Thermoablation (Part 1 and 2) PACS: 43.80.Sh

Ultrasonic hyperthermia and thermo-ablation are two promising alternatives for local tissue overheating of deep seated human tumours. After a short characterisation of the two techniques and the identification of the main parameters, results of an analytical theory of local heat up, cooling, and heat expansion are presented. The theory is based on a spherical model for hyper-thermia with a critical thermal dose and on a cylinder-symmetrical model for thermo-ablation with a critical temperature limit for thermal tissue coagulation. Two representative hard ware concepts are discussed. The hyperthermia applicator consists of a MHz transducer, which ro-tates concentrically in a water filled capsule with acoustically transparent window, and radiates collimated ultrasound under 45 ° into a concentric target area of nearly spherical symmetry. The applicator for thermo-ablation is a MHz transducer which radiates high intensity focussed ultra-sound (HIFU) into a “cigar shaped ” target area at the focal zone. Typical therapy diagrams for both techniques are presented. They show therapeutic target volumes as functions of the ther-apy time with the peak temperature or the radiated acoustic power as parameters. These dia-grams are discussed under consideration of power requirement, maximal sound intensity, and power efficiency at optimized frequency conditions. 1