Gail ter Haar- Gail@icr.ac.uk
Physics Dept.
Royal Marsden Hospital
Sutton, Surrey, SM2 5PT
Popular version of paper 2pBV4
Presented Tuesday Afternoon, June 23,1998
ICA/ASA '98, Seattle, WA
Anyone who has played with a magnifying glass and a dry leaf in the sun will remember that when the leaf and the lens are just the right distance apart, the leaf will begin to smolder, but that at all other separations nothing will happen. It is only when the leaf is at the focus of the magnifying glass that it will catch fire. A similar effect can be achieved with a sound source. If a high power ultrasonic beam is brought to a tight focus within tissue it is possible to destroy all the cells lying at the focus, but no other cells within the piece of tissue are damaged.
This opens up the possibility of holding a source of ultrasound outside the body, and targeting a specific region within a human organ for destruction. Such a region may, for example, be a cancerous tumour in the liver, or a blood vessel that needs to be shut off. It may be possible to destroy this target, while leaving the skin and other tissues overlying it completely unharmed. This technique, referred to as focussed ultrasound surgery (FUS) or high intensity focussed ultrasound (HIFU), was first proposed in the 1940s and 1950s for the selective destruction of regions in the brain for neurological research. It did not gain widespread usage at that time, probably largely because the ability to image structures within the body was poor then, and so aiming the focussed beam through the skin at a specific target was too imprecise to be useful.
Advances in medical imaging, and improvements in the design of ultrasonic therapy sources, have led to a resurgence in interest in FUS. Obvious applications for a technique that allows you to target regions deep within the body selectively without harming anything else, are in benign prostate disease and in cancer therapy, particularly for tumours of the breast, prostate and liver. It can also be used to stop the flow of blood in vessels, and this may find application in fetal medicine, cancer therapy and the treatment of bleeding.
After extensive preliminary research and development of this technique, a prototype clinical treatment device has been developed by the Joint department of Physics at the Institute of Cancer Research and The Royal Marsden Hospital in Sutton, England. A phase I trial is nearing completion, for which patients with malignant tumours of the kidney, prostate or liver which lie 4 - 12 cm below the skin surface are being treated. In this unique trial, in which patients are treated on an outpatient basis, there is no need for any form of anaesthetic or sedation. No attempt at total tumour cure has yet been made, but imaging after treatment has shown that, in patients given the full therapeutic dose, the part of the tumour which was targeted has been destroyed. This trial has been designed to find out whether patients can tolerate such treatments, and whether there are any side effects. So far the results have been very encouraging. The next phase of clinical trials, which is due to start in the autumn, will attempt cure of cancers in the liver and prostate.