Technology: Polymer putty makes for safer tumour treatment

 作者:褚桫秩     |      日期:2019-02-28 01:17:01
By JONATHAN BEARD in NEW YORK A putty made by mixing a polymer with finely powdered metal should reduce the dangers of treating oral tumours. Most such tumours are treated by bombardment with radiation – a risky method, as it endangers the salivary glands and other vulnerable surrounding tissues. The new putty, developed at the American Dental Association Health Foundation and the National Institute of Standards and Technology in Maryland, can be moulded to make cheap, effective shields to protect healthy tissue. The US Department of Health and Human Services calculates that about 4 per cent of all tumours occur in the mouth or pharynx, the area between the mouth and the oesophagus. In 1991 such cancers caused 8000 deaths in the US. The majority of patients are treated with radiation, and most of these would benefit from shielding, according to Frederick Eichmiller, the inventor of the new material. ‘Doctors have struggled for years to shield patients during radiation treatment, using thin sheets of lead, cut or melted and cast into appliances designed to fit into their oral cavities,’ he says. A great deal of time, expertise and money goes into fabricating these shields. The new shielding consists of 90 to 95 per cent metal powder, bound together by polysiloxane, a polymer also used in making dental casts. It is the metal which absorbs the radiation. ‘We have experimented with several metals, but silver, tin and copper alloys seem to have the best all-round properties,’ says Eichmiller. The important property of the metals is that they can be made into spheres 50 micrometres or less in diameter. Particles this small blend easily into the polymer to make a stable, malleable material. Moulding the putty over tissues that need to be protected from radiation makes it possible to treat tumours with electron beams or radiation from cobalt-60 at effective levels, without causing too much other damage. The new polymer could also be used to treat skin cancers and other superficial tumours, suggests Eichmiller . ‘At present we can control how far the radiation penetrates into tissue, but it is hard to irradiate an irregularly shaped melanoma without damaging the healthy skin around it.’ The polymer could be formed into a doughnut-like ring that would fit precisely around the tumour, he says. Although lead or other heavier metals would block more radiation, they do not form powders as easily as the preferred metals. Lead is also poisonous. ‘Making it into microbeads would also expose workers to severe toxicity problems, and the putty itself could be dangerous to patients,’ says Eichmiller . ‘Besides, we have found that the absorbing properties of silver, copper and other metals are almost as good as lead,