Ladies, want another reason to quit smoking? A study presented last week at the annual meeting of the Radiological Society of North America suggests that women who smoke are twice as likely as male smokers to develop lung cancer. Using computed tomography (C.T.) scanning, researchers studied nearly 3,000 male and female smokers 40 and older. Not surprisingly, they found that the risk of developing lung cancer increased with the amount smoked as well as with age. But they also found that independent of those two variables, women smokers still had double the cancer risk of men. Why is unclear, but the prescription quitting now is not.