Radiation doses from common CT procedures vary widely and are higher than generally thought, raising concerns about increased risk for cancer, according to a new study led by UCSF imaging specialists.

"In day-to-day clinical practice, we found significant variation in the radiation doses for the same type of computed tomography procedures within institutions and across institutions," said lead investigator Rebecca Smith-Bindman, MD, a professor of radiology at UCSF. "Our results highlight the need for greater standardization because this is a medical safety issue."

Computed tomography imaging, known as CT, is a diagnostic procedure that uses special x-ray equipment to obtain cross-sectional pictures of the body that provide detailed images of organs, bones, and other tissues. CT is associated with higher radiation exposure than conventional x-rays, yet radiation dosages that patients receive from the newer CT scanners have gone largely unregulated, according to Smith-Bindman, who also is a UCSF professor of epidemiology and biostatistics and obstetrics, gynecology and reproductive sciences.
"Our study provides some initial data documenting the doses that patients receive when they undergo actual CT examinations and this is different than the doses when phantoms-sophisticated plastic models typically used to quantify CT scanner dose-are used. We believe documenting the actual doses that patients are exposed to is the first step to reducing those doses and any attendant risk," she emphasized.

Since 1980 the yearly number of CT exams has increased from about 3 million to 70 million CT procedures. The technology has changed dramatically over that time, improving the quality of imaging, and increasing the clinical questions that could be answered using CT, therefore leading to improvements in patient care, according to Smith-Bindman.

One of the improvements in CT technology has been the dramatic decline in the speed it takes to complete a CT examination. "However, this has been a double-edged sword," she said. "Because the images can be obtained so quickly, it has been very tempting to do multiphase studies - one CT done during the arterial phase of the cardiac cycle, one CT done during the venous phase, and one done after a short delay. This increases the information that we can get from the CT procedure, but increases the radiation dose by a factor of three."

The research team focused on estimating the radiation exposure associated with the 11 most common types of CT procedures in clinical practice in the U.S. and the potential cancer risk associated with each type.

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