Focusing cross-fire applicator for ultrasonic hyperthermia of tumors E.G. Lierke a , T. Hemsel b, * a Former affiliation: Battelle Institute, Frankfurt, Germany b Heinz Nixdorf Institute, University of Paderborn, Germany Available online 31 July 2006 Abstract An improved concept for ultrasonic hyperthermia of tumors is presented. This concept is based on past experience of a German gov- ernment supported project [1], which ended in 1984. It offers a low cost alternative to common RF- and microwave methods for hyper- thermia of tumors with volumes between 1 and 40 ml at treatment times between 30 and 60 min. Our new version of the system considerably improves the temperature suppression in the healthy tissue around the target area and enables the adjustment of the beam width to the actual tumor size and the field geometry to the depth and shape of the tumor. The applicator can be used for moderate hyperthermia with tissue overheating up to 10 K or for ablation therapy with short high temperature pulses. Its central area is free for the integration of a commercial ultrasonic diagnostic sector scanner or a Doppler flow sensor in order to support the adjustment of the transducer and to monitor the whole area during the therapy. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Moderate hyperthermia; Ablation therapy; Ultrasound applicator 1. Introduction Hyperthermia is a therapeutic treatment of human tis- sue, that relies on heating it to a critical temperature level for a predefined duration. Different possible mechanisms of the therapeutic effects of hyperthermia are described in [2]. Fig. 1 shows temperature–time thresholds for histo- logical damage of mammalian tissue irrespective of the heating technique [3]. The damage process follows an exponentially decreasing time versus temperature relation- ship. Microwaves, radio frequency and ultrasound are typical sources of energy which effectively penetrate the human body to be absorbed and converted into heat. However extra-corporal equipment for local heating of deep seated tumors by microwaves or RF is rather sophis- ticated, expensive and only used by specialized research centres, e. g. [4]. Ultrasound with wavelengths around 1 mm has unique properties for precise targeting and effective power conversion. But, with the exception of sev- eral versatile units in a few high ranking research centres, so far only a few commercially available ultrasonic devices for hyperthermia have been reported in the medi- cal literature. All hyperthermia units require temperature control and monitoring, either invasively, with miniature thermocouples, or non-invasively with rather expensive MRI. There are possibilities however for future ultrasonic imaging (elasto-thermography), where research is in pro- gress, see e.g. [5,6]. Our improved concept concentrates on moderate Hyperthermia with tissue overheating by up to 10 K and treatment volumes up to 40 ml. A feasibility study shows that the frequency and power range of commercial ultra- sonic physiotherapy equipment, combined with the moni- toring properties of small sector scanners of widespread commercial ultrasonic diagnostic equipment are the ideal basis for a low cost modular hyperthermia unit. 0041-624X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ultras.2006.07.004 * Corresponding author. Fax: +49 5251 60 6278. E-mail address: hemsel@hni.upb.de (T. Hemsel). www.elsevier.com/locate/ultras Ultrasonics 44 (2006) e341–e344