LOS ANGELES - Approximately 3,020 cancers could be prevented each year if doctors were more judicious about ordering CT scans for children, according to a new study.

A CT scan is essentially a series of X-rays combined to give physicians a three-dimensional view of a patient's insides.

In order to produce clearer pictures, CT scanners use more ionizing radiation than regular X-ray machines - 100 to 500 times more, according to the authors of the new study.

As the American Cancer Society explains: "Ionizing radiation has enough energy to damage the DNA in cells, which in turn may lead to cancer. … Most scientists and regulatory agencies agree that even small doses of ionizing radiation increase cancer risk, although by a very small amount. In general, the risk of cancer from radiation exposure increases as the dose of radiation increases. Likewise, the lower the exposure is, the smaller the increase in risk. But there is no threshold below which ionizing radiation is thought to be totally safe."

Children's growing bodies are particularly sensitive to ionizing radiation.

In addition, they have more years ahead of them, giving damaged DNA more opportunity to develop into cancer.

These are some of the reasons why a team of researchers tried to calculate how many cases of cancer could be traced to CT scans performed on children - and whether that number could be reduced.

The researchers studied records of patients enrolled in several large health plans around the country to estimate the number of CTs done on children ages 15 and younger, as well as the typical dose of radiation associated with those scans.

Overall, they found that CT use has roughly doubled since the mid-1990s.

The biggest jump was in CT scans of the abdomen and pelvis in kids between the ages of 5 and 14, although scans of the chest, spine and head also increased.

Extrapolating their data to the entire country, the researchers estimated that 4.25 million CT scans are performed on children each year, and those scans will result in 4,870 cancers down the line. In girls, about two-thirds of those cancers would be cases of leukemia or tumors in the breast, thyroid or lung. In boys, about half would be cases of leukemia or cancers of the brain, lung and colon.

Previous studies have estimated that one-third of CT scans in children are medically unnecessary, and if these scans were not done, the number of future cancers would be reduced by one-third, the researchers reported. In addition, if the 25 percent of scans that used the highest doses of radiation had instead used a more typical amount of radiation (based on the age of the patient and the organ being studied), the number of cancers would fall by 43 percent.

Implementing both changes would result in a 62 percent drop in future cases of radiation-induced cancers, from 4,870 to 1,850 per year.

The results were published online Monday in JAMA Pediatrics. The study authors emphasized that children who need CTs should still get them.

"From a patient's perspective, the benefits of a medically necessary CT scan far exceed the small increase in radiation-induced cancer risk," they wrote. But they also cited two previous studies that estimated that one-third of CT scans done on children were medically unnecessary.

They also noted that safer imaging techniques, such as ultrasound, could be tried before patients were exposed to the ionizing radiation in CT scans.