Saving millions

时间:2019-03-07 08:14:05166网络整理admin

By Marcus Chown SIMPLE aluminium foil and a cheap laser could prompt a much-needed revolution in cancer therapy by putting one of the most effective treatments within reach of many more hospitals within the next five years. Physicists in the US have generated a stream of energetic protons—which could be used for irradiating tumours—by zapping the foil with a laser. Tumours are usually irradiated by high-energy electrons or gamma rays generated by a linear accelerator. But electrons and gamma rays lose energy as they interact with orbiting electrons along the way. Protons, however, dump most of their energy on their target, enabling tumours to be destroyed with greater precision. The few hospitals that use protons for cancer therapy accelerate them with giant cyclotrons but, because such machines need enormous magnets to accelerate particles, they cost about £10 million, ten times as much as linear accelerators, which use charged plates to accelerate particles. “If there was a cheap source of high-energy protons, there would be huge interest,” says Alan Du Sautoy, head of electron dosimetry at Britain’s National Physical Laboratory in Teddington, Middlesex. A team led by Donald Umstadter of the University of Michigan experimented with aluminium foil 10 micrometres thick using a 400-femtosecond pulse from a laser. The intense electromagnetic field in the laser light ripped electrons from hydrogen atoms in water that had condensed on the foil, accelerating them to near the speed of light in the same direction as the laser light. The protons—hydrogen nuclei—then repelled each other explosively and were dragged along in the wake of the electrons. “The result was a pulse of 10 billion protons with an energy of 2 megaelectronvolts,” says Anatoly Maksimchuk of the Michigan team. To kill cancer cells, the proton source will need a hundred times this energy, but Umstadter believes this can be achieved by hitting the foil 100 times a second with 20 femtosecond pulses from a more efficient laser. Umstadter believes such a device could be ready for use in hospitals within five years, and that it would fit on a table top rather than occupy the several rooms needed for a cyclotron. It would also produce a much finer beam than a cyclotron,