Implant strategies for ultrasound interstitial thermal therapy (USITT)

Multiple applicator implant strategies were evaluated for the ability to control temperature distributions within a volume of tissue. MRI-compatible multi-element ultrasound applicators were fabricated in directional and non-directional configurations using cylindrical piezo-ceramic transducers. These applicators can be inserted into 13 or 14 gage catheters integrated with water-cooling. Thermal lesion formation studies were performed in an in vitro setup using fresh beef muscle, as well as in in vivo experiments in pig thigh muscle, and canine prostate and liver. Temperature distributions were monitored using multiple-junction thermocouple probes. Results from these studies indicated the ability to conform thermal lesions to targeted tissue while protecting surrounding tissue from thermal damage. Thermal lesions confined to a 4 cm diameter treatment volume were produced in vitro within 4 minutes of heating with 10 W applied electrical power delivered to 6 equally spaced transducers. Three and 4 cm diameter conformal thermal lesions were produced in vivo using 3-6 directional and/or non-directional applicators in peripheral or clustered configurations. Peak temperatures measured in the center of the in vivo target volumes exceeded 85°C during heating, while temperatures outside the target volume remained below 45°C. It is anticipated that such treatment strategies may prove beneficial for the management of localized tumors in the prostate, uterus, liver or brain