In the three and a half decades since 1980, the year after the inventors of computed tomography won the Nobel Prize in medicine, CT usage jumped from fewer than 3 million scans per year to more than 80 million now. Have the risks of cumulative radiation been worth the rewards of diagnostic precision?

The obvious and only good answer is sometimes yes and sometimes no. But either way, doctors rarely explain what’s at stake to the patients for whom they’re ordering X-rays as well as CTs.

So shows a Consumer Reports survey of 1,019 adults, which found that just 7 percent of those who had a nondental X-ray and 2 percent of those who had a CT scan questioned the necessity of the tests. Meanwhile, just 4 percent balked when their doctor suggested a CT.

The article also cites recent research showing that about one-third of radiation-based imaging tests “serve little if any medical purpose.”

“Even when CT scans or other radiology tests are necessary, doctors and technicians don’t always take steps to limit radiation exposure,” the authors write, adding that some experts estimate that 15,000 people die each year because of cancers caused by the radiation in CT scans alone.

The authors draw from a 2013 Australian study comparing 680,000 people who had CT scans as children with 10 million children who did not have a CT scan. Overall, the Aussie researchers found, people scanned had a 24 percent increased cancer risk, with each additional scan increasing risk by 16 percent.

“[A]t least 2 percent of all future cancers in the U.S.—approximately 29,000 cases and 15,000 deaths per year—will stem from CT scans alone,” write the authors.

According to the article, the main reasons for excessive scanning are financial incentives, fear of lawsuits, uninformed physicians, misinformed patients, patient demand and lack of regulation.

“About one-third of the people in our survey assumed that laws strictly limit how much radiation a person can be exposed to during a CT scan,” write the authors. “In fact, unlike mammography, there are no federal radiation limits for any kind of CT imaging.”

The article quotes Consumer Reports’ chief medical advisor, Marvin M. Lipman, MD, as encouraging patients to question doctors ordering radiation-based exams, asking if the medical problem at hand can be managed without such tests.

The article is posted online for free, and the American College of Radiology maintains an extensive resource library on radiation safety.