An assessment of the deep heating capabilities of a rotating multi-transducer ultrasound hyperthermia system

Abstract

The HELIOS ultrasound system is a large aperture multitransducer array designed to heat deep-seated tumors for hyperthermia therapy of cancer. Previous studies in phantoms and animals have shown that the HELIOS can effectively heat large target regions up to 10-1 5 cm deep. The present effort describes the development of a treatment simulation program, which uses measured ultrasound beam data to calculate anticipated temperature distributions for various treatment configurations. This program was used to evaluate the effectiveness of the HELIOS applicator in its original configuration, and to investigate the potential improvement from proposed system modifications. Results from this program are presented in terms of practical heating strategies and pre-treatment planning schemes. INTROD UCTlONUltrasound is often the modality of choice for localizing heating energy at depth within tissue for hyperthermia cancer therapy. The large penetration depths and the ability to produce small focal zones with ultrasound energy in the frequency range of 0.5-1 .O MHz allows for preferential targeting of the tumor volume while sparing the surrounding normal tissues. In response to the clinical requirement for precise heating of heat deepseated tumors, several devices are currently under development or in clinical use. Scanned focused ultrasound systems (1-21 which mechanically scan a high intensity focal zone through the tumor volume have shown promising clinical results for tumors which are up to 10 cm deep in the pelvis and abdomen. More recent developments include phased array systems which can synthesize optimized field distributions as a means of improving target localization and avoiding bone and bowel gas [3].