CT Scans and
Radiation Overdoses
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.
In its November press
release, the FDA concludes that the overdoses were caused by scanner operator
error. 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.
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.
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.
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. 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.
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.
Isolated Incidents or
the Tip of the Iceberg?
There are an estimated 150,000 CT
perfusion scans performed annually. As frightening as the overdoses are to the
few hundred patients known to have had them, their implications may be equally
frightening to the 70 million patients who yearly receive other types of CT
scans.
Only
Detected Because of Patient Query
Perhaps the most disturbing aspect is that after going undetected for 18
months, the overdoses were discovered not through safety checks or routine
scanner calibrations, but because of one patient whose hair fell out and
contacted the hospital about it.
If eight-fold radiation overdoses are
only detected because a patient's hair falls out, how many smaller overdoses
routinely occur during other CT scans but go undetected? The FDA recognized
this possibility as early as October 2009: "This situation may reflect
more widespread problems with CT quality assurance programs and may not be
isolated to this particular facility or this imaging procedure (CT brain
perfusion). If patient doses are higher than the expected level, but not high
enough to produce obvious signs of radiation injury, the problem may go
undetected and unreported, putting patients at increased risk for long-term
radiation effects."
To address this possibility, several
of the FDA's recommendations call for carefully checking that a reasonable
radiation dose is planned for each scanning procedure and is actually delivered
to the patient.
Back in 2009, Rebecca Smith-Bindman
proposed recording the individual and lifetime radiation doses a patient is
exposed to through medical procedures and making this part of a patient's
medical record. Such record keeping would almost certainly have revealed the
perfusion scan overdoses well before the 18 months that actually elapsed.
Doses Were Visible; No
One Noticed
The over-exposures,
whether due to the automatic exposure control or other reasons, were not
especially difficult to prevent. The radiation dose each patient was receiving
was visible on the scanner console during the scan. An entire sea of numbers is
displayed on-screen during a CT scan; it's certainly possible that one could
get lost. But not checking the on-screen radiation dosage indicates a certain
complacency about this one particular number: the radiation dose. The dosage
was right in front of the operator's eyes. But no one thought to look; instead,
they placed their trust in the machines.
The FDA suggests that the simplest
way to prevent this from happening again is for scanner manufacturers to
include an obvious indication on the screen of a higher than normal radiation
dose, one that's difficult for the operator to ignore, such as a pop-up warning
or sound. And it also calls on scanner operators to check the display panel
both before and during a scan, to ensure that the expected dose of radiation is
the actual dose the patient receives.
Hospitals Less Than
Forthcoming
Cedars-Sinai first became
aware that there was a problem when a scan patient, Michael Hauser, reported
that he had gone bald in a four-inch wide, donut shaped band that extended from
ear to ear. Hauser had suffered a stroke on July 4, 2009. Over the next two
weeks, Hauser underwent three CT brain perfusion scans, as well as a number of
additional scans. Hauser reports that he learned more about what happened to
him from reading the newspapers than he did from the hospital. Hauser says that
conservative estimates place the radiation his brain was exposed to as equal to
that of 50,000 chest X-rays.
Melissa Adams' hair began to fall out
in June 2008, about two weeks after undergoing a CT brain perfusion scan at
Huntsville hospital in Alabama. It took until December 2009 for her to find out
why. She was told by her hairdresser, who read about similar cases in the local
newspaper.
Laura Morrow reported receiving a
phone call from Cedars-Sinai, where she was asked if she had experienced any
hair loss or reddening of the skin. When she answered that she did not, the
caller said "well, thank you very much," and then hung up. There was
no mention to Morrow that she may have received a radiation overdose from a
February 2009 scan. Other Cedars-Sinai patients reported having similar phone
conversations.
The FDA did not issue any specific
recommendations to hospitals about reporting higher than normal radiation doses
to patients. Its recommendations focus on preventing high doses from occurring
in the first place.
One Hospital
Intentionally Used High Radiation Doses
The largest overdoses
were at Huntsville Hospital in Alabama. Doses were up to 13 times the amount
normally used during a CT perfusion scan. According to an inquiry by GE
Healthcare, the manufacturer of the scanners, hospital officials said they
intentionally used the high levels of radiation to get clearer images. Some
patients who received overdoses in Huntsville say that in addition to hair
loss, they also experienced headaches, memory loss and confusion.
Huntsville Hospital informed patients
of the overdoses in a two-page letter that included the word radiation only
once--in the ninth sentence. The letter states: "At this time, we have no
recommendations for you to have any follow-up treatment."
The FDA did not specifically address
the Huntsville situation. It does call for hospitals to review their dosing
protocols to ensure that a correct dose is planned for each study. It also
calls for any changes to default protocols to be cleared and approved by
several hospital personnel, not just by a single individual.
The recommendations issued by the FDA
are non-binding suggestions, not requirements. If followed, they have the
potential to make radiation overdoses a lot more unlikely. But the FDA leaves
it up to doctors, scanner operators and hospitals to follow them. Only time
will tell just how closely they will choose to do so.
None of the FDA recommendations
embody Smith-Bindman's proposal to track and record the radiation dose each
patient receives from every medical procedure. As a patient or family member of
someone undergoing a CT scan, you can ask for this information yourself. What
follows are the recommendation the agency recently made.
FDA Updated Recommendations for CT facilities and Practitioners
In the Initial Communication of Oct.
8, 2009, the FDA encouraged CT facilities to review their protocols and make
sure that the values displayed on the control panel corresponded to the doses
normally associated with the protocol. We continue to urge this practice for all
protocols.
Based on its investigation to date,
the FDA also recommends that facilities take the following actions, some of
which are safety practices critical for all CT procedures:
Assess whether any of your patients
received excess radiation during CT perfusion scans.
Review your radiation dosing
protocols for all CT perfusion scans to ensure that the correct dose is planned
for each study. Any change to the default protocol should be cleared through
the facility’s quality assurance program and be approved for image quality and
dose by the radiologist and physicist.
If more than one study is performed
on a patient during one CT perfusion imaging session adjust the dose of
radiation so it is appropriate for each study.
Implement quality control procedures
to ensure that dosing protocols are followed every time, and that the planned
amount of radiation is administered.
Check the display panel before
performing each scan to make sure the amount of radiation to be delivered is
appropriate for the individual patient. Be certain and document that radiologic
technologists are trained on the specific scanner and for the specific imaging
protocol they are using. They should understand the meaning of the dose index
reported on the CT control screen, as well as the expected ranges for each
imaging protocol and body scan region.
CT operators should be specifically
trained on dose-saving features such as automatic exposure control (AEC) before
using them. If the user activates AEC without carefully reviewing and adjusting
the associated parameters, the pre-populated ("default") values may
not be appropriate for that scan, which could lead to an overexposure with more
radiation dose than intended or an underexposure with poor image quality.
Protocols using AEC should be reviewed by a radiologist and physicist.
FDA Recommendations to CT
Manufacturers: Possible equipment enhancements that could improve patient
safety:
A console notification to alert the
operator of a high radiation dose
Provide particular information and
training on brain-perfusion protocols to all facilities that receiving base CT
equipment, whether or not the facilities purchase the related software enabling
quantitative analysis of cerebral hemodynamics;
Clarify parameters affecting dose,
along with clear instructions on how to appropriately set those parameters; and
Organize all dose-related
information into one section of each user manual, in a dedicated dose manual,
or indexed comprehensively in a concordance covering all manuals.
On December 2nd, The Radiological
Society of North America convened an expert panel to address safety issues.
.
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