BERLIN, GERMANY (Press Release) - EAU 2007 - "The academic laboratory (INSERM) / hospital (HEH Urology Department) / industrial (Technomed, "the ancestor" of EDAP / TMPS) trip had existed for a long time... but adapting the basic lithotriter principle to the destruction of tissue didn't happen overnight as the phenomena used are not the same" recognised Dr JV Chapelon.

"With shock waves we can break up stones by creating mechanical constraints and cavitation but this is not enough to des tory cells instantly'~ he explained. This is therefore the second effect of the ultrasound, the thermal effect, which is used in Ablatherm@ causing the irreversible coagulation of proteines, like albumen when an egg white is cooked. The cavitation phenomenon (ZOOM 1) potentialises the thermal effect "Cavitation is not necessary as such, but it accelerates the treatment when it is correctly controlled/~ underlined Dr Chapelon, adding "the development of AblatherrrfB> involved playing with the shooting parameters in order to control it". As the interaction of the ultrasound field with cavitation was difficult to control, the original idea was to avoid this last phenomenon, "but this would have been at the expense of the treatment time, extending considerably the time between two shoots" he specified. The challenge to be overcome to reach a treatment which would take less than two hours was to be able to master cavitation. The trick was to associate the two effects so that the cavitation phenomenon converted the mechanical energy of the ultrasound into thermal effect. "When properly controlled, cavitation becomes very useful for potentialising the thermal effect" concluded Dr Chapelon, all the while insisting on the search for the thermal effect as a priority.

What is cavitation?
This is a physical phenomenon present in liquid environments subject to major variations in pressure, like the cloud of bubbles you see in the slipstream behind a boat caused by alternating pressure / depression generated by the turbine turbine (or bubbles appearing when a bottle of fizzy drink is opened). As soon as the negative pressure threshold is exceeded, the gases contained in the environment relax, creating micro-bubbles which will interact with the ultrasound waves emitted by Ablatherm@, resulting in a potentialisation of the thermal effect. This cavitation mode is called "stable cavitation". For more intense negative pressures, there is another cavitation mode - unstable or inertial - which leads to the implosion of the bubbles for which the mechanical effects may lead to the destruction of the surrounding cellular environment. This transitory cavitation is responsible for a haemorragic necrosis which should be excluded because of the risk of disseminating malign cells," underlined Dr Chapelon.

A series of shots to destroy focal volumes.
"We can coagulate small volumes irreversibly and successively thanks to a brief - 5 seconds - intense - up to 90 or 700°C - and targeted increase in temperature" explained Dr Chapelon. The coagulation of proteins, which occurs at 60°C, therefore leads to a reduction in direct cellular necrosis associated with the destruction of the local vascular network. This means that no cellular migration is possible, removing any risk of causing metastases.

"What is a "focal volume"?
This is the elementary volume of the size of a large grain of rice (20mm ling/2mm in diameter) destroyed by a single shot. This corresponds the focal task of the transducer.

Destruction under visual inspection
"Ablatherm@ is coupled with a high performance imaging system but other shooting systems associated with different imagine devices - MRI, Scanner - are being developed" revealed Dr Chapelon. The considerable "plus" provided by the MRI method would be to offer an effective control of the treatment by monitoring the temperature by imaging. But what if the the future were perhaps the ideal ultrasound scan combined with continuous thermal indication? To be continued...

Interview with Nathaly MERMET, scientific and medical journalist for EDAP - March 2006

A testimonial from Institute of Cancer Research
Gail ter Haar, Head of Therapeutic Ultrasound,lnstitute of Cancer Research:Royal Marsden Hospital, Sutton, Surrey, UK : "HIFU is a simple, but elegant technique that allows the selective destruction of a tumour without doing any damage to the other tissues that lie around it. A high intensity focused beam of ultrasound is unique in the way it can selectively kill cancer cells that lie in the targeted region. The way it works is similar to the way in which many of us, as children, used a magnifying glass in the sun to set fire to a dry leaf, It caught light only when the circle of light produced by the lens was at its tightest when the focus was actually on the leat which in this case is the "target", One advantage of using HIFU for treating prostate cancer is that it is simply an extension of the diagnostic procedure that a patient has anyway - trans-rectal ultrasound imaging (TRUS) , This is currently one of the best ways of looking at the prostate, The Ablatherm device is essentially one of these imaging probes to which a treatment source has been added. Apart from the highly localised and precise nature of the treatment HIFU has other advantages over other treatment options. Since there is no surgery, recovery is rapid. The procedure is simple, and the hospital stay is short. Since no radiation is involved, the treatment can if necessary be repeated, and can be used when other methods have failed. Many years of technical and clinical development have gone into this technique and it has now reached a level of maturity that allows it to be used with confidence in the knowledge that it is safe and effective ,"

The Ablatherm-HIFU treatment is now available in the Royal Marsden Hospital.

EAU 2007 Conference Coverage on UroToday.com

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