Despite Lay Press Reports, CT Benefits Outweigh Radiation Risks, Stroke Experts Say

Neurology Today
2 September 2010; Volume 10(17); p 1, 34, 35

Wesolowski, Kierstin

A mid controversy surrounding the increased risk for cancer associated with CT scan overuse, a New York Times article has now exposed numerous incidents of CT brain perfusion (CTP) radiation overdoses, when used to diagnose ischemic stroke.

NEW REPORTS OF CT OVER-RADIATION have sparked discussion among stroke experts and the attention of the FDA.

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This follows the FDA announcement in October 2009 that it had launched a safety investigation into CTP over radiation, on which it has yet to issue a final report. Nevertheless, the FDA still advises patients to follow their doctor's recommendations for receiving CT scans because of their potential health benefits, according to the FDA's interim recommendations regarding CTP scans released in December 2009. (See “FDA Interim Recommendations.”)

The July 31 Times article, “After Stroke Scans, Patients Face Serious Health Risks,” highlights reports of over-radiation by CTP at several hospitals in California and Alabama. It depicts several patients' harrowing experiences after being over radiated, unbeknownst to them, and suffering such adverse effects as banded hair loss, headaches, and confusion.

The article states: “The number of patients nationwide who got higher-than-expected radiation doses exceeds 400 at eight hospitals, six in California alone, according to figures supplied by hospitals, regulators and lawyers representing overdosed patients.”

The FDA's October 2009 report stated that patients at one institution had received 3 to 4 Grays (Gy) of radiation instead of the expected dose of 0.5Gy (maximum).

But stroke experts familiar with the article are concerned that the reports about these errors might create patient anxiety and subsequent refusal of CT scans and other neuroimaging techniques, all potentially life-saving technologies. In interviews with Neurology Today, the experts unanimously agreed: The overall benefits of CT, or any neuroimaging, during stroke outweigh the potential radiation risks.

The experts explained that when a patient arrives at the Emergency Room displaying signs of stroke, a “code stroke” is executed and neurologists quickly perform clinical and diagnostic evaluations, and then traditionally order a non-contrast CT to determine whether a patient has suffered an ischemic or hemorrhagic stroke, or a stroke mimic, such as a brain tumor.

Neurologists have about three hours from the patient's onset of symptoms to diagnose ischemic stroke and administer intravenous thrombolytics, such as tissue plasminogen activator (tPA). It is critical that neurologists determine whether the stroke is ischemic or hemorrhagic, because tPA is contraindicative for the latter, they noted.

“There's no blood marker or clinical evaluation that could replace that imaging,” said Joseph P. Broderick, MD, professor and chair of the department of neurology at the University of Cincinnati Neuroscience Institute and the University of Cincinnati Academic Health Center and member of the AAN Stroke Systems Work Group (SSWG).

Another SSWG member Marilyn Rymer, MD, medical director of St. Luke Health System's Brain and Stroke Institute, said that without neuroimaging neurologists can't offer any stroke-intervention therapies and the stroke will just evolve according to its natural history. However, with “interventions, there's a chance the patient will [fully recover] or have a reduced disability,” she added.

Recent advances in neuroimaging have slightly extended the treatment window for ischemic stroke from three to four-and-a-half hours. Since it sometimes takes people a while to arrive at the hospital after they suffer a stroke, this extra time might increase the number of people who are therapeutic candidates, said Robert D. Zimmerman, MD, past president of the American Society of Neuroradiology and executive vice Chairman and professor of radiology at the Weill Cornell Medical College.

CT brain perfusion offers neurologists an image of the blood flow throughout the patient's brain, he explained. A contrast injection and subsequent scan produce critical information on cerebral blood volume, cerebral blood flow, and mean transit time, the average-travel time of blood through a particular region of the brain. These three-individual studies comprise the CT perfusion map, which illustrates the core of the stroke, or infarct, and also the surrounding penumbra.

“Compared to non-contrast CT, which is best at diagnosing brain hemorrhage, CTP confirms a positive diagnosis that there is a blockage in one of the arteries and subsequently, that there's an area of the brain that's not getting any blood flow,” said Steven Warach, MD, PhD, chief of the NINDS Section on Stroke Diagnostics and Therapeutics. “It adds a degree of confidence and certainty that you're making the correct diagnosis.”

Whether a patient should receive a non-contrast CT versus CTP is largely an individualized choice and institutions have established their own protocol for its use, noted Dr. Warach.

“It's often used in making decisions that patients need more aggressive therapy than just intravenous thrombolytics,” said Dr. Warach. “They may be candidates to receive intra-arterial or other endovascular stroke therapy with clot removing devices, or intra-arterial thrombolytics.”

However, extremely large doses of radiation are not required to obtain good-diagnostic CTP images, experts said. “It's unclear why some institutions have gotten into trouble, but it may have been because[they believe] the higher the radiation dosage, the better quality image,” said Dr. Rymer. “However, a high-quality picture isn't needed to get the same information. Our CTP is only slightly higher than a non-contrast CT scan.”

DR. JOSEPH P. BRODERICK:“There's no blood marker or clinical evaluation that could replace that imaging.”

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A 2008 special report, “Effective Doses in Radiology and Diagnostic Medicine: A Catalogue,” defined the average effective dose (expressed in sieverts – Sv – which equal grays) of a non-contrast head CT scan as .002 Sv of radiation, which the FDA cites in their CT radiation-risks reference Web page. Put into context, the average American is exposed to .003 Sv of background radiation each year, according to the report.

All the experts agreed that if a patient or their caregiver is concerned over the amount of radiation emitted by either a non-contrast CT or CTP that the healthcare provider should provide them with the actual numbers used at that practice.

The Times article reported that government officials said the overdoses were not caused by CT scanner malfunctions. However, hospital officials and the CT scanner manufacturers differed on where to lay blame for the CTP overdoses: CT technician programming errors or ambiguous manufacturer instructions on how to properly use the machines.

If the CTP scans had been done properly, there wouldn't have been any radiation-induced side effects, said Dr. Broderick. “If you use CTP technology properly, it is safe although it still has a higher radiation exposure than a normal CT scan, but if you don't use it properly it can be associated with a high risk. The machines [referenced in the report in The New York Times] were used incorrectly and unsafely. We have to ensure there are systems put in place to guarantee errors such as these aren't made again.”

DR. MARILY RYMER said that without neuroimaging neurologists can't offer any stroke-intervention therapies and the stroke will just play out, adding, however, that with “interventions, there's a chance the patient will [fully recover] or have a reduced disability.”

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Other experts agree: “We need to make sure we partner as closely as possible with industry” in ensuring standards for safe use of the machines, said Carolyn C. Meltzer, MD, chair of the American College of Radiology Neuroradiology Commission and professor and chair of the Department of Radiology at Emory University School of Medicine. “[The health care community] tends not to have as many of those full-proof safety measures that other industries have, but we're looking at ways to now implement them.”

Health-care providers need to develop ways to enhance the safety of medical practice, especially areas that are dependent on technology, in order to minimize human error, Dr. Meltzer added.

Dr. Rymer noted that these unfortunate incidents have now sparked discussion within institutions, and also on a larger scale, about the creation of radiation dosage limits. Yet, she hopes in the meantime that CTP doesn't fall out of favor because it's an immensely helpful tool in determining which patients should go onto intra-aterial therapy.

“We wouldn't have tPA for acute stroke or advances in the treatment of brain tumors without imaging [of the brain],” said Dr. Broderick. “However, it's like any technology, you have to ensure it can be used as safely as possible. As the health care community, we haven't done as well with this particular technology.”

DR. STEVEN WARACH:“Compared to non-contrast CT, which is best at diagnosing brain hemorrhage, CTP confirms a positive diagnosis that there is a blockage in one of the arteries and subsequently, that there's an area of the brain that's not getting any blood flow. It adds a degree of confidence and certainty that you're making the correct diagnosis.”

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Dr. Zimmerman added that although what happened to these particular patients is terrible, it would be even more awful if patients refused neuroimaging: “We can't treat these patients if we don't know what's going on inside their heads.”

Stroke experts are concerned that reports about radiation errors for CT in stroke might create patient anxiety and subsequent refusal of scans and other neuroimaging techniques, all potentially life-saving technologies.

Mettler FA Jr, Huda W, Yoshizumi TT, Mahesh M. Effective doses in radiology and diagnostic nuclear medicine: a catalog. 2008 Jul;248(1):254-63.

Schellinger PD, Bryan RN, Warach S, et al. Evidence-based guideline: The role of diffusion and perfusion MRI for the diagnosis of acute ischemic stroke. Report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology. 2010;75: 177-186.