The two other randomized trials that reported mortality rates and were reviewed by the researchers did not report statistically significant mortality benefits for CT lung screening. However, they were much smaller than the NLST.

Although the NLST guidelines showed mortality benefits, not all doctors were convinced the results meant hospitals should start offering the scans to smokers. CT scans are expensive, deliver more ionizing radiation than chest X-rays and are associated with a rather high false positive rate, which could lead to unnecessary treatments or biopsies.

According to the researchers, after looking at all the studies, it seems about 20 percent of CT screened individuals had positive results in each screening round, although only 1 percent actually had lung cancer. This means a lot of patients could experience unnecessary anxiety and surgical biopsies, which carry a low, but not nonexistent, risk of injury or death.

Also, the researchers said they did not run a cost-effective analysis, but they expect the more patients diverge from their recommended target group -- middle-aged adults who have smoked a lot -- the less cost-effective the procedure would be. Ultimately, the authors said the results of a couple of ongoing studies on low-dose CT screenings for lung cancer should help clarify the harms and benefits.

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