Logo

WASHINGTON: Undergoing CT scans a number of times may increase a patient's risk of cancer, according to a study.
"We found that while most patients accrue small cumulative cancer risks, 7% of the patients in our study had enough recurrent CT imaging to raise their estimated cancer risk by 1% or more above baseline levels," said Dr. Aaron Sodickson, assistant director of Emergency Radiology at Brigham and Women's Hospital and researcher at the Center for Evidence-Based Imaging in Boston. "The techniques implemented in our study can be used to identify higher risk patients who might benefit from enhanced radiation protection efforts," Sodickson added. The new finding has been reported at a time when the use of CT, which has proven to be a valuable clinical tool, is growing rapidly. CT provides detailed images of internal organs, and is a common technique used to make medical diagnoses and help guide medical treatment decisions. The researchers, however, say that CT uses a higher radiation dose than most other imaging exams. For their study, they developed new methodology to estimate cumulative CT radiation doses, and associated radiation-induced cancer risks at the level of the individual patient. The team extracted each patient's CT history from the electronic medical record, and applied standard risk-estimation models that incorporate patient gender and age at exposure. Those involved in the study included 31,462 adult patients who had diagnostic CT scans at Brigham and Women's Hospital or the Dana-Farber Cancer Center in 2007, and had undergone a total of 190,712 CT exams over the prior 22 years. The researchers revealed that approximately 33% of the patients underwent five or more lifetime CT exams, 5% underwent more than 22 exams, and 1% underwent more than 38 exams.
They further revealed that 15 percent received estimated cumulative effective radiation doses of more than 100 millisieverts (mSv), equivalent to the dose one would receive from 1,000 chest x-rays. Four percent received over 250 mSv, and 1% received over 399 mSv, the researchers added. It was observed that about 7.3% of the study group had an estimated lifetime attributable risk (LAR) of cancer of greater than 1%. That, according to the researchers, suggested that the subjects' risk of developing cancer had increased by one percent above the baseline US cancer risk rate of 42%, due to cumulative CT radiation exposure. Among the 315 patients in the top percentile of cumulative LAR, risk increased by 2.7 to 12%, they said. "CT is an excellent diagnostic tool of tremendous clinical value in many situations. Individual decisions about its use should balance the expected clinical benefits against the potential cumulative risks of recurrent imaging," Sodickson said. The researcher says that for those who have not undergone a large number of CT scans, its benefits typically outweigh the potential risks.
"However, we feel that a higher clinical threshold is warranted in patients undergoing a large amount of recurrent CT imaging, particularly if many of their prior CT scans have been negative.
This scenario may result in a combination of high cumulative risk with low clinical benefit," Sodickson said. Sodickson hopes that the findings of this study will help increase awareness of cumulative radiation exposure concerns, so that physicians will be better able to incorporate patient-specific radiation risk estimates into the CT decision-making process.
The study has been published in the journal Radiology.