Ablatherm® HIFU, minimally-invasive treatment for localized prostate cancer

Ablatherm® HIFU was jointly developed by Inserm (French Institute of Medical Research) and EDAP TMS in the early 1990s and is based on High Intensity Focused Ultrasound technology which creates a precise and irreversible coagulation necrosis of the targeted tissue while preserving the surrounding tissue.

Ablatherm® HIFU is a fully robotic device (Robotic HIFU®) with innovative features that guarantee optimal safety and efficiency for each treatment.

This minimally-invasive technology causes few sides effects and helps continue patient quality of life.

Ablatherm® HIFU was the first High Intensity Focused Ultrasound device for the treatment of localized prostate cancer to receive the CE mark in 2000. In fact, the first patient was treated in 1993 with the first Ablatherm® HIFU.

HIFU technology uses a high-intensity convergent ultrasound beam generated by high power transducers to produce heat.

HIFU is intended to allow the surgeon to necrose prostatic tissue without damaging surrounding tissue, thus eliminating the need for incisions, transfusions, general anesthesia and their resulting complications. The development of ultrasound transducers started with the work of P. Langevin, who used, in the 20th century, the piezoelectric properties of quartz crystal to build the first submarine sonar.

Mechanism of HIFU action

The basic principle of transrectal high intensity focused ultrasound (HIFU) is the precise destruction of prostatic tissue in one session, which is achieved by depositing large amounts of energy into it. Ultrasound waves, generated by the high frequency vibration (0.5 – 10 MHz) of a piezoelectric or piezoceramic transducer, are focused into a small discrete region (the focal point) by concave or parabolic arrangement.

Coupling and cooling is performed by degassed colored liquid as interface between the source and the patient’s rectal wall. Due to the similar physical properties of water and tissue as well as the broad flat coupling surface, ultrasound waves penetrate with minimal absorption or reflection. As the converging ultrasound approaches the focal point, the power density increases.

The two principle mechanisms of action of HIFU are based on thermal and mechanical effects.

Thermal effect

The thermal effect of HIFU is associated with the absorption of ultrasound energy into the tissue, which is converted into heat. Temperature elevation in the tissues depends on the absorption coefficient of the tissue as well as the size, shape and thermal response. The biological changes that are induced by heating depend on the temperature reached and the duration of the exposure (the thermal dose). Above a certain threshold, thermal doses induce irreversible tissue damage in the form of coagulative necrosis. Below the threshold, thermal dose effects depend on the sensitivity of the neighboring tissue, as can be seen in the sharp temperature gradient between the necrotic lesion and the normal cells in histological samples.

Cavitation

From the mechanical standpoint, bubbles form inside the cells due to negative pressure of the ultrasound wave and these increase in size to the point at which resonance is achieved. When the bubbles suddenly collapse, high pressure of 20,000 – 30,000 bars develops and damages nearby cells. This acoustic cavitation is complex and must be controlled in its extension. The two activities together lead to a reduction in prostate volume down to 5 ml.