Two Southern California hospitals blamed the manufacturer of their CT scanners for radiation overdoses received by 18 patients.
The statements by Bakersfield Memorial Hospital and Los Angeles County-University of Southern California Medical Center came as federal regulators continue to investigate allegations of similar problems nationwide.
The high doses of radiation at the two California hospitals were found in patients who had brain scans conducted with Toshiba medical-imaging devices.
Bakersfield Memorial Hospital said, "although the dosage guidelines provided by Toshiba were strictly followed," staffers discovered that 16 patients had received "higher-than-recommended dosages of radiation" after getting the scans.
Los Angeles County-USC Medical Center officials said two of its patients received the high doses from a Toshiba machine in late 2009 "after hospital radiologists followed guidelines issued by the manufacturer."
Toshiba officials declined comment, saying they cannot provide a response until the Food and Drug Administration completes its investigation.
FDA spokesman Dick Thompson said the regulatory agency has been made aware of a range of events involving radiation overdoses and has been investigating for the past 10 months.
The number of hospitals affected by the investigation and other details will be released in a report expected in the coming months, he said.
Last year, two other hospitals in Los Angeles County reported patients were given high doses of radiation by CT scanners.
Cedars-Sinai Medical Center reported 269 cases in which overdoses may have occurred, giving some patients eight times the normal dosage in a period spanning more than a year.
Another 10 overdoses were reported in patients treated at Glendale Adventist Medical Center, each receiving three to four times the normal range.
The FDA issued an alert to hospitals nationwide in December to check scanner settings.
In February, a medical imaging manufacturers' trade group pledged to begin installing safety controls on CT scanners to prevent radiation overdoses.
The group has proposed upgrades to scanners that would warn medical professionals if a dose is too high or dangerous as detailed in a hospital's accepted standard, said David Fisher, executive director of the Medical Imaging and Technology Alliance.