It’s a tough call because doctors disagree and insurance doesn’t pay for the test, so if you do opt for it, you’ll be paying out of pocket — around $300.

In October, The New England Journal of Medicine published a massive study of more than 30,000 current and former smokers and came to a provocative conclusion: The noninvasive screening, which can catch lung cancers very early, was linked to a projected 88 percent 10-year survival rate if patients are treated promptly with surgery — dramatically better than the usual survival rate because lung cancers are rarely caught that early.

At first glance the implication of the new study, done by Dr. Claudia Henschke, a radiology professor at Weill Cornell Medical College in New York, seems like a no-brainer: Get screened if you’re at high risk for lung cancer, meaning you’re a current or former smoker who smoked at least half a pack a day for years and years.

But it’s not quite that simple. In part because it had no control group, the Henschke study “cannot answer the question of whether screening reduces deaths from lung cancer,” said Dr. Phillip Boiselle of Beth Israel Deaconess Medical Center.

A different, ongoing study, the National Lung Screening Trial, should be able to answer the question of whether CT screening truly saves lives, but those results won’t be available until 2009 at the earliest.

There are also risks to CT screening, said Dr. Michael Thun , who heads epidemiological research for the American Cancer Society. Among other things, the test is so sensitive that it can pick up small nodules that might not turn out to be life-threatening cancer but could result in unnecessary biopsy, surgery, and the attendant risks from bleeding, infection, and anesthesia.

So here’s my take: If I were a policymaker or an insurance company executive, I’d say CT screening is not ready for prime time. But if I were a smoker, first I’d work harder to quit. Then I’d talk to my doctor about getting tested. The Henschke study, though not perfect, is too important to ignore.

No. Quitting is really the only way to cut the risk of lung cancer, said Dr. Michael Thun, who heads epidemiology research for the American Cancer Society.

Smoking damages lung and the more years you smoke, the greater the damage. In general, it takes six “hits,” or bits of damage to DNA, to produce a lung cancer. With the first hit from a carcinogen, a lung cell begins to develop into a fast-growing patch of similar cells.

If a person quits after, say, three hits, pre-cancerous “sleeper cells are unlikely to become cancer,” said Thun. But if you resume smoking or never quit in the first place these “sleeper cells” acquire more hits and ultimately become full-blown cancers.

As for catching lung cancer early, there is still no recommended screening test because a large clinical trial called NLST (National Lung Screening Trial) is ongoing and won’t produce results for several years yet, said Dr. Phillip Boiselle, director of thoracic imaging at Beth Israel Deaconess Medical Center in Boston.

The NLST trial is designed to see which screening test, chest X-ray or spiral CT scan, is more effective at reducing deaths by catching lung cancer early. Chest X-rays subject a person to low levels of radiation, but can miss 30 percent of nodules that might be cancer. On the other hand, they are not too likely to yield false positives – results that suggest cancer when there is none.

Spiral CT scans, which can cost several hundred dollars and are often not covered by insurance, are better than chest X-rays at finding very small nodules, but they involve 15 times more radiation and are so sensitive they pick up many things that are not cancer yet but subject people to more tests and considerable anxiety.

If you’re worried about lung cancer, you can ask your doctor about getting a chest X-ray or spiral CT scan, but remember, at this point, the doctor’s advice will be based on an educated guess, not clear science.