"A special type of CT scan can detect lung cancer early enough to save some lives the National Cancer Institute announced Thursday  the first evidence that a screening test may help fight the top U.S. cancer killer.    At issue are controversial spiral CT scans where a rotating scanner views the lungs at various angles to spot growths when they are about half the size that a standard chest Xray can detect. Some previous studies have suggested that the earlier detection helps while other research concluded it may do more harm than good by spotting too many benign growths.    The massive National Lung Screening Trial enrolled  current or former smokers to try to settle the debate. It found  percent fewer deaths from lung cancer among those screened with spiral CTs than among those given chest Xrays the NCI said Thursday a difference significant enough that it ended the study early.    The actual number of deaths averted was fairly modest   died in the spiral CT group over the eightyear study period compared with  deaths among those who got chest Xrays.    The NCI said it is not clear that all smokers should get the scans which are not riskfree.    The best advice for avoiding lung cancer remains to quit smoking said NCI Director Dr. Harold Varmus.    Still a validated approach that can reduce lung cancer mortality by even  percent has the potential to spare very significant numbers of people from the ravages of this disease he said.    About  new lung cancers are diagnosed in the U.S. each year and the disease kills about  people annually. It is most often diagnosed at advanced stages and the average fiveyear survival rate is just  percent.    Many smokers already had sought out spiral CTs even though the American Cancer Society hasnt recommended the test  citing a lack of clear evidence that they work  and most insurance doesnt cover the  to  cost.    The scans arent riskfree They frequently mistake scar tissue from an old infection or some other benign lump for cancer leading to unnecessary biopsies or surgery that in turn can cause a collapsed lung infection or other problems.    The NCI still is compiling rates of false alarms and other risks from the study.    Nor is it clear if the study results are applicable to all smokers. The trial enrolled people ages  to  who were or had been very heavy smokers and gave them one scan a year for three years.    While the spiral CTs emit less radiation than standard CT scans used to diagnose disease researchers also will analyze whether the radiation exposures from three scans changes a smokers lifetime risk of other radiationrelated cancers. Letters being mailed to study participants advise them to discuss with their doctors whether they should have additional scans or not."