SonoKnife: feasibility of a line-focused ultrasound device for thermal ablation therapy

Heating technology for malignant tumors: a review

The therapeutic application of heat is very effective in cancer treatment. Both hyperthermia, i.e., heating to 39-45 °C to induce sensitization to radiotherapy and chemotherapy, and thermal ablation, where temperatures beyond 50 °C destroy tumor cells directly are frequently applied in the clinic. Achievement of an effective treatment requires high quality heating equipment, precise thermal dosimetry, and adequate quality assurance. Several types of devices, antennas and heating or power delivery systems have been proposed and developed in recent decades. These vary considerably in technique, heating depth, ability to focus, and in the size of the heating focus. Clinically used heating techniques involve electromagnetic and ultrasonic heating, hyperthermic perfusion and conductive heating. Depending on clinical objectives and available technology, thermal therapies can be subdivided into three broad categories: local, locoregional, or whole body heating. Clinically used local heating techniques include interstitial hyperthermia and ablation, high intensity focused ultrasound (HIFU), scanned focused ultrasound (SFUS), electroporation, nanoparticle heating, intraluminal heating and superficial heating. Locoregional heating techniques include phased array systems, capacitive systems and isolated perfusion. Whole body techniques focus on prevention of heat loss supplemented with energy deposition in the body, e.g., by infrared radiation. This review presents an overview of clinical hyperthermia and ablation devices used for local, locoregional, and whole body therapy. Proven and experimental clinical applications of thermal ablation and hyperthermia are listed. Methods for temperature measurement and the role of treatment planning to control treatments are discussed briefly, as well as future perspectives for heating technology for the treatment of tumors.

Simulation techniques in hyperthermia treatment planning

Abstract Clinical trials have shown that hyperthermia (HT), i.e. an increase of tissue temperature to 39-44 °C, significantly enhance radiotherapy and chemotherapy effectiveness [1]. Driven by the developments in computational techniques and computing power, personalised hyperthermia treatment planning (HTP) has matured and has become a powerful tool for optimising treatment quality. Electromagnetic, ultrasound, and thermal simulations using realistic clinical set-ups are now being performed to achieve patient-specific treatment optimisation. In addition, extensive studies aimed to properly implement novel HT tools and techniques, and to assess the quality of HT, are becoming more common. In this paper, we review the simulation tools and techniques developed for clinical hyperthermia, and evaluate their current status on the path from 'model' to 'clinic'. In addition, we illustrate the major techniques employed for validation and optimisation. HTP has become an essential tool for improvement, control, and assessment of HT treatment quality. As such, it plays a pivotal role in the quest to establish HT as an efficacious addition to multi-modality treatment of cancer.

SonoKnife for ablation of neck tissue: in vivo verification of a computer layered medium model

PURPOSE

This study aimed to determine which treatment parameters of the SonoKnife device can be used to safely and effectively perform non-invasive thermal ablation of subcutaneous tissue.

METHODS

A three-dimensional computational layered medium model was constructed to simulate thermal ablation treatment of the SonoKnife device. The acoustic and thermal fields were calculated with the Fast Object-Oriented C++ Ultrasound-Simulator software and a finite difference code, respectively. Subcutaneous tissue was represented as layers of skin, fat and muscle. The simulations were conducted for ultrasound frequencies of 1 or 3.5 MHz. The thermal dose model was used to predict the size and location of the ablated regions. The computer simulations were verified by using the SonoKnife to perform subcutaneous ablations in the neck area of healthy pigs, in vivo. Triphenyltetrazolium chloride viability stain was used to differentiate viable tissue from ablated regions ex vivo.

RESULTS

The simulations for the layered medium model suggest that operating the SonoKnife at frequency of 1 MHz is more effective and safer than 3.5 MHz providing skin cooling is applied prior to ablation. These predictions were in agreement with the results observed in the animal studies. The required sonication time for ablation increased from 50 to 300 s by using 1 MHz.

CONCLUSION

Our modelling and animal studies suggest that 1 MHz with pretreatment skin cooling are the optimal settings to operate the SonoKnife to safely and effectively perform subcutaneous thermal ablation of porcine skin. More work is needed to optimise skin cooling and define the optimal sonication time.