Reducing Tube Current to Manage CT Radiation Dose

Using lower fixed-tube current or automatic exposure control techniques when performing adult and pediatric head CT scans can reduce radiation dose and ease concern about cancer risk, according to a recent study published in the Journal of the American College of Radiology.

Head CTs account for 28 percent of all CT scans performed annually nationwide, but there is still a lack of data about the long-term effects of the radiation associated with them. This uncertainty makes it your responsibility to limit the amount of radiation you use to only what is absolutely necessary, said Mahadevappa Mahesh, PhD, associate professor of radiology and cardiology at Johns Hopkins Hospital.

“Across the board, there’s no uniform protocol for head CTs or perfusion head CTs,” said Mahesh, the study’s lead author. “Controlling tube current is the most straight forward way to manage radiation because it has a linear relationship with the amount of radiation you use.”

For example, previous research from the American Journal of Neuroradiology found a radiation dose reduction of 47 percent accompanied a 50 percent cut in tube current. Image quality at this dosage is relatively unchanged.

In fact, Mahesh said, low fixed-tube current should be mandatory for perfusion head CTs. Lowering radiation levels in these repeated, same-location scans could prevent or reduce negative effects, such as hair loss.

Implementing the ALARA principle - as low as reasonably achievable - is particularly important with pediatric patients. Not only do they have more years to live with the repercussions of radiation exposure, but they also have less thick and dense skulls that offer less shielding than adult skulls.

“In some cases, kids have to return for multiple follow-ups, especially in cases of shunting,” Mahesh said. “You have to have your CT protocols optimized so you reduce the chances that they’ll have a negative outcome.”

Although equipment advancements over the past decade allow technologists to use pre-set dose levels based on a few patient characteristics, head CTs require more active engagement, he said. Head circumference is variable by body size, age, as well as sex, and should be addressed on an individual basis.

Controlling and lowering radiation dose has already caught on with some hospitals and imaging centers across the country. Gundersen Lutheran Health System, a physician-led health care system in La Crosse, Wis., launched a CT dose reduction program in 2006 by installing a dual-source CT system. The result was a 29 percent drop in average dosages.

Prompted by this success, Gundersen implemented its current reduction program. Key strategies - properly maintaining equipment, training staff, monitoring doses, and optimizing protocols - help the system protect patients from excessive radiation exposure.
In a recent paper published in Journal of the American College of Radiology, Gundersen supports Mahesh’s findings that controlling CT radiation doses is imperative.

“It is good practice and in the interest of patient safety for medical facilities to reduce CT radiation dose to the lowest level necessary for accurate diagnosis,” researchers wrote, noting that CT scans are associated with higher radiation exposure than conventional radiography.