Cedars-Sinai Medical Center is calling it a misunderstanding. Medical experts are calling it something else.
"I consider it a serious mistake to have made," said Richard Semelka from the University of North Carolina.
More than 200 elderly patients who underwent CT brain scans used to diagnose strokes received eight times the proper dose of radiation.
Hospital officials say the mistake occurred in February of last year when it changed the protocol for the scan. That meant overriding pre-programmed instructions on the machine, which is when officials say the error occurred.
"My ballpark estimate is that these individuals have a one in 100 chance of developing cancer," Semelka said.
The error went unnoticed for 18 months until a patient reported losing his hair after a scan.
Cedars later found out that 40 percent of the patients suffered hair loss after the scans.
The FDA is now alerting all hospitals to check their protocols.
Medical experts say this type of mistake could happen anywhere.
"Close to 100,000 people each year die due to medical errors," said ABC News Health and Medical Editor Dr. Richard Besser. "And many of those are preventable."
In a statement, Cedars-Sinai says they immediately reported its findings to the appropriate government agencies and has now changed its safety procedures.
The FDA is also looking at whether manufacturers of CT scanners should install some type of alarm on their systems as an added safeguard.
An outside expert says the fact that patients received eight to ten times the normal dose for a head CT scan means they probably reached their allowable radiation exposure for the whole year just in a single test.