A German radiation dose study presented in a scientific session Wednesday found that four-detector multislice CT (MSCT) exposes patients to up to seven times more radiation than electron beam CT (EBCT) in selected procedures.The conclusion arises from phantom tests performed by Dr. Peter Hunold, a resident radiologist at the University of Essen in Germany. He compared the performances of a Somatom Volume Zoom CT scanner and an Imatron C-150 SB for coronary artery calcium testing and CT coronary angiography.
The effective dose measurements were acquired with an Alderson-Rando anthropomorphic phantom equipped with 36 lithium fluoride thermoluminescent dosimeters per measurement. Organ doses for simulated male and female patients were captured for bone marrow, lung, colon, thyroid gland, esophagus, female breast, stomach, liver, bladder, ovaries, and testes. The effective doses for male and female patients were calculated using International Commission of Radiation Protection weighting factors.
MSCT consistently exposed patients to a higher effective dose of radiation than EBCT, Hunold said. During coronary calcium tests, males received an average of 3.3 mSv, and women received 4.6 mSv. The higher dose for women was caused by the position of their breasts in the scan volume, he said. During coronary calcium testing with EBCT, men received an average of 1 mSv, and women received 1.4 mSv.
The simulated patients were also exposed to more radiation when MSCT was used for coronary angiography than when EBCT was used, according to Hunold. Men were exposed to 10.9 mSv, and women received 13 mSv. By comparison, CT angiography performed with EBCT exposed the male subjects to 1.5 mSv and women to 2 mSv.
The lesson of the study, according to Hunold, is that the improved spatial resolution obtained with MSCT comes with a trade-off measured in substantially higher radiation exposure. This experience strongly suggests that standardized MSCT protocols aimed at optimizing radiation dose should be mandatory, he said.
"The take-home message here is to standardize and optimize your MSCT protocols to keep exposure at a minimum," Hunold said.
