December 6, 2010

CT Scans and Radiation Overdoses

CT scans are a boon to diagnosis, but some may expose patients to way too much radiation.

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 found approximately 385 overdoses received by patients at five hospitals in California and one in Alabama. The New York Times reported more than 400 overdoses at eight hospitals.

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. 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.

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.

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.

Will Suggestions Be Enough?

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.

CT operators should be specifically trained on dose-saving features such as automatic exposure control (AEC) before using them.

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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