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Dr. Edwin Aird is Head of Medical Physics at Mount Vernon Cancer Centre. At our November 2009 meeting he explained that radiotherapy directs highly penetrating X-ray beams into a tumour, to kill it. The beams can harm other tissues so delivery needs to be very carefully delivered.
In the early days doctors drew lines on the patient’s skin and radiotherapy was aimed in a rectangular pattern, with the patient being turned over during treatment, so that the beams could be aimed from different angles.
Now treatment is very different. Complex planning includes intensity-modulated radiotherapy, with precise delivery of the dose using image-guided radiotherapy. Treatment is applied in “fractions”, usually over several weeks, to allow surrounding tissues time for some degree of recovery between treatments.
The position of the tumour is verified daily by low energy imaging. CT scans, MRI scans and PET scans are used to plan the treatment. At Mount Vernon, thanks to the Paul Strickland Scanner Centre, we have state of the art planning equipment.
In treatment, the radiotherapy X-ray beams are produced by high-powered radio waves. These beams can be bent, to come from various angles while the machine moves around the patient, concentrating the dose in the tumour. Geometric accuracy in three dimensions allows shaping of fields, reduction of the target area and greater ability to shape the beam and dose distribution, both to avoid nearby organs and to ensure that the whole of the tumour is treated. .
Mount Vernon now has nine linear accelerators to provide radiotherapy. Each costs between £800,000 and £1.2 million; they are accurate to within one to two millimetres. It is desirable to make maximum use of this expensive equipment, but linear accelerators require complex maintenance and are not suitable for continuous use, so they are not usually used over weekends. Staffing factors are another limitation on their use. Recruitment of experienced staff with the necessary skill-mix is very difficult.
However, some treatments take place on bank holidays and patients being treated by continuous hyperfractionated accelerated radiotherapy, (CHART), have very small doses of radiation three times a day over twelve days, which include one weekend.
Cyberknife is a new robotic linear accelerator which treats either head or body tumours. It is currently available in the USA and in some European countries including France, Switzerland, Italy, and in UK at one private clinic, but in a few months’ time Mount Vernon will be the first NHS Cancer Centre to have this exciting facility. This equipment costs £3.5 million; its accuracy is measured in sub millimetres. It is useful for specific treatments, but the cost of maintenance and treatment is very high. When it is available at Mount Vernon, perhaps up to five patients per week may benefit, possibly with only five or less fractions of treatment needed.
Brachytherapy is another new treatment, available at Mount Vernon due to a generous benefactor. Professor Peter Hoskin of Mount Vernon is the UK expert in this treatment, which inserts radioactivity in various forms directly into tumours under general anaesthetic.
Aren’t we lucky to have all these facilities at our local hospital – even though we all hope we will never need them!
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