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Spiral CT cuts lung cancer death risk in heavy smokers

Heavy smokers who receive screening using low-dose helical computed tomography (CT), also known as spiral CT may be 20 percent less likely to die from lung cancer, compared with standard chest x-rays, a new trial study funded by the National Cancer Institute suggests.

The standard chest x-ray imaging as a lung cancer screening is known to be ineffective in reducing the mortality from the malignancy.  At this time, no radiation-based screening is recommended by the federal government or medical organizations in the United States, according to the background information in the trial report.

The study authored by Constantine A. Gatsonis at Brown University and colleagues and published in Radiology also found all-cause mortality was 7 percent lower among those receiving spiral CT scans compared with that among those who received chest radiography.

The trial enrolled more than 53,000 men and women starting from Aug 2002. Only those who were at the age of 55 to 74, had a 30 or more pack-years (pack-years =packs per day x years smoked) of cigarette smoking history, or smoked, but quit within the previous 15 years and were able to sign informed consent form. The participants were free of lung cancer and had no history of lung cancer. Exclusion criteria included many other things.

For the study, participants were subject to three screenings either using the spiral CT or chest radiography, the first at baseline, the second at year one and the third at year 2 and all of them were followed for a number of years to count deaths in two groups.

The researchers found there were 354 lung cancer deaths among those receiving CT scans and 442 deaths among those who received chest x-rays, a 20 percent difference in mortality, according to Washington Post.  The report on Radiology does not seem to have revealed this detail.

This is a huge reduction in the risk of death from lung cancer. The NCI said on its website that it decided to release the findings earlier than planned because the trial's independent Data and Safety Monitoring Board informed the NCI director that "the accumulated data now provide a statistically convincing answer to the study’s primary question."

Lung cancer, which is believed to be caused largely by smoking cigarettes or tobacco, is expected to be diagnosed in 222,520 men and women in 2010 in the United States and to kill an estimated 157,300 in the same year in the country, according to the NCI. The disease kills more people than breast, colorectal, pancreatic and prostate cancers combined, according to the Post.

In 2008, an estimated 46 million or 20.6 percent of Americans were current cigarette smokers and right now 94 million current and former smokers are considered at risk of lung cancer, the NCI says.

The current trial did not address issues like the balance of benefits to risks. In the trial report, the authors said "Most lung cancer researchers agree that lung cancer screening is of unproved benefit and associated with inescapable harms."

X-ray used in chest radiography and the low dose spiral CT is recognized by the National Toxicology Program as a human carcinogen, which increases risk of cancer and vascular disease. According to the trial report, one low-dose CT delivered an average effective dose of 1.5 mSv radiation compared to 0.02 mSv from one chest x-ray, meaning the CT scan expose patients to 75 times higher level of radiation.  

Nuclear physician Dr. John Gofman, former professor at the University of California said there is no safe threshold for radiation and exposure to any dose increases the cancer risk and the radiation damage is cumulative.

An article reported in jcomjournal.com in July 2010 said a randomized controlled trial showed low-dose computed tomography resulted in much higher false-positive rate for lung cancer screening than chest x-ray.

The trial led apparently by Croswell Baker and colleagues with data published in Ann Intern Med 2010;152:505-12 showed the cumulative incidence of a false positive test results on the low-dose CT arm was 21 percent for 1 screening and 33 percent for 2 screening whereas the rates for chest x-ray were 9 percent and 15 percent respectively. The trial involved 3,190 current and former smokers aged 55 to 74 who had 30 pack-years of smoking history.

The false-positive results led to secondary diagnostic tests in 61 percent of those receiving CT scans and 51 percent in the x-ray group and invasive procedures in 7 percent of those receiving the spiral CT and 4 percent of subjects in those receiving chest x-rays.

According to the article, the US Preventive Service Task Force found no sufficient evidence to support or oppose screening asymptomatic people for lung cancer and the American Cancer Society does not recommend lung cancer screening either.

The NCI trial costs taxpayers $250,000,000, according to the Post.  Each spiral CT based screening costs $300.

By Jimmy Downs

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