Looking for ways to Minimize Radiation

Obese patients appear to receive higher levels of radiation exposure during CT scans

(RxWiki News) If you're obese and scheduled for a CT scan, here's something you may not know: you're possibly receiving more radiation from the scan than those of a healthy weight would receive.

That's the conclusion of a recent study in which researchers have investigated inconsistent CT scan practices.

"Talk to your doctor about risks of any diagnostic tests."

Dr. Aiping Ding led the study with other researchers from the Rensselaer Polytechnic Institute in New York.

According to their calculations, obese patients' organs receive up to 62 percent more radiation than those of lower weight patients when undergoing a CT scan.

The reason has to do with settings for the scan that need to be adjusted to ensure the machine can form a high enough quality image from the scan, said Ding.

For morbidly obese patients undergoing CT scans, the "tube potential" must be increased so that enough x-rays are passing through the body to create an image.

"So far, such optimization has been done by trial and error without the use of patient-specific quantitative analysis," Ding said.

So Ding and his colleagues ran calculations based on computer models they created. They designed five male and five female computerized "people" with body mass indexes that ranged from a normal weight of 23.5 kg/m2 to a morbidly obese measurement of 46.4 kg/m2.

Included in the design of the computerized models, called phantoms, were two kinds of fat - the one under a person's skin and the deeper fat that surrounds organs.

When the chest, abdomen and pelvic areas of the obese phantoms were scanned, the results showed that the deeper organs were getting 59 percent less radiation compared to the organs of patients with a normal BMI because the extra fat was in the way.

That lesser amount of radiation may prevent a good enough image from being produced by the CT scan, so the settings have to be adjusted to increase the radiation enough to reach through the fat and gather enough information for a useable image.

That adjustment - while necessary for the quality image from morbidly obese patients - currently results in approximately 62 percent more radiation for men and 59 percent more radiation for females.

The researchers did not state that this higher level of radiation is necessarily damaging to a person. People receive exposure to radiation daily from cell phones to airplane altitude.

Developing best practices, however, would involve standardizing the best way to adjust the settings to maximize the image quality while minimizing radiation exposure as much as possible.

That's precisely what Ding and his colleagues are attempting to do with the development of a computer software called VirtualDose, which would calculate and track the amount of radiation a person is exposed to from medical diagnostic tests.

"Such a tool could be used to analyze radiation exposure trends in a clinic and to study how to optimize the image quality for a large population of patients," said senior author X. George Xu, also a professor at Rensselaer Polytechnic Institute.

The team hopes to use the data from this study in a clinical trial using VirtualDose this summer.

The study appeared online April 5 in the journal Physics in Medicine & Biology. The research was funded by a grant from the National Institutes of Health and by the National Institute of Biomedical Imaging and Bioengineering.

Review Date: 
April 5, 2012