Who are the oldest old – those 100 years of age and older? And what can these centenarians tell us about aging? More >
FDA Verdict on Patient Radiation Overdoses: Operator Error
A recently-issued FDA press release details a series of safeguards and changes in procedures designed to prevent the dangerous over-exposure to radiation from CT scans. The recommendations were prompted by two studies published in the journal, Archives of Internal Medicine, detailing the huge variation in how much radiation people undergoing CT (computerized tomography) scans are exposed to.
As far back as 2008, hundreds of patients received sizeable radiation overdoses from CT scans. The Food and Drug Administration (FDA) has now investigated, and the conclusions they have reached are both good news and bad news for patients.
The FDA wants scanner manufacturers, doctors and technologists all to pay more attention to the radiation dose each patient receives during every scan. These overdoses were fairly easy to prevent, and following the new recommendations should prevent most future ones from occurring.
Introduction: What the FDA Found
In its November press release, the FDA concludes that the overdoses were caused by scanner operator error.(1) The FDA found no fault with the scanners themselves. The press release suggests several improvements that could prevent a future repeat of these overdoses, including scanners designed to provide a specific, obvious on-screen notification to scanner operators of a high radiation dose.
In a letter to hospitals and medical professionals released the same day, the FDA details many further safety recommendations to hospitals and scanner operators.(2)
The FDA found approximately 385 overdoses received by patients at five hospitals in California and one in Alabama. An article in The New York Times reported more than 400 overdoses at eight hospitals.(3)
Eight Times the Normal Dose
The overdoses all occurred to patients who underwent a CT perfusion scan. This is a rapid series of X-rays usually given to patients who are suspected of having a stroke. Over 200 of the overdoses were of patients in a single California facility, Cedars-Sinai Medical Center. These patients received approximately eight times the radiation dose normally associated with the procedure.(4)
Such excessive radiation can lead to cancer. For various reasons, scientists cannot state with absolute certainty that a specific radiation dose will ultimately cause cancer. But the best estimates predict that each of the eight-fold overdoses has a 1 in 600 probability of causing a cancer.(5) This probability is higher in younger individuals, simply because they are likely to live many more years than an older patient would.
A Safety Feature Gone Awry
A potential stroke is a life or death situation. Proper treatment requires information, quickly, and the amount of radiation a potential stroke victim receives during a CT scan may not be the most important medical issue of the moment. But by all accounts, that is not the reason for the overdoses in these scans.
The overdoses all were from GE and Toshiba scanners and appear to have stemmed from the inappropriate use of a safety feature. GE scanners have a feature called automatic exposure control. It automatically adjusts the radiation dose according to a person's size and the body part being scanned, rather than using a fixed, predetermined radiation level. Its intent is to lower radiation doses. But when used in combination with certain machine settings that govern image clarity, its effect was to significantly raise the dose of radiation delivered to a patient.
GE claims that the feature was designed for procedures that scan multiple body parts of varying thickness. It's of limited usefulness for brain perfusion scans, which target only the brain. Hospital officials claim that GE trainers never properly explained the feature and that manuals do not point out that the feature is not designed for use in brain perfusion scans.(3)
To prevent similar mishaps from occurring in the future, The FDA issued several recommendations to the scanner manufacturers on how to make their manuals both clearer and more specific and also recommended more extensive training for scanner operators.
(3) Comments have been made