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回答题：Screen Test
1 Every year millions of women are screened with X-rays to pickup signs of breast cancer. If this happens early enough, the disease can oftenbe treated successfully. According to a survey published last year, 21countries have screening programmes. Nine of them, including Australia, Canada,the US and Spain, screen women under 50.
2 But the medical benefits of screening these younger women arecontroversial, partly because the radiation brings a small risk of inducingcancer. Also, younger women must be given higher doses of X rays because theirbreast tissue is denser.
3 Researchers at the Polytechnic University of Valencia analysedthe effect of screening more than 160,000 women at 11 local clinics. Afterestimating the women's cumulative dose of radiation, they used two models tocalculate the number of extra cancers this would cause.
4 The mathematical model recommended by Britain's NationalRadiological Protection Board (NRPB) predicted that the screening programmewould cause 36 cancers per 100,000 women, 18 of them fatal. The model preferredby the UN Scientific Committee on the Effects of Atomic Radiation led to alower figure of 20 cancers.
5 The researchers argue that the level of radiation-inducedcancers is "not very significant" compared to the far larger numberof cancers that are discovered and treateD．The Valencia programme,they say,detects between 300 and 450 cases of breast cancer in every 100,000 womenscreened.
6 But they point out that the risk of women contracting cancerfrom radiation could be reduced by between 40 and 80 percent if screening beganat 50 instead of 45, because they would be exposed to less radiation. Theresults of their study, they suggest, could help "optimize thetechnique" for breast cancer screening.
7 "There is a trade-off between the diagnostic benefits ofbreast screening and its risks," admits Michael Clark of the NRPB．But he warnsthat the study should be interpreted with caution. "On the basis of thecurrent data, for every 10 cancers successfully detected and prevented there isa risk of causing one later in life. That's why radiation exposure should beminimized in any screening programme.”
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