HIFU Definition: A type of thermo-therapy or thermo-ablation for the treatment of benign prostateic hyperplasia and still under study for the treatment of cancer. An ultrasound probe focuses sound waves to an area as small as a grain of rice, similar to sunlight focused by a magnifying glass, elevating the tissue temperature to a point that the tissue cannot survive (70- to-90 degrees Centigrade or 158-194 degrees Fahrenheit).
HIFU is highly precise medical procedure using high-intensity focused ultrasound to heat and destroy pathogenic tissue rapidly. Clinical HIFU procedures are typically image-guided to permit treatment planning and targeting before applying a therapeutic or ablative level of ultrasound energy. When MRI is used for guidance, the technique is sometimes called Magnetic Resonance-guided Focused Ultrasound, often shortened to MRgFU.
When ultrasonography is used, the technique is sometimes called Ultrasound-guided Focused Ultrasound, often shortened to USgFUS. Magnetic resonance imaging (MRI) is used to identify tumours or fibroids in the body, before they are destroyed by the ultrasound. MRgFU is currently used in Australia, the United States, Canada, Israel, Europe, and Asia to treat uterine fibroids. Ultrasonography guided HIFU is currently used in the United Kingdom, Italy, Spain, Korea, Japan, Hong Kong, Malaysia, Russia, China, Romania and Bulgaria. Current clinical trials are underway, examining the possible use of HIFU in the treatment of cancers of the brain, breast, liver, bone, and prostate.
Therapeutic ultrasound is a minimally invasive or non-invasive method to deposit acoustic energy into tissue. Applications include tissue ablation (HIFU) (for tumour treatments, for example), hyperthermia treatments (low-level heating combined with radiation or chemotherapy), or the activation or enhanced delivery of drugs.
The ultrasound beam can be focused in these ways:
- Geometrically, for example with a lens or with a spherically curved transducer.
- Electronically, by adjusting the relative phases of elements in an array of transducers (a "phased array").
- By dynamically adjusting the electronic signals to the elements of a phased array, the beam can be steered to different locations, and aberrations due to tissue structures can be corrected.
An acoustic wave propagates through the tissue; part of it is absorbed and converted to heat. With focused beams, a very small focus can be achieved deep in tissues. When hot enough, the tissue is thermally coagulated. By focusing at more than one place or by scanning the focus, a volume can be thermally ablated.
At high enough acoustic intensities, cavitation (microbubbles forming and interacting with the ultrasound field) can occur. Microbubbles produced in the field oscillate and grow (due to factors including rectified diffusion), and eventually implode (inertial or transient cavitation). During inertial cavitation, very high temperatures inside the bubbles occur, and the collapse is associated with a shock wave and jets that can mechanically damage tissue. Because the onset of cavitation and the resulting tissue damage can be unpredictable, it has generally been avoided in clinical applications. However, cavitation is currently being investigated as a means to enhance HIFU ablation and for other applications.
Doctors have been interested in this type of treatment for nearly 50 years. But it is only in the past few years that they have been seriously investigating its use in treating different types of cancer. One advantage of this type of treatment is that because it only uses sound waves to kill the cancer cells, it doesn't have as many side effects as other types of cancer treatments already in use.
Doctors hope to use HIFU to kill cancer cells without damaging healthy cells. Chinese researchers were the first to lead the way using this treatment. They have done trials treating nearly 5,000 people with many different types of cancers. Researchers in Europe are now doing trials to find out if HIFU could be used for people unable to have surgery to remove their cancer. But they are not sure how well this will work as yet.
When can HIFU be used? HIFU is only useful to treat a single tumour or part of a large tumour. It doesn't treat tumours that are more widespread. This means that HIFU is not suitable for people with cancer that has spread to more than one place in their body. HIFU doesn't pass through either solid bone or air. This means that it is not suitable to treat every type of cancer.
At present (2011) HIFU is only available in the UK as part of clinical trials. These trials are only for certain types of cancer. If you take part in a trial, it may mean that you will have HIFU treatment and then have surgery to remove your cancer soon after that. This is so that doctors can look at the area treated with HIFU and the areas that were not treated. They will compare the two so they can see how good HIFU is at killing cancer cells.
What types of cancer HIFU might be able to treat?
Early stage prostate cancer
Primary and secondary liver cancer
HIFU is not a suitable treatment for:
Cancers in the pelvic area
Cancer that has spread to the lymph nodes
Head and neck cancers
Mid to late stage prostate cancer
Because the prostate is positioned deep within the pelvis, you have HIFU for prostate cancer by putting an ultrasound probe (transrectal probe) into your back passage (rectum). From that position, the ultrasound can direct beams more accurately at the prostate. Results from trials so far show that HIFU may be as successful in treating prostate cancer as treatment with radical prostatectomy or radiotherapy. But we also have to be sure that the long term results will be as good as surgery or radiotherapy. The treatment hasn't been around long enough for us to know that yet. The National Institute for Health and Clinical Excellence (NICE) have issued guidelines for the treatment of prostate cancer. The guidelines say that HIFU should only be used as part of a clinical trial. You could be offered HIFU instead of surgery or radiotherapy for localised prostate cancer. Doctors have used it for cancer that has just been diagnosed, or for cancer that has come back in the prostate after earlier treatment (salvage treatment).
Compiled and edited by John Sandham