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Cavitation enhanced Ablation for Focused Ultrasound Surgery

Final Report Summary - CAVABLATE (Cavitation enhanced Ablation for Focused Ultrasound Surgery)

Focused Ultrasound Surgery (FUS) is an emerging, non-invasive (so-called incision-less) modality, setting new clinical standards for the treatment of a range of diseases in various organs, including brain, liver, breast, thyroid and more. FUS procedures involve the extracorporeal administration of High Intensity Focused Ultrasound (HIFU), a non-ionising form of radiation, to mediate the deposition of heat to a target region of diseased tissue via frictional effects. The absorption of acoustic energy at the focus (generally a few mm3) coagulates the cells. The ultrasound energy is focused similarly to light that passes through a magnifying glass. The technique thus offers localised therapy with the significant advantage of substantially reducing the risks of infection, patient recovery time, the need for general anaesthesia, and avoids scarring.
Cavitation, the formation of microscopic bubbles, is being investigated as an approach to substantially enhance these procedures. Currently due to inherent poor energy absorption at the target area the procedure itself can be of several hours if the treated volume is relatively large. Cavitation can be induced when a typical HIFU transducer device is driven at high intensities. Unfortunately, cavitation activity is known to evolve very rapidly and poses significant risk of serious collateral damage to the surrounding healthy tissue. Cavitation also interacts strongly with the HIFU field itself, and can cause malformed and difficult to predict lesions, during FUS.
There is, however, the possibility that cavitation could offer an alternative form of therapy, whereby bubbles act as acoustic scatterer, rendering the area highly susceptible to enhanced therapy. Demonstrating real-time monitoring, control, and manipulation of cavitation activity in focused ultrasound is critical for realizing this potential. The challenge is to generate a reproducible result in terms of cavitation activity. The CavAblate project aimed to investigate the real world challenges of bubble enhanced therapy in the context of established clinical applications. In the first instance, a prototype was created whose characteristics could easily be added onto an existing clinical HIFU device. A modified Echopulse, the device manufactured by the host organization Theralcion, was used to accomplish this task. The Echopulse is a CE marked device for the treatment of thyroid nodules and breast fibro-adenomas, both applications are benign tumors. The long-term goal in the field of HIFU is also to tackle malignant tumours, which nowadays still require invasive surgery.
As part of the Cavablate project, extensive experimental work was conducted to investigate the best parameters for cavitation enhanced thermal ablation. This confirmed that bubble-formation increased the HIFU lesion size by a factor of 5. These parameters were first studied in ex-vivo liver and muscle samples. It was demonstrated that effectively enhanced heat absorption could be achieved. This translates into faster ablation times, effectively allowing a reduction in overall treatment times and decreasing post-focal energy deposition in the healthy tissues. The research was then shifted to in-vivo experiments, in the first instance to evaluate safety parameters, and as a secondary objective to demonstrate efficacy in those established experimental conditions. The higher peak intensities required to produce cavitation compared with traditional ablation techniques pushed the experimental conditions to their limits and required the introduction of a further safety mechanism. The results demonstrate a linear relationship between lesion size and cavitation broadband noise.
We believe that with controlled cavitation enhanced HIFU surgery FUS can overcome its current limitation of inherent low efficiency. Thus making this type of treatment more competitive and increasing its attractiveness compared to traditional surgery. This in turn will benefit the patients and the health care system by reducing recovery times and complications after surgery. Furthermore, the added value of precise cavitation control in a clinical system will allow clinicians to finally apply techniques such as sonoporation and local drug delivery in order to tackle malignant tumors. We believe that calibrated bubble activity combined with thermal ablation is the key for HIFU mediated cancer treatments, increasing in the future survival rates worldwide.