On a recent flight, Dr. Aaron Sodickson learned firsthand about the fallout from studies and media stories about radiation exposure from CT scans.

Sodickson, a radiologist at Brigham and Women's Hospital in Boston, was going to Washington, D.C., to meet with the U.S. Food and Drug Administration to find ways to protect patients from getting too much radiation from CT scans.

"The woman sitting next to me on the plane had a lump in her neck. It was thought to be cancer," Sodickson said in an interview.

The woman's doctor had ordered a CT scan to help determine if the lump was cancerous.

"She refused because she thought she would die of the CT scan," Sodickson said.

A CT scan assembles cross-section images of the body into a vivid picture that gives doctors a much better look at a patient that conventional X-rays, often eliminating the need for exploratory surgery. But too much radiation exposure is believed to raise the risk of cancer and scientists are working to cut down the risk from a CT scan.

A CT scan of the chest exposes a patient to more than 100 times the radiation of an X-ray and an abdominal CT scan is roughly equivalent to 400 chest X-rays.

A report last year by the National Council on Radiation Protection and Measurement found that Americans receive seven times more radiation from diagnostic scans than in 1980. About 70 million CT scans were done on Americans in 2007, up from 3 million in 1980.

A three-year study of Americans aged 18 to 64 last August from a team at Emory University in Atlanta suggests as many as 4 million Americans a year are exposed to what they viewed as high doses of radiation.

Accidental radiation exposure became a major worry in October after the FDA said it was investigating more than 200 cases of patients being exposed to toxic doses of radiation from CT scans at Cedars-Sinai Medical Center in Los Angeles.

"Patients are really scared," Sodickson said.

Regulators and lawmakers have responded with hearings and meetings with scanner makers, urging them to add safety mechanisms to their products to guard against errors.

To reduce radiation from routine scans, companies such as General Electric Co's GE Healthcare are developing computer programs that let radiologists and technicians take sharp pictures while vastly reducing the radiation dose.

Doctors say placing all of the blame on equipment makers will not keep doctors from ordering too many scans. They say they need better tools to determine when scans are warranted.

"What our group is trying to do is to get a better understanding out there of what is the actual magnitude of risk from these scans," Sodickson said.

Sodickson is one of a handful of U.S. physicians developing computerized programs to assess a patient's risk from CT exposure and alert them when a scan may be a potentially risky choice. He wants to have the program available to patients by the end of August.

At Massachusetts General Hospital, radiologists have developed a similar program.

"We have taken the American College of Radiology's appropriateness criteria and basically filled in the dots," Dr. James Thrall, chief of radiology at Mass General and president of the American College of Radiology, said in an interview.

For example, Thrall said a CT scan is often ordered when a patient has a headache but it is generally not needed. Thrall's team worked with the neurology department to put together a program asking a series of questions about the patient's symptoms and giving a score to recommend a CT.

A group at Weill Cornell Medical Center and Columbia University Medical Center in New York has developed a computer-based system that extracts radiation dose information from CT scanners.

The information works even on older CT equipment and is calculated using a patient's size and weight. The system is still in development but the hope is to allow patients to keep a digital record of their radiation exposure.

Equipment manufacturers also are addressing the radiation problem. To reduce the risk of accidental overexposure, the Medical Imaging & Technology Alliance, an industry group, has started adding alerts to CT scanners to warn technicians when patients are getting too much radiation. GE and others have started to offer free training seminars for technicians.

GE and rivals Siemens AG, Toshiba Corp and Philips are working on ways to reduce the amount of radiation required to produce an image.

In 2008, GE launched Adaptive Statistical Iterative Reconstruction or ASIR, a software program that enhances the quality of CT images, allowing radiologists to use up to 50 percent less radiation to produce a high-quality scan.

Late last month, researchers at the International Society for Computed Tomography conference in San Francisco presented the first results of studies using GE's next-generation software program, which may allow doctors to cut the radiation dose by 80 percent.

"We're trying as an industry to stay in front of this but we can't predict what the FDA will do," Ken Denison, CT dose leader for General Electric Co's GE Healthcare unit, said in a telephone interview.

Denison expects the FDA to continue collecting information and eventually issue new regulations.

Sodickson is worried the FDA is focusing too much on manufacturers. "Honestly, my concern is the FDA will overregulate it and make matters worse," he said.

Sodickson said CT manufacturers do not have the medical training to get the best diagnosis from the machines. He likens it to a table saw manufacturer teaching carpenters how to cut wood.

"It's not solvable by the manufacturers," he said.

Thrall worries that patients and doctors will err on the side of caution and decide to skip needed scans, putting patients at risk.

As for the woman on the airplane, Sodickson used his own formula to estimate that the woman's risk of cancer from a CT scan was less than 1 in 10,000 — far less than the risk from the mass in her neck.

She agreed to set up the scan the next day, he said.