Children are often exposed to excessive amounts of radiation when they get a CT scan, Ontario's auditor general reported Tuesday.

Jim McCarter said in almost 50 per cent of the cases he studied, hospitals did not reduce the exposure setting when children took the high-tech diagnostic exam.

Because children's organs are more sensitive to radiation than those of adults, a child who gets a CT scan on their abdomen using an adult setting will be exposed to as much radiation as found in 4,000 X-rays, McCarter said.

This is eight times the radiation an adult would be exposed to in the same setting, he said.

The findings are part of the auditor general's annual report.

"There is a lot of research out there that increased exposure to radiation, over time, can cause radiation-induced cancers," McCarter said after releasing the report Tuesday.

In his report, he noted that Ontario hospitals are not analyzing the number of CT scans adults and children are receiving or monitoring the doses of radiation received by each patient.

He said at the hospitals he visited, he came across 58 children who received more than one CT scan a year. Fourteen children had more than three scans a year and one child had six.

McCarter said in 10 to 20 per cent of cases, adults and children are getting CT scans when they don't necessarily need them. He sourced this finding to a study conducted by the Canadian Association of Radiologists.

He also noted that some staff and physicians he visited were not aware that CT scans expose patients to significantly more radiation than a common X-ray. He said British and American hospitals have guidelines about how much radiation a patient should receive, but Ontario does not.

"Without such reference levels, patients could receive more radiation at one hospital than at another," McCarter wrote in the report.

He also found cases of radiologists who were not wearing dosimeters, a protective device that measures their own level of radiation exposure.