Technique Reduces Exposure in Children Requiring Repeat CT Brain Scans

The clinicians reported that they decreased radiation exposure without losing the diagnostic accuracy of the images or compromising treatment decision-making.

The approach, described online September 20, 2013 in a report in the Journal of Neurosurgery, calls for using fewer X-ray images slices of the brain captured by CT scanners—seven instead of the traditional 32 to 40 slices. This approach, the study revealed, reduced radiation exposure by an average of almost 92% per patient compared with standard head CT scans, while still rendering the images diagnostically accurate. “The traditional thinking has been that fewer slices would, by definition, mean less clarity and less accuracy, rendering a CT scan suboptimal, but our findings show otherwise,” said lead investigator Jonathan Pindrik, MD, chief neurosurgery resident at Johns Hopkins Children’s Center (Baltimore, MD, USA).

The research involved analysis of CT scans of patients with excessive fluid in the brain, a disorder called hydrocephalus that requires periodic fluid-draining surgeries and a head CT before each procedure. The investigators compared two standard CT scans with two limited-slice, low-dose CT scans for each one of 50 children, ages 17 and younger, treated for hydrocephalus over five years at Johns Hopkins Children’s Center. The standard CT scan images were performed prior to the launch of the new radiation-minimizing protocol.

The radiation-minimizing technique in all 50 patients produced clear and 100% accurate images of the brain ventricles. When capturing alterations in ventricle size, however, the low-dose application resulted in a 4% error rate: Two of the 50 images were visually unclear, generating confusion among the clinicians who reviewed them. There were no false negatives in the low-dose images, but three false positives, the study revealed. Therefore, there were no instances of clinicians falsely identifying normal ventricular size, but three instances of clinicians perceiving a change in ventricular size when there was none. Taken as a whole, the radiation-minimizing approach was obviously sufficient, according to the researchers, and would have not compromised treatment outcomes.

The Hopkins team noted that the radiation-minimizing technique could be particularly important in pediatric emergency rooms, where the need for fast diagnosis disqualifies the use of more cumbersome, radiation-free imaging alternatives such as MRI scanning. It also can be used for routine evaluation in smaller community hospitals that may lack MRI equipment, according to the researchers.

CT scans are important imaging tools that have transformed the diagnosis and treatment of many disorders by providing rapid, effective, and accurate images, but they have pushed up levels of radiation exposure in both children and adults, according to the investigators. Ionizing radiation, used in X-rays and CT scans, has been long implicated in the development of specific tumors because of its ability to damage DNA. Children are particularly susceptible to the effects of radiation because of their smaller size, growing tissues and rapidly dividing cells, and because of their longer lifespans that allow slow-growing cancers to emerge years after exposure, the researchers noted.

“We have been searching for ways to minimize radiation exposure in kids without sacrificing the diagnostic accuracy of the images—and that is no easy feat—but we believe our limited-slice CT scans achieved that balance,” stated senior study investigator Edward Ahn, MD, a pediatric neurosurgeon at the Johns Hopkins Children’s Center.

Hydrocephalus is frequently treated by placing a catheter that drains excess fluid from the brain into the abdomen, a procedure known as ventriculoperitoneal shunting. Children with brain shunts require periodic imaging to assess catheter position and function. Shunt failure that occurs when a catheter dislodges or infection occurs is a common and dangerous complication and considered an emergency. However because shunt failure often causes nonspecific symptoms such as headache, vomiting and fever, a definitive diagnosis requires a brain scan.

There are more than 62 million CT scans performed yearly in the United States alone, four million of them in children. Experts estimate that radiation from medical imaging is the single largest source of radiation exposure in the population, and that up to 2% of all cancers stem from exposure to medical radiation.

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