The eyes of the medical community lit up earlier this month when results from a major U.S. government-led trial were released showing that regular computed tomography scans could cut lung cancer deaths in current and former heavy smokers.
Lung-cancer deaths were 20 per cent lower among people who'd had three CT scans a year, compared with people who'd had three annual chest X-rays. It was a major drop, attributed to detection of the disease at earlier, treatable stages, and is being heralded by some medical experts as a breakthrough.
But what seems to have been lost in the excitement over the results is the fact that scientists have already identified an effective way to prevent most new cases of lung cancer: Get people to quit smoking.
The situation illustrates a growing tension between the explosion in use of complex medical tests and the fact that much is still unknown about how well they work, what side effects they cause, and how much it costs to save one patient's life.
"It's very appealing to think there's going to be an easy way to make you healthier that involves going to get a test," said Rebecca Smith-Bindman, a professor of radiology at the University of California at San Francisco who has done extensive research on potential risks of CT scans. "I think we need to really pause and think about are we really helping our patients by doing all this imaging? Sometimes the answer is clearly yes and sometimes the answer is clearly no."
CT scans provide detailed pictures of internal organs, tissues and blood vessels. While they give valuable information, and more comprehensive pictures than typical X-rays, they also have some disadvantages. One of the biggest concerns is the amount of radiation they emit: Radiation from one CT scan is equivalent to 400 or more chest X-rays.
Another major issue is that screening healthy people can increase the risk of "false positives," or identifying cancer in a person who doesn't have the disease.
Some say it's not an effective way to utilize complex, radiation-emitting and very expensive diagnostic tests.
The Canadian Association of Radiologists estimates that as many as 30 per cent of all CT scans performed in Canada are unnecessary or provide no relevant information to doctors.
The results of the new U.S. study seem positive: Regular CT scans can help spot lung cancer in heavy smokers and prompt earlier treatment, which can reduce the number of people who will die from the disease.
Initial results (the full study has not yet been published) found that 354 people who had three CT scans a year died from lung cancer, compared with 442 people who were screened with three annual chest X-rays. The 50,000 people involved in the trial were all current or former heavy smokers aged between 55 and 74.
The study has generated considerable excitement because it's one of the first pieces of research to show CT screening can be effective in early detection of lung cancer. Currently, there are no good screening methods - including X-rays - so many lung cancer cases are detected when it's already too late.
"Screening high-risk populations is always a good thing," said Edward Lyons, president of the Canadian Association of Radiologists, adding that strict criteria would need to be adopted before lung cancer screening was introduced to the wider population.
But many medical experts say the results need to be interpreted with caution to avoid opening a floodgate of thousands, or millions, of additional CT scans every year.
"We shouldn't rush to judgment that everybody should get screened," said Steven Seltzer, chairman of the radiology department at Brigham and Women's Hospital in Boston and a professor at Harvard Medical School. "We're really at the beginning of the debate."
While regular CT scans did seem to reduce death rates, 300 people had to be screened in order to save one life.
That's a major issue, considering that one scan costs several hundred dollars as well as emitting potentially harmful levels of radiation and raising a patient's risk of wrong diagnosis, unnecessary biopsies and other unneeded tests.
"You think of the cost of one CT scan, the cost of following up false positives, the cost of following up nodules that aren't cancer," said John You, assistant professor of medicine and clinical epidemiology at McMaster University in Hamilton. "It's going to be a landmark study … but I think it's just important to keep everything in perspective."
But perspective can be hard to maintain when talking about medical screening.
If 300, or even 1,000 people need to be screened to save one life, who is to say the cost outweighs the benefit?
"How can you tell an individual patient who's sitting in front of you [that] you just don't think [screening]is worth it?" said Dr. You. "If we think there's a chance to save that person's life, I think that's where the challenge is."