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Scientists at the University of Oxford are trying to harness the energy released when bubbles collapse as a way of killing off cancer cells.They have built a device to beam waves of ultrasound into the body, generating bubbles at the site of a tumour.When these bubbles pop, they release energy as heat - killing rogue cells.The UK team plans to apply its new technique in clinical trials; it will be used in treating patients with kidney and liver tumours.These clinical trials of High Intensity Focused Ultrasound (Hifu) are being conducted at the Churchill Hospital in Oxford.No surgery required
Hifu is non-invasive: studies have shown that it is at least as effective as surgery, without the risks of opening up the patient. It also limits the damage to healthy tissue which occurs in radiotherapy.But by harnessing the energy released by the bubbles that form when tissue is exposed to intense ultrasound waves, the researchers say they can provide faster and better targeted Hifu treatment. So far, the trials have mainly involved terminal patients with isolated tumours in the liver and kidneys-organs which can be most difficult to reach with surgery.When any wave moves through matter, it weakens; and some of the energy is turned into heat. This is why microwaves heat up food and light waves from the Sun warm the Earth.In Hifu, ultrasound waves from outside the human body are brought to a focus inside the body, causing intense local heating which kills cells.The principle is the same as burning a hole in paper by focusing sunlight through a magnifying glass.But the existing Hifu technique has two important limitations compared with surgery that are hindering its clinical uptake. First, it is very slow: it takes up to five hours to treat a 10cm tumour, compared with the 45 minutes or so it takes a surgeon to cut the tissue out.Secondly, clinicians are working in the dark: without invasive surgery, the results can only be assessed after the treatment is over.
Temperature boost
By harnessing the tiny bubbles that form in tissue when it is exposed to focused ultrasound, the researchers found they could boost the heating effect by factor of 6-10 compared with conventional Hifu treatment.The enhanced technique, being pioneered by Dr Constantin Coussios from Oxford's Biomedical Ultrasonics and Biotherapy Laboratory (BUBL), is based on a principle called inertial cavitation. Hifu uses relatively low-frequency ultrasound, which allows clinicians to treat tumours deep inside the body. These low-frequency waves also generate bubbles in the fluid that infuses tissue.The bubble continues to grow until it reaches a critical pressure threshold. It then collapses and redistributes the energy as high-frequency "broadband noise"-effectively triggering a miniature explosion.The energy from this little bang gets absorbed locally, so that tumour cells are killed, but healthy tissue is left unscathed."I like to call it the 'energy shovel', because it allows us to grab this energy and use it where it is needed, delivering it as heat," Dr Coussios told BBC News.
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